Whenever a conductor links with the changing flux an e.m.f. is induced in that conductor. In this system there is no moving part. The static induction can be of two types, the self induction and the mutual induction.
Self induction
Fig. 1.
The Fig. 1 Shows a coil connected to a battery through an ammeter, variable resistance so that the current can be varied. When the switch is on the current will increase from zero ampere, the increasing flux will induce an e.m.f. which according to Lenz’s law opposes the causes, when the current is established there is no change of current hence no e.m.f. is induced. But when the current in the circuit is varied by varying the variable resistance the current causes the rate of change of flux and induction of self-induced voltage. This e.m.f. can be given as
\[e=-\frac{d\phi }{dt}\text{ }\times \text{ N volts}\]
Uses.
The phenomenon of the self induction is used for the followings:
- In autotransformer.
- In lightning arrester.
- In fluorescent tube for starting purpose, i.e., choke.
- In fan regulators.
- For smoothing the d.c. pulsating values.