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Study material (Science) (Class 10)
Page 1 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
Electricity
 Electricity is used in our homes, in industry and in transport.
Example: - In homes  lightening, operating fans and for heating purpose.
In industry  used in running machines.
In transport  used in electric trains, street lightning, etc
Types of electric charges
 There are two types of electric charges: positive charges and negative charges.
 The charge acquired by glass rod is positive charge and charge acquired by silk
cloth is negative charge, when glass rod is rubbed with the silk cloth. The charge
acquired by ebonite rod is negative charge and charge acquired by wool is positive
charge, when ebonite rod is rubbed with the wool.
Property of electric charges
1. Opposite charges or unlike charges attract each other. (a positive charge
attract negative charge)
2. Similar charges or like charges repel each other. (two positive charges or two
negative charges repel each other)
 The SI unit of electric charge is “coulomb (C)”.
 One coulomb is the quantity of electric charge which exerts a force of 9 × 109
Newton on an equal charge placed at a distance of 1m from it.
 All matters contain positively charged particles called protons and negatively
charged particles called electrons. A proton carries a positive charge of 1.6 × 10-19 C
and electron carries a negative charge of 1.6 × 10-19.
 The unit of electric charge is much bigger than the charge of proton or electron.
Conductors and insulators
All the substances can be categorized in two electric categories: - conductors and
insulators.
 The substances through which charges can flow easily are called conductors.
 The conductors can also be defined as the substances through which electricity can
flow easily. Example: - all metals (silver, aluminium, etc), metal alloys (manganin,
constantan), carbon in the form of graphite and human body.
 Those substances through electric charges can not flow are called insulators.
 Insulators can also be defined as the substances through which electricity does not
flow. Example: - plastic, glass, ebonite, etc.
 In case of glass rod rubbed with silk and ebonite rod rubbed with wool, the charges
attained by glass rod and ebonite rod are fixed but they don‟t move.
 All the conductors have some free electrons which are loosely held by the nucleus
of their atoms. These free electrons can move from one atom to another throughout
conductor. The presence of these free electrons in the substance makes it a
conductor.
Electricity
Study material (Science) (Class 10)
Page 2 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 The electrons present in the insulators are tightly bound by the nucleus of the
atoms of insulators due to which they can not move from one atom to another, this
property makes a substance insulator.
Types of electricity
Electricity can be divided in two parts on the bases of the movement of charges.
1. Static electricity:-
 The type of electricity in which charges are at rest or do not move is called static
electricity. Example:- the charges acquired by glass rod and silk cloth, when
they are rubbed with each other, the charges acquired by the ebonite rod and
wool, when they are rubbed with each other and lightening in the sky.
2. Current electricity:-
 The type of electricity in which charges are in motion is called current electricity.
Example: - the electricity we use in our homes.
Electric potential
 The electric potential at any point in the electric field is defined as the work done
in moving a unit positive charge from infinity to that point.
 Electric potential is denoted by “V” and its SI unit is “volt”.
 When 1 joule of work is done to move 1 C of positive charge form infinity to a point
then the electric potential at that point is said to be 1 volt or 1 V.
Potential difference
 The difference in the electric potential between two points is called potential
difference.
 The potential difference between the two points in an electric circuit is defined as
amount of work done in moving a unit positive charge from one point to another
point is called potential difference between the two points.
Potential difference (p.d) =
𝑤𝑜 𝑟𝑘 𝑑𝑜𝑛𝑒
𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑
V =
𝑊
𝑄
 The SI unit of potential difference is “volt (V)”.
 The potential difference between the two points is said to be 1 volt if 1 joule of work
is done to move 1 coulomb of positive charge form one point to another point.
1 volt =
1 𝐽
1 𝐶
 1 V = 1 J/C = 1 JC-1
Electric current
 When two bodies kept at different electric potentials are connected by a metal wire
then the electric charges flow from body at high potential to the body at low
potential through the wire till both the bodies are at same potential.
 It is the potential difference between the two bodies which makes the electric
charges to flow in the wire.
 The electric charges which flow in the wire are electrons.
 The electric current can be defined as the flow of electrons in the conductor such
as metal wire.
Study material (Science) (Class 10)
Page 3 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 The magnitude of the electric current in a conductor is the amount of electric
charge passing through a given point of the conductor in one second.
Current (I) =
𝑄
𝑡
, where “Q” is the charge in coulomb and “t” is the time taken in
seconds.
 The SI unit of electric current is ampere (A).
 When 1 C of charge is flows through any cross section of a conductor in 1 second,
then the electric current flowing through the wire is said to be 1 ampere (1 A).
1 A =
1 𝐶
1 𝑠𝑒𝑐𝑜𝑛𝑑
= 1 C /s = 1 C s-1
 1 milliampere =
1
1000
ampere  1 mA = 10-3 A
Measurement of potential difference
 The potential difference is measured by an instrument called voltmeter.
 The voltmeter is always connected in parallel across the two points where the
potential difference is to be measured.
 A voltmeter has a high resistance so that it takes negligible current from the
circuit.
 Voltage is another name of potential difference.
Measurement of electric current
 Current is measured by an instrument called ammeter.
 The ammeter is always connected in series with the circuit with which the current
is to be measured.
 To measure the current in the circuit, the entire current is to be passed through
the ammeter, therefore the ammeter should have very low resistance so that it may
not change the value of the current flowing in the circuit.
How to get the continuous flow of electric current?
 The simplest way to maintain the potential difference
between the two ends of the conductor so as to get the
continuous flow electric current is to connect the
conductor with in the two terminals of the battery or
cell.
Direction of electric current
 In the past electricity was discovered prior to
the electrons. Therefore, the electric current or
electricity was considered to be the flow of
positive charges and the direction of flow
electric charges was taken as the direction of
electric current.
 The conventional direction of electric current is
from the positive terminal to the negative
terminal through the outer circuit.
Study material (Science) (Class 10)
Page 4 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 Later when the electrons were
discovered, it was found that the
positive charges can not flow through a
metal conductor. Therefore, the electric
current through a metal conductor was
defined as the flow of electrons.
 The electrons flow from negative
terminal to positive terminal in the
outer circuit. But the direction of
electric current is from the positive terminal to negative terminal.
How the electric current flows in the
wire?
 When the metal wire has not been
connected to a source like cell or
battery, then the electrons present in it
move at random in all directions
between the atoms of the metal wire.
 When a source of energy like cell or
battery is connected between the ends
of the metal wire, then an electric force acts on the electrons present in the wire.
Since the electrons are negatively charged, they start moving from negative
terminal to positive terminal of the wire.
Electric circuits
 A continuous conducting path consisting of wires and
other resistances and switch, between the two terminals
of the cell or a battery along which an electric current
flows, is called a circuit.
Symbols of electric components (or circuit symbols)
Components Symbols
 An electric cell
 Connecting wire
 An electric battery or a
combination of cells
 Plug key or switch (open)
or
Study material (Science) (Class 10)
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 Plug key or switch (close)
or
 A wire joint
 Wires crossing without joining
 Electric bulb
 A resistor of resistance R
 Variable resistance or rheostat
 Ammeter
 Voltmeter
 Galvanometer
Circuit diagrams
 A diagram which show that how different components are connected by using the
electric symbols for the components called circuit diagram.
G
A circuit diagram consisting of a
cell, a bulb and a closed switch.
A circuit diagram consisting of a
cell, a bulb and an open switch.
Voltmeter connected
parallel with the resistor.
Study material (Science) (Class 10)
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Ohm’s law
 According to ohm‟s law, at constant temperature, the current flowing through a
conductor is directly proportional to the potential difference across its ends.
If I is the current flowing through a conductor and V is the potential difference
across its ends, then according to ohm‟s law:
I  V (at constant temperature)
This can also be written as : V  I
V = R × I
Where “R” is the constant called resistance of the conductor.
R =
𝑉
𝐼
(V = potential difference, I = current and R = resistance)
 The ratio of the potential difference applied between the ends of a conductor to the
current flowing through it is a constant quantity called resistance.
R =
𝑉
𝐼
 current, I =
𝑉
𝑅
 Factors affecting the strength of electric current:
i. Potential difference across the ends of the conductor.
ii. Resistance of the conductor.
Resistance of the conductor
 When the electrons move from one part to another part, they collide with other
electrons and with the atoms and ions present in the body of the conductor.
 The property of a conductor due to which it opposes the flow of current is called
resistance.
Resistance =
𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
 R =
𝑉
𝐼
Ammeter in series with the circuit.
resistor
Connecting wire cell switch
Study material (Science) (Class 10)
Page 7 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 The SI unit of the resistance is “ohm (represented by symbol omega “”)”.
 1 ohm is the resistance of the conductor such that when a potential difference of I
volt is applied across its ends, and a current of 1 ampere flows through it.
1  =
1 𝑉
1 𝐴
Graph between V and I
 current (I)  potential difference (V)
 the graph between V and I is straight line passing through origin
Good conductors and insulators
 Those substances which have low electrical resistance are called good conductors.
Good conductors allow the passage of electric current easily. Silver is the best
conductor. Copper and aluminium are good conductors. Electric wires are made of
Cu and Al because they have low electric resistance.
 Those substances which have comparatively high electric resistance are called
resistors. Example: nichrome, manganin and constantan. Resistors reduces the
current in wire.
 Those substances which have infinitely high electric resistance are called
insulators. They do not allow the electric current to flow. Example: rubber, glass,
etc
Factors affecting the resistance of conductor
i. Length of conductor
ii. Area of cross-section of conductor or thickness of conductor
iii. Nature of the material of the conductor
iv. Temperature of conductor
Effect of length of conductor
 The resistance of the conductor is directly proportional to its length.
Resistance  length of conductor  R  l
When length of conductor is doubled its resistance also gets doubled and if the
length of conductor is halved then its resistance also gets halved.
Effect of Area of cross-section of conductor or thickness of conductor
 The resistance of the conductor is inversely proportional to its Area of cross-section
or thickness of conductor.
Study material (Science) (Class 10)
Page 8 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
Resistance 
1
Area of cro ss−section of conductor or thickness of conductor
 R 
1
𝐴
When Area of cross-section of conductor is doubled its resistance gets halved and if
the Area of cross-section of conductor is halved then its resistance gets doubled.
 Resistance of the conductor is also inversely proportional to the square of the
radius of wire and also inversely proportional to the square of the diameter of wire.
If radius or diameter of wire is doubled then the resistance of the wire gets one-
fourth.
Resistance 
1
radius of wire 2  R 
1
𝑟2
Resistance 
1
diameter of wire 2  R 
1
𝑑2
Effect of Nature of the material of the conductor
 Resistance of the conductor depends on the type of material of which it is made.
Some materials like metals have low resistance but some materials like nichrome
have high resistance.
 Resistance of nichrome wire is 60 times more than the copper wire of same length
and same cross-section area.
Effect of temperature
 The resistance of all pure metals increases on raising the temperature and
decreases on decreasing the temperature.
 Resistance of alloys like manganin, nichrome and constantan is almost unaffected
by temperature.
 Resistance of semiconductor materials like silicon and germanium decreases on
increasing the temperature.
Resistivity
 The resistance of the conductor is directly proportional to its length.
Resistance  length of conductor  R  l ………………. (1)
The resistance of the conductor is inversely proportional to its Area of cross-section
or thickness of conductor.
Resistance 
1
Area of cross −section of conductor or thickness of conductor
 R 
1
𝐴
… (2)
Combining (1) and (2), we get
R 
𝑙
𝐴
R = 
𝑙
𝐴
[ (Rho) is a constant known as resistivity of the material of the conductor.]
 Resistance of the material is directly proportional to the resistivity of the conductor.
If we change the material of the conductor to one whose resistivity is two times
then the resistance of the conductor also becomes two times, and vice versa.
Resistance  resistivity  R  
 The mathematical reaction for the resistivity of the conductor:-
 = R
𝐴
𝑙
Study material (Science) (Class 10)
Page 9 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
(R = resistance of conductor, l = length of conductor and A = area of cross-section of
conductor)
 The resistivity of the substance is numerically equal to the resistance if the rod of
that substance which is 1 meter long and 1 meter in cross-section. Resistivity of a
substance is equal to the resistance between the opposite faces of a 1 meter cube of
the substance.
 SI unit of resistivity:-  = R
𝐴
𝑙
=
𝑜𝑕𝑚 × 𝑚𝑒𝑡𝑟𝑒 2
𝑚𝑒𝑡𝑟𝑒
= ohm – metre
Factors affecting the resistivity of the substance
 Resistivity of the substance depends on the temperature of substance and nature
of substance. It does not depend on the length and area of cross-section of
substance.
 Silver is the best conductor of electricity. But it can not be used to make electrical
wires because it is very costly. Copper and aluminium are used to make electrical
wires because these metals are also having low resistivity and they are not much
costly.
 The heating elements of the heating appliances
such as iron and toasters are made of an alloy
rather than pure metal. Because:- the
resistivity of the alloy is much higher than that
of pure metal due to which the heating element
produces lot of heat on passing the electric
current, an alloy do not burn easily or does not
undergoes oxidation at high temperatures,
when it is red hot. Heating elements of the
heating appliances are made of nichrome alloy.
 The resistivity of insulators like ebonite, glass and diamond is very high and do not
change with temperature.
 The resistivity of semiconductors like silicon and germanium is in between those of
conductors and insulators and decreases on increasing temperature.
Combination of resistances or resistors
 The resistances can be combined in two ways:- (1) In series (2) in parallel
 When two or more resistances are connected end to end consecutively, they are
said to be connected in series.
 When two or more resistances are connected between the same two points, they are
said to be connected in parallel.
Resistances or resistors in series
 The combined resistance of any number of resistances connected in series is equal
to the sum of the individual resistances.
R = R1 + R2
 When a number of resistances are connected in series, then:-
Study material (Science) (Class 10)
Page 10 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
i. Each resistance has a different potential difference across its ends. The sum of
potential differences across all the resistances is equal to the voltage of the
battery applied.
ii. When a number of resistances are
connected in series then same current
flows through them.
Resultant resistances of two resistances
are connected in series
Two resistances R1 and R2 connected in
series. A battery of V volts has been applied
to the ends of the series combination. V1 is
the potential difference across R1 and V2 is
the potential difference across R2.
For the series combination of resistances the
sum of Potential differences across all resistors is equal to the voltage of battery.
V = V1 + V2 ………….(1)
If I is the current flowing in the circuit,
Then by ohm‟s law, V = I × R ………….(2)
Since same current passes through each resistor,
By ohm‟s law V1 = I × R1
………….(3) and V2 = I × R2 ………….(4)
Using (1), (2), (3) and (4)
I × R = I × R1 + I × R2
I × R = I × (R1 + R2)
R = R1 +R2
Resultant resistances of three
resistances are connected in series
Three resistances R1, R2 and R3 connected
in series. A battery of V volts has been
applied to the ends of the series
combination. V1 is the potential difference
across R1, V2 is the potential difference
across R2 and V3 is the potential
difference across R3.
For the series combination of resistances the sum of Potential differences across all
resistors is equal to the voltage of battery.
V = V1 + V2 + V3 …………. (1)
If I is the current flowing in the circuit,
Then by ohm‟s law, V = I × R …………. (2)
Since same current passes through each resistor,
By ohm‟s law V1 = I × R1 ….(3) ,
V2 = I × R2 ……(4) and V3 = I × R3 ….(5)
Using (1), (2), (3), (4) and (5)
Study material (Science) (Class 10)
Page 11 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
I × R = I × R1 + I × R2 + I × R3
I × R = I × (R1 + R2+ R3)
R = R1 +R2+ R3
Resistances or resistors in parallel
 The combined resistance of any number of resistances connected in parallel is
equal to the sum of reciprocals of all the
individual resistances.
1
𝑅
=
1
𝑅1
+
1
𝑅2
 When a number of resistances are connected
in parallel, then:-
i. Each resistance has same potential
difference across its ends, which is equal
to the potential difference of the battery.
ii. When a number of resistances are
connected in parallel then different
amount of current flows through each resistance. The sum of currents through
all the resistors is equal to the total current drawn from the battery.
Resultant resistances of two resistances are connected in parallel
Two resistances R1 and R2 connected in parallel. A battery of V volts has been applied
to the ends of the parallel combination. I1 is the current flowing through R1 and I2 is
the current flowing through R2.
For the parallel combination of resistances the sum of currents flowing through all
resistors is equal to the total current drawn from the battery.
I = I1 + I2 ………….(1)
If I is the total current flowing in the circuit, R is the total resistance of the parallel
combination of resistances and V is the potential difference of the battery applied.
Then by ohm‟s law, I =
𝑉
𝑅
………….(2)
Since there is same potential difference across each resistor,
By ohm‟s law I1 =
𝑉
𝑅1
………….(3) and I2 =
𝑉
𝑅2
………….(4)
Using (1), (2), (3) and (4)
𝑉
𝑅
=
𝑉
𝑅1
+
𝑉
𝑅2
𝑉
𝑅
= V
1
𝑅1
+
1
𝑅2

1
𝑅
=
1
𝑅1
+
1
𝑅2
Resultant resistances of three resistances are connected in parallel
Three resistances R1, R2 and R3 connected in parallel.
Study material (Science) (Class 10)
Page 12 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
A battery of V volts has been applied to the ends of the parallel combination. I1 is the
current flowing through R1, I2 is the current flowing through R2 and I3 is the current
flowing through R3.
For the parallel combination of resistances the sum of currents flowing through all
resistors is equal to the total current drawn from the battery.
I = I1 + I2 + I3 ………….(1)
If “I” is the total current flowing in the circuit, “R” is the total resistance of the parallel
combination of resistances and “V” is the potential difference of the battery applied.
Then by ohm‟s law, I =
𝑉
𝑅
………….(2)
Since there is same potential difference across each resistor,
By ohm‟s law I1 =
𝑉
𝑅1
………….(3) , I2 =
𝑉
𝑅2
………….(4) and I3 =
𝑉
𝑅3
………….(5)
Using (1), (2), (3), (4) and (5)
𝑉
𝑅
=
𝑉
𝑅1
+
𝑉
𝑅2
+
𝑉
𝑅3
𝑉
𝑅
= V
1
𝑅1
+
1
𝑅2
+
1
𝑅3

1
𝑅
=
1
𝑅1
+
1
𝑅2
+
1
𝑅3
Domestic electric circuits (series or parallel)
Disadvantages of series circuit for domestic wiring
 In series circuit if one electrical appliance stops working due to some defect, then
all appliances stop working because the whole circuit is broken.
Example:- in diwali lights the bulbs are connected in series, if one bulb gets fused
then all bulbs stop working.
 In series circuit there is only one switch for all electrical appliances, due to which
they can not be turned on and off separately.
Example:- if all the appliances in our home are connected in series then we will not
be able to run them separately.
 In series circuit all the electrical
appliances do not get the same voltage
(220 V) from the power supply line
because the voltage is shared by all the
appliances, due to which the appliance
getting low voltage do not work properly.
Example:- if some bulbs are connected in
series connection they will not get the
proper voltage and hence they will glow
less brightly.
 In the series connection of electrical
appliances, the over all resistance of the
electrical circuit increases much due to
which the current from the power supply
is low.
Study material (Science) (Class 10)
Page 13 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
Advantages of parallel circuits in domestic wiring
 In parallel circuit if one electrical appliance stops working due to some defect, then
all appliances keep working normally.
Example:- if number of bulbs are connected in parallel and one bulb gets fused
then all bulbs keep working.
 In parallel circuit each electrical appliance has its own switch due to which it can
be turned on and off independently, without affecting other appliances.
Example:- all the appliances in our home are connected in parallel due to which
each appliance can be turned on and off separately.
 In parallel circuit all the electrical appliances get the same voltage (220 V) from the
power supply line because the voltage is not shared by all the appliances, due to
which all the appliances get proper voltage and work properly.
Example:- if some bulbs are connected in parallel connection then they will get the
proper voltage and hence they will glow equally bright.
 In the parallel connection of electrical appliances, the over all resistance of the
electrical circuit is reduced very much due to which the current from the power
supply is high and each appliance draws the required amount of current for its
working.
Electric power
 When an electric current flow through the conductor, electrical energy is used up
and electric work is done.
 Electric power is defined as electric work done per unit time. “Or”. Rate of doing
electric work is also called power. “Or”. Rate at which electrical energy is consumed
by the appliance is called power.
Power =
𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
 P =
𝑊
𝑡
 SI unit of electric power is “watt (W)”. Another unit of electric power is “joule /
second (J/s) or J s-1”.
 The electric power is said to be 1 watt if 1 joule of electric work is done in 1 sec or 1
joule of electrical energy is consumed by appliance in 1 sec.
1 watt =
1 𝑗𝑜𝑢𝑙𝑒
1 𝑠𝑒𝑐𝑜𝑛𝑑
 The bigger units of electric power used for commercial purpose are “kilowatt and
megawatt”.
1 kilowatt = 1000 watt and 1 megawatt = 106 watt
Formula for calculating electric power
 We know that, power is defined as rate at which electric work is done
 Power =
𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
 P =
𝑊
𝑡
………… (1)
Potential difference between two points is defined as the amount of electric work done
in moving a unit amount of charge form one point to another point.
 Potential difference (p.d) =
𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒
𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑
 V =
𝑊
𝑄
 W = V × Q ….. (2)
Electric current is defined as flow of electrons per unit time.
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 Electric current (I) =
𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛
 I =
𝑄
𝑡
 Q = I × t …….. (3)
Using (2) and (3)
W = V × I × t …………. (4)
Using (1) and (4)
P =
V × I × t
𝑡
= V × I  electric power = voltage × current
 The power of an electrical appliance depends upon the potential difference between
the terminals of the appliance and current flowing through it.
 If an electrical appliance is operated at a potential difference of 1 volt and the
appliance carries the current of 1 ampere, then the power of the appliance is 1
watt.
1 watt = 1 volt × 1 ampere  1 W = 1 V × 1 A
Some other formulae of calculating electric power
Power P in terms of I and R
P = V × I …………………… (1)
From ohm‟s law, R =
𝑉
𝐼
 V = I × R ……. (2)
Using (1) and (2),
P = I × I × R
P = I2 × R
I = current, R = resistance
Power P in terms of V and R
P = V × I …………………… (1)
From ohm‟s law, R =
𝑉
𝐼
 I =
𝑉
𝑅
……. (2)
Using (1) and (2),
P = V ×
𝑉
𝑅
P =
𝑉2
𝑅
V = potential difference, R = resistance
Power voltage rating of the electrical appliance
 The power voltage rating of the electrical appliance tells us about the voltage
needed for the effective working of appliance and power used by it.
Electrical energy
 Electrical energy of the appliance is defined as the work done by the electric
current to flow through the appliance.
 Electrical energy of the appliance is given by the product of its power rating and the
time for which it is used.
Electrical energy = power × time  E = P × t
 The SI unit is “joule (J)”.
Study material (Science) (Class 10)
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 One joule of the electric energy is defined as the energy consumed by an appliance
of power 1 watt in 1 sec.
 If we take the unit of power as “watt (W)” and the unit of the time as “hour (h)” then
the unit of the electrical appliance is “watt-hour (Wh)”.
 One watt-hour of the electrical energy is defined as the amount of energy consumed
by an appliance of power 1 watt in 1 hour.
Factors on which electrical energy consumed by the appliance depends
1) Power rating of the appliance
2) Time for which the appliance is used
Commercial unit of electric energy: kilowatt-hour (kWh)
 1 kilowatt-hour is the amount of electrical energy consumed by an appliance of
1kW in 1 hour.
 1 kilowatt-hour is equal to 1 unit of electrical energy.
Relation between the kilowatt-hour and joule
Electrical energy = power × time  E = P × t
1 kWh = 1 kW × 1 h
1 kWh = 1000 W × 3600 s
1 kWh = 3600000 Ws
1 kWh = 3600000 J …………………… (1 Ws = 1 J)
1 kWh = 3.6 × 106 J
Effects produced by electric current
 Heating effects, magnetic effects and chemical effects.
Heating effect of electric current
 When an electric current is passed through a high resistance wire, like nichrome
wire, the resistance wire becomes very hot and produces heat. This is called
heating effects of electric current.
Joule’s law of heating (formula of heat energy)
“R” is resistance of the conductor, “I” is the current flowing through it for time “t”.
When a current flows through the conductor then some work is done the current ato
overcome resistance. Electric charge “Q” moves against the potential difference “V”,
the amount of work done “W” is:
W = Q × V……………………. (1)
Current is defined as the rate of flow of charge.
 Current =
𝑐𝑕𝑎𝑟 𝑔𝑒
𝑡𝑖𝑚𝑒
 I =
𝑄
𝑡
 Q = I × t……………………. (2)
From the ohm‟s law, V = I × R ……………………… (3)
Using (1), (2) and (3)
W = (I × t) × (I × R) = I2 R t
Since the electric work done against the resistance is converted into heat energy.
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 W = H
H = I2 R t
Factors on which the heat produced in a wire depends
1) Square of current (I2):- heat produced in a wire is directly proportional to the
square of current. H  I2
If we will double the current then the heat produced becomes four times. If the
current is halved then the heat becomes one-fourth.
2) Resistance of wire (R):- heat produced in a wire is directly proportional to the
resistance of wire. H  R
If we will double the resistance then the heat produced becomes two times. If the
resistance is halved then the heat becomes half.
3) Time for which current is passed (t):- heat produced in a wire is directly
proportional to time for which current is passed. H  t
If we will double the time then the heat produced becomes two times. If the time is
halved then the heat becomes half.
Applications of heating effect of electric current
 The heating effect of current is used I the working of the electrical heating
appliances such as electric iron, electric kettle, Electric toaster, electric oven, room
heaters, water heaters, electric geysers, etc.
 The heating effect of electric current is utilized in electric bulbs or electric lamps for
producing light.
 The heating effect of electric current is utilized in electric fuse for protecting
household wiring and electrical appliances.
Why does the coil of the heating appliance get heated up to a high temperature
(900C) but the connecting wires of the appliances do not get heated up?
 The resistance of the heating elements of the heating appliance is very high due to
which the amount of heat is very high due to the heating effect of electric current
but the resistance of the connecting wires of the appliance is very low due to which
no heat is produced in the connecting wires.
Why tungsten metal is used in making the filaments of electric bulb?
 Tungsten has high melting point of 3380C due to which it can be kept white hot
without melting away.
Tungsten has high flexibility and low rate of evaporation at high temperature.
What is the temperature of the tungsten filament when it is white hot?
 2500C
Which gases are present in the bulb? Why the gases are filled in the bulb?
 Nitrogen or argon or mixture of both is filled in bulb. The gases like nitrogen and
argon are inert in nature so they do not react with tungsten metal and they also
help tungsten metal to dissipate heat in the surroundings keeping the temperature
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of filament below the melting point (3380C). Due to this action of gases the life of
tungsten filament is prolonged.
What will happen if the tungsten metal is kept in air at high temperature?
 It will burn up quickly reacting wit the oxygen present in the air.
Out of bulb and tube light, which is more power efficient and why?
 Tubelight is more power efficient.
In bulb most of the electric power is used up in producing heat in the filament and
some amount of the electric power is converted into light so bulb is not power
efficient. Io tube light there is no filament due to which most of the power is
converted into light which makes the tubelight power efficient.
What is a fuse wire? How does it work?
 Fuse wire is a short length of thin tin plated copper wire having low melting point
but high resistance than the total resistance of the house.
 When the current in the household circuit exceeds too much due to some reason,
then fuse wire gets heated up, melts and breaks the circuit. Breaking of circuit
leads to stop the flow of large current in the appliances in our house and prevents
the damage to various electrical appliances.
Why the resistance of fuse wire is kept more than the resistance of the
household circuit?
 Resistance of fuse wire is kept more than resistance of the house hold circuit so
that the required amount of the current flows into the household circuit without
any obstruction.
Assignment
I. VERY SHORT ANSWER QUESTIONS (1 MARK)
(Answer the questions in one word or one sentence)
1. Multiple choice questions:
i. The S.I. unit of resistivity is
(a) Ω (b) Ω/cm (c) Ω m (d) Ω/m
ii. One horse power is equal to the
(a) 736 W (b) 746 W (c) 700 W (d) 726 W
iii. The instruments used to measure electric potential difference is
(a) voltmeter (b) ammeter (c) rheostat (d) generator
iv. Which of the following is not the unit of energy?
(a) Joule (b) kWh (c) kWs (d) kW
v. Resistivity of a wire depends upon the
(a) length (b) shape (c) thickness (d) material of wire
vi. Which of the following term does not represent electrical power in a circuit?
(a) I2
R (b) IR2
(c) VI (d) V2
/R
vii. An electric bulb is rated 220 V and 100 W. when it is operated at 110 V, the power consumed will
be
(a) 100 W (b) 75 W (c) 50 W (d) 25 W
viii. The power of a bulb producing 600 J energy in 30 second is
(a)2 W (b) 200 W (c) 1800 W (d) 2000 W
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ix. The net resistance of the above resistors is
(a) 30 Ω (b) 15 Ω (c) 60 Ω (d) 40 Ω
x. The physical quantity which is equal to V/I is
(a) resistivity (b) power (c) electrical energy (d) resistance
2. Define the following:
(i) Electrical current (ii) Electric potential difference (iii) Electric power (iv) Resistance (v) Electricity
(vi) Conductor (vii) Insulator
3. State Ohm’s law.
4. State Joule’s law of heating.
5. What is the resistivity of a material?
6. What does an electric circuit mean?
7. Define the unit of current.
8. Name a device that helps to maintain a potential difference across a conductor.
9. What determines the rate at which energy is delivered by a current?
II. SHORT ANSWER QUESTIONS (2 MARKS)
(Answer the questions in about 30 words)
1. On what factors does the resistance of a conductor depend?
2. What will happen to the current when it flows through a thick wire and thin wire of same material
connected to the same source?
3. Why are the coil of electric toasters and electric irons made of an alloy rather than pure metal?
4. Among iron and mercury, which is the better conductor of electricity and why?
5. What are the advantages of connecting electrical devices in parallel with the battery instead of
connecting them in series?
6. How is voltmeter connected in a circuit to measure the potential difference between two points?
7. Why does an electrician wear rubber gloves while working with electrical devices?
8. What is the need of an external potential difference despite the fact that electrons are in a state of
motion inside the atoms?
9. Why are fluorescent tubes used instead of bulbs?
10. Why are gases like argon and nitrogen filled in electric bulbs?
11. Calculate the number of electrons constituting one coulomb of charge.
12. What is meant by saying that the potential difference between two points is 1 V?
13. Why does the cord of an electric heater not glow while the heating element does?
14. Nichrome wire of length l and radius r has resistance of 10 Ω. How would the resistance of the wire
change when: (i) only length of the wire is doubled? (ii) only diameter of wire is doubled? Justify your
answer.
15. State the factors on which the resistance of a cylindrical conductor depends at a given temperature.
16. What is meant by the statement that the resistance of a wire is 1 Ω?
17. What combination is used for connecting in the circuit to measure the potential difference across two
points?
18. List two differences between a voltmeter and an ammeter.
19. Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at
room temperature. Why?
20. State differences between kilowatt and kilowatt hour.
21. How are resistance connected so that the equivalent resistance in physical quantity remains same in such
case?
22. Amongst iron, silver, nichrome, tungsten and copper, which metal/alloy should be used to make the
(i) heating element of electric geysers
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(ii) filament of incandescent bulbs
23. Give the significance of electric meter in a domestic circuit.
24. Though same current flows through the electric wires and the filament of bulb, yet only the filament
glows. Why?
25. under which conditions charges can move conductor?
26. List three factors on which amount of heat H produced in a resistor due to an electric current depends.
Also, express it mathematically.
27. Name the define commercial unit of energy. Relate it to SI unit of energy.
28. How is an ammeter and a voltmeter connected in an electric circuit?
29. State the advantages of connecting electrical devices in parallel instead of connecting them in series with
the battery.
30. Keeping the potential difference constant, the resistance of a circuit is doubled. By what factor does the
current change in the circuit?
III. SHORT ANSWER QUESTIONS (3 MARKS)
(Answer the questions in about 50 words)
1. Show how would you connect three resistors, each of 6 Ω, so that the combination has a resistance of (i)
9 Ω (ii) 4 Ω. Justify your answer.
2. Let the resistance of an electrical component remain constant while the potential difference across the
two ends of the component decreases to half of its former vale. What change will occur in the current
through it?
3. How much work is done in moving a charge of 2 C, across two points having a potential difference of 12
V?
4. Will current flow more easily through a thick wire or a thin wire of the same material when connected to
the same source? Why?
5. Draw the symbols of following components used in circuit diagrams.
(i) electric cell (ii) battery (iii) plug key (open) (iv) plug key (closed) (v) wire joint (vi) wire crossing
without joining (vii) electric bulb (viii) a resistor (ix) variable resistance (x) ammeter (xi) voltmeter (xii)
conductor
6. Draw a schematic diagram of a circuit consisting of a battery of a three cells of 2 V each, a 5 Ω resistor or
8 Ω resistor and a plug key, all connected in series.
7. How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (i) 4 Ω,
(ii) 1 Ω?
8. What is the cause of electrical resistance in a conductor?
9. (i) Two identical resistors, each of resistance 10 Ω, are connected in (a) series (b) parallel to a 6 V battery.
Calculate the ratio of power consumed in the combination of resistors in two cases.
(ii) draw the circuit diagram of the two cases.
10. State any two factors on which the resistance of a cylindrical conductor depends. Compare the resistance
of a conductor of length ‘l’ and area of cross-section ‘a’ with that of another conductor of same material
but of length and area of cross-section half and double respectively of the farmer.
11. Explain the term heating effects of electric current. Derive an expression for the heat produced by electric
current and state Joule’s law.
12. Why does the cord of an electric heater not glow while the heating element does?
13. Write the SI unit of resistance and define it. Match the correct range of resistivity with the materials
given.
(i) Conductors (a) 10-6
Ω
(ii) Alloys (b) 1012
to 1017
Ω
(iii) Insulators (c) 10-6
to 10-8
Ω
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14. Write one differences between direct current and alternating current. Which one of the two is mostly
produced at power stations in our country. Name one device which provides alternating current. State
one important advantage of using alternating current. State the frequency of power supply generated in
India.
15. Two identical wires, one of nichrome and the other of copper, are connected in series and a current (I) is
passed through them. State the change observed in the temperature of the two wires. Justify your
answers. State the law which explains the above observation.
16. (i) Distinguish between an open and as closed circuit.
(ii) Name the instrument used to measure electric current. How it is connected in a circuit?
(iii) state the direction of conventional current.
17. Two identical resistors are first connected in series and then in parallel. Find the ratio of equivalent
resistance in two cases.
18. Two identical wires are first connected in series and then in parallel to a source of supply. Find the ratio of
the heat produced in the case.
IV. NUMERICAL PROBLEMS (2 OR 3 MARKS)
1. How much energy is given to each coloumb of charge passing through a 6 V battery?
2. Judge the equivalent resistance when the following are connected in parallel-(i) 1 Ω and 106
Ω (ii) 1 Ω and
103
Ω and 106
Ω.
3. An electric lamp of 100 Ω, a toaster of resistance 50 Ω and a water filter of resistance 500 Ω are
connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same
source that takes as much current as all the three appliances, and what is the current through it?
4. What is the highest and lowest total resistance that can be secured by the combination of four coils of
resistance 4 Ω, 8 Ω, 12 Ω and 24 Ω.
5. An electric iron consumes energy at a rate of 840 Ω when heating is maximum and 360 Ω when the
heating is minimum. The voltage is 220 V. what is the current and the resistance in each case?
6. Compute the heat generated while transferring 96000 coulombs of charge in one hour through a
potential difference of 50 V.
7. An electric iron of resistance 20 Ω draws a current of 5 A. calculate the heat developed in 30 seconds.
8. An electric motor draws 5 A from 220 V line. Determine the power of the motor and energy consumed in
2 h.
9. A hot plate of an electric oven is connected to a 220 V line, has two resistance coils A and B, each of 24 Ω
resistance, which may be used separately, in series or in parallel. What are the currents in the three
cases?
10. A copper wire has diameter 0.5 mm and resistivity of 1.6 x 10-8
Ωm. what will be the length of this wire to
make resistance 10 Ω? How much does the resistance change if the diameter is doubled?
11. A wire of resistance 20 Ω is bent in the form of a closed circle. What is the effective resistance between
two points at the ends of any diameter of the circle?
12. A 12 V battery is connected in the arrangement of resistance given alongside:
(i) calculate the total effective resistance of the circuit.
(ii) the total current flowing in the circuit.
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13. In a factory, an electric bulb of 500 watt is used for 2 hours and an electric motor of 0.5 horse power is
used for 5 hours every day. Calculate the cost of using the bulb and the motor for one year, if the cost of
electrical energy is Rs 3 per unit.
14. Two circuits I and II are shown below. In circuit I the key is closed and in circuit II the key is open.
Compare the currents in the two circuits.
15. Electric lamps designed for use on a 220 V electric supply are rated 10 W each. Calculate the number of
lamps that can be connected in parallel to each other across the two wires of 220 V line if the maximum
allowed current is 5 A.
16. The vale of current I flowing in a given resistor for the corresponding values of potential difference V
across the resistor are given below:
I (Amperes) 0.5 1.0 2.0 3.0 4.0
V (Volts) 1.6 3.4 6.7 10.2 13.2
Plot a graph between V and I and calculate the resistance of that resistor.
17. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit.
Find the value of the resistance of the resistor.
18. How many 176 Ω resistor (in parallel) are required to carry 5 A on a 220 V line?
19. Several electric bulbs designed to be used on a 220 V electric supply line are rated 10 W. how many
electric bulbs can be connected in parallel with each other across the two wires of 220 V line if the
maximum allowable current id 5 A?
20. Compare the power used in the 2 Ω resistor in each of the following circuit:
(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and
(ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
21. Two lamps, one rated 100 W at 220 V and the other 60 W at 220 V are connected in parallel to electric
mains supply. What current is drawn from the line if the supply voltage is 220 V?
