Do Now Reflection Question

Do Now Reflection Question

Refraction

Today’s lesson

• Refraction of light• Refraction of light by a

prism is called dispersion • Please remember to

remain in you seats unless given permission

• Mirror Island Homework due in

The mug trick!

Refraction of light

Glass block

Beam of light

Glass block

Beam of light

WHY?

7 of 45 © Boardworks Ltd 2009

A model for refraction

Refraction in a glass block

Refraction

Glass block

Beam of lightLight going from air to glass bends towards the normal

Light going from glass to air bends away from the normal

Refraction

Glass block

Ray of light

A light ray entering along the normal continues in a straight line.

Do Now Can you

carefully add this diagram & notes

to your book?

Today’s lesson

• Refraction of light• Refraction of light by a

prism is called dispersion • Please remember to

remain in you seats unless given permission

• Mirror Island Homework due in today

Please stick into your book; use a double page

and then fill in.

Light waves

Light slows down as it goes from air to glass/water

its speed changes from 3 x 108 m/s to

2 x 108 m/s

or from 300 000 km/s to 200 000 km/s

Water waves

Water waves travel slower in shallow water

Wavelength and speed effects

Refraction – a few notes

The wavelength changes, the speed changes, but the frequency stays the same.

when a waves direction is changed it is deviated (deviation)

Ripple Tank Simulation

Refraction experiment

Typical results air to glass:angle of

incidence / °angle of

refraction / °deviation / °

0 0 0

15 10 5

30 19 11

45 28 17

60 35 25

75 40 35

No deviation occurs when the angle of incidence is zero.

Increasing the angle of incidence increases the deviation.

Refraction experiment Air to Perspex

Typical results air to Perspex :angle of

incidence / °angle of

refraction / °deviation / °

0

15

30

45

60

75

Complete the paths of the RED light rays:

A

B

C

D

E

F

Let’s try some drawing!

object at the bottom of a pool

AIR

WATER

Why a pool appears shallow

image

normals

observer

prism

Refraction by a prism – copy pleaseA prism splits the colours of white light

into the spectrum.

This is called dispersion.

Violet light deviates the most it has the shortest wavelength,

red the deviates the least it has the longest wavelength.

spectrum

whitelight

Choose appropriate words to fill in the gaps below:

Refraction occurs when a wave changes ______ as it crosses the boundary between two regions. The _________ of the wave also usually changes.

Light rays deviate ________ the normal when they pass from less dense air to more dense _________. The greater the angle of incidence the greater is the _________.

Different ______ of light deviate by different amounts. Violet deviates the _____. A prism can be used to split the colours of white light into a spectrum. This is called _________.

most speeddirectiondeviation coloursperspextowards

WORD SELECTION:

dispersion

most

speed

direction

deviation

colours

perspex

towards

dispersion

Refraction

When a wave changes speed (normally when entering another medium) it may refract (change direction)

Ripple Tank Simulation

Choose appropriate words to fill in the gaps below:

Refraction occurs when a wave changes ______ as it crosses the boundary between two regions. The _________ of the wave also usually changes.

Light rays deviate ________ the normal when they pass from less dense air to more dense _________. The greater the angle of incidence the greater is the _________.

Different ______ of light deviate by different amounts. Violet deviates the _____. A prism can be used to split the colours of white light into a spectrum. This is called _________.

most speeddirectiondeviation coloursperspextowards

WORD SELECTION:

dispersion

most

speed

direction

deviation

colours

perspex

towards

dispersion

Do Now and finish reflection and refraction sheet

Solar bottle

Today’s lesson

Refraction of lightRefraction index Snell’s Law

27 of 45 © Boardworks Ltd 2009

Refractive index is calculated by comparing speed of light in a vacuum to that in a given medium:

The speed of light in a vacuum is 300,000,000 m/s, and the speed of light in water is 225,000,000 m/s. What is the refractive index of water?

refractive index = 300,000,000 225,000,000

refractive index = speed of light in vacuum speed of light in medium

Refractive index is a measure of how much a substance slows down light. The higher its value, the more a medium slows light. The more the light is slowed, the more it bends towards the normal.

Refractive index

= 1.33

28 of 45 © Boardworks Ltd 2009

Use the information in the diagram to find the refractive index of glass.

refractive index (n) = sin i sin r

refractive index = sin 45° sin 28°

The refractive index can also be calculated using Snell’s Law, which uses the angle of incidence (i) and angle ofrefraction (r) to establish how much a medium slows light.

Snell’s Law

refractive index = 1.5

normal

29 of 45 © Boardworks Ltd 2009

Using Snell’s Law

If a ray of light enters water at an angle of 15° and has an angle of refraction of 11.2°, find its refractive index.

refractive index = sin 15 sin 11.2

Use Snell’s Law to answer the following:

refractive index = 1.33

Let’s try some questions!

31 of 45 © Boardworks Ltd 2009

Using Snell’s Law

Perspex has a refractive index of 1.5. If a ray of light passing into a perspex block has an angle of refraction of 24°, find the angle of incidence.

sin i = sin r × refractive index

Use Snell’s Law to answer the following:

sin i = (sin 24°) × 1.5 = 0.61

i = sin-1 0.61

i = 37.6°

32 of 45 © Boardworks Ltd 2009

Use Snell’s Law to answer the following:

sin r = sin i refractive index

Using Snell’s Law

Diamond has a refractive index of 2.4. If light passes into a diamond crystal at an angle of 15°, find the angle of refraction.

sin r = sin 15° = 0.12.4

r = sin-1 0.1

r = 6.2°