What is mutual inductance?

• A. When current in one coil induces an identical current in a second coil.
• B. Mutual inductance occurs when two coils are magnetically isolated.
• C. When magnetic flux produced by one coil induces a voltage in a second coil.
• D. Mutual inductance is unrelated to flux.

Answer: (C)

Mutual inductance is about how changing current in one coil can induce voltage in another coil through shared magnetic flux. When the current in the first coil changes, it creates a changing magnetic field that threads the second coil. By Faraday’s law, the rate of change of this linked flux induces an EMF in the second coil. The strength of that coupling is quantified by the mutual inductance, M, and the induced voltage in the second coil is given by e2 = -M di1/dt. The greater the magnetic linkage between the coils, the larger M is, and the stronger the induced voltage for a given change in current.

This description fits the correct choice because it centers on flux linking between coils and the resulting induced voltage. The idea that a changing current would produce an identical current in the second coil is not guaranteed—current in the second coil depends on the external circuit and load. If the coils were magnetically isolated, there would be no mutual inductance at all. And mutual inductance is inherently connected to flux; saying it’s unrelated to flux contradicts the fundamental mechanism.