A ray of light strikes a plane mirror at an angle of incidence `45^@` as shown in Figure . After reflection,l the ray passes through a prism of refractive indes 1.5 whos apex angle is `4^@`. Through what angle must the mirror be rotated it total deviation of the ray be `90^@` ?

Options

A. `1^(@)` clockwise
B. `1^(@)` anticlockwise
C. `2^(@)` clockwise
D. `2^(@)` anticlockwise

Answer

B

Explanation

Deviation by prism `=A(mu-1)=4^(@)(1.5-1)=2^(@)`
For `90^(@)` total deviation, deviation by mirror
`=90^(@)-2^(@)=88^(@)`
`180^(@)-2i=88^(@)`
`2i=92^(@)`
`i=46^(@)`
Mirror should be rotated `1^(@)` anticlockwise.