Page 67 - Basic Electrical Engineering

change in flux linkage by the coil with respect to time, and hence no EMF
will be induced in the coil. Thus, the necessary condition for the
production of induced EMF is that there should be a change in flux

linkage and not merely flux linkage by a coil.

1.14 SELF-INDUCED EMF AND MUTUALLY INDUCED EMF

The EMF induced in a coil due to change in flux linkage when a changing
current flows through the coil is called self-induced EMF.

As shown in Fig. 1.13 (c), when a second coil is brought near a coil
producing changing flux, EMF will be induced in the second coil due to
change in current in the first coil. This is called mutually induced EMF. In

fact, EMF will be induced in both the coils as both the coils are linking a
changing flux. However, in the second coil EMF is induced due to changing

flux created by coil 1. The magnitude of the induced EMF will depend upon
the rate of change of flux linkage and the number of turns of the individual

coils. The induced EMF in the two coils, e and e will be
1
2

and

where N and N are the number of turns of coil 1 and coil 2, respectively.
1
2
You will study in a separate chapter how transformers are built utilizing
the basic principle of mutually induced EMF.

1.15 SELF-INDUCTANCE OF A COIL

Consider a coil of N turns wound on a core of magnetic material. Let an
alternating current i pass through the coil as shown in Fig. 1.14.