The induced emf can be given as the rate of change of flux multiplied by the number of conductors. The production of the e.m.f. can be illustrated as shown in Fig. 1. The coil is connected across the galvanometer. The bar magnet has certain magnetic pole strength. If the coil is kept stationary and the bar magnet is moved as indicated, the flux linking the conductors will induce the voltage as long as the change of flux is continued. The e.m.f. induced is proportional to the rate of change of flux linking. When the magnet is brought back, the flux decreases and the e.m.f. is produced in the reverse direction. But if the magnet is made stationary at any stage, there will not be any change of flux, resulting in no induction and hence no e.m.f.
Fig. 1.
Fig. 2.
It is also observed as shown in Fig. 2. that if the magnet or the magnetic flux is made stationary and the conductor (coil) is moved than the e.m.f. is induced depending upon the flux linkage. If there are more number of turns the e.m.f. induced will be more. The d.c. generator is an example of dynamically induced e.m.f.