A ray of light passes through an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to `(3)/(4)` th the angle of prism. The angle of deviation is :

Options

A. `45 ^(@)`
B. `39^(@)`
C. `20^(@)`
D. `30^(@)`

Answer

D

Explanation

Angle of incidence = angle of emergence,
`i.e.i=I.`
Also, `i=(3)/(4) xx ` angle of equilateral prism
`= 3/4 xx 60^(@) = 45 ^(@)`
Thus, angle of deviation
`= i+I.-A`
`= ( 45 ^(@) + 45 ^(@) - 60^(@)) = 30^(@)`