The electromagnetic waves are the radiations of large of wavelength. What are their velocity (i) in vacuum and (ii) in a medium?

Explanation

The wavelength of electromagnetic wave
ranges form `6xx10^-14m` to `6xx10^6m`. These
waves travel with the same velocity `(=3xx10^8`
`ms^-1)`
in vacuum but with different velocities in
a medium.
In fact, the velocity of an
electromagnetic wave is less in a medium than
vacuum and a medium provides different values
of refractive index to the electromagnetic waves
of different wavelengths.