5.4 Refraction
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Waves can be refracted when they cross a boundary between two substances that have different densities. Refraction changes the speed of a wave, which can change the waves’ direction. Waves travel at different speeds through different substances. A wave will travel more slowly through a denser substance compared to a less dense substance. If a wave hits a boundary between two substances, the wave continues in the same direction. However, when a wave hits the denser substance on an angle, the waves change direction because of refraction.
Glass Window Example
When light hits a glass window, most of it can pass through the glass. Some of the light is reflected off from the glass window at the same angle that it hits the window (remember that the angle of incidence is equal to the angle of reflection and remembering that both angles are measured against the normal). The glass is denser than air and this causes the waves to slow down. As the right side of the wave enters the glass first, the right side of the wave slows down first. This results in the wave changing its direction (moving in a direction more to the right). When the light reaches the other side of the glass, it is refracted again because the wave hits a new substance. The right side of the wave enters the air first and this part of the wave speeds up, resulting in the wave going in a direction that is more to the left. Most of the light enters the air on the other side of the window, but some of the waves are reflected as the light enters the air.
When light hits a glass window, most of it can pass through the glass. Some of the light is reflected off from the glass window at the same angle that it hits the window (remember that the angle of incidence is equal to the angle of reflection and remembering that both angles are measured against the normal). The glass is denser than air and this causes the waves to slow down. As the right side of the wave enters the glass first, the right side of the wave slows down first. This results in the wave changing its direction (moving in a direction more to the right). When the light reaches the other side of the glass, it is refracted again because the wave hits a new substance. The right side of the wave enters the air first and this part of the wave speeds up, resulting in the wave going in a direction that is more to the left. Most of the light enters the air on the other side of the window, but some of the waves are reflected as the light enters the air.
Beyond a certain angle (known as the critical angle), all waves are reflected off a substance. An example of where this occurs is optical fibres. Optical fibres use infrared waves or visible light to send information across long distances. The waves are reflected off the sides of the optical fibre.
We can work out the angles of refraction by using Sneel’s law but this is not required for AQA Physics unit 1.
We can work out the angles of refraction by using Sneel’s law but this is not required for AQA Physics unit 1.