22. Which will consume more energy, a 250 W TV set in 1 hour or a 1200 W toaster in 10 minutes?
23. An electric heater of resistance 8 Ω draws 15 A from the service mains in 2 hours. Calculate the rate at
which heat is developed in the heater.
24. An electric heater rated 800 W operates 6 hours/day. Find the cost of energy to operate it for 30 days at
Rs 3.00 per unit.
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25. How much current will an electric bulb draw from 220 V source of the resistance of the bulb is 1200 Ω? If
in place of bulb, a heater of resistance 100 Ω is connected to the source, calculate the current drawn by it.
26. An electric bulb is connected to a 200 V generator. The current is 0.5 A. what is the power of the bulb?
27. For the circuit diagram given alongside, calculate:
(i) value of current flowing through each resistor
(ii) total current in the circuit
(iii) total effective resistance of the circuit.
28. FIND OUT THE READING OF AMMETER AND VOLTMETER IN THE CIRCUIT GIVEN BELOW:
29. A battery of 12 V is connected to a series combination of resistors 3 Ω, 4 Ω, 5 Ω and 12 Ω. How much
current would flow through the 12 Ω resistor?
30. The potential difference between the terminals of an electric heater is 60 V when it draws current of 4 A
from the source. What current will the heater draw if the potential difference is increased to 120 V?
31. An electric iron consumes energy at a rate of 840 W when heating is at the maximum and 360 W when
the heating is at the minimum. The voltage at which it is running is 220 V. what si the current and
resistance in each case?
32. Calculate the work done in moving a charge of 2 coulombs across two points having a potential difference
of 12 V.
33. Calculate (i) the highest and (ii) the lowest resistance that can be obtained by the combination of four
coils of resistances 4 Ω, 8 Ω, 12 Ω and 24 Ω?
34. In a household 5 tubelights of 40 W each are used for 5 hours and an electric press of 500 W for 4 hours
every day. Calculate the total electrical energy consumed by these appliances in a month of 30 days.
35. An electric charge of 3000
C flows through a circuit of 10 minutes. Find the current that flows in the circuit.
36. Compare the power used in the 2 Ω resistor in each of the following circuit:
(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and
(ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
37. A 6 Ω resistance wire is doubled by folding. Calculate the new resistance.
38. Resistance of a metal wire of length 25 cm is 6.5 Ω. If the diameter of the wire is 0.3 mm, calculate the
resistivity of the metallic wire.
39. In the given circuit, resistors A and B made of the same metal are of the same length but A is thicker than
B. which of the two ammeters will show a higher reading? Justify your answer.
40. A hot plate of an electric oven is connected to a 220 V line. It has two resistance coils A and B each of 30
Ω resistance which may be used separately in series or in parallel. Find the value of the current required
in each of the three cases.
V. LONG ANSWER QUESTIONS (5 MARKS)
1. State and verify the law of combination of resistance.
2. Explain the following:
(i) Why is tungsten used almost exclusively for filament of electric lamps?
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(ii) Why are the conductors of an electric heating devices, such a bread-toaster and electric irons, made of
an alloy rather than a pure metal?
(iii) Why is the series arrangement not used for domestic circuits?
(iv) How does the resistance of a wire vary with its area of cross-section?
(v) why are copper and aluminium wires usually employed for electricity transmission?
3. (i) Calculate the resistance of the wire using the graph.
(ii) DEFINE ELECTRIC POWER.
(iii) Derive relation between power, potential difference and resistance.
(iv) what is meant by the statement that the rating of a fuse in a circuit is 5 A?
4. Given that R1 = 100 Ω, R2 = 40 Ω, R3 = 30 Ω, R4 = 20 Ω and RA is the parallel combination of R1 and R2
whereas RB is the parallel combination R3 and R4. Combination RA is connected to the positive terminal of
12 V battery while combination RB is connected to the negative terminal. Ammeter A is connected
between the resistors RA and Rb.
(i) Find RA and RB. also calculate total resistance in the circuit.
(ii) draw the circuit diagram showing above combination connected to battery and ammeter.
5. (i) The temperature of the filament of bulb is 27000
C when it glows. Why does it not get burnt up at such
a high temperature?
(ii) The filament of an electric lamp, which draws a current of 0.25 A is used for 4 hours. Calculate the
amount of charge flowing through the circuit.
(iii) an electric iron is rated 2 kW at 220 V. calculate the capacity of the use that should be used for the
electric iron.
Magnetic effects of electric current
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Magnet and magnetism: The substances which have the property of attracting small pieces
of iron, nickel, cobalt, etc. are called magnets and this property of attraction is called
magnetism.
Natural magnets: Natural magnets are piece of lodestone, which is a black iron ore (Fe3O4)
called magnetite.
Origin of the word magnetism
Natural magnets called lodestones were found as early as the sixth century B.C. in the
province of Magnesia in ancient Greece, from which the word magnetism derives its name.
Magnetic poles: These regions of concentrated magnetic strength inside the magnet just near
its ends are called magnetic poles.
The end of a freely suspended magnet which points towards north is called the North Pole
while its end pointing towards south is called South Pole.
Basic properties of magnets
1) Attractive property: A magnet attracts small pieces of iron, cobalt, nickel, etc.
2) Directive property: A freely suspended magnet aligns itself nearly in the north-south
direction.
3) Law of magnetic poles: Like magnetic poles repel and unlike magnetic poles attract
each other.
4) Magnetic poles exist in pairs: If we break a magnet into two pieces, we always get two
small dipole magnets. It is not possible to obtain an isolated N-pole or S-pole.
Artificial magnets: Pieces of iron and other magnetic materials can be made to acquire the
properties of natural magnets. Such magnets are called artificial magnets.
Uses of magnets:
1) Magnets are used in radio and stereo speakers.
2) They are used in almirah and refrigerator doors to snap them closed.
3) They are used in video and audio cassette tapes, on the hard discs and floppies for
computers.
4) In children's toys.
5) In medicine, the magnetic resonance imaging (MRI) scanners expose the inner parts of
the patient's body for detailed examination by doctors.
Compass needle. It consists of a small and light magnetic needle pivoted at the centre of a
small circular brass case provided with a glass top, as shown in Fig. The ends of the compass
needle point approximately towards north and south directions. The end pointing towards
north is called North Pole and that pointing towards south is called South Pole. The north pole
of the needle is generally painted black or red.
MAGNETIC FIELD AND FIELD LINES
Magnetic Field
 Define: The space surrounding a magnet in which magnetic force is exerted, is called a
magnetic field.
 Direction: The direction of magnetic field at a point is the direction of the resultant force
acting on a hypothetical north pole placed where it is placed.
Magnetic Field Lines
 Define: The path traced by a north magnetic pole free to move under the influence of a
magnetic field is called a magnetic field line.
Study material (Science) (Class 10)
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 Other name of magnetic field lines: The magnetic field lines are also known as magnetic
lines of force.
 What does the direction of magnetic field lines at any point tells us: The direction of
tangent drawn on a magnetic field line at any point gives the direction of the magnetic
force on a north pole placed at that point.
 Direction of magnetic field line (outside the bar magnet): Since the direction of
magnetic field line is the direction of force on a north pole, so the magnetic field lines
always begin form the N- pole of a magnet and end on the S- pole of the magnet.
Direction of magnetic field line (inside the bar magnet): Inside the magnet, however, the
direction of magnetic field lines is from the S- pole of the magnet to the N- pole of the magnet.
Thus, the magnetic field lines are closed curves.
Methods of plotting lines of force. The following two methods are used for drawing lines of
force of a bar magnet: (i) Iron-filings method. (ii) Compass needle method.
IRON-FILINGS METHOD
 Place a card (thick, stiff paper) over a strong
bar magnet. Sprinkle a thin layer of iron
filings over the card with the help of a
sprinkler, and then tap the card gently. The
iron filings arrange themselves in a regular
pattern.
 This arrangement of iron filings gives us a
rough picture of the pattern of magnetic field
produced by a bar magnet.
How does iron fillings arrange themselves to represent the magnetic field patterm
around the bar magnet?
 The bar magnet exerts a force of magnetic field all around it. The iron filings experience the
force of magnetic field of the bar magnet. The force magnetic field of the bar magnet makes
the iron filings to arrange themselves in a particular pattern. Actually, under the influence
of the magnetic field of the bar magnet, the iron filings behave like tiny magnets and align
themselves along the directions of magnetic field lines. Thus, iron filings show the shape of
magnetic field produced by a bar magnet by aligning themselves with the magnetic field
lines.
Properties (or characteristics) of the Magnetic Field Lines
 The magnetic field lines originate from the north pole of a magnet and end at its south
pole.
 The magnetic field lines come closer to one another near the poles of a magnet but they are
widely separated at other places.
 The magnetic field lines do not intersect (or cross) one another.
How can we say that magnetic force is stronger near the poles of magnet than at other
places near the magnet?
The magnetic field lines of the magnet comes near teach other near the poles and they are
widely separated at other places, due to the more number of magnetic field lines near the
poles and less number of magnetic field lines at other places, the magnetic force is stronger at
poles than at other places
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Why magnetic field lines cannot intersect each other?
This is due to the fact that the resultant force on a north pole at any point can be only in one
direction. But if the two magnetic field lines intersect one another, then the resultant force on
a north pole placed at the point of intersection will be along two directions, which is not
possible.
COMPASS NEEDLE METHOD.
Magnetic Field of Earth
 How can we show that earth
behaves like a magnet: A
freely suspended magnet
always points in the north –
south direction even in the
absence of any other magnet.
This suggests that the earth
itself behaves as a magnet
which causes a freely
suspended magnet (or
magnetic needle) to point
always in a particular
direction: north and south.
 Shape of earth’s magnet: The
shape of the earth‟s magnetic
field resembles that of an
imaginary bar magnet of length
one – fifth of earth‟s diameter buried at its centre.
 Poles of earth’s magnet: The south pole of earth‟s magnet is in the geographical north
because it attracts the north pole of the suspended magnet. Similarly, the north pole of
earth‟s magnet in the geographical south because it attracts the south pole of the
suspended magnet. Thus, there is a magnetic S- pole near the geographical north, and a
magnetic N- pole near the geographical south.
Study material (Science) (Class 10)
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 Why the freely suspended magnet makes an angle of 15 with the geographical axis
of earth: The axis of earth‟s magnetic field is inclined at an angle about 15 with the
geographical axis. Due to this a freely suspended magnet (or magnetic needle) makes an
angle of about 15 with the geographical axis and points approximately in the north- south
directions at a place.
 Reason of earth’s magnetism: The earth‟s magnetism is due to the magnetic effect of
current (which is flowing in the liquid core at the centre of the earth). Thus, earth is a huge
electromagnet.
Magnetic Field Due to a Current in a Conductor
An activity to show that a wire carrying an electric current behaves like a magnet
Danish physicist H.C. Oersted was the first to demonstrate in 1820 that a current carrying
conductor produces a magnetic field around it.
 Take a straight thick copper wire and place it between the
points X and Y in an electric circuit as shown in Fig.
 Place a small compass near to this copper wire. See the
position of its needle.
 Pass the current through the circuit by inserting the key
into the plug.
 As we pass current though the copper wire XY, the compass needle gets deflected from its
position of rest. Since a magnetic needle can be deflected only by a magnetic field, so the
current carrying wire produces a magnetic field around it or it behaves like a magnet.
A current carrying conductor produces a magnetic field around it. This effect is called
magnetic effect of current.
How can detect the position of wires in wall using a magnetic compass?
A concealed current carrying conductor can be located due to the magnetic effect of current by
using a plotting compass. For example, if a plotting compass is moved on a wall, its needle will
show deflection at the place where current – carrying wire is concealed.
On what factor does the Magnetic Field Patterns Produced by current – carrying
conductors depends?
The pattern of magnetic field (or shape of magnetic
field lines) produced by a current conductor depends
on its shape.
Magnetic Field Pattern due to straight Current –
Carrying Conductor (Straight Current – carrying
Wire)
 Magnetic field pattern: The magnetic field lines
around a straight conductor (straight Wire) carrying
current are concentric circles whose centers lie on
the wire.
 Relation between the direction of current and
direction of magnetic field lines: When current in
the wire flows in the upward direction, then the
lines of magnetic field are in the anticlockwise
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direction. If the direction of current in the wire is reversed, the direction of magnetic field
lines also gets reversed.
 Factors on which the magnetic field produced by a straight current carrying
conductor depends:
1. If we increase the current in the conductor, the deflection of the compass needle
increases. This shows that, the magnitude of the magnetic field produced at a given
point is directly proportional to the current passing through the wire.
2. For a given current, if we move the compass needle away from the wire, its deflection
decreases. This shows that the magnitude of the magnetic field produced by a given
current in the wire is inversely proportional to the distance from the wire.
To know the direction of magnetic field we follow these rules
1) Right hand thumb rule: If the current carrying conductor is held in the right hand
such that the thumb points in the direction of the
current, then the direction of the curl of the fingers
will give the direction of the magnetic field, as shown
in Fig.
2) Maxwell's cork screw rule: If a right handed screw
be rotated along the wire so that it advances in the
direction of current, then the direction in which the
screw rotates gives the direction of the magnetic field
as shown in Fig.
Magnetic Field Pattern due to a circular Loop (or Circular Wire) Carrying Current
 Magnetic field pattern: The magnetic field lines are circular near the current – carrying
loop. As we move away, the concentric circles representing magnetic field lines become
bigger and bigger. At the centre of the circular loop, the magnetic field lines are straight.
 Factors affecting the magnitude of magnetic field produced by a current – carrying
circular loop (or circular wire) at its centre:
1) Directly proportional to the current passing through the circular loop (or circular wire.
If current flowing through circular loop increases then magnetic field becomes strong
and vice versa.
2) Inversely proportional to the radius of circular loop (or circular wire). If radius of
circular loop decreases then magnetic field at the center of loop increases.
Study material (Science) (Class 10)
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Clock Face Rule to determine the polarity of any face of a circular current loop
 If the current around the face of circular wire (or
coil) flows in the clockwise direction, then that
face of the circular wire (or coil) will be south -
pole (S-pole).
 If the current around the face of circular wire (or
coil) flows in the Anticlockwise direction, then
that face of circular wire (or coil) will be a North
pole (N-pole)
Magnetic Field due to a Solenoid
 Define: The solenoid is a long coil containing a
large number of close turns of insulated copper
wire.
 Magnetic field pattern: The magnetic field produced by a current – carrying solenoid is
similar to the magnetic field produced by a bar magnet.
 Magnetic field inside the solenoid: The magnetic field lines inside the solenoid are in the
form of parallel straight lines. This indicates that the strength of magnetic field is the same
at all the points inside the solenoid. If the strength of magnetic field is just the same in a
region, it is said to be uniform magnetic field.
 Poles of solenoid: the face of solenoid where the current is clockwise that face acts like
south pole and the face of solenoid where the current is anticlockwise that face acts like
north pole.
 How can we detect the poles of solenoid: We bring the north pole of a bar magnet near
both the ends of a current – carrying solenoid. The end of solenoid which will be repelled
by the north pole of bar magnet will be its north pole, and the end of solenoid which will be
attracted by the north pole of bar magnet will be its south pole.
 Factors affecting the strength of magnetic field produced by a current carrying
solenoid:
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1) The number of turns in the solenoid. Larger the
number of turns in the solenoid, greater will be the
magnetism, produced.
2) The strength of current in the solenoid. Larger the
current passed through solenoid, stronger will be the
magnetic field produced.
3) The nature of „‟core material‟‟ used in making solenoid.
The use of soft iron rod as core in a solenoid produces
the strongest magnetism.
4) Diameter of coil. If the diameter of coil decreases then magnetic field strength increases.
Electromagnet: A soft iron core placed inside a solenoid behaves like a powerful magnet when
a current is passed through the solenoid. This device is called an electromagnet.
When the current is switched off, the iron core loses its magnetism and so it is no longer an
electromagnet. Thus, electromagnets are temporary magnets.
Factors on which the strength of an electromagnet depends:
1) Number of turns in the coil. The larger the number of turns in the coil, greater is the
strength of the electromagnet.
2) Strength of the current. The larger the current passed through the solenoid, more
powerful is the electromagnet.
3) Nature of the core material. The core of the magnetic material like soft iron increases
the strength of the electromagnet.
Uses of electromagnets
 Cranes and lifts use electromagnets to separate and lift large quantities of iron scrap
and steel
 We find them in electrical devices like electric bells, telegraphs, telephones, loud
speakers, electric trains, electric motors and so on
 Doctors use weak electromagnets to remove steel splinters from the eye
Differences between an electromagnet and a permanent magnet
Electromagnet Permanent Magnet
1. It is a temporary magnet. It shows
magnetism only as long as the current is
through its coil.
1. It retains magnetism for a long time
even after the removal of the magnetizing
field (or current).
2. It can produce very strong magnetic
field.
2. It produces a much weaker field than
an electromagnet.
3. The strength of an electromagnet can
be easily varied by changing the strength
of current or number of turns in the coil.
3. Its strength cannot be changed,
4. The polarity of an electromagnet can be
reversed by sending the current in reverse
direction.
The polarity of a permanent magnet
cannot be changed.
Advantages of electromagnets over permanent magnets
1) An electromagnet can produce a very strong magnetic field.
Study material (Science) (Class 10)
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2) The strength of the magnetic field of an electromagnet can be increased/decreased by
increasing/decreasing the strength of current or the number of turns in the solenoid.
3) The polarity of an electromagnet can be reversed by sending the current in the reverse
direction.
MAGNETISM IN HUMAN BEINGS
 Define ionic currents and why they are produced: Extremely weak electric currents are
produced in the human body by the movement of charged particles called ions. These are
called ionic currents.
 Magnetic field produced in our body: When the weak ionic currents flow along the nerve
cells, they produce magnetic field in our body. When we try to touch something with our
hand, our nerves carry electric impulse to the appropriate muscles. And this electric
impulse creates a temporary magnetism in the body.
 Organs of body where magnetic field is produced: The two main organs of the human
body where the magnetic field produced is quite significant are the heart and the brain.
 Principle of MRI: The magnetism produced inside the human body (by the flow of ionic
currents) forms the basis of a technique called Magnetic Resonance Imaging (MRI) which is
used to obtain images (or pictures) of the internal parts of our body.
 Uses: Magnetism has an important use in medical diagnosis because, through MRI scans,
it enables the doctors to see inside the body. For example, MRI can detect cancerous tissue
inside the body of a person.
FORCE ON CURRENT – CARRYING STRAIGHT CONDUCTOR PLACED IN A MAGNETIC
FIELD
 A magnet exerts a mechanical force on a current – carrying wire, and if the free to move,
this force can produce a motion in the wire.
 Discoverer and his discovery: In 1821, Faraday discovered that: When a current –
carrying conductor is placed in a magnetic field, a mechanical force is exerted on the
conductor which can make the conductor move.
 Direction of force exerted on current carrying wire: The direction of force acting on a
current – carrying wire placed in a magnetic field is (i) perpendicular to the direction of
current, and (ii) perpendicular to the direction of magnetic field.
 When the maximum force exerted on a current carrying wire: The maximum force is
exerted on a current – carrying conductor only when it is perpendicular to the direction of
magnetic field.
 When no force exerted on a current carrying wire: No force acts on a current – carrying
conductor when it is parallel to the magnetic field.
