JEE Physics 2023 Question with Solution

Given: Energy transport is in the negative $z$-direction, so the Poynting vector is along $-\hat{k}$. The electric field is along the positive $y$-direction, so $\vec{E} = +\hat{j}$.

Find: The direction of the magnetic field.

For an electromagnetic wave, the direction of energy flow is given by the Poynting vector:

Substitute the given directions:

Using the right-hand rule, we need a vector $\vec{H}$ such that

Since

the magnetic field must be along $+\hat{i}$, that is, the positive $x$-direction.

Therefore, the magnetic field is in the positive direction of $x$. The correct option is A.

The solution contains an inconsistency because it labels the correct option as C, but the worked vector relation and concluding statement both support positive direction of $x$.

Given: $\vec{E}$ is along $+\hat{j}$ and energy flow is along $-\hat{k}$.

Find: The direction of $\vec{H}$.

In an electromagnetic wave, $\vec{E}$, $\vec{H}$, and the direction of propagation form a right-handed set with

So choose the magnetic field direction so that

This is satisfied by $\vec{H} = +\hat{i}$.

Hence, the magnetic field points in the positive $x$-direction.