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 $30 \,MHz$, what is its wavelength (in $m$ )?

Answer 1

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 $v=30 MHz =30 \times 10^{6} Hz$
$\lambda=\frac{c}{v}=\frac{3 \times 10^{8} m / s }{30 \times 10^{6} Hz }=10\, m$