The mutual inductance between two coils is 1.25 henry. If the current in the primary coil changes at the rate of 80 amperes/second, then induced e.m.f. in the secondary coil is 

Concept:

Mutual Induction: Whenever the current passing through a coil or circuit changes, the magnetic flux linked with a neighboring coil or circuit will also change.

Hence, an emf will be induced in the neighboring coil or circuit. This phenomenon is called ‘mutual induction’.

Mutual induction between the two coils of area A, number of turns N1 and N2 with the length of secondary or primary l is given by:

\(M = \frac{{{\mu _{o\;{N_1}{N_2}A}}}}{l}\)

Emf induced in the coil is given by:

\(e=M\frac{{di}}{{dt}}\)

Calculation:

Given that, M = 1.25 H, dI/dt = 80 amp/sec

Emf induced in the coil is given by,

\(e=M\frac{{di}}{{dt}}\)

e = 1.25 × 80

= 100 Volt.