Q 12-08-061JEE MainJEE Main 2024 (29 Jan, Shift 2)Easy
A plane electromagnetic wave of frequency $35\ \text{MHz}$ travels in free space along the $X$-direction. At a particular point (in space and time) $\vec E = 9.6\,\hat j\ \text{V m}^{-1}$. The value of magnetic field at this point is:
Answer: (A) $3.2\times10^{-8}\,\hat k\ \text{T}$
$$B = \frac Ec = \frac{9.6}{3\times10^8} = 3.2\times10^{-8}\ \text{T}$$
$\vec E\times\vec B$ must point along $+\hat i$ (direction of travel). Since $\hat j\times\hat k = \hat i$, $\vec B$ is along $\hat k$:
$$\vec B = 3.2\times10^{-8}\,\hat k\ \text{T}$$
Solution by Sreeraj P, M.Sc Physics