Question

Two coils are having self-inductance of 5 mH and 10 mH and a mutual inductance of 0.5 mH in a differential connection. The equivalent inductance of the combination is ___________

(a) 14 mH

(b) 5.85 mH

(c) 6 mH

(d) 6.15 mH

The question was asked by my school principal while I was bunking the class.

My doubt is from Advanced Problems on Magnetically Coupled Circuits in portion Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

The correct option is (a) 14 mH

The best I can explain: When 2 coils are connected in series, then effective inductance,

LEFF = L1 + L2 ± 2M

For this case, LEFF = L1 + L2 – 2M

= 5 + 10 – 2 × 0.5

= 15 – 1

= 14 mH.