A very thin prism has an apex angle A and its material has refractive index` mu = 1.48` . Light is made to fall on one of the refracting faces at near normal incidence. Interference results from light reflected from the outer surface and that emerging after reflection at the inner surface. When violet light of wavelength `lambda "= 400 nm"` is used, the first construc- tive interference band is observed at a distance `"d = 3.0 cm"` from the apex of the prism.
(a) Find the apex angle A.
(b) If red light `(lambda" = 800 nm")` is used, at what distance from the apex will we observe the first constructive interfer- ence band.

Answer

`(a)1.3xx10^(-4)"degree"` `(b)6 "cm"`