A plane electromagnetic wave of frequency 20 MHz travels in free space along the +x direction. At a particular point in space and time, the electric field vector of the wave is $$E_{y}=9.3Vm^{-1}$$. Then, the magnetic field vector of the wave at that point is

A plane EM wave with $$E_y = 9.3$$ V/m travels along +x direction. Find the magnetic field.

Relate E and B:

For an EM wave: $$B = \frac{E}{c}$$

$$B = \frac{9.3}{3 \times 10^8} = 3.1 \times 10^{-8} \text{ T}$$

Determine direction:

The wave travels along +x, E is along +y. By $$\vec{E} \times \vec{B} \parallel \vec{k}$$ (direction of propagation):

$$\hat{j} \times \hat{k} = \hat{i}$$, so B is along +z.

$$B_z = 3.1 \times 10^{-8}$$ T

The correct answer is Option 2: $$B_z = 3.1 \times 10^{-8}$$ T.