Question

Two identical solenoid coils, each of self-inductance L are connected in series. Their turns are in the same sense and the distance between them is such that the coefficient of coupling is half. Then equivalent inductance of the combination is :

• A. $L$
• B. $2L$
• C. $3L$
• D. $L/2$

Answer 1

Answer: (C)

$3L$

$L_1=L_2=L$

$M=L/2$

As the turns are in the same sense, the mutual flux adds to the individual flux.

therefore $L_{eq}=L_1+L_2+2M=L+L+2\times \frac{L}{2}=3L$