Question

Two coils connected in series have a self-inductance of $50\text{mH}$ and $60\text{mH}$ respectively. The total inductance of the combination was found to be $100\text{mH}$. Determine the amount of mutual inductance that exists between the two coils, assuming that they are opposing each other.

• A. $5\text{mH}$
• B. $6\text{mH}$
• C. $7\text{mH}$
• D. $8\text{mH}$

Answer 1

The correct option is A $5\text{mH}$

We know that, for a series combination of inductors such that their magnetic fields oppose each other, net inductance is given by,

$L_{eq}=L_1+L_2-2M$

$\Rightarrow 100=50+60-2M$

$\Rightarrow M=5\text{mH}$