Light: Mirrors and Lenses | Class 8 Science Notes

10.3 What Are the Laws of Reflection?

The laws of reflection describe how light rays behave when they strike reflective surfaces such as mirrors. The first law states that the angle of incidence (the angle between the incident ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal). The second law states that the incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane. These laws apply to all types of mirrors—plane, concave, and convex. To observe these laws, an experiment can be conducted using a plane mirror, a torch, and a comb to create a thin beam of light. By varying the angle at which the light beam strikes the mirror and measuring the angles of incidence and reflection, it is found that these angles are always equal. Additionally, bending the surface on which the mirror is placed shows that the reflected ray disappears when the plane is disturbed, confirming that all three rays lie in the same plane. These fundamental laws are essential for understanding how images are formed and how light behaves upon reflection, forming the basis for more complex optical phenomena involving spherical mirrors and lenses.

📊 Diagram: Figures 10.8a and 10.8b show beams of light falling on a mirror at different angles. Figures 10.9a to 10.9d illustrate drawing incident and reflected rays, the normal, and measuring angles of incidence and reflection. Figures 10.10a and 10.10b demonstrate reflected beam visibility on a flat and bent paper surface.

🧪 Activity: Activity 10.4 and 10.5: Experiments to observe and verify the laws of reflection using plane mirrors and light beams.

🔗 Connection: Prepares for exploring how these laws apply to spherical mirrors and the behavior of multiple parallel light rays.