Q 12-08-097JEE MainJEE Main 2023 (11 Apr, Shift 1)Medium
The electric field in an electromagnetic wave is given as $\vec E=20\sin\omega\left(t-\dfrac xc\right)\hat j\ \text{N C}^{-1}$, where $\omega$ and $c$ are angular frequency and velocity of electromagnetic wave respectively. The energy contained in a volume of $5\times10^{-4}\ \text{m}^3$ will be (Given $\varepsilon_0=8.85\times10^{-12}\ \text{C}^2\ \text{N}^{-1}\ \text{m}^{-2}$)
Answer: (D) $8.85\times10^{-13}\ \text{J}$
Average energy density (electric plus magnetic) $u=\tfrac12\varepsilon_0E_0^2$.
$$U=\frac12\times8.85\times10^{-12}\times400\times5\times10^{-4}=8.85\times10^{-13}\ \text{J}$$
Solution by Sreeraj P, M.Sc Physics