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A parallel beam of monochromatic, unpolarised light strikes a transparent slab of refractive index sqrt(3). The reflected beam is found to be completely (plane) polarised. What are the angles of incidence (i) and refraction (r)?

1. i = 30 deg, r = 30 deg
2. i = 60 deg, r = 60 deg
3. i = 30 deg, r = 60 deg
4. i = 60 deg, r = 30 deg

Correct answer: i = 60 deg, r = 30 deg

Solution

tan(i) = sqrt(3) gives i = 60 deg. Since the reflected and refracted rays are perpendicular at Brewster incidence, r = 90 - 60 = 30 deg.

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