Two plane mirror are inclined at an angle `theta`. A light ray incident on one of the mirror undergoes multiple reflections. The angle of incidence on the first mirror is `15^(@)`. After reflection from the second mirror, if the light ray retraces its path, determine the volue of `theta`.

Explanation

`angleOAB=90-15=75^(@)`
(`:.` angle of incidence = angle of reflection)

In `DeltaOAB,angleOAB+angleAOB+angleABO=180^(@)`
`75+theta+90=180^(@)`
`impliestheta=180-165`
`=15^(@)`
(`:.` The light ray retraces its path only if it incident along the normal)