Question
How is mutual inductance of a pair of coils affected when
(i) separation between the coils is increased,
(ii) the number of turns of each coil is increased,
(iii) a thin iron sheet is placed between the two coils, other factors remaining the same. Explain your answer in each case.
Solution
(i) When separation between the coils is increased, magnetic flux linked with secondary coil decreases. Therefore, mutual inductance (M) of pair of coils decreases.
(ii) When number of turns of each coil is increased, mutual inductance increases, because
(iii) As 
therefore, mutual inductance will increase on placing a thin iron sheet between the two coils.
