question_answer

A ray of light is incident at\[50{}^\circ \]on the middle of one of the two mirrors arranged at an angle of\[60{}^\circ \]between them. The ray then touches the second mirror, gets reflected back to the first mirror, making an angle of incidence .....:

A)  \[50{}^\circ \]                                  

B)  \[60{}^\circ \]

C)  \[70{}^\circ \]                  

D)         \[80{}^\circ \]

E)  \[90{}^\circ \]

Correct Answer: C

Solution :

Let required angle be\[\theta \]. In\[\Delta ABC,\] \[90{}^\circ -6+140{}^\circ +20{}^\circ =180{}^\circ \] \[\Rightarrow \]                               \[\theta =70{}^\circ \]