Reflection of light

Every time you look into a mirror, or every time you peep into the surface of a pond, you are looking at a reflection of yourself.

Now, to be precise:

A reflection is the change in direction of a ray of light when it strikes a surface without passing through it.

So, when a ray of light strikes a plane mirror, it does not pass through it; instead, the ray of light gets reflected.

Reflections enable you to see non-luminous objects. For example, the moon is a non-luminous object; it is the sun which is responsible to illuminate it and make the moon visible to naked eyes!

The law of reflection

Before we proceed, it is necessary to get familiar with certain terms:

  1. Normal: the line drawn at right angles to a surface at the point where a ray strikes the surface.
  2. Incident ray: an incident ray is a ray of light striking a surface.
  3. Reflected ray: a reflected ray is a ray of light that has been reflected after striking a surface.
  4. Angle of incidence: the angle between an incident ray and the normal to the surface at the point where it meets a surface.
  5. Angle of reflection: the angle between a reflected ray and the normal to the surface at the point where it reflects from a surface.

The law of reflection states that the angle of incidence (i) is equal to the angle of reflection (r).


A periscope is a device that makes clever use of reflections. It consists of two mirrors that are aligned parallel to each other. Light enters the top mirror, gets reflected to the mirror below, and finally enters your eyes. Periscopes are used in many devices such as submarines and army tanks.

Regular and diffuse reflection

When two beans of light fall at the same time on a plane mirror, they get reflected in the same direction and are parallel to each other. This is known as regular reflection.

However, when the same happens on a rigid and unequal surface, the two reflected rays aren’t parallel to each other and are reflected haphazardly in different directions. This is called as diffuse reflection.

Diffuse reflections are extremely important; light rays are scattered over all directions and thus they can be seen.

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