Question 5

Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.


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


  1. Pin a white sheet of plane (mirror) paper on a cardboard.
  2. Place a strip of plane mirror Mon the plane paper.
  3. Pined a 2 pins P1 and P2. Obliquely in front of the plane mirror in a straight line so that the line joining the pins can make an angle of 30◦, 45◦ and 60◦ with the normal drawn at the point of incidence.
  4. See through the mirror from other side and observe the pins P1 and P2 seen on the mirror and pins P3 and P4 appears in the straight line.
  5. Remove the plane mirror and the pins. Encircle the points where pins were fixed on the paper.
  6. Join the P1 and P2 extended the line to meet at point O of the mirror. The ray AO so obtained is an incident ray.
  7. Similarly join P3 and P4 and extend the line to meet at point O of the mirror. The ray O so obtained is a reflected ray.
  8. Draw a normal OC.
  9. Measure the angle of incidence ∠I and the angle of reflection ∠r. We find that ∠i = ∠r

Conclusion: This activity shows that the mirror incident ray, the reflection ray and the normal at the point of incidence, all lie on the same plane. The angle of the incidence is also equal to the angle of reflection. Thus, this activity verifies the laws of reflection.  

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