various parameters like electric circuit , electric current etc, heating effect of electricity and it's magnetic effect

2.  Electricity is the set of physical
phenomena associated with
the presence and
flow of electric
charge. Electricity gives a
wide variety of well-known
effects,
 such as lightning,
static electricity,
electromagnetic induction
and electrical current

3.  An electric current is a flow
of electric charge. In
electric circuits this charge is
often carried by moving
electrons in a wire. It can also be
carried by ions in an electrolyte,
or by both ions and electrons
such as in a plasma The SI unit
for measuring an electric current
is the ampere, one ampere is
constituted by the flow of one
coulomb of charge per second.

4.  An electric circuit is a path in which
electrons from a voltage or current source
flow. Electric current flows in a closed
path called an electric circuit. The point
where those electrons enter an electrical
circuit is called the "source" of electrons.
Direction of electric current in an electric
circuit is taken as opposite to the direction
of the flow of electrons .
 AMMETER – Instrument for measuring
current
 VOLTMETER – Instrument for measuring
voltage

5.  Electric charge is the
physical property of matter
that causes it to
experience a force when
placed
in an electromagnetic
field. There are two types
of electric charges: positive
and negative
The SI derived unit of
electric charge is the
coulomb (C).

6.  It is the amount of electric
potential energy that a unitary
point electric charge would have
if located at any point in space,
and is equal to the work done by
an electric field in carrying a unit
positive charge from infinity to
that point.

7.  The difference in the amount of electric
potential energy between two points in
an electric circuit is called ELECTRIC
POTENTIAL DIFFERENCE. Electric potential
difference is known as voltage, which is
equal to the work done per unit charge to
move the charge between two points
against static electric field.
 SI unit of electric potential difference is volt
and denoted by ‘V’. This is named in honour
of Italian Physicist Alessandro Volta.

8.  Ohm’s Law states that the potential
difference between two points is directly
proportional to the electric current.
 This means; potential difference V varies as
electric current.
 Or, V ∝ I
 Where R is constant for the given conductor
at a given temperature and called
resistance. Resistance is the property of
conductor which resists the flow of electric
current through it.

9.  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.
 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.

11.  Resistance is a property of
conductor due to which it resists
the flow of electric current through
it. Component that is used to resist
the flow of electric current in a
circuit is called resistor.
 In practical applications, resistors
are used to increase or decrease
the electric current.
 Variable Resistance: The
component of an electric circuit
which is used to regulate the
current; without changing the
voltage from the source; is called
variable resistance.
 Rheostat: This is a device which is
used in a circuit to provide variable
resistance.

12.  Flow of electrons in a conductor is
electric current. The particles of
conductor create hindrance to flow of
electrons; because of attraction
between them. This hindrance is the
cause of resistance in the flow of
electricity.
 Resistance in a conductor depends on
nature, length and area of cross section
of the conductor.

13.  Nature of material: Some materials create least
hindrance and hence are called good
conductors. Silver is the best conductor of
electricity. While some other materials create
more hindrance in the flow of electric current,
i.e. flow of electrons through them. Such
materials are called bad conductors. Bad
conductors are also known as insulators. Hard
plastic is the one of the best insulators of
electricity.
 Length of conductor: Resistance R is directly
proportional to the length of the conductor.
This means, Resistance increases with increase
in length of the conductor. This is the cause
that long electric wires create more resistance
to the electric current.

14.  Thus, Resistance (R) ∝ length of
conductor (l)
or R ∝ l --------(i)
 Area of cross section: Resistance
R is inversely proportional to the
area of cross section ( A) of the
conductor. This means R will
decrease with increase in the
area of conductor and vice
versa. More area of conductor
facilitates the flow of electric
current through more area and
thus decreases the resistance.
This is the cause that thick
copper wire creates less
resistance to the electric
current.
Thus, resistance ∝ 1/Area of cross
section of conductor (A)

15.  Where ρ(rho) is the proportionality
constant. It is called the electrical
resistivity of the material of conductors.
 From equation (iii)
The SI unit of resistivity: Since, the SI unit
of R is Ω, SI unit of Area is m2 and SI unit
of length is m. Hence
Thus, SI unit of resistivity (ρ) is Ω m

16.  Resistors in Series: When resistors are
joined from end to end, it is called in
series. In this case, the total resistance of
the system is equal to the sum of the
resistance of all the resistors in the system.
 Let total resistance = R
 Resistance of resistors are R1, R2, R3, … Rn
 Therefore, R = R1 + R2 + R3 + …………+ Rn
Resistors are joined in two ways, i.e. in series and in
parallel.

