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A plane electromagnetic wave travels in a medium with relative permeability mu_r = 1.6 and relative permittivity epsilon_r = 6.44. At a certain point the magnitude of the magnetic field intensity is B = 4.5 x 10⁻² T. Find the approximate magnitude of the electric field intensity at that point. (Speed of light in vacuum c = 3 x 10⁸ m/s)

1. 16.9 V/m
2. 2.25 x 10⁻² V/m
3. 8.48 V/m
4. 4.2 x 10⁶ V/m

Correct answer: 4.2 x 10⁶ V/m

Solution

The wave speed in the medium is v = c/sqrt(mu_r*epsilon_r) = 3e8/sqrt(10.304) ~ 9.35e7 m/s. Then E = v*B = 9.35e7 * 4.5e-2 ~ 4.2e6 V/m.

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