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Light wavesRefraction

Learn about the refraction of light through different materials and its different uses

Part of ScienceVibrations and waves

Refraction

is the change in speed of light as it passes from one medium (material) to another. For example, light passing from air (less dense) to glass (more dense); in this case the light slows down. If the light crossed the boundary between the two materials at an oblique angle the light would change direction.

Example: Light rays passing through a glass block

Step 1

First of three images: A light wave enters a block of glass perpendicular to the surface, then travels through and out of it in a straight line without bending. Labels indicate that the wave slows and its wavelength decreases as it enters the glass, and it returns to its original values as it returns to the air.

Step 2

An image of a light ray changing direction as it enters a glass block and again as it leave the glass block

Step 3

3/3: wave enters block at angle to surface. Angle to normal labelled 'angle of incidence' when entering & 'angle of refraction' as bent inside block. Angle of refraction less than angle of incidence.

As can be seen in the diagram the light ray changes direction as it enters and leaves the block.

In all ray diagrams, all angles of incidence and refraction are measured between the ray and the normal.

At the boundary between two transparent substances:

  • the light slows down going into a denser substance, and the ray changes direction towards the normal
  • the light speeds up going into a less dense substance, and the ray changes direction from the normal

Refraction explains why an object appears to bend when it goes through water.

Pencil appearing bent due to light refraction of water
Refraction at the boundary between air and water
A boy looks into a pond containing a fish. Arrows show that the light from the fish to the boy's eyes leaves the water at an angle, so the fish is actually lower in the water than it appears. The apparent depth and actual depth are labelled.
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