Topic 6 - light, colour, lenses

Question 1

What three things can happen when a wave reaches a boundary between two different materials?

Answer 1

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

Question 2

What is the law of reflection?

Answer 2

Angle of incidence = Angle of reflection

Question 3

What is the angle of incidence?

Answer 3

The angle between the incoming wave and the normal

Question 4

What is the angle of reflection?

Answer 4

The angle between the reflected wave and the normal

Question 5

What is the normal?

Answer 5

The normal is an imaginary line that is perpendicular to the surface at the point of incidence

Question 6

What is specular reflection?

Answer 6

Specular reflection happens when a wave is reflected in a single direction by a smooth surface

Question 7

What is diffuse reflection?

Answer 7

1. Diffuse reflection is when a wave is reflected by a rough surface and the reflected waves are scattered in lots of different directions
2. This happens because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray
3. When light is reflected by a rough surface, the surface appears matte, and you dont get a clear reflection of objects

Question 8

What happens when a wave crosses a boundary between materials at an angle?

Answer 8

It changes direction - it is refracted

Question 9

What affects how much a wave is refracted?

Answer 9

1. How much the wave speeds up or slows down
2. This usually depends on the density of the two materials

Question 10

How does density affect refraction?

Answer 10

1. Usually, the higher the density of a material, the slower a wave travels through it
2. If a wave crosses a boundary and slows down it will bend towards the normal
3. If a wave crosses a boundary and speeds up, it will bend away from the normal

Question 11

How do wavelength and frequency change when a wave is refracted?

Answer 11

1. The wavelength changes
2. The frequency stays the same

Question 12

What is optical density?

Answer 12

A measure of how quickly light can travel through a material - the higher the optical density, the slower light waves travel through it

Question 13

What are the primary colours of light?

Answer 13

Red, blue and green

Question 14

Define opaque objects in terms of light?

Answer 14

1. Opaque objects do not transmit light
2. They absorb some wavelengths and reflect others

Question 15

What does the colour of an opaque object depend on?

Answer 15

1. The colour depends on which wavelengths of light are most strongly reflected
2. A red apple appears to be red because the wavelengths corresponding to the red part of the visible spectrum are most strongly reflected
3. The other wavelengths are absorbed

Question 16

Describe white objects?

Answer 16

White objects reflect all of the wavelengths of visible light equally

Question 17

Describe black objects?

Answer 17

Black objects absorb all wavelengths of visible light

Question 18

Describe transparent and translucent objects?

Answer 18

1. They transmit light - some can pass through

Question 19

Colour filters?

Answer 19

1. Colour filters only let through particular wavelengths
2. Colour filters are used to filter out different wavelengths of light, so that only certain colours are transmitted
3. A primary colour filter only transmits that colour - if a white light is shone at a blue colour filter, only blue light will be let through, the rest of the light will be absorbed
4. If you look at an object through a blue filter than isn’t blue, the object would appear black. All of the light reflected by the object will be absorbed by the filter except blue light

Question 20

What are lenses?

Answer 20

1. Lenses form images by refracting light and changing its direction

Question 21

Describe a convex lens?

Answer 21

1. A convex lens bulges outwards
2. It causes rays of light parallel to the axis to converge at the principal focus

Question 22

Describe a concave lens?

Answer 22

1. A concave lens caves inwards
2. It causes parallel rays of light to diverge (spread out)

Question 23

What is the axis?

Answer 23

1. The axis of a lens is a line passing through the middle of the lens

Question 24

What is the principal focus of a convex lens?

Answer 24

1. The principaal focus of a convex lens is where rays hitting the lens parallel to the axis all meet

Question 25

What is the principal focus of a concave lens?

Answer 25

1. The principal focus of a concave lens is the point where rays hitting the lens parallel to the axis appear to all come from

Question 26

What are the three rules for refracton in a convex lens?

Answer 26

1. An incident ray parallel to the axis refacts light through the lens and passes through the principal focus on the other side 2. An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis 3. An incident ray passing through the cetnre of the lens carries on in the same direction

Question 27

What are the three rules for refracton in a concave lens?

Answer 27

1. An incident ray parallel to the axis refracts through the lens, and travels in line with the principal focus 2. An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis 3. An incident ray passing through the cetnre of the lens carries on in the same direction

Question 28

What is a real image?

Answer 28

A real image is where the light from an object comes together to form an image on a screen

Question 29

What is a virtual image?

Answer 29

A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place