Question

The equivalent inductance of two coils with series opposing flux having inductances 7H and 2H with a mutual inductance of 1H.

(a) 10

(b) 7

(c) 11

(d) 13

I had been asked this question in a job interview.

I would like to ask this question from Inductances in chapter Magnetic Forces and Materials of Electromagnetic Theory

Answer 1

The correct option is (b) 7

The best I can explain: The equivalent inductance of two coils in series with opposing flux is L = L1 + L2 – 2M, where L1 and L2 are the self inductances and M is the mutual inductance. Thus L = 7 + 2 – 2(1) = 7H.