1. Chapter 22
Electromagnetic Induction

2. Learning Outcomes
Deduce from Faraday’s experiments on
electromagnetic induction or other appropriate
experiments:
(i) that a changing magnetic field can induce an e.m.f.
in a circuit;
(ii) that the direction of the induced e.m.f. opposes
the change producing it;
(iii) the factors affecting the magnitude of the induced
e.m.f.

3. Learning Outcomes
Describe a simple form of a.c. generator (rotating coil
or rotating magnet) and the use of slip rings (where
needed).
Sketch a graph of voltage output against time for a
simple a.c. generator.
Describe the structure and principle of operation of a
simple iron-cored transformer as used for voltage
transformation.

4. Learning Outcomes
Recall and apply the equations VP / VS = NP / NS and
VPIP = VSIS to new situations or to solve related
problems.
Describe the energy loss in cables and deduce the
advantages of high voltage transmission.

5. Quiz
In the previous chapter, you have learnt that a current can
produce a magnetic field, is the reverse possible?
Yes, it is possible.
In this chapter you will learn that a magnetic field can
produce an electrical current.

6. 22.1 Electromagnetic Induction
Faraday’s Iron Ring Experiment

7. Faraday’s Iron Ring Experiment
When switch S was closed or opened, Faradays
noticed that the compass needle deflected
momentarily. (The deflection of the compass needle
shows that there was a magnetic field present that was
caused by a current flowing in wire PQ)
However, the compass needle did not deflect when the
switch was left closed or opened.

8. Faraday’s Iron Ring Experiment
From the experiment, it was concluded that when
the current in coil A was ,a
was caused to .
The current in B is called an .

9. Faraday’s Iron Ring Experiment
From the experiment, it was concluded that when
the current in coil A was switched on or off , a
was caused to .
The current in B is called an .

10. Faraday’s Iron Ring Experiment
From the experiment, it was concluded that when
the current in coil A was switched on or off , a
current was caused to
.
The current in B is called an .

11. Faraday’s Iron Ring Experiment
From the experiment, it was concluded that when
the current in coil A was switched on or off , a
current was caused to flow in coil B .
The current in B is called an .

12. Faraday’s Iron Ring Experiment
From the experiment, it was concluded that when
the current in coil A was switched on or off , a
current was caused to flow in coil B .
The current in B is called an induced current .

13. Faraday’s Iron Ring Experiment
The induced current in coil B arose only when there
was a
.

14. Faraday’s Iron Ring Experiment
The induced current in coil B arose only when there
change in the magnetic field in the ring
was a
linking the coil B .

15. Faraday’s Solenoid Experiment
When the magnet is inserted into the solenoid, the
galvanometer needle
, indicating an
through the solenoid.

16. Faraday’s Solenoid Experiment
When the magnet is inserted into the solenoid, the
galvanometer needle deflected momentarily to
one direction , indicating an
through the solenoid.

17. Faraday’s Solenoid Experiment
When the magnet is inserted into the solenoid, the
galvanometer needle deflected momentarily to
one direction , indicating an induced current
flowing in one direction through the solenoid.

18. Faraday’s Solenoid Experiment
When the magnet is withdrawn into the solenoid, the
galvanometer needle
, indicating an
through the
solenoid.

19. Faraday’s Solenoid Experiment
When the magnet is withdrawn into the solenoid, the
galvanometer needle deflected momentarily in
opposite direction , indicating an
through the
solenoid.

20. Faraday’s Solenoid Experiment
When the magnet is withdrawn into the solenoid, the
galvanometer needle deflected momentarily in
opposite direction , indicating an induced
current flowing in opposite
direction through the
solenoid.

21. Faraday’s Solenoid Experiment
When the magnet is stationary (either inside or outside
the solenoid), there will be
.

22. Faraday’s Solenoid Experiment
When the magnet is stationary (either inside or outside
the solenoid), there will be no deflection in the
galvanometer indicating induced current
no
flowing through the solenoid .

