Question

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 $\dots \dots$

• A. $50^{\circ }$
• B. $60^{\circ }$
• C. $70^{\circ }$
• D. $80^{\circ }$

Answer 1

Answer: (C)

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