question_answer

What should be the angle between two plane mirrors so that whatever be the angle of incidence, the incident ray and the reflected ray from the two mirrors be parallel to each other [KCET 1994; SCRA 1994]

A)            \[60{}^\circ \]                      

B)            \[90{}^\circ \]

C)            \[120{}^\circ \]                    

D)            \[175{}^\circ \]

Correct Answer: B

Solution :

                   Incident ray and finally reflected ray are parallel to each other means \[\delta ={{180}^{o}}\] From \[\delta =360-2\theta \]\[\Rightarrow 180=360-2\theta \]\[\Rightarrow \theta ={{90}^{o}}\]