23. QUIZ
What do you think will happen if you
(i) change the number of turns of wire in the coil
(ii) change the strength of the magnet used
(iii) change the speed at which the magnet is moving

24. 22.1 Electromagnetic Induction

25. 22.1 Electromagnetic Induction
It was discovered that the magnitude of
the induced e.m.f. depends on:

26. 22.1 Electromagnetic Induction
It was discovered that the magnitude of
the induced e.m.f. depends on:
(a) number of turns in the solenoid

27. 22.1 Electromagnetic Induction
It was discovered that the magnitude of
the induced e.m.f. depends on:
(a) number of turns in the solenoid
(b) strength of magnet

28. 22.1 Electromagnetic Induction
It was discovered that the magnitude of
the induced e.m.f. depends on:
(a) number of turns in the solenoid
(b) strength of magnet
(c) speed at which the magnet is
inserted or withdraw from the
solenoid

29. The Laws of Electromagnetic Induction
Faraday’s Law of Induction:
The e.m.f. (electromotive force) generated
in a conductor is
.

30. The Laws of Electromagnetic Induction
Faraday’s Law of Induction:
The e.m.f. (electromotive force) generated
in a conductor is to the
proportional
rate of change of magnetic lines of
force flux) linking the
(magnetic
circuit .

31. The Laws of Electromagnetic Induction
Lenz’s Law:
The direction of the induced e.m.f is always
such that
.

32. The Laws of Electromagnetic Induction
Lenz’s Law:
The direction of the induced e.m.f is always
such that its magnetic effect
opposes the motion or change
producing it .

33. Demonstration of the two
laws of electromagnetism

34. Demonstration of the two laws
of electromagnetism
Apparatus:
Copper wire coil of about 20 turns, sensitive centre-zero
galvanometer, bar magnet.

35. Demonstration of the two laws
of electromagnetism
Procedures:
1. Connect the ends of the coil to a sensitive centre-zero
galvanometer by means of long leads (i.e. connecting
wires).

36. Demonstration of the two laws
of electromagnetism
Procedures:
2. Move the S-pole of a permanent bar magnet into the
coil and note any deflection on the galvanometer.

37. Demonstration of the two laws
of electromagnetism
Procedures:
3. Once the bar magnet is inside the coil, hold it
stationary and gain note any deflection on the
a
galvanometer.

38. Demonstration of the two laws
of electromagnetism
Procedures:
4. Next, move the S-pole of the magnet out of the coil
and note any deflection on the galvanometer.

39. Demonstration of the two laws
of electromagnetism
Procedures:
5. Repeat steps 2 to 4 using the N-pole of the same bar
magnet.

40. Demonstration of the two laws
of electromagnetism
S N
S-pole of magnet
moving into the solenoid.

41. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the left -
induced current
S N
flowing through the
circuit.
S-pole of magnet
moving into the solenoid.

42. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the left -
induced current
S N
flowing through the
circuit.
2. The induced current
S-pole of magnet shows that an induced
moving into the solenoid. e.m.f. is generated in the
circuit.

43. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in clockwise
S N
direction. By lenz’s law,
the direction of the
induced current opposes
the change producing it,
S-pole of magnet
hence a S-pole moving in
moving into the solenoid.
will induce a south pole
so as to try to repel it
away.

44. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in clockwise
N S S N
direction. By lenz’s law,
the direction of the
induced current opposes
the change producing it,
S-pole of magnet
hence a S-pole moving in
moving into the solenoid.
will induce a south pole
so as to try to repel it
away.

45. Demonstration of the two laws
of electromagnetism
S N
Magnet remains
stationary
in the solenoid.

46. Demonstration of the two laws
of electromagnetism
S N 1. Galvanometer shows no
deflection - no current
flowing through the
circuit.
Magnet remains
stationary
in the solenoid.

47. Demonstration of the two laws
of electromagnetism
S N
S-pole of magnet
S-pole of magnet
moving into the solenoid.
moving out the solenoid.

48. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the right -
induced current
S N
flowing through the
circuit.
S-pole of magnet
S-pole of magnet
moving into the solenoid.
moving out the solenoid.

49. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the right -
induced current
S N
flowing through the
circuit.
2. The induced current
S-pole of magnet
S-pole of magnet shows that an induced
moving into the solenoid.
moving out the solenoid. e.m.f. is generated in the
circuit.

50. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in anti-
S N
clockwise direction. By
lenz’s law, the direction of
the induced current
opposes the change
S-pole of magnet
S-pole of magnet
producing it, hence a S-
moving into the solenoid.
moving out the solenoid. pole moving out will
induce a north pole so
as to try to attract it.

51. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in anti-
S N S N
clockwise direction. By
lenz’s law, the direction of
the induced current
opposes the change
S-pole of magnet
S-pole of magnet
producing it, hence a S-
moving into the solenoid.
moving out the solenoid. pole moving out will
induce a north pole so
as to try to attract it.

