Question

Define the term 'mutual inductance, between the two coils. Obtain the expression for mutual inductance of a pair of long co-axial solenoids each of length I and radii r1 and r2(r2 >> r1). Total number of turns in the two solenoids are N1 and N2 respectively.

Answer 1

Mutual inductance, between a pair of coils, equals the magnetic flux, linked with one of them due to a change. of unit current flowing in the other.

Alternatively,

The mutual inductance, for a pair.of coils, equals the emf induced, in one of them, when the current in the other coil is changing at a unit rate.