A ray of light strikes an air-glass interface such that a part of it is reflected into air and the rest enters glass as shown in the figure below.

If angle of refraction and refractive index of glass with respect to air is r and `mu` respectively,then value of `alpha` is

Options

A. r
B. `mu` sin r
C. `sin^-1(mu sin r)`
D. `sin^-1 ((sin r)/mu)`

Answer

C