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. $2.5mJ$
• B. $5mJ$
• C. $15mJ$
• D. $20mJ$

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 $\frac{V}{2}$ .
$E=\frac{1}{2}L{i}^2$
$E=\frac{1}{2}L{\left(\frac{\frac{V}{2}}{R}\right)}^2$
$E=\frac{1}{2}\left(5\times 10^{-3}\right){\left(\frac{2}{2\left(1\right)}\right)}^2$
$E=2.5mJ$