Nexus Research Group - Dispersion and Rainbows

Making Rainbows

Is white a proper colour? Find out what rainbows are made of with an old mirror and some sunshine...

Light traveling in a straight line is invisible! Light has to bounce off an object (reflection) and enter your eye before you can see it. But there's more to light than that!

Try this:

PREDICT: Ask your students "What will happen when I pass white light from the sun through a glass prism? If White goes in, what comes out?
OBSERVE: Let the light from the Sun pass through your prism and allow the light coming out to shine onto a piece of white card or paper.
EXPLAIN: What does this show us? (Seniors might like to consider the relationship between the wavelength of a particular colour and how much it bends)

Try and make your own rainbow at home...

Place a mirror in the glass of water at an angle (let it lean against the side of the glass)
Turn the glass so the mirror is facing the sun.
Hold a piece of paper at a slant in front of the glass. Move the paper around until you see the rainbow colours.

You may need to move the paper around slightly until the colours come into focus.

White light is "separated" into 7 different colours! It's a mixture!

These 7 colours are Red, Orange, Yellow, Blue, Green, Indigo, and Violet. An easy way to remember the colours of the visible spectrum (the rainbow) is to think of a boys name; ROY G BIV.

See the prism working above.When sunlight enters a prism, it bends. This is called refraction. Then from one beam of white sunlight, out the other side of prism comes all the colours of the rainbow. This is called dispersion.

A raindrop is like a prism but with a rounded bottom. So think of the rain as a sky full of prisms just waiting for the chance to bend sunbeams!

A double rainbow appears Sunday afternoon, May 25, over Bell Block during a shower of rain.

You see the ROY G BIV colours in the picture above and when light passes through water sprayed from a sprinkler.

So white sunlight is a mixture of the 7 colours. When all 7 colours enter your eye you see white. A white T-shirt then must reflect all the sunlight into your eye. It even reflects infra-red (heat) so you stay cool in white clothes.

A black T-shirt absorbs all (keeps in) the 7 colours so no light bounces off into your eye. You see this as black because it is the absence of light. It even absorbs infra-red (heat) so you get hot in black clothes.

Consider this:

Are white and black really colours at all?

A blue T-shirt absorbs nearly all colours but reflects just blue light to your eye. What must be happening for a T-shirt to look red?

Did you know a light bulb actually produces more red and orange colours? A fluorescent tube light produces more blue and yellow.

FIND OUT MORE:-

If you still don't believe light can be bent then see this next demonstration...
Make a rainbow using chemicals
Find out who Sir Isaac Newton was and what he became famous for.
Design an experiment to record the temperature of a known volume of water stored in a can painted white on the outside compared to an identical can painted black. What did you discover?

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