rays of light strike a horizontal plane mirror at an angle of `45^(@)`. At what angle should be a second plane mirror be placed in order that the reflected ray finally be reflected horizontally from the second mirror.

Options

A. `45^(@)`
B. `60^(@)`
C. `67.5^(@)`
D. `135^(@)`

Answer

C

Explanation

(c ) From the figure in `DeltaABC,45^(@)+90^(@)+2alpha=180^(@)`

`rArr or alpha=22.5^(@)`
`angleOBA=90^(@)-alpha`
In `DeltaOAB, theta+45^(@)+90^(@)-alpha=180^(@)`
`rArr` `theta=67.5^(@)`