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JEE Main 2018 (15 Apr, Shift 2) · Nature of EM Waves & Wave Equation

Nature of EM Waves & Wave Equation question from JEE Main 2018 (15 Apr, Shift 2)

Q73JEE Main 2018 · 15 APR · SHIFT 2Difficult

Nature of EM Waves & Wave Equation

A plane polarized monochromatic EM wave is traveling in vacuum along z direction such that at t = t1 it is found that the electric field is zero at a spatial point z1. The next zero that occurs in its neighbourhood is at z2. The frequency of the electromagnetic wave is:

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Answer: (b)

  1. Neighbouring zeros of a sine wave are half a wavelength apart: ∣z2−z1∣=λ/2|z_2 - z_1| = \lambda/2.
  2. λ=2∣z2−z1∣\lambda = 2|z_2 - z_1|.
  3. ν=cλ=3×1082∣z2−z1∣\nu = \dfrac{c}{\lambda} = \dfrac{3 \times 10^{8}}{2|z_2 - z_1|}.
  4. So the answer is (b) 1.5×108∣z2−z1∣\dfrac{1.5 \times 10^{8}}{|z_2 - z_1|}.
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