 How the direction of force on a current – carrying conductor can be reversed:
1) The direction of force on a current – carrying conductor placed in a magnetic field can
be reversed by reversing the direction of current flowing in the conductor.
2) The direction of force on a current – carrying conductor placed in a magnetic field can
also reversed by reversing the direction of magnetic field.
Fleming’s Left – Hand Rule for the Direction of Force
 Statement: Hold the forefinger, the centre finger and the
thumb of your left hand at right angles to one another.
Adjust your in such a way that the forefinger points in the
direction of magnetic field and the centre finger points in
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the direction of current, then the direction in which thumb points, gives the direction of
fore acting on the conductor.
Q. When is the force exerted on a current-carrying conductor (i) maximum and (ii)
minimum?
Ans. (i) When the current-carrying conductor is held perpendicular to the direction of the
magnetic field, the force exerted on it is maximum.(ii) When the current-carrying conductor is
held parallel to the direction of the magnetic field, the force exerted on it is minimum or zero.
Q.A current carrying straight conductor is placed in east-west direction. What will be
the direction of the force experienced by this conductor due to earth's magnetic field?
How will this force get affected on?(i) Reversing the direction of flow of current ? (ii)
Doubling the magnitude of current?
Ans. The direction of earth's magnetic field is from geographical south to geographical north.
According to Fleming's left hand rule, the current carrying straight conductor placed in east-
west direction will be deflected downwards. (i) On reversing the direction, the conductor is
deflected in the upward direction. (ii) If the magnitude of current is doubled, it will result in
doubling the magnitude of the force.
Q. On what factors does the force experienced by a current carrying conductor placed in
a uniform magnetic field depend?
Ans. Factors on which the force experienced by a current carrying conductor placed in a
magnetic field depends. If a current / is flowing along the wire of length L which is placed
perpendicular to the direction of the magnetic field B, then the force F experienced by the wire
perpendicular to the current and the magnetic field (as given by Fleming's left hand rule) is
expressed as: F = BIL, Thus, F depends on current /, length L and strength of field B.
THE ELECTRIC MOTOR
 Define: A motor is a device which converts electrical energy into mechanical energy.
 Motion of which part of motor is used in various appliances: Every motor has a shaft
or spindle which rotates continuously when current is passed into it. The rotation of its
shaft is used to drive the various types of machines in homes and industry.
 Uses: Electric motor is used in electric fans, washing machines, refrigerators, mixer and
grinder, electric cars and many other appliances.
 Principle of a Motor: A motor works on the principle that when a rectangular coil is
placed in a magnetic field and current is passed through it, a force acts on the coil which
rotates it continuously.
ELECTRIC MOTOR
Electric motor. An electric motor is a rotating device
which converts electric energy into mechanical energy.
Principle. An electric motor works on the principle that a
current carrying conductor placed in a magnetic field
experiences a force, the direction of force is given by
Fleming's left hand rule.
Construction.
I. Field magnet. It is a strong horse shoe type magnet
with concave poles.
II. Armature. It is a rectangular coil ABCD having a
large number of turns of thin insulated copper wire
wound over a soft iron core. The armature is placed
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between the poles the field magnet and it can be rotated about an axis perpendicular to the
magnetic field les.
III. Split ring commutator. It consists of a cylindrical metal ring split into two halves S1 and
S2. The two ends A and D of the armature coil are connected to the split rings S1 and S2
respectively. As the coil rotates, the split rings also rotate about the same axis of rotation. The
function of the split ring commutator is to reverse the direction of current in the coil
after every half rotation.
IV. Brushes. Two graphite or flexible metal rods maintain a sliding contact with split rings S1
and S2, alternately.
V. Battery. A battery of few cells is connected to the brushes. The current from the battery
flows to the armature coil through the brushes and the split rings.
Working of a DC Motor
When the coil is powered, a magnetic field is
generated around the armature. The left side of
the armature is pushed away from the left
magnet and drawn towards the right, causing
rotation.
When the coil turns through 900, the brushes
lose contact with the commutator and the
current stops flowing through the coil.
However the coil keeps turning because of its own
momentum.
Now when the coil turns through 1800, the sides get
interchanged. As a result the commutator ring C1 is now in contact with brush B2 and
commutator ring C2 is in contact with brush B1. Therefore, the current continues to flow in the
same direction.
The Efficiency of the DC Motor Increases by:
 Increasing the number of turns in the coil
 Increasing the strength of the current
 Increasing the area of cross-section of the coil
 Increasing the strength of the radial magnetic field
An electric motor brings about rotational motion in domestic appliances such as
electric fans, washing machines, refrigerators,
mixers, grinders, blenders, computers, MP3 players,
etc.
ELECTROMAGNETIC INDUCTION: ELECTRICITY
FROM MAGNESTISM
 Define: when a conductor is moved in magnetic field
then magnetic field strength linked to conductor
changes and a current in induced in conductor so as
to oppose the change in magnetic field strength. This
phenomenon is called electromagnetic induction.
 Discoverer: The phenomenon of electromagnetic
induction was discovered by a British scientist
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Michael Faraday and an American scientist Joseph Henry independently in 1831.
 Instrument used to find the direction of current: A galvanometer is an instrument
which can be detect the presence of electric current in a circuit. It is connected in series
with the circuit. When no current is flowing through a galvanometer, its pointer is at the
zero mark. When an electric current passes through the galvanometer, then its pointer
deflects (or moves) either to the left side of zero mark or to the right side of the zero mark,
depending on the direction of current.
To Demonstrate Electromagnetic Induction by using a straight Wire and a Horseshoe –
Type Magnet
To Demonstrate Electromagnetic Induction by Using a Coil and a Bar Magnet
 The concept of a fixed coil and a rotating magnet is used to produce electricity on large
scale generators of power house.
 The condition necessary for the production of electric current by electromagnet induction
is that there must be a relative motion between the coil of wire and a magnet.
Observations about electromagnetic induction:
 A current is induced in a coil when it is moved (or rotated) relative to a fixed magnet.
 A current is also induced in a fixed coil when a magnet is moved (or rotated) relative to the
fixed coil.
 No current is induced in a coil when the coil and magnet both are stationary relative to one
another.
 When the direction of motion of coil (or magnet) is reversed, the direction of current
induced in the coil also gets reversed.
 Factors affecting the magnitude of induced current:
 By winding the coil on a soft iron core.
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 By increasing the number of turns in the coil.
 By increasing the strength of magnet.
 By increasing the speed of rotation of coil (or magnet).
Fleming’s Right – Hand rule for the Direction of Induced Current
 According to Fleming‟s right – hand rule: Hold the thumb, the forefinger and the centre
finger of your right – hand at right angles to one another. Adjust your hand in such a way
that forefinger points in the direction of magnetic field, and thumb points in the direction
of motion of conductor, then the direction in which centre finger points, gives the direction
of induced current in the conductor.
ELECTRIC GENERATOR
 Define: The electric generator is a machine for producing electric current or electricity.
 Energy conversion: The electric generator converts mechanical energy into electrical energy.
 Dynamo: A small generator is called a dynamo. For example, the small generator used on
bicycles for lighting purposes is called a bicycle dynamo.
 Principal of Electric Generator: The electric generator works on the principal that when a
straight conductor is moved in a magnetic field, then current is induced in the conductor. In an
electric generator, a rectangular coil (having straight sides) is made to rotate rapidly in the
magnetic field between the poles of a horseshoe – type magnet. When the coil rotates, it cuts the
magnetic field lines due to which a current is produced in the coil.
 Construction.
1. Field magnet. It is a strong horse shoe-type permanent magnet with concave poles.
2. Armature. ABCD is a rectangular armature coil. It consists of a large number of turns of insulated
copper wire wound on a soft iron cylindrical core. It can be rotated about an axis perpendicular to the
magnetic field of the field magnet.
3. Slip rings. These are two brass rings S1 and S2 rigidly connected to the two ends of the armature coil.
As the coil rotates, slip rings also rotate about the same axis of rotation.
4. Brushes. These are two graphite rods B1 and B2 which are kept pressed against the slip rings S1 and S2.
Through these brushes, the current induced in the armature coil is sent to the external circuit.
Working. As shown in Fig, suppose the armature coil ABCD is in the horizontal position. Now the coil is
rotated clockwise. The coil cuts the magnetic lines of force. The arm AB moves upwards while the arm CD
moves downwards. According to Fleming's right hand rule, the induced current flows from A to B in arm AB
and C to D in arm CD i.e., the induced current flows along ABCD. The induced current flows in the circuit
through brush B2 to Bv After half the rotation of the armature, the arm CD moves upwards and AS moves
downwards. The induced current now flows in the reverse direction i.e., along DCBA. The current flows from
Bx to B2. Thus the direction of current in the external circuit changes after every half rotation. Such a current
which changes its direction after equal intervals of time is called alternating current. This device is called
A.C. Generator.
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Current is induced in a coil when the current in
the neighboring coil changes.
We can conclude that a potential difference is
produced in the coil-2 whenever the electric current through the coil-1 is changing (starting or
stopping). Coil-1 is called the primarly coil and
coil-2 is called the secondary coil. As the current
in the first coil changes, the magnetic field
associated with it also changes. Thus the
magnetic field lines around the secondary coil
also change. Hence the change in magnetic field
lines associated with the secondary coil is the
cause of induced electric current in it. This
process, by which a changing magnetic field in a
conductor induces a current in another conductor, is called electromagnetic induction.
Differences between electric motor and generator
Electric motor Generator
1. It converts electrical energy into
mechanical energy.
1. It converts mechanical energy into
electrical energy.
2. It is based on magnetic effect of current. 2. It is based on electromagnetic induction.
3. Current is supplied to the coil placed in
magnetic field by an external source of
electrical energy. As a result of it, coil starts
rotating.
3. The coil is rotated in a magnetic field by an
external arrangement. As a result, an electric
current is induced in the coil.
Direct current. A direct current is that current which flows with constant magnitude in the
same direction.
Alternating current. An alternating current is that current whose magnitude changes
continuously with time and whose direction reverses after equal intervals of time.
Advantage of AC over DC.
Only alternating voltage can be stepped up or stepped down by using a transformer. This
makes AC more suitable than DC for transmission for electric power over long distances
without much loss of energy.
Frequency of a.c. mains in India
In India, the direction of A.C. changes after every 1/100 second, i.e., the frequency of A.C. is
50 Hz.
Domestic Electric Circuits
Domestic Wiring
 The electric power line enters our house through three wires- namely the live wire, the
neutral wire and the earth wire. To avoid confusion we follow a colour code for
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insulating these wires. The red wire is the live wire, and the black wire is neutral. The
earth wire is given green plastic insulation.
 The live wire has a high potential of 220 volts whereas the neutral wire has zero
potential. Thus the potential difference between the live wire and the neutral wire is
220-0 = 220 volts.
 The earth wire is much thicker in size and is made of copper. One end of it is connected
to a copper plate buried deep under the earth. The earth connection is made to the
electric meter and then to the main switch.
 In our homes, we receive supply of electric power through a main supply (mains), either
supported through overhead electric poles or by underground cables.
 The live wire and neutral wire, coming from the electric pole, enter a box fitted just
outside our house which has a main fuse F1. The fuse is connected in series with the
live wire. This is done so because it is only the live wire which has a high potential of
220 volts unlike the neutral wire which carries zero potential. The fuse F1 has a high
rating of about 50 amperes. Thus it prevents any damage such as fire to the entire
electrical wiring entering the house due to short-circuit or overloading.
 The two wires then enter the electricity meter which records the electrical power
consumed by us in kilowatt-hour (kWh). This meter is installed by the electric supply
Department of our city.
 These two wires coming out of the meter are then connected to a main switch which is
placed in a distribution box. Another fuse F2 is placed in series with the live wire in this
box for the sake of consumer safety.
 There are two separate circuits in a house namely lighting circuit and power circuit.
The lighting circuit with a 5 A fuse is used for running electric bulbs, fan, radio, TV,
tube lights etc. and the power circuit with a 15 A fuse is used for running electric
heater, electric iron, geyser, refrigerator etc as it draws more current.
 The distribution circuits are always connected in parallel combination. In a parallel
circuit even if there is a fault or short-circuiting in any one line, the corresponding fuse
blows off leaving the other circuits and appliances intact and prevents damage to the
entire house.
 In case short-circuit occurs in the power circuit, then the power-fuse will blow off but
our lights will continue to burn as the lighting circuit remains unaffected.
 A constant voltage of the main line is available for all other electrical appliances.
 Along with the two wires, a third wire called the earth wire also enters our house as
shown in the fig. The earth connection is first made to the electric meter and then to
the main switch. This wire then goes into the rooms along with the live and neutral
wires.
Study material (Science) (Class 10)
Page 38 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
Why all switches are put in live wire: All the electrical appliances are provided with separate
switches. All the switches are put in the live wire, so that when we switch off an electrical
appliances (like an electric iron), then its connection with the live wire is cut off and there will
be no danger of an electric shock if we touch the metal case of the electrical appliances. If,
however, we put switches in the neutral wire, then the live wire will be in connection with the
electrical appliances even when the switch is in the off position, and there is a danger of an
electric shock.
SAFETY DEVICES IN HOUSEHOLD CIRCUITS
Earthing of Electrical Appliances
 Why earthing is needed: To avoid the risk of electric shocks, the metal body of an electrical
appliances is earthed’. Earthing means to connect the metal case of electrical appliances to the
earth (at zero potential) by means of a metal wire called “earth wire”.
 How earth wire is connected in the house hold circuit: One end of the earth wire is buried in
the earth. We connect the earth wire to the metal case of the electrical appliances by using a
three – pin plug.
 What will happen if we accidentally touch the earthed appliance: If by chance, the live wire
touches the metal case of the electric iron (or any other appliances), which has been earthed,
then the current passes directly to the earth through the earth wire. It does not need our body
to pass the current and, therefore we do get an electric shock.
 What kind of appliances are earthed: We give earth connections to only those electrical
appliances which have metallic body, which draw heavy current, and which we are liable to
touch.
 Why we don’t do earthing of bulbs and tube lights: We, however, do not do earthing of an
electric bulb or a tube – light because we hardly touch them when they are on. The metal
casings of the switches are, however, earthed.
Electric Fuse
 What happens to the copper wire if maximum current passes through them: The electric
wires used in domestic wiring are made of copper metal because copper is a good conductor of
electricity having very low resistance. If the current passing through wires exceeds this
maximum value, the copper wires get over heated and may even cause a fire.
 When a large current can flow in household circuit: An extremely large current can flow
domestic wiring under two circumstances: Short circuiting and overloading.
 Short Circuiting: This touching of the live wire and neutral wire directly is known as short
circuit. When the two wires touch each other, the resistance of the circuit so formed is very,
very small very large current flows through the wires and heats the wires to a dangerously
high temperature, and a fire may be started.
 Overloading: If too many electrical appliances of high power rating (like electric iron, water
heater, air conditioner, etc.,) are switched on at the same time, they draw an extremely large
current from the circuit. This is known as overloading the circuit. Due to an extremely large
current flowing through them, the copper wires of household wiring het heated to a very
high temperature and a fire may be started.
 Define of fuse: A fuse is a safety device having a short length of a thin, tin- plated copper wire
having low melting point, which melts and breaks the circuit if the current exceeds a safe value.
Study material (Science) (Class 10)
Page 39 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 On what factor does the thickness and length of fuse wire depends: The thickness and
length of the fuse wire depends on the maximum current allowed through the circuit.
 On which law does the electric fuse work: An electric fuse works on the heating effect of
current.
 Why we use thin fuse wire: We use a thin wire in a fuse because it has a much greater
resistance the rest of connecting wires. Due to its high resistance, the heating effect of current
will be much more in the fuse wire than anywhere else in the circuit. This will melt the fuse wire
whereas other wiring will remain safe.
 Why we should not use thick fuse wire: We should not use a thick wire as a fuse wire because
it will have a low resistance and hence it will not get heated to its melting point easily.
 Why we should not use copper wire as fuse wire: A pure copper wire cannot be used as a
fuse wire because it has a high melting point due to which it will not melt easily when a short
circuit takes place.
 Disadvantage of fuse wire: A blown fuse should be replaced only after the cause of excessive
current flow has been found and removed.
 What are used these days which have an advantage over fuse wire: These days more and
more houses are using ‘Miniature Circuit Breakers’ (MCBs) to protect the household wiring
from the excessive flow of electric current through it.
 How does MCB work: If the current becomes too large, the miniature circuit breaker puts off a
switch cutting off the electric supply. The MCB can be re-set when the fault has been corrected.
Miniature current breaker (MCB) contains an electromagnet which, when the current exceeds
the rated value of circuit breaker, becomes strong enough to separate a pair of contacts (by
putting of a switch) and breaks the circuit. So, unlike fuses, MCBs do not work on heating effect
of current MCBs work on the magnetic effect of current.
 Where fuses are used these days: Fuses are also used to protect the individual domestic
electrical appliances from damage which may be caused due to excessive current flow through
them.
Hazards of Electricity (or Dangers of Electricity)
 If a person happens to touch a live electric wire, he gets a severe electric shock. In some cases,
electric shock can even kill a person.
 Short – circuiting due to damaged wiring or overloading of the circuit can cause electrical fore in
a building.
 The defects in the household wiring like loose connections and defective switches, sockets and
plugs can cause sparking and lead to fires.
Precautions in the Use of Electricity
Study material (Science) (Class 10)
Page 40 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
 If a person accidently touches a live electric wire or if an electric fir starts in the house, the main
switch should be turned off at once so as to cut off the electricity supply. This will prevent the
fire from spreading.
 The person who happens to touch the live electric wire should be provided an insulated support
wood, plastic or rubber. We should never try to pull away the person who is in contact with the
live wire, otherwise we will also get a shock.
 All the electrical appliances like electric iron, cooler, and refrigerator, etc. should be given
connection to save ourselves from the risk of electric shocks. Even if the earth connection is
there, we should avoid touching the metal body of an electric appliances when it is on.
 All the switches should be put in the live wire of the A.C. circuit, so that when the switch is
turned off, the appliances gets disconnected from live wire and there is no risk of electric shock.
 We should always be connected in the live wire of the circuit. The fuse wire should be of proper
rating and material. We should never use a copper wire (connecting wire) as fuse wire because
a copper wire has a very high current rating due to which a copper wire fuse cannot protect the
wiring against short circuiting or overloading.
 The household wiring should be done by using good quality wires having proper thickness and
insulation. All the wire connections with switches, sockets, and plugs should be tight, and all the
wire joints should be covered with insulated adhesive tape. Defective switches, sockets and
plugs should be replaced immediately.
Energy: Whenever a body is capable of doing work, the body is said to possess energy.
Thus energy is defined as the ability of a body to do work and the amount of energy
Sources of Energy
Study material (Science) (Class 10)
Page 41 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)
possessed by a body is equal to the amount of work it can do when its energy is
released.
Units of energy: On S.I. system, energy is measured in the units of joules or in
calories and on C.G.S. system in ergs. However, the commercial unit of energy is
kilowatt-hour. The energy is said to be one kilowatt-hour, when a body consumes one
kilowatt of energy in one hour.