17.  Resistors in parallel: When resistors are
joined in parallel, the reciprocal of
total resistance of the system is equal
to the sum of reciprocal of the
resistance of resistors.
 Let total resistance = R
 Resistance of resistors are R1, R2, R3, …
Rn

18. RESISTORS
IN SERIES
RESISTORS
IN PARALLEL

19. THERE ARE TWO TYPES OF EFFECTS :
1) HEATING EFFECTS
2) MAGNETIC EFEECTS

20.  When electric current is supplied to a purely resistive
conductor, the energy of electric current is dissipated entirely
in the form of heat and as a result, resistor gets heated. The
heating of resistor because of dissipation of electrical energy
is commonly known as Heating Effect of Electric Current.
Some examples are as follows:
 When electric energy is supplied to an electric bulb, the
filament gets heated because of which it gives light. The
heating of electric bulb happens because of heating effect
of electric current.
 When an electric iron is connected to an electric circuit, the
element of electric iron gets heated because of dissipation of
electric energy, which heats the electric iron. The element of
electric iron is a purely resistive conductor. This happens because of
heating effect of electric current.

21.  Electric current generates heat to
overcome the resistance offered by the
conductor through which it passes. Higher
the resistance, the electric current will
generate higher amount of heat.
 Thus, generation of heat by electric current
while passing through a conductor is an
inevitable consequence. This heating effect
is used in many appliances, such as electric
iron, electric heater, electric geyser, etc.

22.  Let; an electric current I is flowing through a resistor
having resistance equal to R.
 The potential difference through the resistor is equal
to V.
 The charge Q flows through the circuit for the time t.
 Thus, work done in moving of charge Q of potential
difference V, Work done = VQ
 Since, this charge Q flows through the circuit for time
t
 Therefore; power input (P) to the circuit can be given
by following equation:
 We know, electric current I = Q/t
 Substituting Q/t = I in equation (i), we get;
 P = VI ..........(ii)

23.  Since the electric energy is supplied for time t, thus
after multiplying both sides of equation (ii) by time t,
we get
 P x t = VI x t = VIt .....(iii)
 Thus, for steady current I, the heat produced (H) in
time t is equal to VIt
 Or, H = VIt .........(iv)
 We know; according to Ohm's law; V = IR
 By substituting this value of V in equation (iv), we
get;
 H = IR x It Or, ........(v)
 The expression (v) is known as Joule’s Law of
Heating, which states that “heat produced in a
resistor is directly proportional to the square of
current given to the resistor, directly
proportional to the resistance for a given
current and directly proportional to the time for
which the current is flowing through the resistor”

24.  Practical Application of Heating Effect of Electric
Current & Electric Power
 For exploiting the heating effect of electric
current, the element of appliances must have
high melting point to retain more heat. The
heating effect of electric current is used in the
following applications:
 Electric Bulb: In an electric bulb, the filament of
bulb gives light because of heating effect of
electricity. The filament of bulb is generally made
of tungsten metal; having melting point equal to
3380°C.
 Electric iron: The element of electric iron is made
of alloys having high melting point. Electric heater
and geyser work on the same mechanism.

25.  SI unit of electric power is watt (W).
 1W = 1 volt x 1 ampere = 1V x 1A
 1 kilo watt or 1kW = 1000 W
 Consumption of electricity (electric energy)
is generally measured in kilo watt.
 Unit of electric energy is kilo watt hour (kWh)
 1 kWh = 1000 watt X 1 hour = 1000 W x 3600 s
 Or, 1kWh = 3.6 x 106 watt second = 3.6 x
106 J

26.  Electric fuse: Electric fuse is used to protect the
electric appliances from high voltage; if any.
Electric fuse is made of metal or alloy of metals,
such as aluminium, copper, iron, lead, etc. In
the case of flow of higher voltage than
specified, fuse wire melts and protects the
electric appliances.
 Fuse of 1A, 2A, 3A, 5A, 10A, etc. are used for
domestic purpose.
 Suppose, if an electric heater consumes 1000W
at 220V.
 Then electric current in circuit I = P/V
 Or, I = 1000 W − 220 V = 4.5 A
 Thus, in this case a fuse of 5A should be used to
protect the electric heater in the case of flow
of higher voltage.

27. Properties of magnet:
 A free suspended magnet always point towards north and
south direction.
 The pole of a magnet which points toward north direction is
called north pole or north seeking.
 The pole of a magnet which points toward south direction is
called south pole or south seeking.
 Like poles of magnets repel each other while unlike poles of
magnets attract each other.
 Similar to other effects; electric current also produces
magnetic effect. The magnetic effect of electric current is
known as electromagnetic effect.
 It is observed that when a compass is brought near a current
carrying conductor the needle of compass gets deflected
because of flow of electricity. This shows that electric current
produces a magnetic effect.

