Question

A plane electromagnetic wave travels in vacuum along $Z$-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is $30MHz$, what is its wavelength (in $m$ )?

Answer 1

Answer: 10

The electric field vector, $\vec{E}$ and magnetic field vector, $\vec{B}$ associated with the electromagnetic wave are perpendicular to each other and also to its direction of propagation. Since electromagnetic wave propagates along $Z$-direction, $\vec{E}$ and $\vec{B}$ lie in $X-Y$ plane in mutually perpendicular directions.
Since $v=30MHz=30\times 10^{6}Hz$
$\lambda =\frac{c}{v}=\frac{3\times 10^{8}m/s}{30\times 10^{6}Hz}=10m$