Chapter 9 - Light

Question 1

Draw the diagram to show how we see a object in a mirror.

Answer 1

Do it it’s very important

Question 2

What are the features of an image in a mirror ?

Answer 2

• virtual
• the same size as the object
• laterally inverted
• the same distance behind the mirror as in front of the mirror

Question 3

What is the speed of light in air (or vacuum) , water and glass ?

Answer 3

Air (or vacuum) : 3 x 10^8
Water: 2.25 x 10^8
Glass: 2 x 10^8

Question 4

What is the definition of refraction ?

Answer 4

Where a (light) wave passes from one material into another and change in the wave speed results in a change in wave speed

Question 5

What is the angle between the incident ray and the normal called ?

Answer 5

angle of incedence

Question 6

What is the angle between the normal and the refracted ray called ?

Answer 6

angle of refraction

Question 7

What is the angle between the emergent ray and the normal called ?

Answer 7

angle of emergence

Question 8

When light speeds up which way does it bend ?

Answer 8

Away from the normal

Question 9

When light slows down which way does it bend ?

Answer 9

Towards the normal

Question 10

What are the colours of the spectrum in order of fastest to slowest ?

Answer 10

Fastest: red
orange
yellow
green
blue
indigo 
Slowest: violet

Question 11

What is dispersion ?

Answer 11

When light is passed through a triangular glass block, the effect called dispersion and you can see a spectrum of all the colours of the rainbow

Question 12

What is the critical angle ?

Answer 12

The critical angle is the angle of incidence in a material for which the angle of refraction in air is 90*

Question 13

What happens at angles of incidence less than the critical angle ?

Answer 13

at angles of incidence les than the critical angle, both reflection and refraction occur

Question 14

What happens at angles of incidence greater than the critical angle ?

Answer 14

at angles greater than the critical angle , no refraction occurs and the light is totally internally reflected

Question 15

When does total internal reflection occur in parallel-sided glass blocks ?

Answer 15

At angles of incidence above the critical angle

Question 16

Why is monochromatic light used ?

Answer 16

it is used to avoid unwanted dispersion

Question 17

Read page 119 in text book

Answer 17

Hard to write fc for so

Question 18

What are optical fibres ?

Answer 18

optical fibres are lengths of solid glass core with an outer plastic sheath

Question 19

What are optical fibres used for ?

Answer 19

To transmit both telephone and video signals over long distances

Question 20

Why are optical fibres so good ?

Answer 20

They can carry much more information than a copper wire of the same diameter

Question 21

What is one use of optical fibres in medicine ?

Answer 21

Endoscope are made up of optical fibres and allow the doctor to look inside the patients body. They allow light to travel into the body and allow image info to be passed back out.

Question 22

What are the two main types of lens ?

Answer 22

Converging and diverging

Question 23

Draw a converging lens

Answer 23

Fatter one

Question 24

Draw a diverging lens

Answer 24

Thinner one

Question 25

What are the two features of a converging lens ?

Answer 25

- Rays of light parallel to the principal axis of a converging lens all converge to the same point on the other side of the lens - This point is called the principal focus

Question 26

What are the two features of a diverging lens ?

Answer 26

- Rays of light parallel to the principal axis of a diverging lens all appear to diverge from the same point after refraction in the lens - This point lies on the principal axis, and is called the principal focus

Question 27

What is the definition of focal length ?

Answer 27

The distance between the principal focus and the optical centre, C, of any lens is called the focal length

Question 28

Look at page 126 and draw the ray diagrams

Answer 28

DO IT PLEASE.

Question 29

Where does most refraction of light occur in the eye ?

Answer 29

The cornea

Question 30

What is the purpose of the lens in the eye ?

Answer 30

To produce a sharp image on the retina

Question 31

What is the optical nerve ?

Answer 31

How nerve endings pass messages to the brain

Question 32

What is the far point ?

Answer 32

The farthest point hat can be seen clearly by the eye is called the far point

Question 33

How long is the far point for the eye ?

Answer 33

infinity

Question 34

How does light from afar reach the eye ?

Answer 34

Light rays from a far reaches the eye as parallel rays. The rays are refracted by the cornea and lens so the image is sharp on the retina.

Question 35

What is the near point ?

Answer 35

The nearest point that can be seen clearly with the unaided eye without causing muscles to strain is called the near point.

Question 36

How long is the near point ?

Answer 36

About 25cm

Question 37

How does light get to the eye from the near point ?

Answer 37

The light reaches the eye from the near point as diverging rays.

Question 38

What is another name for short sightedness ?

Answer 38

myopia

Question 39

What are people with myopia unable to do ?

Answer 39

They cannot make the lens thin enough to view distant objects. This causes the light to converge just in front of the retina making the image blurry.

Question 40

How do you correct myopia ?

Answer 40

A diverging lens is used. The light diverges just before just before the eye. The lens and the cornea can then bring these diverging rays to a shar focus on the retina.

Question 41

What is the other name for long sightedness ?

Answer 41

hypermetropia

Question 42

What can a person with hypermetropia not do ?

Answer 42

Their eye muscles are not strong enough to make the lens thick enough for the light to form a sharp object

Question 43

How do you correct hypermetropia ?

Answer 43

Use a converging lens. This light is now less diverging then before. The cornea and the eye lens can now bend the light so that a sharp image is formed on the retina