Class 12 NEET Physics Electromagnetic Waves Questions

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

õ0E0

=vλ‌vacuum ‌‌‌‌⋅⋅⋅⋅⋅⋅⋅(i)
Velocity of electromagnetic wave in the medium
v‌medium ‌=‌

1

√µ0µrE0Er

=‌

c

õrEr

whereµrandErbe relative permeability and relative permittivity of the medium.
For dielectric medium,µr=1
∴‌‌v‌undium ‌=‌

c

√Eγ

Here,Er=4.0
∴‌‌v‌meddium ‌=‌

c

√4

=‌

c

2

‌‌‌⋅⋅⋅⋅⋅⋅⋅(ii)
Wavelength of the wave in medium
λ‌medium ‌=‌

ν‌medium ‌

v

=‌

c

2v

=‌

λ‌yacuum ‌

2

(Using (i) and (ii))