Down to Earth
Colour
How to make a rainbow
Isaac Newton is one the most famous scientists in the world. He is best known for discovering how gravity works, but he worked on so many different topics that he completely changed how we understand the world.
Make a rainbow
You will need...
A glass of water
A mirror that will fit in the glass
Some sunlight
How long does it take?
It takes only a few minutes to set this experiment up.
What to do...
You can use this as a demonstration or ask the class to set it up in small groups.
To get a good rainbow you need to have strong sunlight and a clear place on the wall or ceiling to see it. If there isn't an obvious rainbow, or if it is too faint to see on a far wall, use a piece of paper as a screen to produce the rainbow closer to the glass.
You may even want to use the paper to try to trace the colours of the rainbow back to the glass to see how the light is split up.
Be careful! Do NOT look directly at the sun or at the reflected sunlight from your mirror. It can permanently damage your eyes. Watch out for spilling water too.
What is happening?
The light from the sun bends as it enters the water, just like it bent when it entered Newton's glass prism. White light is made up of all the colours of the rainbow. Blue light bends more than red light, so the colours are spread out.
This bending of light is called refraction. Rainbows are formed when sunlight refracts in drops of rainwater. The light is split into different colours as it enters the drop of water, it is then reflected (by total internal reflection) and refracts again as it leaves the drop.
Each drop only refracts one specific colour to the person watching, lower drops refract blues while high ones refract red. This is why the blues and purples are found in the centre of a rainbow.
To spot a rainbow you need to stand with your back to the sun. If you have rain in front of you there is a chance a rainbow will form.
Curriculum Links
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Science: |
Sc4 |
Physical Processes Light and Sound |
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QCA Unit 6F |
How we see things |
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Art & Design: |
4a-c |
Knowledge and understanding |
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ICT: |
2c |
Developing ideas and making things happen |
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Literacy: |
En1 |
Speaking and listening |
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3a-d |
Group discussion and interaction |
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En3 |
Writing |
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2a-f |
Planning and drafting |
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Numeracy: |
Ma3 |
Shape, space and measures |
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4c |
Recognise angles |
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QCA Music: |
QCA Unit 13 |
Painting with sound - Exploring sound colours |
Scottish Curriculum
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Science:
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SCN 2-11b |
Forces, electricity and waves - Vibrations and waves |
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Social Studies: |
SOC 2-06a |
People, past events and societies |
Colour
In the 1670s, Newton discovered colour. Not that everything was black and white before then! It was just that no-one had worked out why different things are different colours.
Newton shone light on a prism - a triangle block of glass - and found that the light separated into different colours. He discovered that white light is actually made of all the colours of the rainbow mixed together. Things look green or red or blue when white light shines on them because they reflect the green, red or blue part of the white light.
While Newton was
investigating coloured light, many painters were investigating the
chemistry of colour. Artists made their paints from natural
pigments, which give the paint colour, found in earth and
plants. These paints were often difficult to work with.
Blues often faded, or were very expensive, like the paint called
ultramarine which was made with a ground up semi-precious
stone. Sometimes you may see old paintings of baby Jesus or
Mary wearing blue robes. Because blue was a very expensive colour
to use, it showed that the artist thought these to be very
important people.
At the start of the 18th century, about the time that Newton published his book on light, a new kind of blue, known as Prussian Blue was discovered. This was the beginning of many new man-made pigments which meant paints became cheaper and easier to use.
Scientists and art historians test for Prussian Blue paint. If they find it on a painting that was supposed to have been painted before the 1800s they know it is either a forgery, or someone has painted over it at a later date.
You will need...
A glass
of water
A mirror that will fit in the glass
Some sunlight
What to do...
Fill the glass with water and put the mirror in it so it lies on its edge.
Let sunlight fall on the mirror and watch as it forms a rainbow outside the glass. Sometimes the rainbow will fall on the table, or on a wall or ceiling, so have a good look for it.
Be careful! Do NOT look directly at the sun or at the reflected sunlight from your mirror. It can permanently damage your eyes.
What is happening?
The light from the sun bends as it enters the water, just like it bent when it entered Newton's glass prism. White light is made up of all the colours of the rainbow. Blue light bends more than red light, so the colours are spread out.