Sources of energy: A source of energy is that which is capable of providing enough
useful energy at a steady rate over a long period of time.
A good source of energy should be:
(i) Safe and convenient to use, e.g., nuclear energy can be used only by highly
trained engineers with the help of nuclear power plants. It cannot be used for
our household purpose.
(ii) Easy to transport, e.g., coal, petrol, diesel, LPG etc. Have to be transported
from the places of their production to the consumers.
(iii) Easy to store, e.g., huge storage tanks are required to store petrol, diesel, LPG
etc.
Characteristics of an ideal or a good fuel:
1. It should have a high calorific or a heat value, so that it can produce
maximum energy by low fuel consumption.
2. It should have a proper ignition temperature, so that it can burn easily.]
3. It should not produce harmful gases during combustion.
4. It should be cheap in cost and easily available in plenty for everyone.
5. It should be easily and convenient to handle, store and transport from one
place to another.
6. It should not be valuable to any other purpose than as a fuel.
7. It should burn smoothly and should not leave much residue after its
combustion.
Classification of sources energy:
The sources of energy can be classified as follows:
(i) Renewable (ii) Non-Renewable.
Renewable sources of energy
 Renewable sources of energy are those which are Inexhaustible, i.e., which can
be replaced as we use them and can be used to produce energy again and again.
 These are available in an unlimited amount in nature and develop within a
relatively short period of time.
 Examples of Renewable Sources of Energy: (i)Solar energy, (ii) Wind Energy,
(iii) water energy (hydro-energy), (iv) Geothermal energy, (v) Ocean energy, (vi)
Biomass energy (firewood, animal dung and biodegradable waste from cities and
crop residues constitute biomass).
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Sa 1... science .. class 10

  • 1. Study material (Science) (Class 10) Page 1 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Electricity  Electricity is used in our homes, in industry and in transport. Example: - In homes  lightening, operating fans and for heating purpose. In industry  used in running machines. In transport  used in electric trains, street lightning, etc Types of electric charges  There are two types of electric charges: positive charges and negative charges.  The charge acquired by glass rod is positive charge and charge acquired by silk cloth is negative charge, when glass rod is rubbed with the silk cloth. The charge acquired by ebonite rod is negative charge and charge acquired by wool is positive charge, when ebonite rod is rubbed with the wool. Property of electric charges 1. Opposite charges or unlike charges attract each other. (a positive charge attract negative charge) 2. Similar charges or like charges repel each other. (two positive charges or two negative charges repel each other)  The SI unit of electric charge is “coulomb (C)”.  One coulomb is the quantity of electric charge which exerts a force of 9 × 109 Newton on an equal charge placed at a distance of 1m from it.  All matters contain positively charged particles called protons and negatively charged particles called electrons. A proton carries a positive charge of 1.6 × 10-19 C and electron carries a negative charge of 1.6 × 10-19.  The unit of electric charge is much bigger than the charge of proton or electron. Conductors and insulators All the substances can be categorized in two electric categories: - conductors and insulators.  The substances through which charges can flow easily are called conductors.  The conductors can also be defined as the substances through which electricity can flow easily. Example: - all metals (silver, aluminium, etc), metal alloys (manganin, constantan), carbon in the form of graphite and human body.  Those substances through electric charges can not flow are called insulators.  Insulators can also be defined as the substances through which electricity does not flow. Example: - plastic, glass, ebonite, etc.  In case of glass rod rubbed with silk and ebonite rod rubbed with wool, the charges attained by glass rod and ebonite rod are fixed but they don‟t move.  All the conductors have some free electrons which are loosely held by the nucleus of their atoms. These free electrons can move from one atom to another throughout conductor. The presence of these free electrons in the substance makes it a conductor. Electricity
  • 2. Study material (Science) (Class 10) Page 2 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  The electrons present in the insulators are tightly bound by the nucleus of the atoms of insulators due to which they can not move from one atom to another, this property makes a substance insulator. Types of electricity Electricity can be divided in two parts on the bases of the movement of charges. 1. Static electricity:-  The type of electricity in which charges are at rest or do not move is called static electricity. Example:- the charges acquired by glass rod and silk cloth, when they are rubbed with each other, the charges acquired by the ebonite rod and wool, when they are rubbed with each other and lightening in the sky. 2. Current electricity:-  The type of electricity in which charges are in motion is called current electricity. Example: - the electricity we use in our homes. Electric potential  The electric potential at any point in the electric field is defined as the work done in moving a unit positive charge from infinity to that point.  Electric potential is denoted by “V” and its SI unit is “volt”.  When 1 joule of work is done to move 1 C of positive charge form infinity to a point then the electric potential at that point is said to be 1 volt or 1 V. Potential difference  The difference in the electric potential between two points is called potential difference.  The potential difference between the two points in an electric circuit is defined as amount of work done in moving a unit positive charge from one point to another point is called potential difference between the two points. Potential difference (p.d) = 𝑤𝑜 𝑟𝑘 𝑑𝑜𝑛𝑒 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑 V = 𝑊 𝑄  The SI unit of potential difference is “volt (V)”.  The potential difference between the two points is said to be 1 volt if 1 joule of work is done to move 1 coulomb of positive charge form one point to another point. 1 volt = 1 𝐽 1 𝐶  1 V = 1 J/C = 1 JC-1 Electric current  When two bodies kept at different electric potentials are connected by a metal wire then the electric charges flow from body at high potential to the body at low potential through the wire till both the bodies are at same potential.  It is the potential difference between the two bodies which makes the electric charges to flow in the wire.  The electric charges which flow in the wire are electrons.  The electric current can be defined as the flow of electrons in the conductor such as metal wire.
  • 3. Study material (Science) (Class 10) Page 3 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  The magnitude of the electric current in a conductor is the amount of electric charge passing through a given point of the conductor in one second. Current (I) = 𝑄 𝑡 , where “Q” is the charge in coulomb and “t” is the time taken in seconds.  The SI unit of electric current is ampere (A).  When 1 C of charge is flows through any cross section of a conductor in 1 second, then the electric current flowing through the wire is said to be 1 ampere (1 A). 1 A = 1 𝐶 1 𝑠𝑒𝑐𝑜𝑛𝑑 = 1 C /s = 1 C s-1  1 milliampere = 1 1000 ampere  1 mA = 10-3 A Measurement of potential difference  The potential difference is measured by an instrument called voltmeter.  The voltmeter is always connected in parallel across the two points where the potential difference is to be measured.  A voltmeter has a high resistance so that it takes negligible current from the circuit.  Voltage is another name of potential difference. Measurement of electric current  Current is measured by an instrument called ammeter.  The ammeter is always connected in series with the circuit with which the current is to be measured.  To measure the current in the circuit, the entire current is to be passed through the ammeter, therefore the ammeter should have very low resistance so that it may not change the value of the current flowing in the circuit. How to get the continuous flow of electric current?  The simplest way to maintain the potential difference between the two ends of the conductor so as to get the continuous flow electric current is to connect the conductor with in the two terminals of the battery or cell. Direction of electric current  In the past electricity was discovered prior to the electrons. Therefore, the electric current or electricity was considered to be the flow of positive charges and the direction of flow electric charges was taken as the direction of electric current.  The conventional direction of electric current is from the positive terminal to the negative terminal through the outer circuit.
  • 4. Study material (Science) (Class 10) Page 4 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  Later when the electrons were discovered, it was found that the positive charges can not flow through a metal conductor. Therefore, the electric current through a metal conductor was defined as the flow of electrons.  The electrons flow from negative terminal to positive terminal in the outer circuit. But the direction of electric current is from the positive terminal to negative terminal. How the electric current flows in the wire?  When the metal wire has not been connected to a source like cell or battery, then the electrons present in it move at random in all directions between the atoms of the metal wire.  When a source of energy like cell or battery is connected between the ends of the metal wire, then an electric force acts on the electrons present in the wire. Since the electrons are negatively charged, they start moving from negative terminal to positive terminal of the wire. Electric circuits  A continuous conducting path consisting of wires and other resistances and switch, between the two terminals of the cell or a battery along which an electric current flows, is called a circuit. Symbols of electric components (or circuit symbols) Components Symbols  An electric cell  Connecting wire  An electric battery or a combination of cells  Plug key or switch (open) or
  • 5. Study material (Science) (Class 10) Page 5 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  Plug key or switch (close) or  A wire joint  Wires crossing without joining  Electric bulb  A resistor of resistance R  Variable resistance or rheostat  Ammeter  Voltmeter  Galvanometer Circuit diagrams  A diagram which show that how different components are connected by using the electric symbols for the components called circuit diagram. G A circuit diagram consisting of a cell, a bulb and a closed switch. A circuit diagram consisting of a cell, a bulb and an open switch. Voltmeter connected parallel with the resistor.
  • 6. Study material (Science) (Class 10) Page 6 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Ohm’s law  According to ohm‟s law, at constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. If I is the current flowing through a conductor and V is the potential difference across its ends, then according to ohm‟s law: I  V (at constant temperature) This can also be written as : V  I V = R × I Where “R” is the constant called resistance of the conductor. R = 𝑉 𝐼 (V = potential difference, I = current and R = resistance)  The ratio of the potential difference applied between the ends of a conductor to the current flowing through it is a constant quantity called resistance. R = 𝑉 𝐼  current, I = 𝑉 𝑅  Factors affecting the strength of electric current: i. Potential difference across the ends of the conductor. ii. Resistance of the conductor. Resistance of the conductor  When the electrons move from one part to another part, they collide with other electrons and with the atoms and ions present in the body of the conductor.  The property of a conductor due to which it opposes the flow of current is called resistance. Resistance = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑐𝑢𝑟𝑟𝑒𝑛𝑡  R = 𝑉 𝐼 Ammeter in series with the circuit. resistor Connecting wire cell switch
  • 7. Study material (Science) (Class 10) Page 7 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  The SI unit of the resistance is “ohm (represented by symbol omega “”)”.  1 ohm is the resistance of the conductor such that when a potential difference of I volt is applied across its ends, and a current of 1 ampere flows through it. 1  = 1 𝑉 1 𝐴 Graph between V and I  current (I)  potential difference (V)  the graph between V and I is straight line passing through origin Good conductors and insulators  Those substances which have low electrical resistance are called good conductors. Good conductors allow the passage of electric current easily. Silver is the best conductor. Copper and aluminium are good conductors. Electric wires are made of Cu and Al because they have low electric resistance.  Those substances which have comparatively high electric resistance are called resistors. Example: nichrome, manganin and constantan. Resistors reduces the current in wire.  Those substances which have infinitely high electric resistance are called insulators. They do not allow the electric current to flow. Example: rubber, glass, etc Factors affecting the resistance of conductor i. Length of conductor ii. Area of cross-section of conductor or thickness of conductor iii. Nature of the material of the conductor iv. Temperature of conductor Effect of length of conductor  The resistance of the conductor is directly proportional to its length. Resistance  length of conductor  R  l When length of conductor is doubled its resistance also gets doubled and if the length of conductor is halved then its resistance also gets halved. Effect of Area of cross-section of conductor or thickness of conductor  The resistance of the conductor is inversely proportional to its Area of cross-section or thickness of conductor.
  • 8. Study material (Science) (Class 10) Page 8 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Resistance  1 Area of cro ss−section of conductor or thickness of conductor  R  1 𝐴 When Area of cross-section of conductor is doubled its resistance gets halved and if the Area of cross-section of conductor is halved then its resistance gets doubled.  Resistance of the conductor is also inversely proportional to the square of the radius of wire and also inversely proportional to the square of the diameter of wire. If radius or diameter of wire is doubled then the resistance of the wire gets one- fourth. Resistance  1 radius of wire 2  R  1 𝑟2 Resistance  1 diameter of wire 2  R  1 𝑑2 Effect of Nature of the material of the conductor  Resistance of the conductor depends on the type of material of which it is made. Some materials like metals have low resistance but some materials like nichrome have high resistance.  Resistance of nichrome wire is 60 times more than the copper wire of same length and same cross-section area. Effect of temperature  The resistance of all pure metals increases on raising the temperature and decreases on decreasing the temperature.  Resistance of alloys like manganin, nichrome and constantan is almost unaffected by temperature.  Resistance of semiconductor materials like silicon and germanium decreases on increasing the temperature. Resistivity  The resistance of the conductor is directly proportional to its length. Resistance  length of conductor  R  l ………………. (1) The resistance of the conductor is inversely proportional to its Area of cross-section or thickness of conductor. Resistance  1 Area of cross −section of conductor or thickness of conductor  R  1 𝐴 … (2) Combining (1) and (2), we get R  𝑙 𝐴 R =  𝑙 𝐴 [ (Rho) is a constant known as resistivity of the material of the conductor.]  Resistance of the material is directly proportional to the resistivity of the conductor. If we change the material of the conductor to one whose resistivity is two times then the resistance of the conductor also becomes two times, and vice versa. Resistance  resistivity  R    The mathematical reaction for the resistivity of the conductor:-  = R 𝐴 𝑙
  • 9. Study material (Science) (Class 10) Page 9 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) (R = resistance of conductor, l = length of conductor and A = area of cross-section of conductor)  The resistivity of the substance is numerically equal to the resistance if the rod of that substance which is 1 meter long and 1 meter in cross-section. Resistivity of a substance is equal to the resistance between the opposite faces of a 1 meter cube of the substance.  SI unit of resistivity:-  = R 𝐴 𝑙 = 𝑜𝑕𝑚 × 𝑚𝑒𝑡𝑟𝑒 2 𝑚𝑒𝑡𝑟𝑒 = ohm – metre Factors affecting the resistivity of the substance  Resistivity of the substance depends on the temperature of substance and nature of substance. It does not depend on the length and area of cross-section of substance.  Silver is the best conductor of electricity. But it can not be used to make electrical wires because it is very costly. Copper and aluminium are used to make electrical wires because these metals are also having low resistivity and they are not much costly.  The heating elements of the heating appliances such as iron and toasters are made of an alloy rather than pure metal. Because:- the resistivity of the alloy is much higher than that of pure metal due to which the heating element produces lot of heat on passing the electric current, an alloy do not burn easily or does not undergoes oxidation at high temperatures, when it is red hot. Heating elements of the heating appliances are made of nichrome alloy.  The resistivity of insulators like ebonite, glass and diamond is very high and do not change with temperature.  The resistivity of semiconductors like silicon and germanium is in between those of conductors and insulators and decreases on increasing temperature. Combination of resistances or resistors  The resistances can be combined in two ways:- (1) In series (2) in parallel  When two or more resistances are connected end to end consecutively, they are said to be connected in series.  When two or more resistances are connected between the same two points, they are said to be connected in parallel. Resistances or resistors in series  The combined resistance of any number of resistances connected in series is equal to the sum of the individual resistances. R = R1 + R2  When a number of resistances are connected in series, then:-
  • 10. Study material (Science) (Class 10) Page 10 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) i. Each resistance has a different potential difference across its ends. The sum of potential differences across all the resistances is equal to the voltage of the battery applied. ii. When a number of resistances are connected in series then same current flows through them. Resultant resistances of two resistances are connected in series Two resistances R1 and R2 connected in series. A battery of V volts has been applied to the ends of the series combination. V1 is the potential difference across R1 and V2 is the potential difference across R2. For the series combination of resistances the sum of Potential differences across all resistors is equal to the voltage of battery. V = V1 + V2 ………….(1) If I is the current flowing in the circuit, Then by ohm‟s law, V = I × R ………….(2) Since same current passes through each resistor, By ohm‟s law V1 = I × R1 ………….(3) and V2 = I × R2 ………….(4) Using (1), (2), (3) and (4) I × R = I × R1 + I × R2 I × R = I × (R1 + R2) R = R1 +R2 Resultant resistances of three resistances are connected in series Three resistances R1, R2 and R3 connected in series. A battery of V volts has been applied to the ends of the series combination. V1 is the potential difference across R1, V2 is the potential difference across R2 and V3 is the potential difference across R3. For the series combination of resistances the sum of Potential differences across all resistors is equal to the voltage of battery. V = V1 + V2 + V3 …………. (1) If I is the current flowing in the circuit, Then by ohm‟s law, V = I × R …………. (2) Since same current passes through each resistor, By ohm‟s law V1 = I × R1 ….(3) , V2 = I × R2 ……(4) and V3 = I × R3 ….(5) Using (1), (2), (3), (4) and (5)
  • 11. Study material (Science) (Class 10) Page 11 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) I × R = I × R1 + I × R2 + I × R3 I × R = I × (R1 + R2+ R3) R = R1 +R2+ R3 Resistances or resistors in parallel  The combined resistance of any number of resistances connected in parallel is equal to the sum of reciprocals of all the individual resistances. 1 𝑅 = 1 𝑅1 + 1 𝑅2  When a number of resistances are connected in parallel, then:- i. Each resistance has same potential difference across its ends, which is equal to the potential difference of the battery. ii. When a number of resistances are connected in parallel then different amount of current flows through each resistance. The sum of currents through all the resistors is equal to the total current drawn from the battery. Resultant resistances of two resistances are connected in parallel Two resistances R1 and R2 connected in parallel. A battery of V volts has been applied to the ends of the parallel combination. I1 is the current flowing through R1 and I2 is the current flowing through R2. For the parallel combination of resistances the sum of currents flowing through all resistors is equal to the total current drawn from the battery. I = I1 + I2 ………….(1) If I is the total current flowing in the circuit, R is the total resistance of the parallel combination of resistances and V is the potential difference of the battery applied. Then by ohm‟s law, I = 𝑉 𝑅 ………….(2) Since there is same potential difference across each resistor, By ohm‟s law I1 = 𝑉 𝑅1 ………….(3) and I2 = 𝑉 𝑅2 ………….(4) Using (1), (2), (3) and (4) 𝑉 𝑅 = 𝑉 𝑅1 + 𝑉 𝑅2 𝑉 𝑅 = V 1 𝑅1 + 1 𝑅2  1 𝑅 = 1 𝑅1 + 1 𝑅2 Resultant resistances of three resistances are connected in parallel Three resistances R1, R2 and R3 connected in parallel.
  • 12. Study material (Science) (Class 10) Page 12 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) A battery of V volts has been applied to the ends of the parallel combination. I1 is the current flowing through R1, I2 is the current flowing through R2 and I3 is the current flowing through R3. For the parallel combination of resistances the sum of currents flowing through all resistors is equal to the total current drawn from the battery. I = I1 + I2 + I3 ………….(1) If “I” is the total current flowing in the circuit, “R” is the total resistance of the parallel combination of resistances and “V” is the potential difference of the battery applied. Then by ohm‟s law, I = 𝑉 𝑅 ………….(2) Since there is same potential difference across each resistor, By ohm‟s law I1 = 𝑉 𝑅1 ………….(3) , I2 = 𝑉 𝑅2 ………….(4) and I3 = 𝑉 𝑅3 ………….(5) Using (1), (2), (3), (4) and (5) 𝑉 𝑅 = 𝑉 𝑅1 + 𝑉 𝑅2 + 𝑉 𝑅3 𝑉 𝑅 = V 1 𝑅1 + 1 𝑅2 + 1 𝑅3  1 𝑅 = 1 𝑅1 + 1 𝑅2 + 1 𝑅3 Domestic electric circuits (series or parallel) Disadvantages of series circuit for domestic wiring  In series circuit if one electrical appliance stops working due to some defect, then all appliances stop working because the whole circuit is broken. Example:- in diwali lights the bulbs are connected in series, if one bulb gets fused then all bulbs stop working.  In series circuit there is only one switch for all electrical appliances, due to which they can not be turned on and off separately. Example:- if all the appliances in our home are connected in series then we will not be able to run them separately.  In series circuit all the electrical appliances do not get the same voltage (220 V) from the power supply line because the voltage is shared by all the appliances, due to which the appliance getting low voltage do not work properly. Example:- if some bulbs are connected in series connection they will not get the proper voltage and hence they will glow less brightly.  In the series connection of electrical appliances, the over all resistance of the electrical circuit increases much due to which the current from the power supply is low.
