Unit of mutual inductance:
The unit of mutual inductance is also henry (H).
If iA = 1 A and N2Φ21 = 1 Wb turns, then M21 = 1 H.
Therefore, the mutual inductance between two coils is said to be one henry if a current of 1A in coil 1 produces unit flux linkage in coil 2.
Therefore, the mutual inductance between two coils is one henry if a current changing at the rate of lAs-1 in coil 1 induces an opposing emf of IV in coil 2.