JEE Main 2025 — Electromagnetic Waves Question with Solution

For an electromagnetic wave in free space, the magnitudes of the electric and magnetic fields are related by the speed of light, $$c\approx 3\times 10^{8}m/s,$$ through the equation

$$E=cB.$$

Here's how to determine the magnetic field:

We are given the electric field magnitude: $$E=9.3V/m.$$

Use the relationship to find the magnetic field magnitude:

$$B=\frac{E}{c}=\frac{9.3}{3\times 10^8}\mathrm{T}.$$

Calculating the value gives:

$$B\approx 3.1\times 10^{-8}\mathrm{T}.$$

Since the electric field is along the $$y$$ direction and the wave propagates along the $$+x$$ direction, by the right-hand rule, the magnetic field is oriented along the $$z$$ direction.

Thus, the magnetic field vector is

$${\mathrm{B}}_z=3.1\times 10^{-8}\mathrm{T},$$

which corresponds to Option C.