1. Electromagnetic induction occurs when a changing magnetic field induces a current in a conductor. This can be generated by moving a magnet near a coil or changing the current in a neighboring circuit. 2. Faraday's law states that an electromotive force (EMF) is induced in a conductor whenever the magnetic flux through the conductor changes. The magnitude of the induced EMF is proportional to the rate of change of flux. 3. Transformers use electromagnetic induction to change the voltage of alternating current. A step-up transformer increases voltage by having fewer turns in the primary coil, while a step-down transformer decreases voltage with more turns in the primary coil.

1. Electromagnetic Effect

2. What is magnetic effect?
• Magnetism is induced when current flow through circuit.
• This phenomenon is called magnetic effects of current.
• Similarly, current can be generated, using magnets.
• The process of producing of electric current by induced
potential differences between or due to electromotive force
due to changing in magnetic field lines passing through
circuit.
• Magnetic field lines passing through circuit can be changed
by :
1. Moving a magnet to and fro near a coiled conductor
2. Moving the coiled conductor near a magnet or
3. Changing the magnitude of current in the neighboring
circuit.
What is electromagnetic induction?

3. This method was discovered by Faraday:
 This scientist concluded the following laws called faraday’s law.
1. Whenever, there is changing in number of magnetic filed lines passing through the
conductor, emf is induced in the conductor.
2. The induced emf exists in the circuit so long the change in the magnetic field
continues
3. The magnitude of induced emf is directly proportional to the rate of change of the
magnetic filed continuous.
Direction of induced current:- Fleming’s right hand rule
 Thumb represent direction of motion of conductor,
 Forefinger – direction of the magnetic field,
 Middle finger- direction of induced current.

4. Uses of electromagnetic induction
• In device like electric generators and transformer.
• Principle of electromagnetic induction state that “whenever, there is
a change in the number of magnetic field lines passing through a
conductor, voltage is induced in it”.
a.c Generator (Dynamo)
• Is a device which produce electric current
from mechanical energy.
• It is a coil of wire which is made to rotate in
a magnetic field.
• As coil rotates, it cuts through the magnetic
field, and current is induced on it.
• It produce either d.c or a.c.

5. Construction
C
B
A
D
C

6. Working Principle
• In initial, armature coil is parallel to the magnetic
field line.
• Let arm AB and arm CD turn, such that arm AB is
coming out perpendicular to the magnetic field
line, and arm CD is going into the magnetic field.
• By using Fleming’s right hand rule, current is
induced along ABCD.
• Direction of current generated is from B2 to B1.
• On completing half of the rotation of the
armature, the arm AB and CD interchanged their
positon.
• Now, direction of induced current reverses from
B1 to B2. Thus, a.c current is obtained as output.

7. • As coil rotates, number of magnetic field lines passing through the coil
continuously changes from maximum to minimum and vise versa.
• Number of field line is minimum, when coil is parallel to magnetic field and
maximum when coil is perpendicular to field line.
• Therefore, induced voltage is maximum when coil is parallel and minimum when
coil is perpendicular to field lines
• Hence, an alternating voltage of changing magnitude and direction is induced in
the circuit.

8. The magnitude of the induced voltage produced by
generator depends on
• Speed of coil: the faster the coil moves, the greater the voltage. That
means, more the speed during rotation, greater the generation of
electricity.
• Strength of the magnetic field: Stronger the magnetic field, greater the
generation of electricity.
• Number of turns on the coil: More the number of turns, larger the amount
of electricity generated.

9. Transformer
• A transformer is a device that increases or decreases the voltage of an
alternating electric current. OR
• Is an arrangement which transfers a.c power from primary winding to the
secondary winding at higher or lower voltage.
• Electric appliance in home and offices were designed and made for
different purposes and all the appliances do not work on the same voltage
and current.
• Some appliances need lower voltage and some needs high voltage to
operate.
• Generally, electrical appliance operated at the voltage of 220V-240V mains
a.c supply.
• Transformer works on the principle of electromagnetic induction.

10. Transmission of power from power station to the
household.
• Electrical power in the stations is usually generated at high voltage of 11kV.
This voltage further increased to 132 kV using special device called
transformer and then it is transmitted over long distances to the main-
substation. While electric power is transmitted in longer distance, high voltage
and low current is maintained in order to minimize the loss of energy in the
form of heat. It also reduces material for the wires as high current would
require thicker wire. After that, voltage is brought from 132kV to 33kV by
transformer at the main substation.
• The voltage cannot be used it directly to electric appliance at home and office,
therefore, transformer is required to bring down the voltage to standard
operating voltage of 220V – 240 V.

11. Transformer consist of two set of coils:
• Primary coil (P) and Secondary Coil (S).
• Coils are wound over a common soft iron core and turnings of coils
are insulated from each other.
• The core is formed by laminated sheets insulated from each other to
reduce the loss of energy as a heat.
• Input voltage is generally connected to the primary coil and the
output voltage is obtained from the secondary coil.
• Number of turns in both the primary and secondary coil will be
different due to dependent on capacity of the transformer.

12. There are two types of transformer.
Step up transformer Step down transformer
1. Secondary coil is made of thin
copper wire as compared to
primary coil
2. It provides less output current
3. Output voltage is more than
input voltage.
4. It has less number of turns in the
primary coil and more number of
turns in the secondary coil.
1. Primary coil is made of thin
copper wire as compared to
secondary coil
2. It provides more output current.
3. Output voltage is less than input
voltage
4. It has more number of turns in
the primary coil and less number
of turns in the secondary coil.

13. • The ratio of the input voltage to output voltage is equivalent to ratio
of number of turns in primary coil to secondary coil.
𝑉𝑠(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑜𝑢𝑡𝑝𝑢𝑡)
𝑉𝑝(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑖𝑛𝑝𝑢𝑡)
=
𝑁𝑠(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑟𝑛𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑐𝑜𝑖𝑙)
𝑁𝑝(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡𝑢𝑟𝑛𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 𝑐𝑜𝑖𝑙)
• This ration is called transformer ratio (k)
• In ideal condition, i.e. if the transformer is 100% efficient, the output
power across secondary coil and input power across primary coil is
equal. Hence,
• Output power across secondary coil = Input power across primary
coil.
• Secondary voltage × secondary currient = Primary voltage ×primary
current
OR
𝑆𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒(𝑉𝑠)
(𝑃𝑟𝑖𝑚𝑎𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒)𝑉𝑝
=
𝑃𝑟𝑖𝑚𝑎𝑟𝑦 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 (𝐼𝑝)
𝑆𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 (𝐼𝑠)

14. • Therefore, when the voltage is stepped down, the corresponding
current is stepped up and vice versa. This is the reason for taking
thicker primary coil in step up transformer and thicker secondary coil
in step down transformer in order to withstand heavy current.
• Transformer can never be 100% efficient due to following energy
losses in the transformer.
1. Energy lost in the form of heat due to resistance of the wire.
2. Energy lost due to incomplete transfer of magnetic field as a
result of the imperfect windings of primary coil and secondary
coil.
3. Energy lost in the form of heat due to induced current in the core
of the transformer.
• Alternating current (a.c) is preferred over direct current (d.c) in the
power supply systems, as alternating voltage can be increased or
decreased by using transformers unlike in the case of d.c (direct
current) voltage.

15. Both the electric motor and a generator consist of similar parts like
armature coil magnetic field, slip rings and wire brushes. In what ways
are they different from each other?
Electric Motor Electric Generator
The shaft of the motor is
driven by the magnetic force
generated between the
armature and the field.
In electric generators, the
shaft is attached to the
rotor and is driven by the
mechanical force.