Question

If the angle between incident ray and
reflected ray is 120°, what is the angle of
incidence ?
(A) 60°
(B) 90°
(C) 30°
(D) 45°​

Answer 1

Answer:-

The angle of incidence is 60°.

Explanation:-

Here in this question, concept of law of reflection is used. According to this law, angle of incidence must be equal to angle of reflection. We have given the angle between incident ray and reflected ray, it means that the given angle is the sum of angle of incidence and angle of reflection. So we can find the angle of reflection by using law of reflection and some mathmatical calculation.

So let's start!

Let us assume the angle of incidence be x.

As angle of reflection is equal to angle of reflection, angle of reflection will also be x.

$\leadsto$ Angle between incident ray and reflected ray=120°

$\leadsto$ Angle of incidence+ angle of reflection=120°

$\leadsto$ x+x=120°

$\leadsto$ 2x=120°.

$\leadsto$ Divide 2 from both sides ( LHS &RHS).

$\leadsto$ x=60°.

Hence the angle of reflection=x=60°.