NCERT Class XII Chapter
Electromagnetic Waves
Questions With Solutions
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Question : 10
Total: 15
In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 2.0 × 10 10 Hz and amplitude 48 V m – 1 .
(a) What is the wavelength of the wave?
(b) What is the amplitude of the oscillating magnetic field?
(c) Show that the average energy density of the
field equals the average energy density of the
field. [c = 3 × 10 8 m s – 1 .]
(a) What is the wavelength of the wave?
(b) What is the amplitude of the oscillating magnetic field?
(c) Show that the average energy density of the
Solution:
(a) Wavelength of electromagnetic wave is
λ =
=
= 1.5 × 10 − 2 m
(b) Amplitude of magnetic field,
= c
B 0 =
=
= 16 × 10 − 8 T
(c) Energy density as electric field,u E =
ε 0 E 2
Here,
= c
So,u E =
ε 0 c 2 B 2
where speed of electromagnetic wave, c =
sou E =
B 2 =
= µ B
[Energy density as magnetic field]
λ =
(b) Amplitude of magnetic field,
(c) Energy density as electric field,
Here,
So,
where speed of electromagnetic wave, c =
so
[Energy density as magnetic field]
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