Henry

This is the unit of self-inductance and mutual inductance. It can be defined in two ways ,

1. in the case of self-inductance,

it is defined as the ratio of average emf in the coil to the time rate of change of current in the small coil

2.in the case of mutual inductance,

it is defined as the mutual inductance of the pair of coil in which a rate of change of current one ampere per second in the primary causes an induced emf of one volt in the secondary coil