Frequency of electromagnetic wave does not change with change in medium but wavelength and velocity of wave changes with change in medium. Velocity of electromagnetic wave in vacuum c=
1
√µ0∈0
=vλvacuum .....(i) Velocity of electromagnetic wave in the medium vmedium =
1
√µ0µr∈0∈r
=
c
√µr∈r
where µr and ∈r be relative permeability and relative permittivity of the medium. For dielectric medium, µr=1 ∴vmedium=
c
√∈r
Here, ∈r=4.0 ∴vmedium =
c
√4
=
c
2
....(ii) Wavelength of the wave in medium λmedium =