Unpolarised light is incident on a plane transparent surface. The reflected and the refracted rays are found to be perpendicular to each other. The angle of incidence is then . [Refractive index of the medium is 1.73]

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(4) 60°. Given: unpolarised light on a plane surface of refractive index μ = 1.73, with the reflected and the refracted rays at right angles. Idea: that right angle is the Brewster condition, so the angle of incidence asked for is the polarising angle. With the two rays perpendicular, r = 90° - i_B, and Snell's law μ = (sin i_B)/(sin r) becomes μ = (sin i_B)/(cos i_B) = tan i_B. i_B = tan⁻¹(1.73), and tan 60° = √3 = 1.73. So the angle of incidence is 60°, and the refracted ray leaves at 30° on the other side of the normal.

Unpolarised light is incident on a plane transparent surface. The reflected and the refracted rays are found to be perpendicular to each other. The angle of incidence is then ________. [Refractive index of the medium is 1.73]

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