HOMEWORKCan you please put your

homework (Ray diagrams) in the plastic wallet on my desk labelled

‘Y8 homework’.

Anyone who has not completed their homework or has ‘forgotten’

it, can join me at break time in S6.

What would life be like without colour?

Dull.

10.4 Colour!

Colour moodsDifferent colours can affect how we feel:•RED can make people angry•ORANGE is a happy colour•YELLOW is a cheerful colour•GREEN is calming•BLUE is a cool but restful colour

Do you agree? Write a list of colours at the back of your books and next to them, write what they make you feel.

How do these colours make you feel?

Learning OutcomesToday you will:1.Draw a diagram to show the different colours that make up white light2.Plan and carry out a presentation about how the different theories of what makes up white light

Memorise these. You have 30 seconds. GO!Today you will:1.Draw a diagram to show the different colours that make up white light2.Plan and carry out a presentation about how the different theories of what makes up white light

What was Learning Outcome 2?

What was Learning Outcome 2?

2. Plan and carry out a presentation about how the different theories of what makes up white light

Lesson ObjectiveTo be able to explain how white light can be dispersed into 7 different

colours, according to their wavelengths.

Let’s watch a demo.What colour is the light that we see

‘come out’ of a light bulb?

What colours do we see in a rainbow?

10.4 Dispersing light

Breaking up white lightYou’ve just seen how a prism can break up white light into 7 colours.

This breaking up of white light is called dispersion. The prism disperses the light.

Dispersion

KEY WORD ALERT!

10.4 Dispersing light

ColoursThis breaking up of white light is called dispersion. The prism disperses the light.

When white light is broken up like this the 7 colours are always in the same order.

REDORANGEYELLOWGREENBLUEINDIGOVIOLET

top

bottom

Dispersion

10.4 Dispersing light

ColoursHow can you remember the order?

There’s the famous spy:ROY GBIV

Or a defeated British king:Richard Of York Gained Battle In Vain

See if you can think of your own.

ROY GBIV

10.4 Dispersing light

ColoursYou can see the order in this rainbow.

Rainbows

10.4 Dispersing light

Why does light disperse like this?Remember that light is a wave.

The size of a wave is measured from one peak to the next and is called its wavelength.

wavelength

KEY WORD ALERT!

Wavelengths

10.4 Dispersing light

Why does light disperse like this?White light is made up of all the colours of the rainbow.Each colour has its own wavelength.Red has the longest and violet has the shortest wavelength.

Wavelength and Dispersion

CAN SOMEONE

PLEASE SHOW ME WHERE I WOULD

MEASURE THE

WAVELENGTH ON THESE

DIAGRAMS?

10.4 Dispersing light

Why does light disperse like this?When light enters a glass prism it slows down.But the shorter wavelengths slow down most and so bend more sharply.Blue is a short wavelength.Red is the longest one.

Wavelength and Colour

10.4 Dispersing light

Why does light disperse like this?As each wavelength, or colour, slows down at a different rate it therefore has a different angle of refraction to the rest.This means the different colours spread out.REMEMBER! Blue bends best.

KEY PHRASE ALERT!

Blue Bends Best

10.4 Dispersing light

Why does light disperse like this?The shape of the prism means they spread out even more on leaving the prism.

You may see a small spectrum with a rectangular glass block but the colours do not spread out as much.

KEY WORD ALERT!

Spectrum of Colour

IN YOUR BOOK, COPY AND COMPLETE THE DIAGRAM ABOVE TO SHOW WHITE LIGHT

DISPERSING INTO IT’S 7 COLOURS. COLOUR IN THE SPECTRUM ON THE RIGHT TO SHOW THE

SPECTRUM OF COLOUR. REMEMBER: ROYGBIV!

SWAP BOOKS, LOOK AT THE ANSWER ABOVE, AND GIVE YOUR PARTNER TWO STARS AND A

WISH.STARS = WHAT WENT WELL

WISH = WHAT THEY COULD IMPROVE FOR NEXT TIME

Let’s watch a demo.So we know how to split white light

into it’s seven colours.

Can we turn these colours back into white light?

How?

10.4 Dispersing light

Recombining coloursWhen a second prism is added ‘upside down’ the dispersion of the second prism is in the opposite direction to the original dispersion.White light is formed again.

Making white light again

10.4 Dispersing light

Recombining coloursLook carefully. The two triangular prisms form a parallel-sided glass block.

We didn’t see dispersion when we passed a ray of light through a rectangular glass block.

Making white light again

10.4 Dispersing light

Spinning discThe image stays on the retina at the back of the eye for about 1/10 of a second.When the disc spins very fast all the colours of the rainbow appear on the retina together.The colours all combine to form white light.

Making white light again

10.4 Dispersing lightPresentationsDifferent scientists have different theories about light. I am going to put you in groups of three. Then I am going to give each of your groups a number. Whatever number I give you,

that is the scientist I want you to research, and prepare a quick, 1 minute presentation on, to be presented at the end of the lesson. All groups MUST answer questions 1 and 2 on p120

in the ‘How do we think about light’ box, in your exercise books.

Group 1. Isaac Newton

Group 2. Christian Huygens

10.4 Dispersing lightPresentationsLet’s use the random name

generator to select groups to present…

Group 1. Isaac Newton

Group 2. Christian Huygens

Today I have learned:From our class discussion, write three bullet points to describe three things you have learned today, in your exercise book.

You have 56 seconds. Go.

Thumbs up, in the middle, or down, depending on how confident you feel our lesson objective.

To be able to explain how white light can be

separated into 7 different colours, according to their

wavelengths.