Two plane mirrors are inclined at `70^@`. A ray incident on one mirror at incidence angle `theta` after reflection falls on the second mirror and is reflected from there parallel to the first mirror, The value of `theta` is

Options

A. `50^@`
B. `45^@`
C. `30^@`
D. `55^@`

Answer

A

Explanation

From `Delta ` law
`x = 180^@ - (90^@ - q) - 70^@`
`implies x = 20 + q`
According to the question : AB is parallel to `r_c = 70^@`
also due to reflection `x = y implies 20 + q = 70^@`
`implies q = 50^@`