# Light - Reflection

In this Section, We will Focus on Light Energy and how it interacts with the World around us. Light moves as a Wave in straight lines at a very high Speed ( 300 Million ms-1 ).

Humans use Light Energy to 'See', it is detected by special Cells in the back of the Eye in a part called the Retina. In order to see an Object, the Object must either Emit ( give out ) Light or Reflect Light.

## Reflection

When a Wave 'hits' an Object, the Wave can change direction and 'Bounce off' the Object. This is known as Reflection.

There are two types of Reflection :- • Mirror Reflection - If the Object has a very smooth surface, then all of the Light is Reflected in the same way, making a Mirror Image.

• Diffuse Reflection - If the Object has a rough surface, then each ray of light will be Reflected in different directions, scattering the Light. This is how most Objects Reflect Light.

## The Law of Reflection

When Light hits a Mirror, the Ray of Light is Reflected from its Surface. The Diagram below shows an example of this :- Where :-

• θi = Incident angle ( Angle going in ) in Degrees

• θR = Reflected Angle ( Angle coming out ) in Degrees

In Optics, all angles are measured from the same place, a line called the Normal. This is a line at a right angle to the surface of the Mirror. Never measure an angle from the Mirror itself.

By experiment, we can show that :-

" For a Mirrored Surface, The Angle of Incidence of a Ray of Light is Equal to the Angle of Reflection."

This is known as The Law of Reflection.

## Curved Reflectors

If the Mirror is Curved instead of Flat ( Plane ), then an unusual effect can be seen. Each part of the Curved Surface acts as a tiny Plane Mirror, following the Law of Reflection. With the Right Shape, all of the Light hitting the Mirror will be Focussed to a single Point.

This is how Satellite Dishes Work. By Reflecting the Signal all to the same Point, the Signal will be made Stronger :- 