When you have your eyes tested, the optician might test different lenses in front of each of your eyes. Each lens changes the direction of light passing through it. This change of direction is known as refraction. People with sharp eyes don't need extra lenses. Each eye already has a perfectly good lens in it.
When a light ray passes through a glass block, it will:
- bend towards the normal when travelling from air to glass. . This is the refraction. The angle of refraction, 'r', is smaller than the angle of incidence, 'i'.
- bend away from the normal when travelling from the glass to the air. The angle of refraction is greater than the angle of incidence.
REFRACTION OF LIGHT IS THE CHANGE OF DIRECTION OF A LIGHT RAY WHEN IT CROSSES THE BOUNDARY BETWEEN 2 TRANSPARENT SUBSTANCES.
Refraction is a property of all forms of waves including light and sound.
The speed of light:
Light travels slower in glass than in air. When a light ray travels from air to glass, it refracts towards the normal because it slows down on entering the glass. When a light ray travels from glass to air, it refracts away from the normal because it speeds up on leaving the glass.
Refraction in a prism:
If you direct a beam of white light into a glass prism, you should find that the beam is split into the colours of the spectrum. Each colour is refracted slightly differently. This is because the speed of light in glass depends on the wavelength of the light. Blue light has a shorter wavelength than red light, so it travels slower than red light in glass. So it is refracted more than red light.