P14 - Light

Question 1

What is the angle of incidence?

Answer 1

The angle between the incident ray and the normal

Question 2

What is the angle of reflection?

Answer 2

Angle between the reflected ray and the normal

Question 3

What is diffuse reflection?

Answer 3

Reflection from a rough surface - the light rays are scattered in different directions

Question 4

What is the normal?

Answer 4

A straight line through a surface or boundary perpendicular to the surface or boundary

Question 5

What is a real image?

Answer 5

An image formed by a lens that can be projected onto a screen

Question 6

What is refraction?

Answer 6

The change of direction of a light ray as it passes across a boundary between 2 transparent substances

Question 7

What is specular reflection?

Answer 7

Reflection from a smooth surface. Each light ray is reflected in a single direction

Question 8

What is a virtual image?

Answer 8

An image, seen in a lens or a mirror, from which light rays appear to come after being refracted by a lens or reflected by a mirror. They cannot be projected onto a screen

Question 9

When would sound be relfected?

Answer 9

In an echo

Question 10

What is the law of reflection?

Answer 10

The angle of incidence = the angle of reflection

Question 11

What is reflection on a smooth surface known as and why?

Answer 11

Specular reflection, this is because parallel light rays are reflected in a single direction, they are not scattered. Each of the incident angles are the same, therefore each of the angles of reflection are the same

Question 12

What is reflection on a rough surface known as and why?

Answer 12

diffuse reflection, this is because parallel light rays reflected from a rough surface are scattered in different directions. Each of the incident angles are different, therefore each of the angles of reflection are different

Question 13

What happens to the velocity of a wave as it travels from an optically rare medium to an optically dense medium?

Answer 13

decreases

Question 14

What happens to the wavelength of a wave as it travels from an optically rare medium to an optically dense medium?

Answer 14

Decreases

Question 15

What happens to the frequency of a wave as it travels from an optically rare medium to an optically dense medium?

Answer 15

does not change

Question 16

What happens to the direction of a wave as it travels from an optically rare medium to an optically dense medium?

Answer 16

bends towards the normal

Question 17

What happens to the velocity of a wave as it travels from an optically dense medium to an optically rare medium?

Answer 17

increases

Question 18

What happens to the wavelength of a wave as it travels from an optically dense medium to an optically rare medium?

Answer 18

increase

Question 19

What happens to the frequency of a wave as it travels from an optically dense medium to an optically rare medium?

Answer 19

Does not change

Question 20

What happens to the direction of a wave as it travels from an optically dense medium to an optically rare medium?

Answer 20

bends away from the normal

Question 21

What causes refraction?

Answer 21

Waves change speed as they pass between substances of different densities, this causes them to change direction

Question 22

What is the law of refraction?

Answer 22

• If the light ray moves from a less dense medium into a dense medium, the wave bends towards the normal. Therefore the angle of refraction is smaller than the angle of incidence
• If the light ray moves from a more dense medium into a less dense medium, the wave bends away from the normal. Therefore the angle of refraction is greater than the angle of incidence

Question 23

Describe what occurs when light travels from air into a glass block and then back out into air:

Answer 23

When light enters the glass block, it slows down, this is because glass is more dense than air. The wavelength of the light ray decreases and the direction of the wave moves towards the normal. As the ray moves out of the glass block into air it speeds up, this is because air is less dense than glass. The wavelength of the light ray increases and the direction moves away from the normal line.

Question 24

Describe the investigation in order to investigate refraction of light:

Answer 24

1) Place the glass block in the centre of the piece of paper and draw around the perimeter of the box
2) remove the block and draw a dotted normal line perpendicular to the edge of the long side of the block, roughly half way along
3) Draw a line to represent the incident ray 30* to the normal
4) Place the glass block back within the rectangle you have drawn
5) Switch on the ray box with a narrow slit in front of the light bulb and shine the ray along the incident ray you have drawn
6) Observe the path of the light through the block and out the other side
7) Mark the path of the emergent light ray on the other side
8) Remove the glass block. Draw a normal at the point where the light emerged from the glass block.
9) Draw a line to join the incident ray and emergent ray through the rectangle representing the glass block to give the refracted ray
10) Measure the incident and refracted angles
11) Repeat experiment with a range of angles for the incident ray
12) Repeat experiment and find mean average for each result

*Possible inaccuracies:
The width of the light ray may make it difficult to draw along the centre of the line

Question 25

Explain what happens if white light is shone through a prism

Answer 25

White light is made from all the colours of the colour spectrum. As different colours have a different frequency and a different wavelength, they travel at different speeds through the glass of the prism, so they get refracted at different amounts, which allows the prism to split white light into the spectrum

Question 26

What is the wavelength and frequency of Violet light (closest to ultraviolet and x rays)

Answer 26

short wavelength, high frequency

Question 27

What is the wavelength and frequency of red light (closest to infrared and microwaves)

Answer 27

long wavelength, low frequency

Question 28

Why are some lights different colours?

Answer 28

Light is a type of electromagnetic wave. The only difference between the different colours of light are the wavelength / frequency of the electromagnetic wave

Question 29

What is said to happen when white light splits up into separate colours?

Answer 29

White light has been dispersed

Question 30

What light is refracted the most?

Answer 30

Violet (short wavelength, high frequency)

Question 31

What light is refracted the least?

Answer 31

Red light (long wavelength, low frequency)

Question 32

Describe the image formed by a plane mirror

Answer 32

The image is virtual, upright, the same size as the object, and the same distance behind the mirror as the object is infront

Question 33

Draw the ray diagram for the image formed on a plane mirror:

Answer 33

Question 34

What 3 things may occur when a wave arrives at a boundary?

Answer 34

• The wave may be absorbed by the material the wave is trying to cross into - this transfers energy to the materials energy stores
• The wave may be transmitted - the waves carry on travelling through the new material. This often leads to refraction
• The wave is reflected

Question 35

Describe what occurs when light travels from air into a glass block and then back out into air:

Answer 35

When light enters the glass block, it slows down, this is because glass is more dense than air. The wavelength of the light ray decreases and the direction of the wave moves towards the normal. The wave may have a slightly lower amplitude and carry less energy than the incident ray as some light may have been reflected or absorbed by the glass block. As the ray moves out of the glass block into air it speeds up, this is because air is less dense than glass. The wavelength of the light ray increases and the direction moves away from the normal line.