Determine the minimum angle of incidence for light traveling

Determine the minimum angle of incidence for light traveling in flint glass in order to undergo total internal reflection from ethanol. The indices of refraction respectively for flint glass and ethanol are 1.66 and 1.36.

Solution

The minimum angle of incidence for light traveling in flint glass in order to undergo total internal reflection from ethanol is Critical angle.

The indices of refraction of flint glass n = 1.66

The indices of refraction of ethanol n \' =1.36

At critical angle ,angle of incidence i = C

Angle of refraction r = 90 o

From Snell\'s alw , sin i / sin r = n \' / n

                       sin C / sin 90 = 1.36 / 1.66

                                  sin C = 0.8192

                                        C = sin ^{- 1}( 0.8192)

                                           = 55.01 ^o

                                           = 55 ^o        ( two significant figures)