Light Energy — Question 6

The laws of reflection of light can be verified by the following experiment:

1. Take a drawing board and a white sheet of paper. Fix the white sheet of paper on the drawing board. Draw a straight line MM₁ on the paper.
2. On the line MM₁ take a point O at its middle and draw a line OA such that ∠MOA is less than 90°. Draw a normal ON on MM₁ at point O.
3. Take a small plane mirror and place along the line MM₁. Use plasticine to fix the mirror on the paper so that it stands upright.
4. Fix pins P and Q vertically on the line OA. Set your eye on the other side of the normal ON along the direction as shown in below figure.
5. You will see images P^', Q^' of pins P and Q in the mirror.
6. Set your eye in line with the two images P^', Q^' and fix two more pins R and S on the paper in front of the mirror such that both the pins R and S are in line with P^', Q^'.

7. Remove the mirror and draw small circles around pins P, Q, R and S. Draw a line OB joining the points R and S.
8. AO is incident ray, OB is reflected ray and ON is normal at the point of incidence O.
9. Using a protractor measure angle of incidence i (∠AON), angle of reflection r (∠BON). We will find two angles are equal.

This experiment verifies the two laws of reflection:

1. Angle of incidence = Angle of reflection.
2. Incident ray, reflected ray and normal all lie in the same plane of paper which is the second law of reflection.