A beam of unpolarised light is incident from air onto a transparent glass slab. It is observed that the reflected light is completely plane-polarised. If the angle of refraction is 30^ , the refractive index of the glass is:

Step-by-step solution

Since the reflected light is completely plane-polarised, the light must be incident at Brewster's angle ( i_p ). At Brewster's angle, the reflected and refracted rays are mutually perpendicular, which gives the relation: i_p + r = 90^ Given the angle of refraction r = 30^ : i_p + 30^ = 90^ i_p = 60^ According to Brewster's law, the refractive index of the medium is given by: = (i_p) = (60^ ) = 3 Answer: 3