LIGHT | Class 8 Science Notes

13.2 Laws of Reflection

Reflection of light occurs when a light ray strikes a surface and bounces back. To study this phenomenon, we perform experiments using a plane mirror and a narrow beam of light. In Activity 13.1, a comb with only one opening is used to create a narrow beam of light from a torch. When this beam strikes a plane mirror, it is reflected in another direction. The incoming ray is called the incident ray, and the ray that bounces back is called the reflected ray. At the point where the incident ray strikes the mirror, a line perpendicular to the surface is drawn, called the normal. The angle between the incident ray and the normal is the angle of incidence (∠i), and the angle between the reflected ray and the normal is the angle of reflection (∠r). Repeated measurements show that the angle of incidence is always equal to the angle of reflection. This is the first law of reflection. The second law states that the incident ray, the reflected ray, and the normal all lie in the same plane. These laws hold true for reflection from any smooth surface. When light is incident along the normal, it is reflected back along the same path. These laws help us understand how mirrors work and how images are formed.

📊 Diagram: Fig. 13.1 : Arrangement for showing reflection; Fig. 13.2: Drawing the normal; Fig. 13.3: Angle of incidence and angle of reflection; What would happen if I threw the light on the mirror along the normal.

🧪 Activity: Activity 13.1: Using a comb with one opening and a torch to produce a narrow beam of light, reflect it from a plane mirror, and measure angles of incidence and reflection to verify the laws of reflection.

🔗 Connection: Understanding the laws of reflection sets the foundation for exploring image formation by mirrors and the difference between regular and diffused reflection.