Two coils of self inductance $2 \mathrm{mH}$ and 8 $\mathrm{mH}$ are placed so close together that the…
Two coils of self inductance $2 \mathrm{mH}$ and 8 $\mathrm{mH}$ are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:
$16 \mathrm{mH}$
$10 \mathrm{mH}$
$6 \mathrm{mH}$
$4 \mathrm{mH}$
Solution
Mutual inductance between coils is
$\begin{aligned}
M & =k \sqrt{I_1 I_2} \\
M & =1 \sqrt{2 \times 10^{-3} \times 8 \times 10^{-3}}\{x=1\} \\
& =4 \times 10^{-3}=4 \mathrm{mH}
\end{aligned}$