Question Detail

Mutual inductance (M) relates the induced electromotive force (e.m.f) in one coil to the rate of change of current in a different (coupled) coil. The induced e.m.f in the secondary coil (e₂) is proportional to the rate of change of current in the primary coil (di₁/dt), and vice versa. The formula is e₂ = -M (di₁/dt) (or e₁ = -M (di₂/dt)). Therefore, M = -e₂ / (di₁/dt). The negative sign indicates Lenz's law (opposing the change).