Q 12-06-107JEE MainJEE Main 2021 (25 Feb, Shift 1)Easy
A coil of inductance 2 H having negligible resistance is connected to a source of supply whose voltage is given by $V = 3t$ volt (where $t$ is in second). If the voltage is applied when $t = 0$, then the energy stored in the coil after 4 s in J is ______.
Numerical value type. Enter your answer.
Answer: 144
$L\dfrac{di}{dt} = 3t \Rightarrow i = \dfrac{3t^2}{2L} = \dfrac{3t^2}{4}$. At $t = 4$ s, $i = 12$ A.
$$U = \frac12Li^2 = \frac12\times2\times144 = 144\ \text{J}$$
Solution by Sreeraj P, M.Sc Physics