Question

When induced emf in inductor coil is $50\%$ of its maximum value then stored energy in inductor coil in the given circuit will be

• A. $2.5 \, mJ$
• B. $5 \, mJ$
• C. $15 \, mJ$
• D. $20 \, mJ$

Answer 1

Answer: (A)

If the maximum value of induced EMF is $V$ then $50\%$ of induced EMF is $\frac{V}{2}$ . Also, at this moment voltage across resistor will be $\frac{V}{2}$ .
$E=\frac{1}{2}Li^{2}$
$E=\frac{1}{2}L\left(\frac{\frac{V}{2}}{R}\right)^{2}$
$E=\frac{1}{2}\left(5 \times 1 0^{- 3}\right)\left(\frac{2}{2 \left(1\right)}\right)^{2}$
$E=2.5 \, mJ$