What principle states that a changing current in one coil induces a voltage in another coil?

The principle that describes how a changing current in one coil induces a voltage in another coil is mutual inductance. This phenomenon occurs when two coils are situated in proximity and the magnetic field created by the changing current in the first coil affects the second coil, leading to the induction of voltage across it.

In mutual inductance, the voltage induced in the second coil is directly related to the rate of change of current in the first coil. This principle forms the basis of many electrical devices, such as transformers and inductors, where energy transfer between coils is utilized for efficient electrical energy management.