52. Demonstration of the two laws
of electromagnetism
N S
S-pole of magnet
N-pole of magnet
moving into the solenoid.
moving into the solenoid.

53. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the right -
induced current
N S
flowing through the
circuit.
S-pole of magnet
N-pole of magnet
moving into the solenoid.
moving into the solenoid.

54. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the right -
induced current
N S
flowing through the
circuit.
2. The induced current
S-pole of magnet shows that an induced
N-pole of magnet
moving into the solenoid.
moving into the solenoid. e.m.f. is generated in the
circuit.

55. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in anti-
N S
clockwise direction. By
lenz’s law, the direction of
the induced current
opposes the change
S-pole of magnet
N-pole of magnet producing it, hence a N-
moving into the solenoid.
moving into the solenoid. pole moving in will induce
a north pole so as to try
to repel it away.

56. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in anti-
S NN S
clockwise direction. By
lenz’s law, the direction of
the induced current
opposes the change
S-pole of magnet
N-pole of magnet producing it, hence a N-
moving into the solenoid.
moving into the solenoid. pole moving in will induce
a north pole so as to try
to repel it away.

57. Demonstration of the two laws
of electromagnetism
N S
Magnet remains
stationary
in the solenoid.

58. Demonstration of the two laws
of electromagnetism
N S 1. Galvanometer shows no
deflection - no current
flowing through the
circuit.
Magnet remains
stationary
in the solenoid.

59. Demonstration of the two laws
of electromagnetism
N S
S-pole of magnet
N-pole of magnet
moving into the solenoid.
moving out the solenoid.

60. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the left -
induced current
N S
flowing through the
circuit.
S-pole of magnet
N-pole of magnet
moving into the solenoid.
moving out the solenoid.

61. Demonstration of the two laws
of electromagnetism
1. Galvanometer shows a
deflection to the left -
induced current
N S
flowing through the
circuit.
2. The induced current
S-pole of magnet
N-pole of magnet shows that an induced
moving into the solenoid.
moving out the solenoid. e.m.f. is generated in the
circuit.

62. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in clockwise
N S
direction. By lenz’s law,
the direction of the
induced current opposes
the change producing it,
S-pole of magnet
N-pole of magnet hence a N-pole moving
moving into the solenoid.
moving out the solenoid. out will induce a south
pole so as to try to
attract it.

63. Demonstration of the two laws
of electromagnetism
3. The induced current on
the right-hand side of the
coil flows in clockwise
N S N S
direction. By lenz’s law,
the direction of the
induced current opposes
the change producing it,
S-pole of magnet
N-pole of magnet hence a N-pole moving
moving into the solenoid.
moving out the solenoid. out will induce a south
pole so as to try to
attract it.

64. Lenz’s Law and Conservation of Energy
• By Lenz’s law, the direction of the induced current is
such as to
the change causing it.
• When we move the magnet into the coil, we have to
do in overcoming the
between the like poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

65. Lenz’s Law and Conservation of Energy
• By Lenz’s law, the direction of the induced current is
such as to
oppose the change causing it.
• When we move the magnet into the coil, we have to
do in overcoming the
between the like poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

66. Lenz’s Law and Conservation of Energy
• By Lenz’s law, the direction of the induced current is
such as to
oppose the change causing it.
• When we move the magnet into the coil, we have to
do work in overcoming the
between the like poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

67. Lenz’s Law and Conservation of Energy
• By Lenz’s law, the direction of the induced current is
such as to
oppose the change causing it.
• When we move the magnet into the coil, we have to
do work in overcoming the repulsion
force
between the like poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

68. Lenz’s Law and Conservation of Energy
• By Lenz’s law, the direction of the induced current is
such as to
oppose the change causing it.
• When we move the magnet into the coil, we have to
do work in overcoming the repulsion
force
between the like poles. Hence mechanical energy is
transformed into electrical energy as indicated by
the induced current flowing in the circuit.

69. Lenz’s Law and Conservation of Energy
• When we move the magnet out the coil, we have to
do in overcoming the
between the unlike poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

70. Lenz’s Law and Conservation of Energy
• When we move the magnet out the coil, we have to
do work in overcoming the
between the unlike poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

71. Lenz’s Law and Conservation of Energy
• When we move the magnet out the coil, we have to
do work in overcoming the attraction force
between the unlike poles. Hence mechanical energy is
transformed into as indicated by
the induced current flowing in the circuit.

