Refraction of waves

Question 1

how does refraction occur

Answer 1

Refraction occurs when a wave slows down or speeds up at a boundary between two materials.

Question 2

how can waves be refracted?

Answer 2

1) Waves travel at different speeds in substances which have different densities. EM waves travel more slowly in denser media (usually). Sound waves travel faster in denser substances.
2) So when a wave crosses a boundary between two substances, from glass to air, say, it changes speed.

Question 3

Draw a ray diagram for a refracted wave?

Answer 3

1) First, start by drawing the boundary between your two materials and the normal (a line that is at 90˚ to the boundary).
2) Draw an incident ray that meets the normal at the boundary.
3) The angle between the ray and the normal is the angle of incidence. (If you’re given this angle, make sure to draw it carefully using a protractor.)
4) Now draw the refracted ray on the other side of the boundary.
5) If the second material is denser than the first, the refracted ray bends towards the normal (like on the right). The angle between the refracted ray and the normal (the angle of refraction) is smaller than the angle of incidence.
6) If the second material is less dense, the angle of refraction is larger than the angle of incidence.

Question 4

Practical Experiment

Draw and explain rays paasing through a glass block are refracted twice?

Answer 4

1) You can experiment with refraction using a light source and a rectangular block of a particular material (e.g. glass) resting on top of a piece of paper…
2) Shine a light ray at an angle into the block, as shown. Some of the light is reflected, but a lot of it passes through the glass and gets refracted as it does so.
3) Trace the incident and emergent rays on to the paper and remove the block. You can draw in the refracted ray through the block by joining the ends of the other two rays with a straight line.
4) You should see that as the light passes from the air into the block (a denser medium), it bends towards the normal. This is because it slows down.
5) When the light reaches the boundary on the other side of the block, it’s passing into a less dense medium. So it speeds up and bends away from the normal. (Some of the light is also reflected at this boundary.)
6) The light ray that emerges on the other side of the block is now travelling in the same direction it was to begin with — it’s been refracted towards the normal and then back again by the same amount.

Question 5

Practical Experiment

How does triangulat prisms disperse wjite light?

Answer 5

1) You’ll get an interesting effect if you shine white light into a triangular prism.
2) Different wavelengths of light refract by different amounts, so white light (which is a mixture of all visible frequencies) disperses into different colours as it enters the prism and the different wavelengths are refracted by different amounts.
3) A similar effect happens as the light leaves the prism, which means you get a nice rainbow effect.

Question 6

What is refraction?

Answer 6

• A change in direction of waves when they travel across a boundary from one medium
  to another

Question 7

Describe how a light ray changes direction when it enters and leaves a glass block?

Answer 7

• Bends towards the normal as it enters the block
• Bends away from the normal as it leaves the block