A coupling magnetic field inside a rotating machine or static

a-coupling-magnetic-field-inside-a-rotating-machine-or-static

A coupling magnetic field inside a rotating machine or static machine like transformers must involve with _________

A. mechanical parts

B. electrical parts

C. both electrical and mechanical

D. either of the electrical or mechanical parts

This question was addressed to me during an internship interview.

Query is from Transformer Construction in chapter Transformers of Electrical Machines

The correct answer is A. mechanical parts

The best I can explain: The coupling field should interact with both the electrical as well as mechanical parts in order to achieve electromechanical energy conversion.