When a current $I$ flows through a coil, it stores the energy $E_1$ in it. Now the current is reduced to…
When a current $I$ flows through a coil, it stores the energy $E_1$ in it. Now the current is reduced to $\frac{l}{2}$, the energy stored in the coil becomes $E_2$. The change in the energy is
$\frac{E_1}{4}$
$\frac{3 E_1}{4}$
$\frac{4 E_1}{3}$
$\frac{E_1}{2}$
Solution
Energy stored in the coil $E \propto I^2$
$\therefore E_1 \propto I^2 \text { and } E_2 \propto\left(\frac{I}{2}\right)^2$
On taking the ratio:
$E_1=4 E_2$
The change in energy is $E_1-E_2=E_1-\frac{E_1}{4}=\frac{3 E_1}{4}$
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