28.  The influence of force surrounding a
magnet is called magnetic field. In
the magnetic field, the force exerted
by a magnet can be detected using
a compass or any other magnet.
 The imaginary lines of magnetic field
around a magnet are called field line
or field line of magnet. When iron
fillings are allowed to settle around a
bar magnet, they get arranged in a
pattern which mimicks the magnetic
field lines. Field line of a magnet can
also be detected using a compass.
Magnetic field is a vector quantity,
i.e. it has both direction and
magnitude.

29.  Direction of Field Line: Outside the
magnet, the direction of magnetic
field line is taken from north pole to
South Pole. Inside the magnet, the
direction of magnetic field line is taken
from south pole to north pole.
 Strength of magnetic field: The
closeness of field lines shows the
relative strength of magnetic field, i.e.
closer lines show stronger magnetic
field and vice-versa. Crowded field
lines near the poles of magnet show
more strength.

30.  Magnetic field due to current through a straight conductor:
 A current carrying straight conductor has magnetic field in
the form of concentric circles; around it. Magnetic field of
current carrying straight conductor can be shown by
magnetic field lines.
 The direction of magnetic field through a current carrying
conductor depends upon the direction of flow of electric
current. The direction of magnetic field gets reversed in
case of a change in the direction of electric current.
 Let a current carrying conductor be suspended vertically
and the electric current is flowing from south to north. In
this case, the direction of magnetic field will be
anticlockwise. If the current is flowing from north to south,
the direction of magnetic field will be Clockwise.

31.  The direction of magnetic field;
 in relation to direction
 of electric current through
 a straight conductor can be
 depicted by using the Right
 Hand Thumb Rule. It is also
known as Maxwell’s Corkscrew
Rule.
 If a current carrying conductor
is held by right hand; keeping
the thumb straight and if the direction
of electric current is in the direction
of thumb, then the direction of wrapping
of other fingers will show the direction
of magnetic field.

32.  As per Maxwell’s corkscrew rule,
 if the direction of forward
 movement
 of screw shows the direction of
 current, then the direction of
 rotation of screw shows the
 direction of magnetic field.
 Properties of Magnetic Field:
 The magnitude of magnetic field increases with
increase in electric current and decreases with
decrease in electric current.
 The magnitude of magnetic field produced by electric
current; decreases with increase in distance and vice-
versa. The size of concentric circles of magnetic field
lines increases with distance from the conductor, which
shows that magnetic field decreases with distance.
 Magnetic field lines are always parallel to each other.
 No two field lines cross each other.

33.  In case of a circular current carrying
conductor, the magnetic field is
produced in the same manner as it is in
case of a straight current carrying
conductor.
 In case of a circular current carrying
conductor, the magnetic field lines would
be in the form of concentric circles
around every part of the periphery of the
conductor. Since, magnetic field lines
tend to remain closer when near the
conductor, so the magnetic field would
be stronger near the periphery of the
loop.

34.  . On the other hand, the magnetic field
lines would be distant from each other
when we move towards the centre of
the current carrying loop. Finally; at the
centre, the arcs of big circles would
appear as a straight lines.
 The direction of magnetic field can be
identified using Right Hand Thumb’s Rule.
Let us assume that the current is moving
in anti-clockwise direction in the loop. In
that case, the magnetic field would be
in clockwise direction; at the top of the
loop. Moreover, it would be in
anticlockwise direction at the bottom of
the loop

35.  Clock Face Rule: A current carrying loop works
like a disc magnet. The polarity of this magnet
can be easily understood with the help of
clock face rule. If the current is flowing in anti-
clockwise direction, then the face of the loop
shows north pole. On the other hand, if the
current is flowing in clockwise direction, then
the face of the loop shows south pole.
 Magnetic field and number of turns of
coil: Magnitude of magnetic field gets
summed up with increase in the number of
turns of coil. If there are ‘n’ turns of coil,
magnitude of magnetic field will be ‘n’ times
of magnetic field in case of a single turn of
coil.

