Refraction of Light

In this article we will learn about refraction of light, types of refraction, how does refraction work, examples of refraction, and refraction in lenses.

When you put a pencil in a glass full of water, it appears to be broken. But when you take the pencil out of the glass to throw it away, it comes out all in one piece.

Is this some kind of trick? No, this is not a prank, and this does happen when you put a pencil in water. But why? The answer is the refraction of light. Due to the refraction of light, a pencil appears to be broken when putting in a glass of water.


What is the refraction of light? / How does refraction work?

Refraction is the bending of light when it travels from one medium to another medium. When light crosses the boundary between both of the mediums, then there is a deviation that occurs in the path of the light ray. This phenomenon is known as refraction.

The medium from where the light is incident is called the incident medium, and the medium where refraction occurs is called a refractive medium.

Refraction is caused by the change in direction and speed of light. This happens because light travels at different speeds in different mediums.

For example, when the light travels through the air and passes into the water, the speed of light decreases, and its direction also changes.


The amount of refraction depends upon the following factors:

  • The optical density of the materials. The higher the optical density, the lower the transmittance. (Optical density – how much material is able to slow down the speed of light)
    • Opaque object – absorbs and or reflects most of the light back.
    • Transparent object – transmits most of the light.
  • The angle at which the light enters the material. NOTE: when light is incident along the normal, the ray passes without deviation.
  • Wavelength – causes colors of white light to separate when passing through a prism.

Types of refraction

When light travels from rarer (air) to a denser medium (water, glass):
  • speed of light decreases.
  • light bends towards the normal.
  • The angle of refraction is less than the angle of incidence.
When light travels from denser (water, glass) to rarer medium(air)
  • speed of light increases.
  • light bends away from the normal.
  • The angle of refraction is greater than the angle of incidence.

Examples of refraction of light

The formation of a rainbow, mirage, prism, twinkling stars, swimming pool that looks shallow than its actual depth are some of the perfect examples of refraction.

Refraction in lenses

A lens is a piece of glass or other transparent substance that refracts light. A lens concentrates or disperses rays of light when passed through them by refraction.

There are two main kinds of lenses: Concave lens and Convex lens.

Concave lens: A concave lens is thin in the middle and thicker at the edges. It is shaped like a cave. It is a diverging lens that makes light rays spread out as they pass through. As a result, when we see an object through a concave lens, it looks smaller than its actual size.

A concave lens with two inward curved surfaces is known as a bi-concave lens or double-concave lens.

Concave lenses always produce images that are:

  • upright
  • diminished
  • virtual

Convex lens: A convex lens is thicker at the centre and gets thinner as we move towards the edges. It is a converging lens that makes light rays converge as they pass through. As a result, when we see an object through a convex lens, it looks larger than its actual size.

A convex lens with two outward curved surfaces is known as a bi-convex lens or double-convex lens.

A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus.

Images produced by a camera or human eye are:

  • inverted
  • diminished
  • real

Images produced by projectors are:

  • inverted
  • magnified
  • real

Images produced by magnifying glasses are:

  • upright
  • magnified
  • virtual


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