A circular beam of light of diameter (width) falls on a plane surface of glass. The angle of incidence is .I., angle of refraction is .r. and refractive index of glass is `mu`. Then the diameter of the refracted beam d. is…….

Explanation

Let d be the diameter of incident beam and d. be the diameter of refracted beam.
Then from figure `cos i = (d)/(PQ) , d = PQ cos i `
From figure` cos r = (d.)/(PQ) ` and `d. = PQ cos r `
`i.e., (d.)/(d) = (cos r)/(cos i)`