  • 13. Study material (Science) (Class 10) Page 13 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Advantages of parallel circuits in domestic wiring  In parallel circuit if one electrical appliance stops working due to some defect, then all appliances keep working normally. Example:- if number of bulbs are connected in parallel and one bulb gets fused then all bulbs keep working.  In parallel circuit each electrical appliance has its own switch due to which it can be turned on and off independently, without affecting other appliances. Example:- all the appliances in our home are connected in parallel due to which each appliance can be turned on and off separately.  In parallel circuit all the electrical appliances get the same voltage (220 V) from the power supply line because the voltage is not shared by all the appliances, due to which all the appliances get proper voltage and work properly. Example:- if some bulbs are connected in parallel connection then they will get the proper voltage and hence they will glow equally bright.  In the parallel connection of electrical appliances, the over all resistance of the electrical circuit is reduced very much due to which the current from the power supply is high and each appliance draws the required amount of current for its working. Electric power  When an electric current flow through the conductor, electrical energy is used up and electric work is done.  Electric power is defined as electric work done per unit time. “Or”. Rate of doing electric work is also called power. “Or”. Rate at which electrical energy is consumed by the appliance is called power. Power = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛  P = 𝑊 𝑡  SI unit of electric power is “watt (W)”. Another unit of electric power is “joule / second (J/s) or J s-1”.  The electric power is said to be 1 watt if 1 joule of electric work is done in 1 sec or 1 joule of electrical energy is consumed by appliance in 1 sec. 1 watt = 1 𝑗𝑜𝑢𝑙𝑒 1 𝑠𝑒𝑐𝑜𝑛𝑑  The bigger units of electric power used for commercial purpose are “kilowatt and megawatt”. 1 kilowatt = 1000 watt and 1 megawatt = 106 watt Formula for calculating electric power  We know that, power is defined as rate at which electric work is done  Power = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛  P = 𝑊 𝑡 ………… (1) Potential difference between two points is defined as the amount of electric work done in moving a unit amount of charge form one point to another point.  Potential difference (p.d) = 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑  V = 𝑊 𝑄  W = V × Q ….. (2) Electric current is defined as flow of electrons per unit time.
  • 14. Study material (Science) (Class 10) Page 14 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  Electric current (I) = 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑐𝑕𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑒𝑑 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛  I = 𝑄 𝑡  Q = I × t …….. (3) Using (2) and (3) W = V × I × t …………. (4) Using (1) and (4) P = V × I × t 𝑡 = V × I  electric power = voltage × current  The power of an electrical appliance depends upon the potential difference between the terminals of the appliance and current flowing through it.  If an electrical appliance is operated at a potential difference of 1 volt and the appliance carries the current of 1 ampere, then the power of the appliance is 1 watt. 1 watt = 1 volt × 1 ampere  1 W = 1 V × 1 A Some other formulae of calculating electric power Power P in terms of I and R P = V × I …………………… (1) From ohm‟s law, R = 𝑉 𝐼  V = I × R ……. (2) Using (1) and (2), P = I × I × R P = I2 × R I = current, R = resistance Power P in terms of V and R P = V × I …………………… (1) From ohm‟s law, R = 𝑉 𝐼  I = 𝑉 𝑅 ……. (2) Using (1) and (2), P = V × 𝑉 𝑅 P = 𝑉2 𝑅 V = potential difference, R = resistance Power voltage rating of the electrical appliance  The power voltage rating of the electrical appliance tells us about the voltage needed for the effective working of appliance and power used by it. Electrical energy  Electrical energy of the appliance is defined as the work done by the electric current to flow through the appliance.  Electrical energy of the appliance is given by the product of its power rating and the time for which it is used. Electrical energy = power × time  E = P × t  The SI unit is “joule (J)”.
  • 15. Study material (Science) (Class 10) Page 15 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  One joule of the electric energy is defined as the energy consumed by an appliance of power 1 watt in 1 sec.  If we take the unit of power as “watt (W)” and the unit of the time as “hour (h)” then the unit of the electrical appliance is “watt-hour (Wh)”.  One watt-hour of the electrical energy is defined as the amount of energy consumed by an appliance of power 1 watt in 1 hour. Factors on which electrical energy consumed by the appliance depends 1) Power rating of the appliance 2) Time for which the appliance is used Commercial unit of electric energy: kilowatt-hour (kWh)  1 kilowatt-hour is the amount of electrical energy consumed by an appliance of 1kW in 1 hour.  1 kilowatt-hour is equal to 1 unit of electrical energy. Relation between the kilowatt-hour and joule Electrical energy = power × time  E = P × t 1 kWh = 1 kW × 1 h 1 kWh = 1000 W × 3600 s 1 kWh = 3600000 Ws 1 kWh = 3600000 J …………………… (1 Ws = 1 J) 1 kWh = 3.6 × 106 J Effects produced by electric current  Heating effects, magnetic effects and chemical effects. Heating effect of electric current  When an electric current is passed through a high resistance wire, like nichrome wire, the resistance wire becomes very hot and produces heat. This is called heating effects of electric current. Joule’s law of heating (formula of heat energy) “R” is resistance of the conductor, “I” is the current flowing through it for time “t”. When a current flows through the conductor then some work is done the current ato overcome resistance. Electric charge “Q” moves against the potential difference “V”, the amount of work done “W” is: W = Q × V……………………. (1) Current is defined as the rate of flow of charge.  Current = 𝑐𝑕𝑎𝑟 𝑔𝑒 𝑡𝑖𝑚𝑒  I = 𝑄 𝑡  Q = I × t……………………. (2) From the ohm‟s law, V = I × R ……………………… (3) Using (1), (2) and (3) W = (I × t) × (I × R) = I2 R t Since the electric work done against the resistance is converted into heat energy.
  • 16. Study material (Science) (Class 10) Page 16 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  W = H H = I2 R t Factors on which the heat produced in a wire depends 1) Square of current (I2):- heat produced in a wire is directly proportional to the square of current. H  I2 If we will double the current then the heat produced becomes four times. If the current is halved then the heat becomes one-fourth. 2) Resistance of wire (R):- heat produced in a wire is directly proportional to the resistance of wire. H  R If we will double the resistance then the heat produced becomes two times. If the resistance is halved then the heat becomes half. 3) Time for which current is passed (t):- heat produced in a wire is directly proportional to time for which current is passed. H  t If we will double the time then the heat produced becomes two times. If the time is halved then the heat becomes half. Applications of heating effect of electric current  The heating effect of current is used I the working of the electrical heating appliances such as electric iron, electric kettle, Electric toaster, electric oven, room heaters, water heaters, electric geysers, etc.  The heating effect of electric current is utilized in electric bulbs or electric lamps for producing light.  The heating effect of electric current is utilized in electric fuse for protecting household wiring and electrical appliances. Why does the coil of the heating appliance get heated up to a high temperature (900C) but the connecting wires of the appliances do not get heated up?  The resistance of the heating elements of the heating appliance is very high due to which the amount of heat is very high due to the heating effect of electric current but the resistance of the connecting wires of the appliance is very low due to which no heat is produced in the connecting wires. Why tungsten metal is used in making the filaments of electric bulb?  Tungsten has high melting point of 3380C due to which it can be kept white hot without melting away. Tungsten has high flexibility and low rate of evaporation at high temperature. What is the temperature of the tungsten filament when it is white hot?  2500C Which gases are present in the bulb? Why the gases are filled in the bulb?  Nitrogen or argon or mixture of both is filled in bulb. The gases like nitrogen and argon are inert in nature so they do not react with tungsten metal and they also help tungsten metal to dissipate heat in the surroundings keeping the temperature
  • 17. Study material (Science) (Class 10) Page 17 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) of filament below the melting point (3380C). Due to this action of gases the life of tungsten filament is prolonged. What will happen if the tungsten metal is kept in air at high temperature?  It will burn up quickly reacting wit the oxygen present in the air. Out of bulb and tube light, which is more power efficient and why?  Tubelight is more power efficient. In bulb most of the electric power is used up in producing heat in the filament and some amount of the electric power is converted into light so bulb is not power efficient. Io tube light there is no filament due to which most of the power is converted into light which makes the tubelight power efficient. What is a fuse wire? How does it work?  Fuse wire is a short length of thin tin plated copper wire having low melting point but high resistance than the total resistance of the house.  When the current in the household circuit exceeds too much due to some reason, then fuse wire gets heated up, melts and breaks the circuit. Breaking of circuit leads to stop the flow of large current in the appliances in our house and prevents the damage to various electrical appliances. Why the resistance of fuse wire is kept more than the resistance of the household circuit?  Resistance of fuse wire is kept more than resistance of the house hold circuit so that the required amount of the current flows into the household circuit without any obstruction. Assignment I. VERY SHORT ANSWER QUESTIONS (1 MARK) (Answer the questions in one word or one sentence) 1. Multiple choice questions: i. The S.I. unit of resistivity is (a) Ω (b) Ω/cm (c) Ω m (d) Ω/m ii. One horse power is equal to the (a) 736 W (b) 746 W (c) 700 W (d) 726 W iii. The instruments used to measure electric potential difference is (a) voltmeter (b) ammeter (c) rheostat (d) generator iv. Which of the following is not the unit of energy? (a) Joule (b) kWh (c) kWs (d) kW v. Resistivity of a wire depends upon the (a) length (b) shape (c) thickness (d) material of wire vi. Which of the following term does not represent electrical power in a circuit? (a) I2 R (b) IR2 (c) VI (d) V2 /R vii. An electric bulb is rated 220 V and 100 W. when it is operated at 110 V, the power consumed will be (a) 100 W (b) 75 W (c) 50 W (d) 25 W viii. The power of a bulb producing 600 J energy in 30 second is (a)2 W (b) 200 W (c) 1800 W (d) 2000 W
  • 18. Study material (Science) (Class 10) Page 18 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) ix. The net resistance of the above resistors is (a) 30 Ω (b) 15 Ω (c) 60 Ω (d) 40 Ω x. The physical quantity which is equal to V/I is (a) resistivity (b) power (c) electrical energy (d) resistance 2. Define the following: (i) Electrical current (ii) Electric potential difference (iii) Electric power (iv) Resistance (v) Electricity (vi) Conductor (vii) Insulator 3. State Ohm’s law. 4. State Joule’s law of heating. 5. What is the resistivity of a material? 6. What does an electric circuit mean? 7. Define the unit of current. 8. Name a device that helps to maintain a potential difference across a conductor. 9. What determines the rate at which energy is delivered by a current? II. SHORT ANSWER QUESTIONS (2 MARKS) (Answer the questions in about 30 words) 1. On what factors does the resistance of a conductor depend? 2. What will happen to the current when it flows through a thick wire and thin wire of same material connected to the same source? 3. Why are the coil of electric toasters and electric irons made of an alloy rather than pure metal? 4. Among iron and mercury, which is the better conductor of electricity and why? 5. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? 6. How is voltmeter connected in a circuit to measure the potential difference between two points? 7. Why does an electrician wear rubber gloves while working with electrical devices? 8. What is the need of an external potential difference despite the fact that electrons are in a state of motion inside the atoms? 9. Why are fluorescent tubes used instead of bulbs? 10. Why are gases like argon and nitrogen filled in electric bulbs? 11. Calculate the number of electrons constituting one coulomb of charge. 12. What is meant by saying that the potential difference between two points is 1 V? 13. Why does the cord of an electric heater not glow while the heating element does? 14. Nichrome wire of length l and radius r has resistance of 10 Ω. How would the resistance of the wire change when: (i) only length of the wire is doubled? (ii) only diameter of wire is doubled? Justify your answer. 15. State the factors on which the resistance of a cylindrical conductor depends at a given temperature. 16. What is meant by the statement that the resistance of a wire is 1 Ω? 17. What combination is used for connecting in the circuit to measure the potential difference across two points? 18. List two differences between a voltmeter and an ammeter. 19. Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at room temperature. Why? 20. State differences between kilowatt and kilowatt hour. 21. How are resistance connected so that the equivalent resistance in physical quantity remains same in such case? 22. Amongst iron, silver, nichrome, tungsten and copper, which metal/alloy should be used to make the (i) heating element of electric geysers
  • 19. Study material (Science) (Class 10) Page 19 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) (ii) filament of incandescent bulbs 23. Give the significance of electric meter in a domestic circuit. 24. Though same current flows through the electric wires and the filament of bulb, yet only the filament glows. Why? 25. under which conditions charges can move conductor? 26. List three factors on which amount of heat H produced in a resistor due to an electric current depends. Also, express it mathematically. 27. Name the define commercial unit of energy. Relate it to SI unit of energy. 28. How is an ammeter and a voltmeter connected in an electric circuit? 29. State the advantages of connecting electrical devices in parallel instead of connecting them in series with the battery. 30. Keeping the potential difference constant, the resistance of a circuit is doubled. By what factor does the current change in the circuit? III. SHORT ANSWER QUESTIONS (3 MARKS) (Answer the questions in about 50 words) 1. Show how would you connect three resistors, each of 6 Ω, so that the combination has a resistance of (i) 9 Ω (ii) 4 Ω. Justify your answer. 2. Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former vale. What change will occur in the current through it? 3. How much work is done in moving a charge of 2 C, across two points having a potential difference of 12 V? 4. Will current flow more easily through a thick wire or a thin wire of the same material when connected to the same source? Why? 5. Draw the symbols of following components used in circuit diagrams. (i) electric cell (ii) battery (iii) plug key (open) (iv) plug key (closed) (v) wire joint (vi) wire crossing without joining (vii) electric bulb (viii) a resistor (ix) variable resistance (x) ammeter (xi) voltmeter (xii) conductor 6. Draw a schematic diagram of a circuit consisting of a battery of a three cells of 2 V each, a 5 Ω resistor or 8 Ω resistor and a plug key, all connected in series. 7. How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (i) 4 Ω, (ii) 1 Ω? 8. What is the cause of electrical resistance in a conductor? 9. (i) Two identical resistors, each of resistance 10 Ω, are connected in (a) series (b) parallel to a 6 V battery. Calculate the ratio of power consumed in the combination of resistors in two cases. (ii) draw the circuit diagram of the two cases. 10. State any two factors on which the resistance of a cylindrical conductor depends. Compare the resistance of a conductor of length ‘l’ and area of cross-section ‘a’ with that of another conductor of same material but of length and area of cross-section half and double respectively of the farmer. 11. Explain the term heating effects of electric current. Derive an expression for the heat produced by electric current and state Joule’s law. 12. Why does the cord of an electric heater not glow while the heating element does? 13. Write the SI unit of resistance and define it. Match the correct range of resistivity with the materials given. (i) Conductors (a) 10-6 Ω (ii) Alloys (b) 1012 to 1017 Ω (iii) Insulators (c) 10-6 to 10-8 Ω
  • 20. Study material (Science) (Class 10) Page 20 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) 14. Write one differences between direct current and alternating current. Which one of the two is mostly produced at power stations in our country. Name one device which provides alternating current. State one important advantage of using alternating current. State the frequency of power supply generated in India. 15. Two identical wires, one of nichrome and the other of copper, are connected in series and a current (I) is passed through them. State the change observed in the temperature of the two wires. Justify your answers. State the law which explains the above observation. 16. (i) Distinguish between an open and as closed circuit. (ii) Name the instrument used to measure electric current. How it is connected in a circuit? (iii) state the direction of conventional current. 17. Two identical resistors are first connected in series and then in parallel. Find the ratio of equivalent resistance in two cases. 18. Two identical wires are first connected in series and then in parallel to a source of supply. Find the ratio of the heat produced in the case. IV. NUMERICAL PROBLEMS (2 OR 3 MARKS) 1. How much energy is given to each coloumb of charge passing through a 6 V battery? 2. Judge the equivalent resistance when the following are connected in parallel-(i) 1 Ω and 106 Ω (ii) 1 Ω and 103 Ω and 106 Ω. 3. An electric lamp of 100 Ω, a toaster of resistance 50 Ω and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all the three appliances, and what is the current through it? 4. What is the highest and lowest total resistance that can be secured by the combination of four coils of resistance 4 Ω, 8 Ω, 12 Ω and 24 Ω. 5. An electric iron consumes energy at a rate of 840 Ω when heating is maximum and 360 Ω when the heating is minimum. The voltage is 220 V. what is the current and the resistance in each case? 6. Compute the heat generated while transferring 96000 coulombs of charge in one hour through a potential difference of 50 V. 7. An electric iron of resistance 20 Ω draws a current of 5 A. calculate the heat developed in 30 seconds. 8. An electric motor draws 5 A from 220 V line. Determine the power of the motor and energy consumed in 2 h. 9. A hot plate of an electric oven is connected to a 220 V line, has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series or in parallel. What are the currents in the three cases? 10. A copper wire has diameter 0.5 mm and resistivity of 1.6 x 10-8 Ωm. what will be the length of this wire to make resistance 10 Ω? How much does the resistance change if the diameter is doubled? 11. A wire of resistance 20 Ω is bent in the form of a closed circle. What is the effective resistance between two points at the ends of any diameter of the circle? 12. A 12 V battery is connected in the arrangement of resistance given alongside: (i) calculate the total effective resistance of the circuit. (ii) the total current flowing in the circuit.
  • 21. Study material (Science) (Class 10) Page 21 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) 13. In a factory, an electric bulb of 500 watt is used for 2 hours and an electric motor of 0.5 horse power is used for 5 hours every day. Calculate the cost of using the bulb and the motor for one year, if the cost of electrical energy is Rs 3 per unit. 14. Two circuits I and II are shown below. In circuit I the key is closed and in circuit II the key is open. Compare the currents in the two circuits. 15. Electric lamps designed for use on a 220 V electric supply are rated 10 W each. Calculate the number of lamps that can be connected in parallel to each other across the two wires of 220 V line if the maximum allowed current is 5 A. 16. The vale of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below: I (Amperes) 0.5 1.0 2.0 3.0 4.0 V (Volts) 1.6 3.4 6.7 10.2 13.2 Plot a graph between V and I and calculate the resistance of that resistor. 17. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor. 18. How many 176 Ω resistor (in parallel) are required to carry 5 A on a 220 V line? 19. Several electric bulbs designed to be used on a 220 V electric supply line are rated 10 W. how many electric bulbs can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current id 5 A? 20. Compare the power used in the 2 Ω resistor in each of the following circuit: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors. 21. Two lamps, one rated 100 W at 220 V and the other 60 W at 220 V are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V? 22. Which will consume more energy, a 250 W TV set in 1 hour or a 1200 W toaster in 10 minutes? 23. An electric heater of resistance 8 Ω draws 15 A from the service mains in 2 hours. Calculate the rate at which heat is developed in the heater. 24. An electric heater rated 800 W operates 6 hours/day. Find the cost of energy to operate it for 30 days at Rs 3.00 per unit.
