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

Angle of deviation for thin prism is given by,
`delta=(mu-1)A=(1.5-1)xx5^@`
`therefore delta=0.5xx5^@=2.5^@`
Here angle of refraction is `5^@` at the first surface and so from the geometry of figure,

`delta=theta-r`
`therefore theta=delta+r`
`2.5^@+5.0^@`
`7.5^@`