Question

I have a doubt. Please help.

The angle of incidence and refraction are equal in a transparent slab, when the angle of incidence is:
a) 0
b) 45
c) 90
d) depends on the material of the slab

I marked c) 90. Is it correct?

Answer 1

no its d.)depends on the material of the slab?..
that's the correct answer!...
:)

Answer 2

How? We performed experiment. And I wrote 90 degreees. I thought it to be glass slab.

Answer 3

let index of air be n1
index of glass be n2
see the diagram
n1*sin i=n2 sin r
n1=1
sin i=n2 sin r
sin i = sin r
that can only happen when i=r=0
if i=r=90
then
1=n2
not possible
so it should be 0 degrees, the ray is entering perpendicularly in the glass slab