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JEE Main 2015 (10 Apr, Shift 1) · Nature of EM Waves & Wave Equation

Nature of EM Waves & Wave Equation question from JEE Main 2015 (10 Apr, Shift 1)

Q79JEE Main 2015 · 10 APR · SHIFT 1Medium

Nature of EM Waves & Wave Equation

An electromagnetic wave travelling in the x-direction has frequency of 2 ×\times 1014 Hz and electric field amplitude of 27 Vm−1{}^{-1}. From the options given below, which one describes the magnetic field for this wave?

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Answer: (b)

  1. B0=E0c=273×108=9×10−8B_0 = \dfrac{E_0}{c} = \dfrac{27}{3\times10^{8}} = 9\times10^{-8} T, so (a) is out.
  2. B⃗\vec B must be perpendicular to xx, so (c) (i^\hat i) is out.
  3. λ=c/f=1.5×10−6\lambda = c/f = 1.5\times10^{-6} m; phase is 2π(x/λ−ft)2\pi(x/\lambda - ft), the 2π2\pi is missing in (d).
  4. So the answer is (b).
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