Electromagnetic Induction Faradays law and Lenz Law

1. Chandrashekhar S Patil
Sharad Institute of Technology
Polytechnic
Yadrav
Unit 1.4-Electric and Magnetic Circuits
(Electromagnetic induction,Faradays Law, Lenz Law)

2. Contents:-
Sr
No.
Topic Slide Number
01. Faradays Law of Electromagnetic
Induction.
3
02. Faradays First Law and Second Law 4
03. Magnitude of the Induced EMF 5
04. Direction of Induced EMF 6
05. Lenz Law 7 & 8
2

3. Faradays Law of Electromagnetic Induction
3
 The faradays law of Electromagnetic induction states
that whenever the lines of force linking with a circuit
changes an emf is always induced in it.
 The magnitude of this induced emf is proportional to the
rate of change of flux linkages. (Flux X Turns). Such an
emf lasts as long as the change is taking place.
Alternatively the law can be stated as follows:
• When ever a conductor cuts or is cut by the magnetic
flux, an emf is generated in the conductor and the
magnitude of generated emf is proportional to the rate at
which conductor cuts or is cut by the magnetic flux.

4. Faradays First Law and Second Law
4
Faradays First law:-It states that whenever the number of
lines of force linking with a circuit changes, an emf is
always induced in it or whenever a conductor cuts or is cut
by the magnetic flux, an emf is always generated on it.
Faradays Second Law:-It states that magnitude of the
induced emf in any circuit is proportional to the rate of
change of its flux linkages (flux X turns) or the magnitude
of the generated emf in any conductor is proportional to
the rate at which it cuts or is cut by the magnetic flux.

5. Magnitude of the Induced EMF.
5
If the flux linking with a particular coil having N turns changes from
§1to §2 webers in small time of t seconds then.
Rate of change of Flux linkages=
(Final Flux Linkage)-(Initial Flux Linkage)
Time
=N §2-N §1 Volts
t
According to Faradays law of electromagnetic induction the induced
emf (e)is given by
e∝N §2-N §1 =K N §2-N §1 Volts
t t
Expression in differential form we get
e=N d§ Volts ------- Equation 1
dt

6. Direction of Induced EMF
6
Flemings Right hand rule:-
Arrange the thumb and the first two fingers of your right hand
mutually
at right angles to one another. Let the first finger point in the
direction of lines of force (N to S) and the thumb in the direction
of the induced emf or (current)

7. Lenz Law
7
Lenz Law: The direction of an induced emf produced during
the process of electromagnetic induction is always such
that it tends to set up a current opposing the basic cause
responsible for inducing that emf.
Consider a coil (C) connected to the galvanometer as
shown in figure

8. 8
 Assuming that the magnet is being withdrawn from the coil.
The induced current in this condition will flow in such a
direction that the end of the coil facing the magnet will be
south pole. Thus the force of attraction exerted by the south
pole of the coil working as an electromagnet on the North
pole of the magnet will oppose the withdrawal of the magnet
from the coil. The direction of current in this condition will be
therefore as indicated in the previous figure.
 Opposite will be the case when the magnet is moved towards
the coil.
 Thus the motion of the magnet in either direction which is
responsible for inducing the emf in the coil will be opposed
by the current set up by that emf.
 Owing to the fact that the induced EMF circulates a current
tending to oppose the alteration of flux linking with the circuit,
its direction is regarded as negative Hence the equation 1.
which gives the magnitude of the induced emf is usually
modified as follows:-
e= -N d§ Volts

9. 9