A coil having an inductance of 100 mH is magnetically coupled to another coil having an inductance of 900 mH. The coefficient of coupling between the coils is 0.45. Calculate the equivalent inductance if the two coils are connected in series aiding.

• A. 932 mH
• B. 730 mH
• C. 1135 mH
• D. 1270 mH

Answer: (D)

Mutual inductance (M) = k*√(L1*L2)
k = 0.45
M = 0.45*√(900*100*10⁻⁶) = 135 mH
Leq = L1 + L2 + 2M
Leq = 900 + 100 + 270
Leq = 1270 mH