Refraction

Question 1

“The speed of light is greater than the speed of sound.”

True or false?

Answer 1

True.

Speed of sound = 330 metres per second

Speed of light = 300,000,000 metres per second.

Question 2

If a person is short-sighted (cannot see far-away objects clearly), what type of lens should they use to correct this?

Answer 2

A short-sighted person will need to use a concave lens.

Question 3

Draw a diagram to show rays of light in the eye of a person who is long-sighted.

Answer 3

Question 4

Name three devices which use lenses.

Answer 4

Telescope, binoculars, spectacles, magnifying glass, projector, camera, CD player…

Question 5

What eyesight defect is shown in this diagram?

Answer 5

This person is long-sighted.

Question 6

If a person is long-sighted (cannot see close-up objects clearly), what type of lens should they use to correct this?

Answer 6

A long-sighted person will need to use a convex lens.

Question 7

Does the diagram attached show a magnifying glass (producing a virtual image) or a projector (producing a real image)?

Answer 7

The diagram shows a magnifying glass used to produce a virtual image.

Question 8

What happens to the speed of light when it goes from perspex into air?

Answer 8

The speed increases (the light speeds up).

Question 9

What happens to the speed of light when it goes from water into air?

Answer 9

The speed increases (the light speeds up).

Question 10

What happens to the speed of light when it goes from air into water?

Answer 10

The speed decreases (the light slows down).

Question 11

Draw a ray diagram to show how light travels through a magnifying glass to form an image.

Answer 11

This is not easy. See diagram:

Question 12

Draw a diagram to show a convex lens.

Answer 12

Question 13

What is refraction?

Answer 13

Refraction is when light ‘bends’ (changes direction) when it enters or exits another material.

Question 14

Describe an experiment to measure the focal length of a lens.

Answer 14

• hold the lens up against a wall or plain surface
• move the lens slowly away from the wall until you get a clear focused image of a distant object
• measure the distance from the wall to the lens

Question 15

Draw a diagram to show rays of light in the eye of a person who is short-sighted.

Answer 15

Question 16

Draw a diagram to show parallel rays of light travelling through a convex lens.

Answer 16

Question 17

What eyesight defect is shown in this diagram?

Answer 17

This person is short-sighted.

Question 18

What happens to the speed of light when it goes from air into glass?

Answer 18

The speed decreases (the light slows down).

Question 19

Draw a diagram to show a concave lens.

Answer 19

Question 20

Draw a diagram to show light travelling through a concave lens.

Answer 20

Question 21

If a person needs to wear glasses when going to the cinema, but they can read their phone screen without any problem, what type of sight defect do they have?

Answer 21

The person is short-sighted.

Question 22

If a person needs to wear glasses to read a book, but they can drive their car and see objects around them without any problem, what type of sight defect do they have?

Answer 22

The person is long-sighted.

Question 23

“Light travels in straight lines.”

True or false?

Answer 23

True. Light does travel in straight lines.

It cannot ‘bend’ around a corner.

It can only change direction when it enters a different material.

Question 24

Why does light change direction when it enters (or exits) a different material?

Answer 24

When light enters a different material, it changes speed. This (sometimes) causes it to change direction.

(If the light ray is entering at 90°, it will keep going in the same direction)

Question 25

Name three applications of lasers.

Answer 25

CD/DVD players, barcode readers, laser eye surgery, cutting materials, carrying signals through optical fibres…