72. Lenz’s Law and Conservation of Energy
• When we move the magnet out the coil, we have to
do work in overcoming the attraction force
between the unlike poles. Hence mechanical energy is
transformed into electrical energy as indicated by
the induced current flowing in the circuit.

73. 22.2 Alternating Current Generators
• The a.c. generator is an electromagnetic device,
which transforms
into .
• The d.c. motor is an electromagnetic device, which
transforms into
.

74. 22.2 Alternating Current Generators
• The a.c. generator is an electromagnetic device,
which transforms kinetic energy (mechanical
energy) into
.
• The d.c. motor is an electromagnetic device, which
transforms into
.

75. 22.2 Alternating Current Generators
• The a.c. generator is an electromagnetic device,
which transforms kinetic energy (mechanical
energy) into
electrical energy .
• The d.c. motor is an electromagnetic device, which
transforms into
.

76. 22.2 Alternating Current Generators
• The a.c. generator is an electromagnetic device,
which transforms kinetic energy (mechanical
energy) into
electrical energy .
• The d.c. motor is an electromagnetic device, which
transforms electrical energy into
.

77. 22.2 Alternating Current Generators
• The a.c. generator is an electromagnetic device,
which transforms kinetic energy (mechanical
energy) into
electrical energy .
• The d.c. motor is an electromagnetic device, which
transforms electrical energy into
kinetic energy (mechanical energy) .

78. 22.2 Alternating Current Generators
• An a.c. generator
consists of a
rectangular coil of
wire that is mounted
on an axle. By turning
the axle, the coil is
made to rotate
between the poles of
a permanent magnet.

79. 22.2 Alternating Current Generators
• As the coil rotates,
the
and therefore
between the ends of
the coil.

80. 22.2 Alternating Current Generators
• As the coil rotates,
the coil cuts the
magnetic field
lines (magnetic
field the
through
coil is changing)
and therefore
between the ends of
the coil.

81. 22.2 Alternating Current Generators
• As the coil rotates,
the coil cuts the
magnetic field
lines (magnetic
field the
through
coil is changing)
and therefore
induced
current is
between the ends of
the coil.

82. 22.2 Alternating Current Generators
• Note: the ends of the
coil must be
connected to an
external circuit with
an electrical load
such as a resistor for
the current to flow.)

83. 22.2 Alternating Current Generators
• The slip rings allow the transfer of the
induced in the rotating coil to the external
circuit.
D C C D
N S N S
A B B A
Slip rings

84. 22.2 Alternating Current Generators
• The slip rings allow the transfer of the alternating
current induced in the rotating coil to the external
circuit.
D C C D
N S N S
A B B A
Slip rings

85. 22.2 Alternating Current Generators
• The carbon brushes provides the contact between
the slip rings and the external circuit which prevents
wear and tear of the rings.
D C C D
N S N S
A B B A
Slip rings

86. 22.2 Alternating Current Generators
• When the coil is horizontal,
• The rate at which the coil
.
• Hence the induced e.m.f. is the
.
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

87. 22.2 Alternating Current Generators
• When the coil is horizontal,
• The rate at which the coil the magnetic field
cuts
lines is the greatest .
• Hence the induced e.m.f. is the
.
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

88. 22.2 Alternating Current Generators
• When the coil is horizontal,
• The rate at which the coil the magnetic field
cuts
lines is the greatest .
• Hence the induced e.m.f. is the maximum induced
e.m.f. .
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

89. 22.2 Alternating Current Generators
• When the coil is vertical,
• The coil is moving parallel to the magnetic field
lines, hence it is
.
• Hence the induced e.m.f. is the .
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

90. 22.2 Alternating Current Generators
• When the coil is vertical,
• The coil is moving parallel to the magnetic field
lines, hence it is not cutting the magnetic field
lines .
• Hence the induced e.m.f. is the .
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

91. 22.2 Alternating Current Generators
• When the coil is vertical,
• The coil is moving parallel to the magnetic field
lines, hence it is not cutting the magnetic field
lines .
• Hence the induced e.m.f. is the zero .
B
A
e.m.f./V
EO
0
time/s
-– EO
one revolution

92. 22.2 Alternating Current Generators
• When the number of turns on the coil is doubled
without changing the frequency of the rotation of
the coil,
• The maximum output voltage will .
• The frequency of the changing of direction of
current flow will .
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

