(a) Define mutual inductance and write its S.I. unit.

(b) Derive an expression for the mutual inductance of two long co-axial solenoids of same length wound one over the other.

© In an experiment, two coils ${ c }*{ 1 }$
and ${ c }*{ 2 }$

are placed close to each other. Find out the expression for the emf induced the coil ${ c }

*{ 2 }$*

due to a change in the current through the coil ${ c }{ 2 }$.

due to a change in the current through the coil ${ c }