question_answer

A light ray is incident on a plane mirror \[{{M}_{1}}\] at an angle of incidence\[45{}^\circ \]. At what angle from mirror \[{{M}_{1}}\] a second plane mirror \[{{M}_{2}}\] be placed in order that the finally reflected ray from mirror \[{{M}_{2}}\] goes parallel to the mirror\[{{M}_{1}}\]?

A) \[22.5{}^\circ \]                       

B) \[30{}^\circ \]

C) \[45{}^\circ \]              

D)   \[67.5{}^\circ \]

Correct Answer: D

Solution :

from figure \[2\theta +45{}^\circ =180{}^\circ \] \[2\theta \,\,=\,\,135{}^\circ \] \[\theta \,\,=\,\,67.5{}^\circ \]