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NCERT Class XII Chapter
Electromagnetic Waves
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Question : 8 of 15
Marks: +1, -0
Suppose that the electric field amplitude of an electromagnetic wave is E0E_0 = 120 N C1C^{-1} and that its frequency is υ = 50.0 MHz.
(a) Determine B0B_0, ω, k, and λ.
(b) Find expressions for E\overset{\rightarrow}{E} and B\overset{\rightarrow}{B}.
Solution:  
(a) By relation, E0B0\frac{E_0}{B_0} = c
Peak value of magnetic field, B0B_0 = E0c\frac{E_0}{c} = 1203×108\frac{120}{3 \times 10^8} = 40 × 10810^{-8} T
Angular frequency, ω = 2πu = 100π × 10610^6 Hz = π × 10810^8 Hz.
Speed of light c = uλ
Wavelength, λ = cv\frac{c}{v} = 3×10850×106\frac{3 \times 10^8}{50 \times 10^6} , λ = 6 m
Propagation constant, k = 2πλ\frac{2\pi}{\lambda} = π3\frac{\pi}{3} rad m1m^{-1} = 1.05 rad m1m^{-1}
(b) Let the wave is propagating along x-direction, electric field E\overset{\rightarrow}{E} is along y - direction and magnetic field B\overset{\rightarrow}{B} along z-direction.
Ey\overset{\rightarrow}{E_y} = E0E_0 sin (kx - ωt) j^\hat{j}
Ey\overset{\rightarrow}{E_y} = 120 sin (π3xπ×108t)j^\left(\frac{\pi}{3}x - \pi \times 10^8 t\right)\hat{j}
B^z\hat{B}_z = B0B_0 sin (kx - ωt) k^\hat{k} = 40 × 10810^{-8} sin (π3xπ×108t)k^\left(\frac{\pi}{3}x - \pi \times 10^8 t\right)\hat{k}
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