A lossless non-magnetic dielectric has refractive index n. A plane electromagnetic wave in this medium has the same electric-field amplitude E₀ as a wave in vacuum. If the vacuum-wave intensity is I, the intensity in the dielectric is:
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Question

A lossless non-magnetic dielectric has refractive index n. A plane electromagnetic wave in this medium has the same electric-field amplitude E₀ as a wave in vacuum. If the vacuum-wave intensity is I, the intensity in the dielectric is:

Options

G1 Physics · Accepted Answer

For a non-magnetic dielectric, μ = μ₀ and the wave speed is v = c/n. For a plane wave, B₀ = E₀/v = nE₀/c. Average intensity in the dielectric is I′ = E₀B₀/(2μ₀) = nE₀²/(2μ₀c) = n(½ε₀cE₀²). The quantity in parentheses is the vacuum intensity I for the same E₀. Therefore, I′ = nI. Correct option: B.