Self induction and Mutual induction

Explanation

Self Induction :

Consider a coil negligible resistance connected with source of e.m.f. E and a key K in series as shown in figure (a).
When the key K is closed, the current increases from zero value. This increase in the current again produces an induced e.m.f. in the same coil. Thus, during growth or decay of current in the coil, an opposing e.m.f. is induced in the coil. This phenomenon is called self induction.
Mutual Induction:

Consider two P and S placed very close to each other as shown in figure (b). The coil P connected in series with the source of e.m.f. (battery) and key K in series is called primary coil. The coil S is connected to sensitive galvanometer is called as secondary coil.
When key K is closed, the galvanometer shows momentary deflection in one direction and when key is made open, the galvanometer shows deflection in the opposite direction. When the current flowing through primary (P) is constant or zero, no deflection is produced in the galvanometer. But when the current flowing through primary coil changes, an e.m.f. is induced in the secondary coil. changes, an e.m.f. is induced in the secondary coil. This phenomenon is called 'Mutual Induction.'