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

(a) Since, deviation, `delta=(mu-1)A=(1.5-1)xx5^(@)=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^(@)`