When unpolarised light is incident on a plane glass surface and the reflected ray is found to be plane polarised, what is the angle between the reflected ray and the refracted ray?

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(3) 90°. Given: unpolarised light on glass, at the angle of incidence that makes the reflected ray completely plane polarised. Idea: that angle is Brewster's angle, and Brewster's law tan iₚ=μ follows from Snell's law together with the condition iₚ+r=90°. The reflected ray leaves at iₚ on the far side of the normal and the refracted ray continues at r below the surface. The angle between them is 180°-(iₚ+r)=180°-90°. =90°. Recognising this perpendicularity is the quickest way to spot that a problem is set at Brewster's angle.

When unpolarised light is incident on a plane glass surface and the reflected ray is found to be plane polarised, what is the angle between the reflected ray and the refracted ray?

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