Refraction of waves

What happens when light is refracted in water?

It appears to change direction as it passes through the water.

What is important about when waves change speed?

Waves can change direction when they change speed, moving from one medium to another.

What happens when light passes from air into glass? (look at a diagram)

The velocity of light decreases. This causes the direction of the waves to change.

What happens when waves slow down?

They bend towards the normal.

What happens when the waves pass from the glass back to air?

Their velocity increases.

What happens when waves speed up?

They bend away from the normal. This causes the image of the object to appear to have shifted position.

When can refraction happen?

When any wave changes speed as it passes from one medium to another.

What is the exception to this rule?

If the waves enter or leave the medium at right angles to the surface then they do not change direction.

What is the wavefront?

An imaginary line that connects all the same points in a set of waves.

Why are wavefronts useful?

They make it easier to visualise lots of waves moving together.

How do wavefronts show why waves can change direction when they pass from one medium to another? (watch freescience lessons for more).

• When the first wavefronts start to move into the glass, those parts of the wavefronts slow down.

• This causes those parts of the wavefronts to get closer together. The wavelengths get smaller.