Page 66 - Basic Electrical Engineering

Figure 1.13 (a) Change in flux linkage in a coil due to switching ON and switching OFF of dc
current; (b) change in flux linkage due to alternating current supply;(c) induced emf in coils 1 and 2 due
to changing flux produced by alternating current flowing in coil 1

In Fig. 1.13 (a), a coil of certain number of turns is wound on a former, i.e.,
its core. Current is supplied from a battery by closing a switch S. If the switch

is continuously turned on and off, flux linkage by the coil will change. The
rate of change of the flux linkage will induce EMF in the coil.

A similar effect will be there if an ac supply is applied across the coil as
shown in Fig. 1.13 (b). The direction of current in the coil is shown for the
positive half cycle of the alternating current. The direction of current will

change in every half cycle, and hence the direction of flux produced will
change in every half cycle. The magnitude of current changes continuously

since a sinusoidal current is flowing. This changing current will create a
changing flux linkage, thereby inducing EMF in the coil in both the cases as
shown in Fig. 1.13 (a) and (b). Note that in Fig. 1.13 (a), if the switch S is

kept closed, a steady direct current, i.e., a constant current will flow through
the coil. This constant current will produce a constant flux. There will be no