A ray of light incident at an angle `theta` on a refracting face of a prism emerges from the other face normally. If the angle of the prism is `5^@` and the prism is made of a material of refractive index `1.5`, the angle of incidence is.

Options

A. `7.5^(@)`
B. `5^(@)`
C. `15^(@)`
D. `2.5^(@)`

Answer

A

Explanation

Since, deviation `delta = (mu -1) A = (1.5 - 1) xx 5^(@) = 2.5^(@)`
By geometry, angle of refraction by first surface is `5^(@)`
But `delta = theta - r` ,
So, we have `2.5^(@) = theta - 5^(@) ` on solving `theta = 7.5^(@)`.