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In a coil, the current changes from $-2 \mathrm{~A}$ to $+2 \mathrm{~A}$ in $0.2 \mathrm{~s}$ and induces an emf of $0.1 \mathrm{~V}$. The self inductance of the coil is :
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Verified Answer
The correct answer is:
$5 \mathrm{mH}$
$(E m f)_{\text {induced }}=-L \frac{d i}{d t}$
In magnitude form,
$\begin{aligned}
& \left|\operatorname{Emf}_{\text {ind }}\right|=\left|(-) L \frac{\mathrm{di}}{\mathrm{dt}}\right| \\
& \Rightarrow 0.1=\frac{(\mathrm{L})[+2-(-2)]}{0.2} \\
& \Rightarrow \mathrm{L}=\frac{0.1 \times 0.2}{4}=5 \mathrm{mH}
\end{aligned}$
In magnitude form,
$\begin{aligned}
& \left|\operatorname{Emf}_{\text {ind }}\right|=\left|(-) L \frac{\mathrm{di}}{\mathrm{dt}}\right| \\
& \Rightarrow 0.1=\frac{(\mathrm{L})[+2-(-2)]}{0.2} \\
& \Rightarrow \mathrm{L}=\frac{0.1 \times 0.2}{4}=5 \mathrm{mH}
\end{aligned}$
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