36.  Solenoid is the coil with many circular turns of insulated
copper wire wrapped closely in the shape of cylinder.
 A current carrying solenoid produces similar pattern of
magnetic field as a bar magnet. One end of solenoid
behaves as the north pole and another end behaves as
the south pole. Magnetic field lines are parallel inside
the solenoid; similar to a bar magnet; which shows that
magnetic field is same at all points inside the solenoid.
 By producing a strong magnetic field inside the
solenoid, magnetic materials can be magnetized.
Magnet formed by producing magnetic field inside a
solenoid is called electromagnet

37.  A current carrying conductor exerts a force
when a magnet is placed in its vicinity.
Similarly, a magnet also exerts equal and
opposite force on the current carrying
conductor. This was suggested by Marie
Ampere, a French Physicist and considered
as founder of science of electromagnetism.
 The direction of force over the conductor
gets reversed with the change in direction
of flow of electric current. It is observed that
the magnitude of force is highest when the
direction of current is at right angles to the
magnetic field.

38.  If direction of electric current is
perpendicular to the magnetic field, the
direction of force is also perpendicular to
both of them. The Fleming’s Left Hand Rule
states that “if the left hand is stretched in
a way that the index finger, the middle
finger and the thumb are in mutually
perpendicular directions; then the index
finger and middle finger of a stretched
left hand show the direction of magnetic
field and direction of electric current
respectively and the thumb shows the
direction of motion or force acting on the
conductor”. The directions of electric
current, magnetic field and force are
similar to three mutually perpendicular
axis, i.e. x, y and z axes.
 Many devices, such as electric motor,
loudspeaker, etc. works on the Fleming’s
left Hand Rule.

39.  Electrical energy is converted into mechanical energy by
using an electric motor. Electric motor works on the basis of
rule suggested by Marie Ampere and Fleming’s Left Hand
Rule.
 In an electric motor, a rectangular coil is suspended between
the two poles of a magnetic field. The electric supply to the
coil is connected with a commutator . Commutator is a
device which reverses the direction of flow of electric current
through a circuit.
 When electric current is supplied to the coil of electric motor,
it gets deflected because of magnetic field. As it reaches the
half way, the split ring which acts as commutator reverses the
direction of flow of electric current. Reversal of direction of
current reverses the direction of forces acting on the coil.

40. The change in direction of force pushes the
coil; and it moves another half turn. Thus, the
coil completes one rotation around the axle.
 Continuation of this process keeps the motor
in rotation.
 In commercial motor,
electromagnet: instead
of permanent magnet;
and armature is used.
 Armature is a soft iron core with large
number of conducting wire turns over it.
Large number of turns of conducting wire
enhances the magnetic field produced by
armature.

41.  Michael Faraday, an English Physicist is
supposed to have studied the generation of
electric current using magnetic field and a
conductor.
 When a conductor is set to move inside a
magnetic field or a magnetic field is set to be
changing around a conductor, electric
current is induced in the conductor. This is just
opposite to the exertion of force by a current
carrying conductor inside a magnetic field. In
other words, when a conductor is brought in
relative motion vis-à-vis a magnetic field, a
potential difference is induced in it. This is
known as electromagnetic induction.

42.  Electromagnetic induction can be explained with the
help of Fleming’s Right Hand Rule. If the right hand is
stretched in a way that the index finger, middle finger
and thumb are in mutually perpendicular directions,
then the thumb shows the direction of movement of
the conductor, index finger shows the direction of
magnetic field and the middle finger shows the
direction of induced current in the conductor. The
directions of movement of conductor, magnetic field
and induced current can be compared to three
mutually perpendicular axes, i.e. x, y and z axes.
 The mutually perpendicular directions also point to an
important fact that the when the magnetic field and
movement of conductor are perpendicular, the
magnitude of induced current would be maximum.
 Electromagnetic induction is used in the conversion of
kinetic energy into electrical energy.

43.  The structure of electric generator
is similar to that of an electric
motor. In case of an electric
generator a rectangular armature
is placed within the magnetic
field of a permanent magnet. The
armature is attached to wire and is
positioned in way that it can move
around an axle. When the armature
moves within the magnetic field an
electric current is induced. The direction of induced current
changes, when the armature crosses the halfway mark of its
rotation. Thus, the direction of current changes once in every
rotation. Due to this, the electric generator usually produces
alternate current, i.e. AC. To convert an AC generator into a DC
generator, a split ring commutator is used. This helps in producing
direct current.

44.  AC – Alternate current: Current in which
direction is changed periodically is called
Alternate Current. In India, most of the power
stations generate alternate current. The
direction of current changes after every 1/100
second in India, i.e. the frequency of AC in
India is 50 Hz. AC is transmitted upto a long
distance without much loss of energy is
advantage of AC over DC
 DC – Direct current: Current that flows in one
direction only is called Direct current.
Electrochemical cells produce direct current