9011041155 / 9011031155

• Live Webinars (online lectures) with

recordings.

• Online Query Solving

• Online MCQ tests with detailed

solutions

• Online Notes and Solved Exercises

• Career Counseling

Electromagnetic Induction

1

9011041155 / 9011031155

electromagnetic induction with the help of

Faraday’s expt.

Ans:

Change in the magnetic flux linked with the coil

produces emf in the coil, which causes electric

current to flow through it. This emf is called

induced emf and the current is called induced

current.

Production of induced emf in the coil due to

change in the magnetic field associated with it is

called electromagnetic induction.

Coil and Magnet experiment

2

9011041155 / 9011031155

Coil and Coil experiment :

3

9011041155 / 9011031155

Faraday’s laws of electromagnetic induction.

Ans:

1. Whenever there is change in the magnetic

field associated with a coil, an emf in induced

in it.

2. The magnitude of this emf is directly

proportional to the rate of change of flux

associated with it.

4

9011041155 / 9011031155

Lenz’s law.

Ans

“The direction of induced emf is such as to

oppose the change in the magnetic flux which

produces it.”

Thus, faraday’s law gives the magnitude and

Lenz’s law gives the direction of induced emf.

5

9011041155 / 9011031155

theoretical proof of laws of electromagnetic

induction.

Ans:

The mathematical statement of the laws of

induction is

F = q v × B,

to it. Hence, it is acted up on by a force F’ given

by F’ = Biℓ sin θ . But as θ = π/2,

6

9011041155 / 9011031155

sin θ = 1 and the force is F’ = Biℓ

the work dW done in this process is

dW = -F’dx ( -ve sign as the force is applied

opposite to F’)

∴ dW = - Biℓ × dx

But, ℓ × dx is the area A of the frame swept by the

force.

∴ dW = - BiA

If dφ is the magnetic flux through area A,

B = dφ ℓ A

∴ dφ = BA

∴ dW = - i dφ------(1)

If e is the induced emf and i is the induced current,

the electrical power generated in the frame is

p = ei

If this power is generated in time dt,

electrical work done = eidt-----(2)

7

9011041155 / 9011031155

This work must be equal to the work done by force

F’

∴ eidt = - idφ----- from 1 &2

Hence, the laws of electromagnetic induction are

proved.

Fleming’s right hand rule.

8

9011041155 / 9011031155

Ans:

9

9011041155 / 9011031155

Eddy currents

Ans:

Applications :

1. Dead beat galvanometer

10

9011041155 / 9011031155

2. Induction Furnace

11

9011041155 / 9011031155

i. fast operation

ii. better control over the temperature

iii. surface heating

iv. less pollution etc.

3. Electric brakes

12

9011041155 / 9011031155

M.C.Q.

Q.6    A coil having an area of 2m2 is placed in a magnetic field which changes from 2Wb/m2 to 5Wb/m2 in 3s. The e.m.f. induced in the coil will Be     (a.6) 4V       (b.6) 3V        (c.6) 2V       (d.6) 1VQ.7    The magnetic flux in a coil is Ф= 4t2 + 4t + 4. What is the magnitude of induced e.m.f. at t=3sec?          (a.7) 14V     (b.7) 28V     (c.7) 7V       (d.7) 35V

13

9011041155 / 9011031155

Q.8    The two rails of a railway track separated by 1metre and insulated from each other, are connected to a millivoltmeter. What is the

reading of the millivoltmeter when a train passes at a speed of 180km/hour along the track? [The vertical component of earth’s magnetic field is 0.2×10-4Wb/m2]

          (a.8) 1volt    (b.8) 100mV           (c.8) 1mV    (d.8) 10mV

Self inductance.

Ans:

Production of induced emf in a coil due to

changing magnetic flux produced due the varying

current in the coil itself is called self induction.

14

9011041155 / 9011031155

Flux φ associated with the coil is proportional to

current i in the coil.

i.e. φ α i

or φ = Li where L is a constant which depends on

size and shape of the coil. The induced emf

generated in the coil is given as

The constant L is called self inductance of the

coil. If di/dt = 1, them e = - L

“Thus, self inductance of a coil is equal to the emf

induced in the coil, due to unit rate of change

of current through it”.

15

9011041155 / 9011031155

The unit of self inductance is henry (H).

1 henry :-

The self inductance of a coil is 1 henry, if the emf

of 1V is induced in the coil, when the

current through the coil changes at 1 ampere per

second.

Mutual inductance.

Ans:

Production of induced emf in a coil due to

changes in current in the second coil near it is

called mutual induction.

16

9011041155 / 9011031155

When dIA /dt = 1,

e2 = - M

Thus, mutual inductance between two coils is

equal to the emf induced in the second coil due to

unit rate of change of current in the first coil.

The unit of mutual inductance is henry (H).

17

9011041155 / 9011031155

1 henry :

The mutual inductance between two coils is 1

henry, if the emf of 1V is induced in the second

coil, when the current through the first coil

changes at 1 ampere per second.

Transformer action.

18

9011041155 / 9011031155

19

9011041155 / 9011031155

Power output = Power input

E2I2 = E1I1

20

9011041155 / 9011031155

21

9011041155 / 9011031155

• Ask Your Doubts

• For inquiry and registration, call 9011041155 /

9011031155.

22