Question

The angle between incident ray and plane mirror is 40 degrees. What is the total angle through which ray of light turns.

Answer 1

Angle between incident ray & plane mirror = 40
We know, angle b/w perpendicular & plane mirror = 90

So, angle of incidence = 90-40 = 50

According to first law of reflection,
angle of reflection = angle of incidence = 50

Total angle = Angle of reflection + angle of incidence
Total angle = 50 + 50

So,your final answer is 100 degrees

Hope this helps!

Answer 2

This total angle through which light Ray turns is called "angle of deviation"