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JEE Main 2026 (21 Jan, Shift 1) · Nature of EM Waves & Wave Equation

Nature of EM Waves & Wave Equation question from JEE Main 2026 (21 Jan, Shift 1)

Q5JEE Main 2026 · 21 JAN · SHIFT 1Medium

Nature of EM Waves & Wave Equation

The electric field in a plane electromagnetic wave is given by:

Ey=69sin⁡[0.6×103x−1.8×1011t] V/m.E_y = 69\sin\left[0.6\times 10^{3}x - 1.8\times 10^{11}t\right]\text{ V/m.}

The expression for magnetic field associated with this electromagnetic wave is ______ T.

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Answer: (a)

  1. (kx−ωt)(kx - \omega t): wave moves along +x+x, v=1.8×10110.6×103=3×108v = \dfrac{1.8\times10^{11}}{0.6\times10^{3}} = 3\times10^{8} m/s.
  2. B0=693×108=2.3×10−7B_0 = \dfrac{69}{3\times10^{8}} = 2.3\times10^{-7} T
  3. y^×z^=x^\hat y\times\hat z = \hat x, so B⃗\vec B is along +z+z with the same phase.
  4. So the answer is (a) Bz=2.3×10−7sin⁡[0.6×103x−1.8×1011t]B_z = 2.3\times10^{-7}\sin[0.6\times10^{3}x - 1.8\times10^{11}t].
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