Unpolarised light is incident on a plane glass surface. What should the angle of incidence be so that the reflected and the refracted rays are perpendicular to each other? (μ=1.54)

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(3) 57°. Given: unpolarised light falling on glass of μ=1.54, with the reflected and refracted rays to be at right angles. Idea: if the reflected ray leaves at i and the refracted ray at r from the normal, the angle between them is 180°-(i+r); requiring 90° gives i+r=90°. Putting r=90°-i into Snell's law turns it into Brewster's law, tan iₚ=μ. iₚ=tan⁻¹1.54. tan 57°=1.54. iₚ=57°. At this angle the reflected beam is also completely plane polarised, which is the other half of what Brewster's law says.

Unpolarised light is incident on a plane glass surface. What should the angle of incidence be so that the reflected and the refracted rays are perpendicular to each other? (μ=1.54)

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