Question

while we tressing a path of ray in glass prism we generally take the angle of insident has 30 degree and 60 degree why​

Answer 1

1. 0 degree making with normal : the light ray will go undeviated (means without refraction), will strike the inner surface of prism then got deviated.

2. O degree making with interface( intersection of two mediums) : the light ray will travel along the interface without entering the prism.

(This answer is my assumption. I regret for any kind of mistake/mistakes.)