Question

For the circuit given below, the effective inductance of the circuit across the terminal AB, is ___________

(a) 9 H

(b) 21 H

(c) 11 H

(d) 6 H

This question was addressed to me during an interview.

This intriguing question comes from Fourier Series Analysis using Circuits in section Fourier Analysis on Complex Spaces of Signals and Systems

Answer 1

Right choice is (c) 11 H

Explanation: LEFF across AB = L1 + L2 + L3 – 2M12 – 2M13 + 2M23

= (4 + 5 + 6 – 2×1 – 2×3 + 2×2)

= (15 – 2 – 6 + 4)

= (15 – 8 + 4)

= (15 – 4)

= 11.