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Electromagnetic Waves question

2009 · Q130
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Electromagnetic Waves question

2009 · Q130

NEETPhysicsElectromagnetic WavesMCQ+4 / −1
The electric field part of an electromagnetic wave in a medium is represented by Ex = 0;

Ey=2.5NCcos⁡[(2π×106radm)t−(π×10−2rads)x];{E_y} = 2.5{N \over C}\cos \left[ {\left( {2\pi \times {{10}^6}{{rad} \over m}} \right)t - \left( {\pi \times {{10}^{ - 2}}{{rad} \over s}} \right)x} \right];Ey​=2.5CN​cos[(2π×106mrad​)t−(π×10−2srad​)x];

Ez = 0.
  1. A
    moving along x direction with frequency 106 Hz and wavelength 100 m.
  2. B
    moving along x direction with frequency 106 Hz and wavelength 200 m.
  3. C
    moving along −-−x direction with frequency 106 Hz and wavelength 200 m.
  4. D
    moving along y direction with frequency 2π×106 Hz2\pi \times {10^6}\,Hz2π×106Hz and wavelength 200 m.
View written solutionFree

Correct answer: B

Since coefficient of x is negative, but is moving along +ve x-axis,

so This is the form Ey = E0(ω\omega ωt – kx)

ω\omega ω = 2π×106{2\pi \times {{10}^6}}2π×106

f = ω2π{\omega \over {2\pi }}2πω​ = 106 Hz

k = π×10−2\pi \times {10^{ - 2}}π×10−2

Also, λ=2πk\lambda = {{2\pi } \over k}λ=k2π​ = 2ππ×10−2{{2\pi } \over {\pi \times {{10}^{ - 2}}}}π×10−22π​ = 200 m

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