93. 22.2 Alternating Current Generators
• When the number of turns on the coil is doubled
without changing the frequency of the rotation of
the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will .
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

94. 22.2 Alternating Current Generators
• When the number of turns on the coil is doubled
without changing the frequency of the rotation of
the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will remains constant .
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

95. 22.2 Alternating Current Generators
• When the number of turns on the coil is doubled
without changing the frequency of the rotation of
the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will remains constant .
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

96. 22.2 Alternating Current Generators
• When the frequency of the rotation of the coil is
doubled without changing the number of turns
on the coil,
• The maximum output voltage will .
• The frequency of the changing of direction of
current flow will . (i.e. Period is .)
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

97. 22.2 Alternating Current Generators
• When the frequency of the rotation of the coil is
doubled without changing the number of turns
on the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will . (i.e. Period is .)
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

98. 22.2 Alternating Current Generators
• When the frequency of the rotation of the coil is
doubled without changing the number of turns
on the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will doubled . (i.e. Period is halved .)
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

99. 22.2 Alternating Current Generators
• When the frequency of the rotation of the coil is
doubled without changing the number of turns
on the coil,
• The maximum output voltage will doubled .
• The frequency of the changing of direction of
current flow will doubled . (i.e. Period is halved .)
e.m.f./V
2EO
EO
0
– EO time/s
– 2EO
previous output
voltage

100. 22.2 Alternating Current Generators

101. 22.2 Alternating Current Generators
• The alternating voltage output of an a.c. generator
increases with

102. 22.2 Alternating Current Generators
• The alternating voltage output of an a.c. generator
increases with
• an increase in the number of turns of coil
used.

103. 22.2 Alternating Current Generators
• The alternating voltage output of an a.c. generator
increases with
• an increase in the number of turns of coil
used.
• an increase in the speed of rotation of the
coil.

104. 22.2 Alternating Current Generators
• The alternating voltage output of an a.c. generator
increases with
• an increase in the number of turns of coil
used.
• an increase in the speed of rotation of the
coil.
• a stronger magnet used.

105. 22.2 Alternating Current Generators
• The alternating voltage output of an a.c. generator
increases with
• an increase in the number of turns of coil
used.
• an increase in the speed of rotation of the
coil.
• a stronger magnet used.
• a soft iron core placed in the centre of the coil
of wire.

106. Other A.C. Generators (Practical design)
• To generate large currents (as in turbine in power
stations), it is more practical and advantageous to
keep the and to
.
• Hence instead of the coil cutting the magnetic field
(discussed previously), now the magnetic field cuts
the coil.
• Using this method, we can do away with the
which is prone to
wear & tear and not capable of carrying large currents.

107. Other A.C. Generators (Practical design)
• To generate large currents (as in turbine in power
stations), it is more practical and advantageous to
keep the fixed and to
coil
.
• Hence instead of the coil cutting the magnetic field
(discussed previously), now the magnetic field cuts
the coil.
• Using this method, we can do away with the
which is prone to
wear & tear and not capable of carrying large currents.

108. Other A.C. Generators (Practical design)
• To generate large currents (as in turbine in power
stations), it is more practical and advantageous to
keep the fixed and to rotate the magnetic
coil
field
(electromagnet/magnet) around the coil .
• Hence instead of the coil cutting the magnetic field
(discussed previously), now the magnetic field cuts
the coil.
• Using this method, we can do away with the
which is prone to
wear & tear and not capable of carrying large currents.

109. Other A.C. Generators (Practical design)
• To generate large currents (as in turbine in power
stations), it is more practical and advantageous to
keep the fixed and to rotate the magnetic
coil
field
(electromagnet/magnet) around the coil .
• Hence instead of the coil cutting the magnetic field
(discussed previously), now the magnetic field cuts
the coil.
• Using this method, we can do away with the slip
rings and the carbon brushes which is prone to
wear & tear and not capable of carrying large currents.

110. Other A.C. Generators

111. Fleming’s Right Hand Rule
• When a straight wire is moved inside a magnetic field,
a current is induced in the wire.
!
Right!hand!
!
• Fleming’s Right Hand Rule (Dynamo rule) can be used
to determine the
in the wire.

112. Fleming’s Right Hand Rule
• When a straight wire is moved inside a magnetic field,
a current is induced in the wire.
!
Right!hand!
!
• Fleming’s Right Hand Rule (Dynamo rule) can be used
to determine the
of the induced current
direction
in the wire.

