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NCERT Class XII Chapter
Electromagnetic Waves
Questions With Solutions

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Question : 8
Total: 15
Suppose that the electric field amplitude of an electromagnetic wave is E0 = 120 N C–1 and that its frequency is υ = 50.0 MHz.
(a) Determine B0, ω, k, and λ.
(b) Find expressions for
→
E
 and
→
B
.
Solution:  
(a) By relation,
E0
B0
 = c
Peak value of magnetic field, B0 =
E0
c
 =
120
3×108
 = 40 × 10−8 T
Angular frequency, ω = 2πu = 100π × 106 Hz = π × 108 Hz.
Speed of light c = uλ
Wavelength, λ =
c
v
 =
3×108
50×106
 , λ = 6 m
Propagation constant, k =
2π
λ
 =
π
3
 rad m−1 = 1.05 rad m−1
(b) Let the wave is propagating along x-direction, electric field
→
E
 is along y - direction and magnetic field
→
B
 along z-direction.
→
Ey
 = E0 sin (kx - ωt)
^
j
→
Ey
 = 120 sin (
π
3
x−π×108t)
^
j
^
Bz
 = B0 sin (kx - ωt)
^
k
 = 40 × 10−8 sin (
π
3
x−π×108t)
^
k
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