Which statement best distinguishes mutual inductance M from leakage inductance?

Which statement best distinguishes mutual inductance M from leakage inductance?

• A. M describes ideal coupling; leakage inductance arises from imperfect coupling.
• B. M is the leakage inductance.
• C. Mutual inductance is a form of eddy current loss.
• D. Leakage inductance only exists in air-core transformers.

Answer: (A)

The main idea here is how much magnetic flux links both windings. Mutual inductance M measures how strongly the two coils couple: if all the flux from one winding links the other, the coupling is ideal and M is at its maximum for the given windings (often described with the coupling coefficient k = 1). Leakage inductance, on the other hand, comes from flux that does not link the other winding due to imperfect coupling; that unshared flux behaves as an inductance in series with the winding and grows as coupling gets worse. So the statement that best distinguishes them is that M describes ideal coupling, while leakage inductance arises from imperfect coupling. The other ideas—M being the leakage inductance, mutual inductance being an eddy current loss, or leakage only existing in air-core transformers—don’t fit the physics: leakage exists whenever not all flux links both windings, regardless of core, and mutual inductance is not a loss term.

The main idea here is how much magnetic flux links both windings. Mutual inductance M measures how strongly the two coils couple: if all the flux from one winding links the other, the coupling is ideal and M is at its maximum for the given windings (often described with the coupling coefficient k = 1). Leakage inductance, on the other hand, comes from flux that does not link the other winding due to imperfect coupling; that unshared flux behaves as an inductance in series with the winding and grows as coupling gets worse.

So the statement that best distinguishes them is that M describes ideal coupling, while leakage inductance arises from imperfect coupling. The other ideas—M being the leakage inductance, mutual inductance being an eddy current loss, or leakage only existing in air-core transformers—don’t fit the physics: leakage exists whenever not all flux links both windings, regardless of core, and mutual inductance is not a loss term.