113. 22.3 Transformer
• A transformer is a device used to
of an a.c. supply.
• To change a at
to a at
or vice versa.

114. 22.3 Transformer
• A transformer is a device used to vary the voltage
output of an a.c. supply.
• To change a at
to a at
or vice versa.

115. 22.3 Transformer
• A transformer is a device used to vary the voltage
output of an a.c. supply.
• To change a low alternating voltage at
high current to a high alternating voltage at
low current or vice versa.

116. 22.3 Transformer
• It is a useful electrical device that is essential for
• from power
stations to the consuming loads (households and
factories).
• for proper operation of
electrical appliances such as the mains-operated
television and record player.

117. 22.3 Transformer
• It is a useful electrical device that is essential for
• electrical power transmission from power
stations to the consuming loads (households and
factories).
• for proper operation of
electrical appliances such as the mains-operated
television and record player.

118. 22.3 Transformer
• It is a useful electrical device that is essential for
• electrical power transmission from power
stations to the consuming loads (households and
factories).
• regulating voltages for proper operation of
electrical appliances such as the mains-operated
television and record player.

119. Structure of a Closed-Core Transformer
Circuit Symbol
• It consists of a of wire and a
of wire wound round a
which consists of
(this is to reduce heat
loss due to induced eddy current).

120. Structure of a Closed-Core Transformer
Circuit Symbol
• It consists of a of wire and a
of wire wound round a
which consists of
(this is to reduce heat
loss due to induced eddy current).

121. Structure of a Closed-Core Transformer
Circuit Symbol
• It consists of a primary coil of wire and a
secondary coil of wire wound round a
laminated soft iron core which consists of
thin sheets of soft-iron insulated from each
other by a coat of
lacquer (this is to reduce heat
loss due to induced eddy current).

122. The Working Principle of Transformer
• The transformer is based on
, it transfer supplied
from the to the by
between the two coils.

123. The Working Principle of Transformer
• The transformer is based on Faraday’s iron ring
experiment , it transfer energy
electrical supplied
from the primary coil to the secondary coil by
electromagnetic induction between the two coils.

124. The Working Principle of Transformer
• At the primary coil, the
sets up a in the
secondary coil
. (Note: the frequency of the
alternating current in both the primary coil and the
secondary coil is .)

125. The Working Principle of Transformer
• At the primary coil, the applied alternating voltage
sets up a changing magnetic field in the
secondary coil induces an e.m.f. the
which in
secondary coil . (Note: the frequency of the
alternating current in both the primary coil and the
secondary coil is same .)
the

126. The Working Principle of Transformer
• A step-up transformer is one where the e.m.f in the
primary coil is than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil
• A step-down transformer is one where the e.m.f in
the primary coil is than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil.

127. The Working Principle of Transformer
• A step-up transformer is one where the e.m.f in the
primary coil is smaller than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil
• A step-down transformer is one where the e.m.f in
the primary coil is than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil.

128. The Working Principle of Transformer
• A step-up transformer is one where the e.m.f in the
primary coil is smaller than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is lesser
than the secondary coil
• A step-down transformer is one where the e.m.f in
the primary coil is than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil.

129. The Working Principle of Transformer
• A step-up transformer is one where the e.m.f in the
primary coil is smaller than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is lesser
than the secondary coil
• A step-down transformer is one where the e.m.f in
the primary coil is larger than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is
than the secondary coil.

130. The Working Principle of Transformer
• A step-up transformer is one where the e.m.f in the
primary coil is smaller than the e.m.f. in the
secondary coil.
• The number of turns in the primary coil is lesser
than the secondary coil
• A step-down transformer is one where the e.m.f in
the primary coil is larger than the e.m.f. in the
secondary coil.
greater
• The number of turns in the primary coil is
than the secondary coil.

