Question

The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to:

• A. The ratio of magnetic permeability to the electric susceptibility of vacuum
• B. Unity
• C. The speed of light in vacuum
• D. Reciprocal of speed of light in vacuum

Answer 1

The correct option is D Reciprocal of speed of light in vacuum

For electromagnetic wave in any medium,

$\frac{E}{B}=\frac{1}{\sqrt{\mu ϵ}}$

Thus in a vacuum,

$\frac{E_0}{B_0}=\frac{1}{\sqrt{{ϵ}_0{\mu }_0}}$

$\frac{1}{\sqrt{{\mu }_0{ϵ}_0}}$ is the speed of light in vacuum$=c$.

Thus $\frac{B_0}{E_0}=\frac{1}{c}$