  • 22. Study material (Science) (Class 10) Page 22 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) 25. How much current will an electric bulb draw from 220 V source of the resistance of the bulb is 1200 Ω? If in place of bulb, a heater of resistance 100 Ω is connected to the source, calculate the current drawn by it. 26. An electric bulb is connected to a 200 V generator. The current is 0.5 A. what is the power of the bulb? 27. For the circuit diagram given alongside, calculate: (i) value of current flowing through each resistor (ii) total current in the circuit (iii) total effective resistance of the circuit. 28. FIND OUT THE READING OF AMMETER AND VOLTMETER IN THE CIRCUIT GIVEN BELOW: 29. A battery of 12 V is connected to a series combination of resistors 3 Ω, 4 Ω, 5 Ω and 12 Ω. How much current would flow through the 12 Ω resistor? 30. The potential difference between the terminals of an electric heater is 60 V when it draws current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V? 31. An electric iron consumes energy at a rate of 840 W when heating is at the maximum and 360 W when the heating is at the minimum. The voltage at which it is running is 220 V. what si the current and resistance in each case? 32. Calculate the work done in moving a charge of 2 coulombs across two points having a potential difference of 12 V. 33. Calculate (i) the highest and (ii) the lowest resistance that can be obtained by the combination of four coils of resistances 4 Ω, 8 Ω, 12 Ω and 24 Ω? 34. In a household 5 tubelights of 40 W each are used for 5 hours and an electric press of 500 W for 4 hours every day. Calculate the total electrical energy consumed by these appliances in a month of 30 days. 35. An electric charge of 3000 C flows through a circuit of 10 minutes. Find the current that flows in the circuit. 36. Compare the power used in the 2 Ω resistor in each of the following circuit: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors. 37. A 6 Ω resistance wire is doubled by folding. Calculate the new resistance. 38. Resistance of a metal wire of length 25 cm is 6.5 Ω. If the diameter of the wire is 0.3 mm, calculate the resistivity of the metallic wire. 39. In the given circuit, resistors A and B made of the same metal are of the same length but A is thicker than B. which of the two ammeters will show a higher reading? Justify your answer. 40. A hot plate of an electric oven is connected to a 220 V line. It has two resistance coils A and B each of 30 Ω resistance which may be used separately in series or in parallel. Find the value of the current required in each of the three cases. V. LONG ANSWER QUESTIONS (5 MARKS) 1. State and verify the law of combination of resistance. 2. Explain the following: (i) Why is tungsten used almost exclusively for filament of electric lamps?
  • 23. Study material (Science) (Class 10) Page 23 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) (ii) Why are the conductors of an electric heating devices, such a bread-toaster and electric irons, made of an alloy rather than a pure metal? (iii) Why is the series arrangement not used for domestic circuits? (iv) How does the resistance of a wire vary with its area of cross-section? (v) why are copper and aluminium wires usually employed for electricity transmission? 3. (i) Calculate the resistance of the wire using the graph. (ii) DEFINE ELECTRIC POWER. (iii) Derive relation between power, potential difference and resistance. (iv) what is meant by the statement that the rating of a fuse in a circuit is 5 A? 4. Given that R1 = 100 Ω, R2 = 40 Ω, R3 = 30 Ω, R4 = 20 Ω and RA is the parallel combination of R1 and R2 whereas RB is the parallel combination R3 and R4. Combination RA is connected to the positive terminal of 12 V battery while combination RB is connected to the negative terminal. Ammeter A is connected between the resistors RA and Rb. (i) Find RA and RB. also calculate total resistance in the circuit. (ii) draw the circuit diagram showing above combination connected to battery and ammeter. 5. (i) The temperature of the filament of bulb is 27000 C when it glows. Why does it not get burnt up at such a high temperature? (ii) The filament of an electric lamp, which draws a current of 0.25 A is used for 4 hours. Calculate the amount of charge flowing through the circuit. (iii) an electric iron is rated 2 kW at 220 V. calculate the capacity of the use that should be used for the electric iron. Magnetic effects of electric current
  • 24. Study material (Science) (Class 10) Page 24 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Magnet and magnetism: The substances which have the property of attracting small pieces of iron, nickel, cobalt, etc. are called magnets and this property of attraction is called magnetism. Natural magnets: Natural magnets are piece of lodestone, which is a black iron ore (Fe3O4) called magnetite. Origin of the word magnetism Natural magnets called lodestones were found as early as the sixth century B.C. in the province of Magnesia in ancient Greece, from which the word magnetism derives its name. Magnetic poles: These regions of concentrated magnetic strength inside the magnet just near its ends are called magnetic poles. The end of a freely suspended magnet which points towards north is called the North Pole while its end pointing towards south is called South Pole. Basic properties of magnets 1) Attractive property: A magnet attracts small pieces of iron, cobalt, nickel, etc. 2) Directive property: A freely suspended magnet aligns itself nearly in the north-south direction. 3) Law of magnetic poles: Like magnetic poles repel and unlike magnetic poles attract each other. 4) Magnetic poles exist in pairs: If we break a magnet into two pieces, we always get two small dipole magnets. It is not possible to obtain an isolated N-pole or S-pole. Artificial magnets: Pieces of iron and other magnetic materials can be made to acquire the properties of natural magnets. Such magnets are called artificial magnets. Uses of magnets: 1) Magnets are used in radio and stereo speakers. 2) They are used in almirah and refrigerator doors to snap them closed. 3) They are used in video and audio cassette tapes, on the hard discs and floppies for computers. 4) In children's toys. 5) In medicine, the magnetic resonance imaging (MRI) scanners expose the inner parts of the patient's body for detailed examination by doctors. Compass needle. It consists of a small and light magnetic needle pivoted at the centre of a small circular brass case provided with a glass top, as shown in Fig. The ends of the compass needle point approximately towards north and south directions. The end pointing towards north is called North Pole and that pointing towards south is called South Pole. The north pole of the needle is generally painted black or red. MAGNETIC FIELD AND FIELD LINES Magnetic Field  Define: The space surrounding a magnet in which magnetic force is exerted, is called a magnetic field.  Direction: The direction of magnetic field at a point is the direction of the resultant force acting on a hypothetical north pole placed where it is placed. Magnetic Field Lines  Define: The path traced by a north magnetic pole free to move under the influence of a magnetic field is called a magnetic field line.
  • 25. Study material (Science) (Class 10) Page 25 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  Other name of magnetic field lines: The magnetic field lines are also known as magnetic lines of force.  What does the direction of magnetic field lines at any point tells us: The direction of tangent drawn on a magnetic field line at any point gives the direction of the magnetic force on a north pole placed at that point.  Direction of magnetic field line (outside the bar magnet): Since the direction of magnetic field line is the direction of force on a north pole, so the magnetic field lines always begin form the N- pole of a magnet and end on the S- pole of the magnet. Direction of magnetic field line (inside the bar magnet): Inside the magnet, however, the direction of magnetic field lines is from the S- pole of the magnet to the N- pole of the magnet. Thus, the magnetic field lines are closed curves. Methods of plotting lines of force. The following two methods are used for drawing lines of force of a bar magnet: (i) Iron-filings method. (ii) Compass needle method. IRON-FILINGS METHOD  Place a card (thick, stiff paper) over a strong bar magnet. Sprinkle a thin layer of iron filings over the card with the help of a sprinkler, and then tap the card gently. The iron filings arrange themselves in a regular pattern.  This arrangement of iron filings gives us a rough picture of the pattern of magnetic field produced by a bar magnet. How does iron fillings arrange themselves to represent the magnetic field patterm around the bar magnet?  The bar magnet exerts a force of magnetic field all around it. The iron filings experience the force of magnetic field of the bar magnet. The force magnetic field of the bar magnet makes the iron filings to arrange themselves in a particular pattern. Actually, under the influence of the magnetic field of the bar magnet, the iron filings behave like tiny magnets and align themselves along the directions of magnetic field lines. Thus, iron filings show the shape of magnetic field produced by a bar magnet by aligning themselves with the magnetic field lines. Properties (or characteristics) of the Magnetic Field Lines  The magnetic field lines originate from the north pole of a magnet and end at its south pole.  The magnetic field lines come closer to one another near the poles of a magnet but they are widely separated at other places.  The magnetic field lines do not intersect (or cross) one another. How can we say that magnetic force is stronger near the poles of magnet than at other places near the magnet? The magnetic field lines of the magnet comes near teach other near the poles and they are widely separated at other places, due to the more number of magnetic field lines near the poles and less number of magnetic field lines at other places, the magnetic force is stronger at poles than at other places
  • 26. Study material (Science) (Class 10) Page 26 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Why magnetic field lines cannot intersect each other? This is due to the fact that the resultant force on a north pole at any point can be only in one direction. But if the two magnetic field lines intersect one another, then the resultant force on a north pole placed at the point of intersection will be along two directions, which is not possible. COMPASS NEEDLE METHOD. Magnetic Field of Earth  How can we show that earth behaves like a magnet: A freely suspended magnet always points in the north – south direction even in the absence of any other magnet. This suggests that the earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle) to point always in a particular direction: north and south.  Shape of earth’s magnet: The shape of the earth‟s magnetic field resembles that of an imaginary bar magnet of length one – fifth of earth‟s diameter buried at its centre.  Poles of earth’s magnet: The south pole of earth‟s magnet is in the geographical north because it attracts the north pole of the suspended magnet. Similarly, the north pole of earth‟s magnet in the geographical south because it attracts the south pole of the suspended magnet. Thus, there is a magnetic S- pole near the geographical north, and a magnetic N- pole near the geographical south.
  • 27. Study material (Science) (Class 10) Page 27 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  Why the freely suspended magnet makes an angle of 15 with the geographical axis of earth: The axis of earth‟s magnetic field is inclined at an angle about 15 with the geographical axis. Due to this a freely suspended magnet (or magnetic needle) makes an angle of about 15 with the geographical axis and points approximately in the north- south directions at a place.  Reason of earth’s magnetism: The earth‟s magnetism is due to the magnetic effect of current (which is flowing in the liquid core at the centre of the earth). Thus, earth is a huge electromagnet. Magnetic Field Due to a Current in a Conductor An activity to show that a wire carrying an electric current behaves like a magnet Danish physicist H.C. Oersted was the first to demonstrate in 1820 that a current carrying conductor produces a magnetic field around it.  Take a straight thick copper wire and place it between the points X and Y in an electric circuit as shown in Fig.  Place a small compass near to this copper wire. See the position of its needle.  Pass the current through the circuit by inserting the key into the plug.  As we pass current though the copper wire XY, the compass needle gets deflected from its position of rest. Since a magnetic needle can be deflected only by a magnetic field, so the current carrying wire produces a magnetic field around it or it behaves like a magnet. A current carrying conductor produces a magnetic field around it. This effect is called magnetic effect of current. How can detect the position of wires in wall using a magnetic compass? A concealed current carrying conductor can be located due to the magnetic effect of current by using a plotting compass. For example, if a plotting compass is moved on a wall, its needle will show deflection at the place where current – carrying wire is concealed. On what factor does the Magnetic Field Patterns Produced by current – carrying conductors depends? The pattern of magnetic field (or shape of magnetic field lines) produced by a current conductor depends on its shape. Magnetic Field Pattern due to straight Current – Carrying Conductor (Straight Current – carrying Wire)  Magnetic field pattern: The magnetic field lines around a straight conductor (straight Wire) carrying current are concentric circles whose centers lie on the wire.  Relation between the direction of current and direction of magnetic field lines: When current in the wire flows in the upward direction, then the lines of magnetic field are in the anticlockwise
  • 28. Study material (Science) (Class 10) Page 28 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) direction. If the direction of current in the wire is reversed, the direction of magnetic field lines also gets reversed.  Factors on which the magnetic field produced by a straight current carrying conductor depends: 1. If we increase the current in the conductor, the deflection of the compass needle increases. This shows that, the magnitude of the magnetic field produced at a given point is directly proportional to the current passing through the wire. 2. For a given current, if we move the compass needle away from the wire, its deflection decreases. This shows that the magnitude of the magnetic field produced by a given current in the wire is inversely proportional to the distance from the wire. To know the direction of magnetic field we follow these rules 1) Right hand thumb rule: If the current carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field, as shown in Fig. 2) Maxwell's cork screw rule: If a right handed screw be rotated along the wire so that it advances in the direction of current, then the direction in which the screw rotates gives the direction of the magnetic field as shown in Fig. Magnetic Field Pattern due to a circular Loop (or Circular Wire) Carrying Current  Magnetic field pattern: The magnetic field lines are circular near the current – carrying loop. As we move away, the concentric circles representing magnetic field lines become bigger and bigger. At the centre of the circular loop, the magnetic field lines are straight.  Factors affecting the magnitude of magnetic field produced by a current – carrying circular loop (or circular wire) at its centre: 1) Directly proportional to the current passing through the circular loop (or circular wire. If current flowing through circular loop increases then magnetic field becomes strong and vice versa. 2) Inversely proportional to the radius of circular loop (or circular wire). If radius of circular loop decreases then magnetic field at the center of loop increases.
  • 29. Study material (Science) (Class 10) Page 29 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Clock Face Rule to determine the polarity of any face of a circular current loop  If the current around the face of circular wire (or coil) flows in the clockwise direction, then that face of the circular wire (or coil) will be south - pole (S-pole).  If the current around the face of circular wire (or coil) flows in the Anticlockwise direction, then that face of circular wire (or coil) will be a North pole (N-pole) Magnetic Field due to a Solenoid  Define: The solenoid is a long coil containing a large number of close turns of insulated copper wire.  Magnetic field pattern: The magnetic field produced by a current – carrying solenoid is similar to the magnetic field produced by a bar magnet.  Magnetic field inside the solenoid: The magnetic field lines inside the solenoid are in the form of parallel straight lines. This indicates that the strength of magnetic field is the same at all the points inside the solenoid. If the strength of magnetic field is just the same in a region, it is said to be uniform magnetic field.  Poles of solenoid: the face of solenoid where the current is clockwise that face acts like south pole and the face of solenoid where the current is anticlockwise that face acts like north pole.  How can we detect the poles of solenoid: We bring the north pole of a bar magnet near both the ends of a current – carrying solenoid. The end of solenoid which will be repelled by the north pole of bar magnet will be its north pole, and the end of solenoid which will be attracted by the north pole of bar magnet will be its south pole.  Factors affecting the strength of magnetic field produced by a current carrying solenoid:
  • 30. Study material (Science) (Class 10) Page 30 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) 1) The number of turns in the solenoid. Larger the number of turns in the solenoid, greater will be the magnetism, produced. 2) The strength of current in the solenoid. Larger the current passed through solenoid, stronger will be the magnetic field produced. 3) The nature of „‟core material‟‟ used in making solenoid. The use of soft iron rod as core in a solenoid produces the strongest magnetism. 4) Diameter of coil. If the diameter of coil decreases then magnetic field strength increases. Electromagnet: A soft iron core placed inside a solenoid behaves like a powerful magnet when a current is passed through the solenoid. This device is called an electromagnet. When the current is switched off, the iron core loses its magnetism and so it is no longer an electromagnet. Thus, electromagnets are temporary magnets. Factors on which the strength of an electromagnet depends: 1) Number of turns in the coil. The larger the number of turns in the coil, greater is the strength of the electromagnet. 2) Strength of the current. The larger the current passed through the solenoid, more powerful is the electromagnet. 3) Nature of the core material. The core of the magnetic material like soft iron increases the strength of the electromagnet. Uses of electromagnets  Cranes and lifts use electromagnets to separate and lift large quantities of iron scrap and steel  We find them in electrical devices like electric bells, telegraphs, telephones, loud speakers, electric trains, electric motors and so on  Doctors use weak electromagnets to remove steel splinters from the eye Differences between an electromagnet and a permanent magnet Electromagnet Permanent Magnet 1. It is a temporary magnet. It shows magnetism only as long as the current is through its coil. 1. It retains magnetism for a long time even after the removal of the magnetizing field (or current). 2. It can produce very strong magnetic field. 2. It produces a much weaker field than an electromagnet. 3. The strength of an electromagnet can be easily varied by changing the strength of current or number of turns in the coil. 3. Its strength cannot be changed, 4. The polarity of an electromagnet can be reversed by sending the current in reverse direction. The polarity of a permanent magnet cannot be changed. Advantages of electromagnets over permanent magnets 1) An electromagnet can produce a very strong magnetic field.