131. The Working Principle of Transformer
• The equation that relates the number of turns of coil
and e.m.f. is shown in the formula below:

132. The Working Principle of Transformer
• The equation that relates the number of turns of coil
and e.m.f. is shown in the formula below:
NP = VP
NS VS
NP = No. of turns of coil in primary coil
NS = No. of turns of coil in secondary coil
VP = Applied e.m.f. in primary coil
VS = Induced e.m.f. in secondary coil

133. Power Transfer in a Transformer
• For an ideal transformer (100% efficient), the power
supplied to the primary coil is fully transferred to the
secondary coil.
By principle of Conservation of Energy,

134. Power Transfer in a Transformer
• For an ideal transformer (100% efficient), the power
supplied to the primary coil is fully transferred to the
secondary coil.
By principle of Conservation of Energy,
Power in primary coil = Power in secondary coil

135. Power Transfer in a Transformer
• For an ideal transformer (100% efficient), the power
supplied to the primary coil is fully transferred to the
secondary coil.
By principle of Conservation of Energy,
Power in primary coil = Power in secondary coil
VP IP = VS IS

136. Power Transfer in a Transformer
• For an ideal transformer (100% efficient), the power
supplied to the primary coil is fully transferred to the
secondary coil.
By principle of Conservation of Energy,
Power in primary coil = Power in secondary coil
VP IP = VS IS
VP = Applied e.m.f. in primary coil
IP = Applied current in primary coil
VS = Induced e.m.f. in secondary coil
IS = Induced current in secondary coil

137. Power Transfer in a Transformer
• However there is no ideal or 100% efficiency
transformer as
• in the form in the primary
coil, secondary coil and soft iron coil.
• There is a of . Not all the
produced by the primary coil is
to the secondary coil.

138. Power Transfer in a Transformer
• However there is no ideal or 100% efficiency
transformer as
• Energy is lost in the form of heat in the primary
coil, secondary coil and soft iron coil.
• There is a of . Not all the
produced by the primary coil is
to the secondary coil.

139. Power Transfer in a Transformer
• However there is no ideal or 100% efficiency
transformer as
• Energy is lost in the form of heat in the primary
coil, secondary coil and soft iron coil.
• There is a leakage of flux . Not all the
magnetic
magnetic flux produced by the primary coil is
linked to the secondary coil.

140. Power Transfer in a Transformer
• In order to increase the efficiency of a transformer, it
should have
• for
primary and secondary coils so that the heating
effect is reduced.
• primary coil and secondary coils are
of the soft iron core to reduce
leakage of magnetic flux

141. Power Transfer in a Transformer
• In order to increase the efficiency of a transformer, it
should have
• Low-resistance (thicker) copper wire for
primary and secondary coils so that the heating
effect is reduced.
• primary coil and secondary coils are
of the soft iron core to reduce
leakage of magnetic flux

142. Power Transfer in a Transformer
• In order to increase the efficiency of a transformer, it
should have
• Low-resistance (thicker) copper wire for
primary and secondary coils so that the heating
effect is reduced.
• primary coil and secondary coils are wound on
the same part of the soft iron core to reduce
leakage of magnetic flux

143. Example 1
An ideal transformer is used to step down the mains supply
from 240 V to 12 V to operate a lamp rated at 12 V, 60 W.
(a) Write down the turns ratio of the transformer.
(b) How many turns are on the secondary coil if the primary
coil has 2400 turns?

144. Example 1
An ideal transformer is used to step down the mains supply
from 240 V to 12 V to operate a lamp rated at 12 V, 60 W.
(c) Calculate the current flowing in the lamp when it is
working optimally.
(d) Find the current flowing in the primary coil.

145. Example 1
An ideal transformer is used to step down the mains supply
from 240 V to 12 V to operate a lamp rated at 12 V, 60 W.
(e) For such transformer, the secondary coil is usually made
of thick wire. Explain this.

146. Example 1
An ideal transformer is used to step down the mains supply
from 240 V to 12 V to operate a lamp rated at 12 V, 60 W.
(e) For such transformer, the secondary coil is usually made
of thick wire. Explain this.
This is to reduce the heat loss as resistance is low
for a thick wire.
(Or to increase the efficiency of the transformer as
heat lost is reduced with a thick low resistance
wire.)

147. Example 2
A lamp labelled 5.0 V, 35 W is connected to a power
supply. When the lamp is in normal operation, its potential
difference is 5.0 V. A step down transformer is connected
between a 240 V power supply and the bulb.
Calculate the current flowing in the 240 V power supply.

