A ray of light is incident at `50^(@)` on the middle of one of the two mirrorrs arranged at an angle of `60^(@)` between them . The ray then touches the second mirrorr, get reflected back to the first mirrorr, making an angle of incidence of

Options

A. `50^(@)`
B. `60^(@)`
C. `70^(@)`
D. `90^(@)`

Answer

C

Explanation

In `DeltaPQR,x+40^(@)+60^(@)=180^(@)`
`x=80^(@)`
`angley+anglex=90^(@)`
`angley=10^(@)`

Now In `DeltaPRS`
`anglePRS=20^(@)`
`angleSPR=90^(@)+50^(@)=140^(@)`
`anglePRS+angleSPR+anglePSR=180^(@)`
`20^(@)+140^(@)+anglePSR=180^(@)`
`anglePSR=20^(@)`
`angleZ+anglePSR=90^(@)`
`anglez=90^(@)-20^(2)=70^(@)`