question_answer

A ray of light making an angle \[10{}^\circ \] with the horizontal is incident on a plane mirror making angle\[\theta \]with the horizontal. What should be the value of \[\theta \] so that the reflected ray goes vertically upward?

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

B)        \[40{}^\circ \]

C) \[50{}^\circ \]  

D)        \[60{}^\circ \]

Correct Answer: C

Solution :

The situation is as shown in figure: The reflected ray makes an angle, \[100-\theta \]with the normal. This is also equal to\[\theta \]. \[\therefore \]  \[100-\theta =\theta \] \[\Rightarrow \]                        \[\theta ={{50}^{o}}\]