Can light bend? REFRACTION - WordPress.com · 2016. 3. 16. · 2) Refraction occurs because: A...

$: Can light bend? REFRACTION - WordPress.com · 2016. 3. 16. · 2) Refraction occurs because: A light speeds up when it goes from air to glass or water B light slows down when it goes$
REFRACTION

Can light bend?

3/16/2016 ©cgrahamphysics.com 2016

Have you ever wondered

Disappearing Coin Trick

Can you explain what happens?


Refraction Of Light in water - Disappearing Coin Trick - Исчезающая монета Magic.mp4

Refraction Of Light in water - Disappearing Coin Trick - Исчезающая монета Magic.mp4

Refraction

Starter: Why does the pencil appear bent in the water?


•The pencil appears bent because light travels at different speeds in different materials.

•This causes the light to bend/refract.

•Refraction is the change in the direction of light.


Objectives:

• Describe what happens to light when it passes through materials of different densities

• Draw ray diagrams to show refraction of light

Key word

• Refraction – the bending of light when it passes through a different medium

Refraction


3/16/2016

Imagine you’re running along this beach and then into the

water. Would you be moving slower in the water or on the

beach?

• The speed of light also changes from one medium to another-

as the density changes.

• How do you think the speed of light changes with density?

©cgrahamphysics.com 2016

Refraction at an air-glass boundary


Angle of Incidence (°)

Angle of Refraction (°)

0

30

42

60

90

• An investigation to find out what happens when light travels through a glass block

• Draw table.....

Investigating Refraction


Refraction in a glass block


1) Draw around a rectangular block

2) Draw a normal line 90º from the top of the block

3) Shine light into the block, making sure it hits it where the normal line crosses the glass surface.

•Angle i

•Angle r

4) Draw the rays of light entering and leaving your block onto your paper

5) Remove the block and draw a line across the block

Investigation


Investigation Questions:

1) What happens to the ray as it enters the glass?

2) What happens to the ray as it re-enters the air?


angle of incidence > angle of refraction i > r

If light rays move

from a less dense medium (air) to a more dense medium (glass) they move towards the normal.

i > r

•Air to Glass:


angle of incidence < angle of refraction i < r

If light rays move from a more dense medium (glass) to a less dense medium (air) they ‘move’ away from the normal.

i < r

•Glass to Air:


Refraction ray diagram


The archer fish is a predator that shoots jets of water at insects near the surface of the water.

Effects of refraction – the Archer fish

The archer fish allows

for the refraction of

light at the surface

of the water when

aiming at its prey.

The fish does not

aim at the refracted

image it sees but at

a location where it

knows the prey to be.

image of

prey

prey

location


Why is light refracted? The speed of light depends on the material through which the

light is travelling. When light enters a different material (e.g.

when moving from air into glass), the speed of light changes.

This causes the light to bend or refract.

The speed of light is affected by the density of the

material through which it is travelling.

When light enters a more dense medium, its speed

decreases and this is why refraction occurs.

air

glass


Effects of refraction Light from the part of the pencil in the

water is refracted as it travels from the

water into the air, making it appear bent.

Light rays from the stone are

refracted as they leave the water.

How does refraction make this

stone look closer to the surface

of the water than it really is?

The brain assumes the rays

have travelled in straight lines,

and is fooled into forming an

image where it thinks the light

rays came from. 3/16/2016 ©cgrahamphysics.com 2016

When light bends this

is called ----------

---------- happens because the light changes speed.

When light enters a ---- dense medium [e.g. glass],

it bends ------ the normal.

When light enters a ---- dense medium [e.g. air], it

bends --------the normal.

more

less

refraction

Refraction

towards

away from 3/16/2016 ©cgrahamphysics.com 2016

Uses of Refraction?

Lenses: • Your eye • Magnifying glass • Spectacles • Cameras • Telescopes • Microscopes


Refraction – true or false?


Plenary: Answer A, B, C or D

1) Refraction is what happens when light:

A hits an opaque object B bounces off a mirror C is scattered unevenly by a rough surface D changes direction as it goes from one substance into another



2) Refraction occurs because:

A light speeds up when it goes from air to glass or water B light slows down when it goes from air to glass or water C light stops when it goes from air to glass or water D light reflects inside transparent materials 3/16/2016 ©cgrahamphysics.com 2016


3) Why does a lens change the path of light?

A Light changes direction when it goes into the glass and when it comes out of it B Light changes direction in the centre of the lens C Light is reflected by the surface of the lens D Light travels faster in glass than it does in air


Can light bend? REFRACTION - WordPress.com · 2016. 3. 16. · 2) Refraction occurs because: A...

Documents

Transcript of Can light bend? REFRACTION - WordPress.com · 2016. 3. 16. · 2) Refraction occurs because: A...