Question

Figure shows a ray of light p striking a mirror AB. The mirror AB and the mirror CD make an angle of ${120}^{\circ }$ with each other. The angle of reflection of ray P at CD is --------

• A. ${20}^{\circ }$
• B. ${30}^{\circ }$
• C. ${50}^{\circ }$
• D. ${70}^{\circ }$

Answer 1

The correct option is C ${50}^{\circ }$

After reflection the beam of light will make a triangle between two mirror.
Let point L on first mirror and M on second mirror at which beam reflects.
$\angle PLA=\angle MLB={20}^0,\angle B={120}^0$
${180}^0=\angle B+\angle MLB+\angle LMC$
${180}^0={120}^0+{20}^0+\angle LMC$
$\angle LMC={40}^0$
so,angle of incidence at second mirror $={90}^0-{40}^0={50}^0$
hence,option C is correct.