Question

The angle between the incident ray and mirror is 20, the angle of incidence and the angle of reflection will be:
(A) Angle of incidence = 20
Angle of reflection = 50

(B) Angle of incidence = 20
Angle of reflection = 20

(C) Angle of incidence = 70
Angle of reflection = 70

(D) Angle of incidence = 160
Angle of reflection = 50

Answer 1

Hint Angle of incidence is the angle made by the incident ray with the normal of the surface. Since the angle between the normal and the mirror is ${90^0}$ , the difference between ${90^0}$ and the given angle gives the angle of incidence. According to the laws of reflection the angle of incidence is always equal to the angle of reflection, so from the difference both the angles can be known.

Complete step by step solution
In this question we are given the angle between the incident ray and the mirror, which is 20. As the mirror is always perpendicular to the normal, the angle between normal and the incident ray is
i = 90-20 = 70
This angle is always equal to the angle of reflection, so r is also equal to 70.

Therefore, the correct answer is option C

Note
Remember that the angle of reflection and the angle of incidence is always measured with respect to the normal of the plane