(WVS) Refraction Lesson

Refraction

Refraction occurs when waves bend as they enter a new medium at an angle. You can see an example of refraction in the picture of the pencil in a glass of water. Light bends when it passes from air to water. The bending of the light causes the pencil to appear broken.

Why do waves bend as they enter a new medium? Waves usually travel at different speeds in different media. For example, light travels more slowly in water than in air. This causes it to refract when it passes from air to water.

Considering a group of soldiers marching into a muddy field at an angle to their direction of travel can explain how a beam of light will be refracted. As the soldiers try to stay in a line, the direction of travel would bend because marching in mud would slow them down, starting with the first group to enter the field. Then, as they leave the muddy area, they go to their original speed, thus bending the direction of travel again. The original direction and the final direction are parallel but displaced.

The same thing happens when a beam of light enters a transparent material at an angle.

Why is it important that fishermen using a spear understand the principle of refraction? If not, then they would never be able to catch any fish.

This is because as the light from the fish leaves the water it bends away from the normal (right-angled line to the surface) making the fish appear to be nearer to the surface. If the fisherman aims at the center of the fish the spear will miss (the spear passing in front of the fish).

However, if they aim at where they think the tail is, then they will hit the body of the fish. (All this assumes that they are standing behind the fish when they throw the spear).

The picture below shows the case where the fisherman aims along the line where they think the tail of the fish is and hits the body of the fish (dotted line).

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION