Light

TargetsTo know about the colours of light

Dispersion• Each of the colours has a slightly different?

They each have a different wavelength [].

The Light Spectrum

• White light is not made up of just one colour, it is a mixture of all the seven colours of the rainbow – red, orange, yellow, green, blue, indigo and violet.

• This is called the light light spectrumspectrum.

Notes

The light spectrum• If white light travels through

a glass prism the waves are bent – some colours change speed and therefore direction more than others – this splits up light into all its colours

• A second prism will turn the coloured light back to white light

Notes

Applications of the spectrum

The rainbow – light travelling through rainbows is refracted and dispersed to give rainbow.

Primary ColoursYou can make any colour by mixing three

colours. Do you know what they are?

Red Green

Blue

The colours labelled in black text are the PRIMARY COLOURS.

The colours labelled in blue text are called SECONDARY COLOURS. They can be

made by mixing the

primary colours

Cyan

Yellow

Magenta

Primary ColoursPRIMARY COLOURS are RED, GREEN and BLUE

SECONDARY COLOURS are YELLOW, CYAN and MAGENTA

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Red objectsWhy does a red snooker ball look red in white light?

Remember white light is made of a spectrum

of colours.

The snooker ball absorbs all the colours of the

spectrum EXCEPT red, red light is reflected into our eye. The snooker ball

appears red.

Black objects

Why does a black snooker ball look

black in white light?

The snooker ball absorbs all the colours of the spectrum. NO light is

reflected into our eye. The snooker ball appears

black.

White objects

Why does a white snooker ball look

white in white light?

The snooker ball doesn’t absorb any of the colours

of the spectrum. The whole spectrum of light is

reflected into our eye. The snooker ball appears

white.

Red, blue and green filters

Red filters absorb all colours….

Blue filters absorb all colours….

Green filters absorb all colours….

… apart from red light

… apart from blue light

… apart from green light

PRISMSDispersion of white light

PRISMSSingle coloured light (Red)

PRISMSSingle coloured light (Blue)

COLOURED OBJECTSWhite object in white light

All colours reflected

White objects reflect all colours and absorb none

Object appears white

COLOURED OBJECTSWhite object in blue light

Blue light reflected

White objects reflect all colours and absorb none

Object appears blue

OBJECTS IN COLOURED LIGHTWhite object in red light

Red light is reflected

White objects reflect all colours and absorb none

Object appears Red

OBJECTS IN COLOURED LIGHTRed object in red light

Red is reflected

Red Objects reflect red light

Object appears Red

OBJECTS IN COLOURED LIGHTRed object in blue light

No light is reflected

Red Objects reflect red light and absorb all others

Object appears black

A red apple A green pear

A white plate

THE FRUIT BOWL IN WHITE LIGHT

A red apple A green pear

A white plate

THE FRUIT BOWL IN RED LIGHT

A red apple A green pear

A white plate

THE FRUIT BOWL IN BLUE LIGHT

FILTERS white light – red filter

FILTERS white light – blue filter

FILTERS blue light – blue filter

FILTERS blue light – red filter

FILTERS white light – red and blue filter

How we see colours

• Coloured object reflect one colour and absorb all other colours.

• White objects reflect all colours of the rainbow.

• Black objects absorb all colours and reflect none

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What colour is it?

• Coloured object have a specific colour because they absorb some colours and reflect others.

What colour is it?

• This picture shows why grass is green.

• So the red post box on green grass looks like this

What colour is it?

• How does the post box on the green grass look in red light?

What colour is it?

• How does the red post box on the green grass look in green light?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

TESTING COLOUR TESTING COLOUR BLINDNESS. WHAT DO BLINDNESS. WHAT DO YOU SEE?YOU SEE?

Key words

• Spectrum• Reflection• Transmission• Filters• Absorption• Refracted• Dispersed