JEE Physics 2025 Question with Solution

Given: A plane electromagnetic wave propagates along the $+x$ direction in free space.

Find: The correct components of $\vec{E}$ and $\vec{B}$ in the Cartesian frame.

In an electromagnetic wave, the electric field, magnetic field, and direction of propagation are mutually perpendicular to each other.

Since the wave propagates along the $x$-axis, both $\vec{E}$ and $\vec{B}$ must lie in the plane perpendicular to the $x$-axis.

For the stated orientation,

Hence, the correct field components are $E_y$ and $B_z$.

Therefore, the correct option is B.

Given: The direction of propagation is $+x$.

Find: Which pair of field components can represent the electric and magnetic fields.

A plane electromagnetic wave satisfies the perpendicular relation among three directions:

• direction of propagation
• electric field direction
• magnetic field direction

Because propagation is along $+x$, neither field can have an $x$-component in the required pair.

So options containing $E_x$ or $B_x$ are not suitable. The remaining consistent transverse arrangement is $E_y$ with $B_z$.

Therefore, the correct answer is $E_y, B_z$, which corresponds to option B.