Q 12-08-219JEE MainJEE Main 2019 (12 Apr, Shift 1)Easy
An electromagnetic wave is represented by the electric field $\vec{E} = E_0\hat{n}\sin[\omega t + (6y - 8z)]$. Taking unit vectors in $x$, $y$ and $z$ directions to be $\hat{i}$, $\hat{j}$, $\hat{k}$, the direction of propagation $\hat{s}$ is:
Answer: (B) $\hat{s} = \dfrac{-3\hat{j} + 4\hat{k}}{5}$
A wave $\sin(\omega t + \vec{k}\cdot\vec{r})$ travels along $-\vec{k}$. Here $\vec{k} = 6\hat{j} - 8\hat{k}$, so
$$\hat{s} = \frac{-6\hat{j} + 8\hat{k}}{10} = \frac{-3\hat{j} + 4\hat{k}}{5}$$
Solution by Sreeraj P, M.Sc Physics