22 april 2021 lecture

ELECTRICITY…………………………………..CLASS 10th
Lecture no. 5 Date..30-04-2021
Physics... Class 10th
Chapter 10… light
Chapter 11 – eyes and colourful world
Chapter 12.. Electricity
Chapter 13 magnetic effect of electric current
Chapter 14 sources of energy
Chapter name: electricity
Mechanical energy
Wind energy, hydroelectricity, geothermal
energy, solar energy….

Electricity:
Electricity is form of energy its convert into
mechanical energy to electrical energy
And it is use to operate various appliances or
electrical devices.
1. Electric current
2. Electric circuit
3. And some devices used in
electric circuit
4. Ammeter
5. Voltmeter
6. Electric charge

Electric current:
Flow of charges per unit time is called electric
current.
Flow of electric charges per unit time is called
electric current
Symbol of electric current= I
I=q/t
I= charge/time
Si unit of current is ampere
Si unit of charge is coulomb
Unit of current is coulomb/sec.
1 amp currentwhen 1 coulomb charge
passing through 1 sec. it is known as 1
ampere current.
I=q/t
I=1/1
I= 1 amp.

Electric circuit
Battery=
It is the collection of cells.
Plug-key 

Open switch- - circuit is broken somewhere….
Closed switch—circuit is completed
Direction of current
Current is flowing from positive terminal of
battery to negative terminal of battery.
Direction of electron is opposite to the
direction of current

Electric charge
It is the property of matter.
Basically two types of charges
1. Positive charge
2. Negative charge
Positive charge is due to protons.
Negative charge is due to electrons.
Proton and neutron we found in nucleus of
atoms
Electrons revolves around the circular orbits
of atoms.

There are three types of material
Conductors …. All metals
Insulators.. Plastic, wood etc.
Alloys—mixture of two or more
metals… constantan, magnine,
nichrome etc.
Semiconductor-
The property of semiconductorbased on,
intermediate property of metals and
nonmetals. Hence it is called metalloids.
Ex. Silicon, germanium, gallium arsenide,
cadmium phosphide etc.
1 coulomb charge
Q= it

If 1 amp. Current flowing through in 1 sec., it
is known as 1coulomb charge.
Smaller units of ampere
Micro amp= 10^-6
Mili amp=10^-3
Pico amp=10^-9
Que.1. Find no. of electron in each coulomb
of charge?
Q= ne
N=q/e
Q= 1 coulomb charge
N=1/1.6*10^-19

N=10^19/1.6
N=10^20/16
N=100*10^18/16
N=6.25*10^18
Charge of electron = 1.6* 10^-19 coulomb
Current = charge /time
Si unit of current is ampere
Coulomb /sec.
Si unit of charge... Coulomb

1 amp current if flow of charge is 1
coulomb per unit time, is known as 1 amp
current.
I=q/t
If q= 1c and t= 1 sec.
I= 1/1 = 1 amp current
Ammeter
It’s an instrument to measure electric current
in the circuit. It is always connected series in
the circuit.

Here r1 and r2 is the resistance are in series.
In first fig.
Ammeter also connected in series
In second fig. r1 and r2 are parallel to each
other
And voltmeter is connecter parallel to these
resistance
Voltmeter=it is a device to measure potential
difference across the circuit
It is always connected in parallel. Across the
end of the circuit.

Ideal voltmeter current is zero. V=I r
Ideal voltmeter resistance is infinite
If current is zero, then resistance is max.
Ideal ammeter current is infinite
Ideal ammeter resistance is zero
Ideal voltmeter has infinite resistance so no
current will flow. This is why voltmeters are
placed in parallel to the circuit, not in series.
Ammeter is placed in series however and has
low resistance.

Electric potential:
Definition: The
electrical potential is defined as the
capability of the charged body to do work.
When the body is charged, either electric
electrons are supplied to it, or they are
removed from it. In both the cases, the
work is done. This work is stored in the
body in the form of electric potential. Thus,
the body can do the work by exerting a
force of attraction or repulsion on the
other charged particles.

Today’s lecture topics:
Potential difference and electric potential
1 volt
Voltmeter
Electrical devices symbols

Ohm’s law
1 ohm resistance
Some numerical based on ohm’s law,
potential difference and electrical potential
ELETRICAL POTENTIAL:
Definition: The
electrical potential is defined as the
capability of the charged body to do work.

When the body is charged, either electric
electrons are supplied to it, or they are
removed from it. In both the cases, the
work is done. This work is stored in the
body in the form of electric potential. Thus,
the body can do the work by exerting a
force of attraction or repulsion on the
other charged particles.
The capacity of the charged body to do
work determines the electrical potential on
it. The measure of the electrical potential is
the work done to charge a body to one
coulomb, i.e.,

Units: Since the work done is measured in
joules and charge in coulombs, the unit of
electric potential is joules /coulombs, the
unit of electric potential
is joules/coulomb or volts.
1 volts:
Hence a body is said to have an electrical
potential of 1 volt if one joule of work is
done to charge the body to one coulomb.
POTENTIAL DIFFERENCE:

The electrical potential difference is
defined as the amount of work done to
carrying a unit charge from one point to
another in an electric field. In other words,
the potential difference is defined as the
difference in the electric potential of the
two charged bodies.
When a body is charged to a different
electric potential as compared to the other
charged body, the two bodies are said to a
potential difference. Both the bodies are
under stress and strain and try to attain
minimum potential
Unit: The unit of potential difference
is volt.
Va-Vb= work done/ charge

