Question

72. The angle of incidence for which glancing angle is equal to sum of angle of incidence and
angle of reflection is
a) 30°
b) 45°
d) 90°
c) 60°​

Answer 1

The angle of incidence is 30°. Means option first is correct.

Explanation:

• Let

        Angle of incidence = ∠i

        Angle of reflection = ∠r

        Angle of glancing = ∠g

• It is given that

        Angle of glancing =Angle of incidence +Angle of reflection

        means

        ∠g = ∠i +∠r       ...1)

• From first law of reflection

        Angle of incidence = Angle of reflection

        ∠i = ∠r             ...2)

• Glancing angle is complement angle of incidence angle.

        Means

        Angle of glancing +Angle of incidence = 90°

        ∠g +∠i =  90°    ..3)

• From equation 1) and equation 3)

       ∠i +∠r +∠i =  90°       ... 4)

• From equation 2) and equation 4)

        ∠i +∠i +∠i =  90°      

        So

        ∠i =  30°  = The angle of incidence