A beam of unpolarized light is incident on the surface of a liquid and is partially reflected and partially refracted as shown below.

The reflected light is completely horizontally polarized. Which of the following is the refractive index of the liquid?

A. tan 40°

B. tan 50°

C. \(\frac{{\sin 40^\circ }}{{\sin 50^\circ }}\)

D. \(\frac{{\sin 40^\circ }}{{\cos 50^\circ }}\)

B

The majority of the candidates got the answer to this question but an almost equal number thought that the refractive index was given by the ratio of sines in option C. This shows clearly that candidates thought they were dealing with Snell's law and not Brewster's law.