Que.1. What is the difference between
electrical potential energy and potential
difference?
AnsElectric Potential Energy
and Potential Difference
Electric potential energy results from
forces between charges; potential
difference is the energy needed to move a
charge from point A to B.
Que.2. what is the roll of potential
difference?
Ans
The potential difference tells you how
much energy per coulomb the charges
have to lose. Potential difference is
measured in volts, symbol V, where 1 volt
is equivalent to an energy difference of 1
joule for each coulomb of charge. Potential

difference is commonly referred to
as voltage.
Que.3. what causes potential difference?
Ans When a voltage is connected across
a wire, an electric field is produced in the
wire. Metal wire is a conductor . Some
electrons around the metal atoms are free
to move from atom to atom. ...
This causes a difference in energy across
the component, which is known as an
electrical potential difference (p.d.)
Que. 4.
A voltmeter is to be connected in the
circuit to measure potential difference
across a conductor.
Mention the type of combination in which
it should be connected with the conductor.
Answer:
The voltmeter is always connected in
parallel across the conductor.
Question 5.
(a) What is least count of voltmeter?
(b) In a voltmeter there are 20 divisions

between the ‘0’ mark and 0.5 V mark.
Calculate its least count. (2017 OD)
Answer:
(a) The minimum potential difference
measured by a voltmeter between the two
given terminals is called the least count of
that voltmeter.
(b) Two given marks of the voltmeters = 0
and 0.5 V
Potential difference = 0.5 – 0 = 0.5V
No. of divisions between these two marks
= 20
Electrical devices symbol

Ohm’s law:
Georg Ohm found that, at a constant
temperature, the electrical current flowing
through a fixed linear resistance is directly
proportional to the voltage applied across it,
and also inversely proportional to the
resistance. This relationship between the
Voltage, Current and Resistance forms the
basis of Ohms Law and is shown below.
By knowing any two values of the Voltage,
Current or Resistance quantities we can
use Ohms Law to find the third missing
value. Ohms Law is used extensively in
electronics formulas and calculations so it
is “very important to understand and
accurately remember these formulas”.

To find the Voltage, ( V )
[ V = I x R ] V (volts) = I (amps) x R (Ω)
To find the Current, ( I )
[ I = V ÷ R ] I (amps) = V (volts) ÷ R (Ω)
To find the Resistance, ( R )
[ R = V ÷ I ] R (Ω) = V (volts) ÷ I (amps)
It is sometimes easier to remember this
Ohms law relationship by using pictures.
Here the three quantities of V, I and R have
been superimposed into a triangle
(affectionately called the Ohms Law
Triangle) giving voltage at the top with
current and resistance below. This
arrangement represents the actual
position of each quantity within the Ohms
law formulas.

Ohm’s law in simple statements:
Ohm’s law state that current flowing
through the conductor is directly
proportional to the potential difference
across its ends, provided temperature and
other physical quantity remains constant.
V is directly proportional to I.
IF v is increase and I will also increased.
And if v is decreased than I will also
decreased.
V= ir
V=IR
V = potential difference

I = current
R= resistance
SI unit of resistance is ohm ( )
SI Unit of resistance is ohm. Ohm is
denoted by Greek letter ‘Ω’.
1 ohm (Ω) of Resistance (R) is equal to the
flow of 1 A of current through a conductor
between two points having potential
difference equal to 1 V.
This means 1Ω=1V1A1Ω=1V1A
From the expression of Ohm’s Law it is
obvious that electric current through a
resistor is inversely proportional to

resistance. This means electric current will
decrease with increase in resistance and
vice versa.
The graph of V (potential difference)
versus I (electric current) is always a
straight line.
Example 1: Calculate the resistance if 5 A
of electric current flows through a
conductor having potential difference
between two points is equal to 15 V.
Solution: Given, electric current (I) = 5 A
Potential difference (V) = 15 V
Resistance (R) =?
We know from Ohm’s Law that
R=V/R=VI

Or, R=15V5A=3ΩR=15V5A=3Ω
Example 2: If the potential difference
between the terminals of an electric motor
is 220 V and an electric current of 5 A is
flowing through it what will be the
resistance of electric motor?
Resistance (R) =?
R=VIR=VI
Or, R=220V5A=44ΩR=220V5A=44Ω
Example 3: An electric current of 15 A is
flowing through an electric fan. If the
potential difference between two terminals
of electric fan is 240 V, what will be
resistance?
Resistance (R) =?

R=VIR=VI
Or, R=240V15A=16ΩR=240V15A=16Ω
Example 4: If the resistance of an electric
iron is 48 Ω and an electric current of 5 A
is flowing through it, what will be the
potential difference between two terminals
of electric iron.
Resistance (R) = 48Ω
Potential difference (V) =?
R=VIR=VI
Or, V=R×IV=R×I
Or, V=48Ω×5A=240VV=48Ω×5A=240V
Example 5: Calculate the potential
difference between two points of a
terminal, if an electric current of 10 A is

flowing through it having resistance of
20Ω.
Potential difference (V) =?
R=VIR=VI
Or, V=R×IV=R×I
Or, V=20Ω×10A=200VV=20Ω×10A=200V
Example 6: If the resistance between two
terminals of an electric heater is 15Ω and
an electric current of 15 A is flowing
through it then what will be the voltage of
electric current?
Given, electric current (I) = 15 A
Voltage, i.e. Potential difference (V) =?
R=VIR=VI

Or, V=R×IV=R×I
Or, V=15Ω×15A=225VV=15Ω×15A=225V

22 april 2021 lecture

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22 april 2021 lecture