P14 Light

Question 1

What is the RULE for all reflection RAY DIAGRAMS?

Answer 1

Angle of incidence = Angle of reflection

• the ‘normal’ is the imaginary line perpendicular to the boundary
• the angle of incidence is the angle between the incoming ray and the normal
• the angle of reflection is the angle between the ‘normal’ and the reflected ray

Question 2

What is specular reflection?

Answer 2

When a wave is reflected in a single direction by a smooth surface

E.g. when light is reflected by a mirror and you get a clear reflection

Question 3

What us Diffuse reflection?

Answer 3

When a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions

The rule - (Angle of incidence = angle of reflection) still applies

Question 4

What is refraction?

Answer 4

• When a wave crosses a boundary between materials at an angle, it changes direction
• how much it changes direction depends on how much the wave speeds up or slows down
• this depends on the density of the material

Question 5

How do you talk about the change in direction of a wave

Answer 5

• If a wave crosses a boundary at an angle and slows down, it will bend towards the normal
• If it speeds up then it will bend away from the normal

(The ‘normal’ is perpendicular to the boundary)

Question 6

What happens to the wavelength and the frequency when a wave is refracted?

Answer 6

• Wavelength will change

- Frequency will stay the same

Question 7

When is a wave NOT refracted but still crosses a boundary

Answer 7

When the wave is travelling along the ‘normal’

Question 8

What is optical density?

Answer 8

• Optical density is a measure of how quickly light can travel through it
• The more optically dense material, the slower the light waves travel through it

Question 9

What are the 2 main types of lens?

Answer 9

Convex () and concave )(

Question 10

What is a convex lens?

Answer 10

• A convex lens bulges outwards ()

- It causes light rays that are parallel to the axis to be brought together (converge) at the principal focus

Question 11

What is a concave lens?

Answer 11

• A concave lens caves inwards )(

- It causes light rays to spread out (diverge)

Question 12

What is the ‘axis’ of a lens

Answer 12

A line passing though the centre of the lens

Question 13

What is the principal focus for a CONCAVE lens?

Answer 13

• The point where rays hitting the lens parallel to the axis appear to all come from
• You can trace the refracted rays back to the principal of focus

Question 14

What is the focal length?

Answer 14

The distance from the centre of a lens to the principal focus is the focal length.

Question 15

What are the 3 RULES for refraction in a convex lens ()

Answer 15

• An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
• An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
• An incident ray passing through the centre of the ray carries on in the same direction.

Question 16

What are the 3 RULES for refraction in a convex lens )(

Answer 16

• An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus so it appears to come from the principal focus
• An incident ray passing through the lens towards the centre of principal focus refracts through the lens and travels parallel to the axis
• An incident ray passing through the centre of the lens carries on in the same direction

Question 17

What lenses produce what images?

Answer 17

• The image produced by a convex lens can be either real or virtual.
• The image produced by a concave lens is always virtual.

Question 18

What is the equation for magnafication?

Answer 18

IAM triangle

Magnification = image height / object height

Question 19

How do colour filters work?

Answer 19

Colour filters work by absorbing certain wavelengths (and colour)
and transmitting other wavelengths (and colour).

Question 20

How are objects black or white?

Answer 20

Black objects absorb all wavelengths of visible light. Your eyes see black as a lack of visible light

White objects reflect all wavelengths of visible light equally

Question 21

What are objects that transmit light called?

Answer 21

Partially transmit light - Translucent

Fully transmit light - Transparent

Question 22

Draw a ray diagram for a convex lens

Answer 22

Cool

Check in cgp

Question 23

Draw ray diagram for a concave lens

Answer 23

Cool check cgp

Question 24

What determines the colour of an opaque object?

Answer 24

The wavelengths of light that are most strongly reflected