148. Transmission of Electrical Power
• Electrical energy generated in a power station is
transmitted to consumers using .
• However, is lost in the transmission cables in
the form of as the cables have .
• [The power loss in cables, P = .]
!
•
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

149. Transmission of Electrical Power
• Electrical energy generated in a power station is
transmission cable
transmitted to consumers using .
• However, is lost in the transmission cables in
the form of as the cables have .
• [The power loss in cables, P = .]
!
•
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

150. Transmission of Electrical Power
• Electrical energy generated in a power station is
transmission cable
transmitted to consumers using .
• However, energy is lost in the transmission cables in
the form of heat as the cables have .
resistance
• [The power loss in cables, P = .]
!
•
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

151. Transmission of Electrical Power
• Electrical energy generated in a power station is
transmission cable
transmitted to consumers using .
• However, energy is lost in the transmission cables in
the form of heat as the cables have .
resistance
• [The power loss in cables, P = I2 R .]
!
•
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

152. Transmission of Electrical Power
• To minimize the lost of power due to heat, we can use
cables which reduces the resistance but we
will have to support very heavy cables and the
construction cost is high. Hence the other solution is
to in the transmission cables.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

153. Transmission of Electrical Power
• To minimize the lost of power due to heat, we can use
thick cables which reduces the resistance but we
will have to support very heavy cables and the
construction cost is high. Hence the other solution is
to in the transmission cables.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

154. Transmission of Electrical Power
• To minimize the lost of power due to heat, we can use
thick cables which reduces the resistance but we
will have to support very heavy cables and the
construction cost is high. Hence the other solution is
to transmit high voltage in the transmission cables.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

155. Transmission of Electrical Power
• The output a.c. voltage from the generator is
by a so that the
transmission current is .
• The very high voltage is then by a
before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

156. Transmission of Electrical Power
• The output a.c. voltage from the generator is
step up by a
so that the
transmission current is .
• The very high voltage is then by a
before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

157. Transmission of Electrical Power
• The output a.c. voltage from the generator is
step up by a step-up transformer so that the
transmission current is .
• The very high voltage is then by a
before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

158. Transmission of Electrical Power
• The output a.c. voltage from the generator is
step up by a step-up transformer so that the
transmission current is kept low .
• The very high voltage is then by a
before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

159. Transmission of Electrical Power
• The output a.c. voltage from the generator is
step up by a step-up transformer so that the
transmission current is kept low .
• The very high voltage is then step down by a
before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

160. Transmission of Electrical Power
• The output a.c. voltage from the generator is
step up by a step-up transformer so that the
transmission current is kept low .
• The very high voltage is then step down by a
step-down transformer before it is used in homes.
!
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

161. Transmission of Electrical Power
• Advantage of using a.c. voltage: It can be
easily using a
.(This is not possible by using d.c.)
• Advantage of high voltage transmission: It
in the transmission cables.
! •
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

162. Transmission of Electrical Power
• Advantage of using a.c. voltage: It can be
step-up & step-down easily using a
.(This is not possible by using d.c.)
• Advantage of high voltage transmission: It
in the transmission cables.
! •
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

163. Transmission of Electrical Power
• Advantage of using a.c. voltage: It can be
step-up & step-down easily using a
transformer .(This is not possible by using d.c.)
• Advantage of high voltage transmission: It
in the transmission cables.
! •
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

164. Transmission of Electrical Power
• Advantage of using a.c. voltage: It can be
step-up & step-down easily using a
transformer .(This is not possible by using d.c.)
• Advantage of high voltage transmission: It
reduces power loss in the transmission cables.
! •
230 kV
25 kV 11 kV 230 V
Power Step up Network of power Step down
station transformer cables transformer

165. Example 3
The figure below shows a simple illustration of how
electrical power is transmitted from a power station to a
factory. !
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
The power station transmits power of 24 kW at 10 kV to
the sub-station. At the substation, the voltage is stepped
down to Vs = 2 kV before this power is transmitted to the
factory for use.

166. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(a) Calculate the current in the power cables between the
power station and the sub-station.

167. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(b) If the resistance of the power cables between the
power station and the sub-station is 0.05 Ω for every
1 km of cable, calculate the potential drop across the
power cables.

168. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(c) Hence or otherwise calculate the power loss from the
power station to the sub-station.

169. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(d) Find the primary voltage of the transformer at the sub-
station before it is stepped down to 2 kV.
(e)

170. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(e) What is the turns ratio of the transformer at the sub-
station in order for the transformer to step-down the
voltage to 2 kV?
(f)

171. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(f) Explain why electricity from the power station is
transmitted at a high voltage.

172. Example 3
!
(step-down
transformer)
24 kW 200 km Vs = 2 kV
10 kV
(f) Explain why electricity from the power station is
transmitted at a high voltage.
This is to reduce power loss