P5.3

Question 1

What are the 3 things that can happen to a wave when it meets a material interface?

Answer 1

Reflection
Absorption
Transmission

Question 2

What does it mean for a wave to absorbed?

Answer 2

The waves energy is transferred to the to the materials energy stores.

Question 3

Give examples of when waves are absorbed.

Answer 3

• Walls absorb visible light so you need windows for the light to be transmitted and seen.
• Walls absorb UV light so you don’t get sunburnt when you are in a building.
• Gamma rays from the sun are absorbed by the atmosphere (so are normal X - Rays)
• Gamma rays from rocks can be detected in your home.

Question 4

What does it mean for a wave to be transmitted?

Answer 4

The wave travels through the new material and is refracted. at a different velocity.

Question 5

Give examples of when waves are transmitted.

Answer 5

Walls transmit radio waves and microwaves so that your mobile phones and televisions can receive the signals and function.

Question 6

What does it mean for a wave to be reflected?

Answer 6

The incoming ray isn’t absorbed or transmitted, it is sent back (reflected) away from the second material.

Question 7

Give examples of when waves are reflected.

Answer 7

Sending radio waves over long distances, the waves are reflected from the layer of atmosphere called the ionosphere.

Question 8

What are the two rays involved in reflection?

Answer 8

Incident light ray

Reflected light ray

Question 9

How does visible light let us see things?

Answer 9

Reflected visible light is bounced off of objects into our eyes.

Question 10

When drawing ray diagrams what are the rules?

Answer 10

• Reflection: Angle of Incidence = Angle of Reflection
• Draw the ‘normal’ at 90 degrees to the surface at the point where the ray hits it.
• Angles measure from the normal to the ray.

Question 11

What is specular reflection?

Answer 11

When multiple waves are reflected in a single direction by a smooth surface. This results in clear reflection.
E.g. light is reflected by a mirror.

Question 12

What is scattering in reflection?

Answer 12

Waves are reflected off a rough surface and they reflect in many directions. There is no clear image viewed as the normal is different for each incident ray.

Question 13

What happens when white light is reflected?

Answer 13

White light is a mixture of different colours with different wavelengths, all the colours reflect at the same angle so the light doesn’t split.

Question 14

What happens when a wave crosses a boundary?

Answer 14

• Waves travel at different speeds through materials with different optical densities.
• When a wave travels through different materials with different densities the speed changes as frequency stays the same but wavelength changes.

Question 15

What happens to the speed of a wave is the wavelength changes?

Answer 15

• If wavelength decreases, speed decreases vice versa.

v = f x wavelength.

Question 16

How is wavelength affected by the density of a material?

Answer 16

• If an EM wave travels into a denser material, it slows down and bends toward the normal reducing its wavelength.
• If an EM wave travels into a less dense material, it speeds up and bends away from the normal increasing its wavelength.

Question 17

Explain how a triangular prism disperses white light.

Answer 17

• Light enters prism and bends towards the normal (prism is denser than air)
• Different wavelengths of light bend by different amounts (red the least and violet the most)
• Light leaves prism bending away from the normal as it is entering a less dense material.