  • 31. Study material (Science) (Class 10) Page 31 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) 2) The strength of the magnetic field of an electromagnet can be increased/decreased by increasing/decreasing the strength of current or the number of turns in the solenoid. 3) The polarity of an electromagnet can be reversed by sending the current in the reverse direction. MAGNETISM IN HUMAN BEINGS  Define ionic currents and why they are produced: Extremely weak electric currents are produced in the human body by the movement of charged particles called ions. These are called ionic currents.  Magnetic field produced in our body: When the weak ionic currents flow along the nerve cells, they produce magnetic field in our body. When we try to touch something with our hand, our nerves carry electric impulse to the appropriate muscles. And this electric impulse creates a temporary magnetism in the body.  Organs of body where magnetic field is produced: The two main organs of the human body where the magnetic field produced is quite significant are the heart and the brain.  Principle of MRI: The magnetism produced inside the human body (by the flow of ionic currents) forms the basis of a technique called Magnetic Resonance Imaging (MRI) which is used to obtain images (or pictures) of the internal parts of our body.  Uses: Magnetism has an important use in medical diagnosis because, through MRI scans, it enables the doctors to see inside the body. For example, MRI can detect cancerous tissue inside the body of a person. FORCE ON CURRENT – CARRYING STRAIGHT CONDUCTOR PLACED IN A MAGNETIC FIELD  A magnet exerts a mechanical force on a current – carrying wire, and if the free to move, this force can produce a motion in the wire.  Discoverer and his discovery: In 1821, Faraday discovered that: When a current – carrying conductor is placed in a magnetic field, a mechanical force is exerted on the conductor which can make the conductor move.  Direction of force exerted on current carrying wire: The direction of force acting on a current – carrying wire placed in a magnetic field is (i) perpendicular to the direction of current, and (ii) perpendicular to the direction of magnetic field.  When the maximum force exerted on a current carrying wire: The maximum force is exerted on a current – carrying conductor only when it is perpendicular to the direction of magnetic field.  When no force exerted on a current carrying wire: No force acts on a current – carrying conductor when it is parallel to the magnetic field.  How the direction of force on a current – carrying conductor can be reversed: 1) The direction of force on a current – carrying conductor placed in a magnetic field can be reversed by reversing the direction of current flowing in the conductor. 2) The direction of force on a current – carrying conductor placed in a magnetic field can also reversed by reversing the direction of magnetic field. Fleming’s Left – Hand Rule for the Direction of Force  Statement: Hold the forefinger, the centre finger and the thumb of your left hand at right angles to one another. Adjust your in such a way that the forefinger points in the direction of magnetic field and the centre finger points in
  • 32. Study material (Science) (Class 10) Page 32 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) the direction of current, then the direction in which thumb points, gives the direction of fore acting on the conductor. Q. When is the force exerted on a current-carrying conductor (i) maximum and (ii) minimum? Ans. (i) When the current-carrying conductor is held perpendicular to the direction of the magnetic field, the force exerted on it is maximum.(ii) When the current-carrying conductor is held parallel to the direction of the magnetic field, the force exerted on it is minimum or zero. Q.A current carrying straight conductor is placed in east-west direction. What will be the direction of the force experienced by this conductor due to earth's magnetic field? How will this force get affected on?(i) Reversing the direction of flow of current ? (ii) Doubling the magnitude of current? Ans. The direction of earth's magnetic field is from geographical south to geographical north. According to Fleming's left hand rule, the current carrying straight conductor placed in east- west direction will be deflected downwards. (i) On reversing the direction, the conductor is deflected in the upward direction. (ii) If the magnitude of current is doubled, it will result in doubling the magnitude of the force. Q. On what factors does the force experienced by a current carrying conductor placed in a uniform magnetic field depend? Ans. Factors on which the force experienced by a current carrying conductor placed in a magnetic field depends. If a current / is flowing along the wire of length L which is placed perpendicular to the direction of the magnetic field B, then the force F experienced by the wire perpendicular to the current and the magnetic field (as given by Fleming's left hand rule) is expressed as: F = BIL, Thus, F depends on current /, length L and strength of field B. THE ELECTRIC MOTOR  Define: A motor is a device which converts electrical energy into mechanical energy.  Motion of which part of motor is used in various appliances: Every motor has a shaft or spindle which rotates continuously when current is passed into it. The rotation of its shaft is used to drive the various types of machines in homes and industry.  Uses: Electric motor is used in electric fans, washing machines, refrigerators, mixer and grinder, electric cars and many other appliances.  Principle of a Motor: A motor works on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it, a force acts on the coil which rotates it continuously. ELECTRIC MOTOR Electric motor. An electric motor is a rotating device which converts electric energy into mechanical energy. Principle. An electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force, the direction of force is given by Fleming's left hand rule. Construction. I. Field magnet. It is a strong horse shoe type magnet with concave poles. II. Armature. It is a rectangular coil ABCD having a large number of turns of thin insulated copper wire wound over a soft iron core. The armature is placed
  • 33. Study material (Science) (Class 10) Page 33 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) between the poles the field magnet and it can be rotated about an axis perpendicular to the magnetic field les. III. Split ring commutator. It consists of a cylindrical metal ring split into two halves S1 and S2. The two ends A and D of the armature coil are connected to the split rings S1 and S2 respectively. As the coil rotates, the split rings also rotate about the same axis of rotation. The function of the split ring commutator is to reverse the direction of current in the coil after every half rotation. IV. Brushes. Two graphite or flexible metal rods maintain a sliding contact with split rings S1 and S2, alternately. V. Battery. A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings. Working of a DC Motor When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn towards the right, causing rotation. When the coil turns through 900, the brushes lose contact with the commutator and the current stops flowing through the coil. However the coil keeps turning because of its own momentum. Now when the coil turns through 1800, the sides get interchanged. As a result the commutator ring C1 is now in contact with brush B2 and commutator ring C2 is in contact with brush B1. Therefore, the current continues to flow in the same direction. The Efficiency of the DC Motor Increases by:  Increasing the number of turns in the coil  Increasing the strength of the current  Increasing the area of cross-section of the coil  Increasing the strength of the radial magnetic field An electric motor brings about rotational motion in domestic appliances such as electric fans, washing machines, refrigerators, mixers, grinders, blenders, computers, MP3 players, etc. ELECTROMAGNETIC INDUCTION: ELECTRICITY FROM MAGNESTISM  Define: when a conductor is moved in magnetic field then magnetic field strength linked to conductor changes and a current in induced in conductor so as to oppose the change in magnetic field strength. This phenomenon is called electromagnetic induction.  Discoverer: The phenomenon of electromagnetic induction was discovered by a British scientist
  • 34. Study material (Science) (Class 10) Page 34 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Michael Faraday and an American scientist Joseph Henry independently in 1831.  Instrument used to find the direction of current: A galvanometer is an instrument which can be detect the presence of electric current in a circuit. It is connected in series with the circuit. When no current is flowing through a galvanometer, its pointer is at the zero mark. When an electric current passes through the galvanometer, then its pointer deflects (or moves) either to the left side of zero mark or to the right side of the zero mark, depending on the direction of current. To Demonstrate Electromagnetic Induction by using a straight Wire and a Horseshoe – Type Magnet To Demonstrate Electromagnetic Induction by Using a Coil and a Bar Magnet  The concept of a fixed coil and a rotating magnet is used to produce electricity on large scale generators of power house.  The condition necessary for the production of electric current by electromagnet induction is that there must be a relative motion between the coil of wire and a magnet. Observations about electromagnetic induction:  A current is induced in a coil when it is moved (or rotated) relative to a fixed magnet.  A current is also induced in a fixed coil when a magnet is moved (or rotated) relative to the fixed coil.  No current is induced in a coil when the coil and magnet both are stationary relative to one another.  When the direction of motion of coil (or magnet) is reversed, the direction of current induced in the coil also gets reversed.  Factors affecting the magnitude of induced current:  By winding the coil on a soft iron core.
  • 35. Study material (Science) (Class 10) Page 35 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  By increasing the number of turns in the coil.  By increasing the strength of magnet.  By increasing the speed of rotation of coil (or magnet). Fleming’s Right – Hand rule for the Direction of Induced Current  According to Fleming‟s right – hand rule: Hold the thumb, the forefinger and the centre finger of your right – hand at right angles to one another. Adjust your hand in such a way that forefinger points in the direction of magnetic field, and thumb points in the direction of motion of conductor, then the direction in which centre finger points, gives the direction of induced current in the conductor. ELECTRIC GENERATOR  Define: The electric generator is a machine for producing electric current or electricity.  Energy conversion: The electric generator converts mechanical energy into electrical energy.  Dynamo: A small generator is called a dynamo. For example, the small generator used on bicycles for lighting purposes is called a bicycle dynamo.  Principal of Electric Generator: The electric generator works on the principal that when a straight conductor is moved in a magnetic field, then current is induced in the conductor. In an electric generator, a rectangular coil (having straight sides) is made to rotate rapidly in the magnetic field between the poles of a horseshoe – type magnet. When the coil rotates, it cuts the magnetic field lines due to which a current is produced in the coil.  Construction. 1. Field magnet. It is a strong horse shoe-type permanent magnet with concave poles. 2. Armature. ABCD is a rectangular armature coil. It consists of a large number of turns of insulated copper wire wound on a soft iron cylindrical core. It can be rotated about an axis perpendicular to the magnetic field of the field magnet. 3. Slip rings. These are two brass rings S1 and S2 rigidly connected to the two ends of the armature coil. As the coil rotates, slip rings also rotate about the same axis of rotation. 4. Brushes. These are two graphite rods B1 and B2 which are kept pressed against the slip rings S1 and S2. Through these brushes, the current induced in the armature coil is sent to the external circuit. Working. As shown in Fig, suppose the armature coil ABCD is in the horizontal position. Now the coil is rotated clockwise. The coil cuts the magnetic lines of force. The arm AB moves upwards while the arm CD moves downwards. According to Fleming's right hand rule, the induced current flows from A to B in arm AB and C to D in arm CD i.e., the induced current flows along ABCD. The induced current flows in the circuit through brush B2 to Bv After half the rotation of the armature, the arm CD moves upwards and AS moves downwards. The induced current now flows in the reverse direction i.e., along DCBA. The current flows from Bx to B2. Thus the direction of current in the external circuit changes after every half rotation. Such a current which changes its direction after equal intervals of time is called alternating current. This device is called A.C. Generator.
  • 36. Study material (Science) (Class 10) Page 36 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Current is induced in a coil when the current in the neighboring coil changes. We can conclude that a potential difference is produced in the coil-2 whenever the electric current through the coil-1 is changing (starting or stopping). Coil-1 is called the primarly coil and coil-2 is called the secondary coil. As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction. Differences between electric motor and generator Electric motor Generator 1. It converts electrical energy into mechanical energy. 1. It converts mechanical energy into electrical energy. 2. It is based on magnetic effect of current. 2. It is based on electromagnetic induction. 3. Current is supplied to the coil placed in magnetic field by an external source of electrical energy. As a result of it, coil starts rotating. 3. The coil is rotated in a magnetic field by an external arrangement. As a result, an electric current is induced in the coil. Direct current. A direct current is that current which flows with constant magnitude in the same direction. Alternating current. An alternating current is that current whose magnitude changes continuously with time and whose direction reverses after equal intervals of time. Advantage of AC over DC. Only alternating voltage can be stepped up or stepped down by using a transformer. This makes AC more suitable than DC for transmission for electric power over long distances without much loss of energy. Frequency of a.c. mains in India In India, the direction of A.C. changes after every 1/100 second, i.e., the frequency of A.C. is 50 Hz. Domestic Electric Circuits Domestic Wiring  The electric power line enters our house through three wires- namely the live wire, the neutral wire and the earth wire. To avoid confusion we follow a colour code for
  • 37. Study material (Science) (Class 10) Page 37 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) insulating these wires. The red wire is the live wire, and the black wire is neutral. The earth wire is given green plastic insulation.  The live wire has a high potential of 220 volts whereas the neutral wire has zero potential. Thus the potential difference between the live wire and the neutral wire is 220-0 = 220 volts.  The earth wire is much thicker in size and is made of copper. One end of it is connected to a copper plate buried deep under the earth. The earth connection is made to the electric meter and then to the main switch.  In our homes, we receive supply of electric power through a main supply (mains), either supported through overhead electric poles or by underground cables.  The live wire and neutral wire, coming from the electric pole, enter a box fitted just outside our house which has a main fuse F1. The fuse is connected in series with the live wire. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential. The fuse F1 has a high rating of about 50 amperes. Thus it prevents any damage such as fire to the entire electrical wiring entering the house due to short-circuit or overloading.  The two wires then enter the electricity meter which records the electrical power consumed by us in kilowatt-hour (kWh). This meter is installed by the electric supply Department of our city.  These two wires coming out of the meter are then connected to a main switch which is placed in a distribution box. Another fuse F2 is placed in series with the live wire in this box for the sake of consumer safety.  There are two separate circuits in a house namely lighting circuit and power circuit. The lighting circuit with a 5 A fuse is used for running electric bulbs, fan, radio, TV, tube lights etc. and the power circuit with a 15 A fuse is used for running electric heater, electric iron, geyser, refrigerator etc as it draws more current.  The distribution circuits are always connected in parallel combination. In a parallel circuit even if there is a fault or short-circuiting in any one line, the corresponding fuse blows off leaving the other circuits and appliances intact and prevents damage to the entire house.  In case short-circuit occurs in the power circuit, then the power-fuse will blow off but our lights will continue to burn as the lighting circuit remains unaffected.  A constant voltage of the main line is available for all other electrical appliances.  Along with the two wires, a third wire called the earth wire also enters our house as shown in the fig. The earth connection is first made to the electric meter and then to the main switch. This wire then goes into the rooms along with the live and neutral wires.
  • 38. Study material (Science) (Class 10) Page 38 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) Why all switches are put in live wire: All the electrical appliances are provided with separate switches. All the switches are put in the live wire, so that when we switch off an electrical appliances (like an electric iron), then its connection with the live wire is cut off and there will be no danger of an electric shock if we touch the metal case of the electrical appliances. If, however, we put switches in the neutral wire, then the live wire will be in connection with the electrical appliances even when the switch is in the off position, and there is a danger of an electric shock. SAFETY DEVICES IN HOUSEHOLD CIRCUITS Earthing of Electrical Appliances  Why earthing is needed: To avoid the risk of electric shocks, the metal body of an electrical appliances is earthed’. Earthing means to connect the metal case of electrical appliances to the earth (at zero potential) by means of a metal wire called “earth wire”.  How earth wire is connected in the house hold circuit: One end of the earth wire is buried in the earth. We connect the earth wire to the metal case of the electrical appliances by using a three – pin plug.  What will happen if we accidentally touch the earthed appliance: If by chance, the live wire touches the metal case of the electric iron (or any other appliances), which has been earthed, then the current passes directly to the earth through the earth wire. It does not need our body to pass the current and, therefore we do get an electric shock.  What kind of appliances are earthed: We give earth connections to only those electrical appliances which have metallic body, which draw heavy current, and which we are liable to touch.  Why we don’t do earthing of bulbs and tube lights: We, however, do not do earthing of an electric bulb or a tube – light because we hardly touch them when they are on. The metal casings of the switches are, however, earthed. Electric Fuse  What happens to the copper wire if maximum current passes through them: The electric wires used in domestic wiring are made of copper metal because copper is a good conductor of electricity having very low resistance. If the current passing through wires exceeds this maximum value, the copper wires get over heated and may even cause a fire.  When a large current can flow in household circuit: An extremely large current can flow domestic wiring under two circumstances: Short circuiting and overloading.  Short Circuiting: This touching of the live wire and neutral wire directly is known as short circuit. When the two wires touch each other, the resistance of the circuit so formed is very, very small very large current flows through the wires and heats the wires to a dangerously high temperature, and a fire may be started.  Overloading: If too many electrical appliances of high power rating (like electric iron, water heater, air conditioner, etc.,) are switched on at the same time, they draw an extremely large current from the circuit. This is known as overloading the circuit. Due to an extremely large current flowing through them, the copper wires of household wiring het heated to a very high temperature and a fire may be started.  Define of fuse: A fuse is a safety device having a short length of a thin, tin- plated copper wire having low melting point, which melts and breaks the circuit if the current exceeds a safe value.
  • 39. Study material (Science) (Class 10) Page 39 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  On what factor does the thickness and length of fuse wire depends: The thickness and length of the fuse wire depends on the maximum current allowed through the circuit.  On which law does the electric fuse work: An electric fuse works on the heating effect of current.  Why we use thin fuse wire: We use a thin wire in a fuse because it has a much greater resistance the rest of connecting wires. Due to its high resistance, the heating effect of current will be much more in the fuse wire than anywhere else in the circuit. This will melt the fuse wire whereas other wiring will remain safe.  Why we should not use thick fuse wire: We should not use a thick wire as a fuse wire because it will have a low resistance and hence it will not get heated to its melting point easily.  Why we should not use copper wire as fuse wire: A pure copper wire cannot be used as a fuse wire because it has a high melting point due to which it will not melt easily when a short circuit takes place.  Disadvantage of fuse wire: A blown fuse should be replaced only after the cause of excessive current flow has been found and removed.  What are used these days which have an advantage over fuse wire: These days more and more houses are using ‘Miniature Circuit Breakers’ (MCBs) to protect the household wiring from the excessive flow of electric current through it.  How does MCB work: If the current becomes too large, the miniature circuit breaker puts off a switch cutting off the electric supply. The MCB can be re-set when the fault has been corrected. Miniature current breaker (MCB) contains an electromagnet which, when the current exceeds the rated value of circuit breaker, becomes strong enough to separate a pair of contacts (by putting of a switch) and breaks the circuit. So, unlike fuses, MCBs do not work on heating effect of current MCBs work on the magnetic effect of current.  Where fuses are used these days: Fuses are also used to protect the individual domestic electrical appliances from damage which may be caused due to excessive current flow through them. Hazards of Electricity (or Dangers of Electricity)  If a person happens to touch a live electric wire, he gets a severe electric shock. In some cases, electric shock can even kill a person.  Short – circuiting due to damaged wiring or overloading of the circuit can cause electrical fore in a building.  The defects in the household wiring like loose connections and defective switches, sockets and plugs can cause sparking and lead to fires. Precautions in the Use of Electricity
  • 40. Study material (Science) (Class 10) Page 40 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com)  If a person accidently touches a live electric wire or if an electric fir starts in the house, the main switch should be turned off at once so as to cut off the electricity supply. This will prevent the fire from spreading.  The person who happens to touch the live electric wire should be provided an insulated support wood, plastic or rubber. We should never try to pull away the person who is in contact with the live wire, otherwise we will also get a shock.  All the electrical appliances like electric iron, cooler, and refrigerator, etc. should be given connection to save ourselves from the risk of electric shocks. Even if the earth connection is there, we should avoid touching the metal body of an electric appliances when it is on.  All the switches should be put in the live wire of the A.C. circuit, so that when the switch is turned off, the appliances gets disconnected from live wire and there is no risk of electric shock.  We should always be connected in the live wire of the circuit. The fuse wire should be of proper rating and material. We should never use a copper wire (connecting wire) as fuse wire because a copper wire has a very high current rating due to which a copper wire fuse cannot protect the wiring against short circuiting or overloading.  The household wiring should be done by using good quality wires having proper thickness and insulation. All the wire connections with switches, sockets, and plugs should be tight, and all the wire joints should be covered with insulated adhesive tape. Defective switches, sockets and plugs should be replaced immediately. Energy: Whenever a body is capable of doing work, the body is said to possess energy. Thus energy is defined as the ability of a body to do work and the amount of energy Sources of Energy
  • 41. Study material (Science) (Class 10) Page 41 Notes Assembled by Anupam Narang (8802442964)(anupam23189@gmail.com) possessed by a body is equal to the amount of work it can do when its energy is released. Units of energy: On S.I. system, energy is measured in the units of joules or in calories and on C.G.S. system in ergs. However, the commercial unit of energy is kilowatt-hour. The energy is said to be one kilowatt-hour, when a body consumes one kilowatt of energy in one hour. Sources of energy: A source of energy is that which is capable of providing enough useful energy at a steady rate over a long period of time. A good source of energy should be: (i) Safe and convenient to use, e.g., nuclear energy can be used only by highly trained engineers with the help of nuclear power plants. It cannot be used for our household purpose. (ii) Easy to transport, e.g., coal, petrol, diesel, LPG etc. Have to be transported from the places of their production to the consumers. (iii) Easy to store, e.g., huge storage tanks are required to store petrol, diesel, LPG etc. Characteristics of an ideal or a good fuel: 1. It should have a high calorific or a heat value, so that it can produce maximum energy by low fuel consumption. 2. It should have a proper ignition temperature, so that it can burn easily.] 3. It should not produce harmful gases during combustion. 4. It should be cheap in cost and easily available in plenty for everyone. 5. It should be easily and convenient to handle, store and transport from one place to another. 6. It should not be valuable to any other purpose than as a fuel. 7. It should burn smoothly and should not leave much residue after its combustion. Classification of sources energy: The sources of energy can be classified as follows: (i) Renewable (ii) Non-Renewable. Renewable sources of energy  Renewable sources of energy are those which are Inexhaustible, i.e., which can be replaced as we use them and can be used to produce energy again and again.  These are available in an unlimited amount in nature and develop within a relatively short period of time.  Examples of Renewable Sources of Energy: (i)Solar energy, (ii) Wind Energy, (iii) water energy (hydro-energy), (iv) Geothermal energy, (v) Ocean energy, (vi) Biomass energy (firewood, animal dung and biodegradable waste from cities and crop residues constitute biomass).