Physics - EMI/AC Question with Solution | TestHub

The resistance seen by the inductor is the series combination below.

$R_{\mathrm{eq}}=4+\frac{6\times 12}{6+12}=8\Omega$

$\tau =\frac{L}{R_{\mathrm{eq}}}=\frac{2}{8}=\frac{1}{4}\mathrm{s}$