13.3.1. Activity 13.4

Imagine that parallel rays are incident on an irregular surface as shown in Fig. 13.6. Remember that the laws of reflection are valid at each point of the surface. Use these laws to construct reflected rays at various points. Are they parallel to one another? You will find that these rays are reflected in different directions. (Fig. 13.7)

In this activity, we consider what happens to parallel rays of light when they hit an irregular surface. The laws of reflection state that the angle of incidence is equal to the angle of reflection. However, on an irregular surface, where there are bumps and dips, the angles of incidence can vary greatly at different points. As a result, the reflected rays do not remain parallel but scatter in different directions.

Think of throwing a basketball against a concrete wall compared to throwing it against a bumpy surface, like a rock wall. In the former, the ball rebounds back in a relatively straight path, but when it hits the bumps of the rock surface, it bounces off in many different directions, similar to how light behaves when hitting an irregular surface.

When all the parallel rays reflected from a rough or irregular surface are not parallel, the reflection is known as diffused or irregular reflection. Remember that the diffused reflection is not due to the failure of the laws of reflection. It is caused by the irregularities in the reflecting surface, like that of a cardboard.

Diffused reflection occurs when rays of light strike a rough surface. Unlike smooth surfaces, where the light reflects in an orderly fashion, a rough surface scatters the rays of light in various directions. This is not a failure of the laws of reflection; it's simply that the surface doesn't have a uniform angle of incidence. The roughness causes different angles of reflection for incoming rays, resulting in a diffused appearance.

Consider how you see different colors and textures in a crumpled piece of paper compared to a shiny sheet of metal. The shiny surface gives a clear reflection, letting you see a defined image of yourself, while the crumpled paper scatters light, making the reflection vague and unclear. This illustrates diffused reflection; the crumpled paper surface reflects light in many directions, creating a softer appearance.

On the other hand, reflection from a smooth surface like that of a mirror is called regular reflection (Fig. 13.8). Images are formed by regular reflection.

Regular reflection happens on smooth surfaces where the light rays strike at consistent angles, allowing them to bounce back in parallel lines. This phenomenon enables clear and defined images to be created. For example, mirrors reflect light parallelly, allowing us to see ourselves distinctly. This characteristic distinguishes regular reflection from diffused reflection, where clarity is lost due to the scattering of light.

Think of how you use a mirror to check your appearance. The smooth reflective surface of the mirror allows you to see a clear image of yourself because all angles of light striking it reflect back to you uniformly. Conversely, if you try to look at yourself in a rough surface, like a car door or textured wall, the image would become unclear because the light is scattered—this illustrates the difference between regular and diffused reflections.

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