In a plane electromagnetic wave,the average value of ....... is zero.

If ${\varepsilon _0}$ and ${\mu _0}$ are respectively the electric permittivity and the magnetic permeability of free space,and ${\varepsilon}$ and ${\mu}$ are the corresponding quantities in a medium,the refractive index of the medium is:

What is the displacement variable in a simple pendulum and the propagation of light?

If $\overrightarrow E$ and $\overrightarrow B$ are the electric and magnetic field vectors of electromagnetic waves,then the direction of propagation of the electromagnetic wave is along the direction of:

The wavelength of an electromagnetic wave radiated by a charge oscillating with a frequency of $1 \, \text{kHz}$ is ..... $km$.

The electric and the magnetic field,associated with an electromagnetic wave propagating along the $+z$-axis,can be represented by