Scientific Fun with Light and Colour

I hope everybody had an enjoyable Easter despite our current ‘lock-down’ situation. This post is going to suggest a few science activities for next week around the subject of light and colour, and the human eye! I hope that you will find them fun.

The first two activities don’t take very long to organise and the pin-hole camera activity is definitely good fun, but relies on a few simple resources (eg black sugar paper and tracing paper). I’m sure that not everybody will readily have these at home. When we re-open on Monday (for children of key workers), we have organised the spelling booklets for our junior aged children to be collected. If you require some of the resources for the science activities, such as the black sugar paper and tracing paper, I have left a pile under the table on the left hand side as you enter our reception area.

Please take one large sheet of black sugar paper, along with one smaller sheet of black paper and a sheet of tracing paper. If you want to try the contrast activity then I’ve also left a tray of sticky paper squares, just help yourself to a couple of these.

If your child is in the infants, but you’d still like to have a go at the pin-hole camera activity, you are most welcome to pop in on Monday and collect the above resources but we obviously need to emphasise the importance of sticking to the current advice on social distancing if you wish to pick up the necessary resources.

Retinal Fatigue Activity – Complementary Colours

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Have a look at the diagram of our eye. Light enters our eye through the pupil. The iris is very clever, it constricts or dilates to control the amount of light that comes in through our pupils (too much light would give us a headache!) Think of dilating as simply ‘opening up’ and constricting as ‘closing up’. So our pupils look bigger on dull days when our iris dilates, and smaller on very sunny days when our iris constricts.

Through looking at the diagram, find the retina. Think of the retina as a screen at the back of the eye that captures images of everything that we see. Everything we see is created by light entering through our pupils. If you have a go at the pin-hole camera activity, the tracing paper takes on the role of the retina and acts as the screen.

If we see too much of one colour our eyes become ‘tired’ of this colour and something known as ‘retinal fatigue’ happens. This is a chemical reaction where the retina basically compensates due to ‘over-stimulation’ of one particular colour, so it creates the complementary colour to cope with the over-stimulation.

So, here’s the activity. Take a square of coloured paper (let’s say red) and a sheet of plain white A4. Place them next to each other. Then stare intently at the red square for about 30 seconds. Then move your eyes to look at the white paper and you will see a greenish square of light (that is complementary to red) appear on your white sheet. Try it again, this time with a piece of blue paper. Stare intently at the blue for 30 seconds and then move your eyes onto the blank A4 and you should see a square of yellowy/orange light (complementary to blue). This is a simple experiment to demonstrate retinal fatigue (and don’t worry, it won’t damage your eyes!)

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Contrast Effect Experiment– Colours appear darker on lighter backgrounds.

Our brain is very clever, and because of the way it visually processes information, it can make colours appear to be lighter or darker depending upon the background. This is simply an optical illusion. To demonstrate this cut two squares of paper that are exactly the same colour (say red) and size say 3cms squared. Stick one of your red squares on a piece of black paper and one on a piece of white. Now stand back and look at your two red squares. The red square on the white background will ‘appear’ darker than the red square on the black background. This is called the ‘contrast effect’. You KNOW that both red squares are exactly the same yet one appears darker. You can try this experiment with a few different colours, the ones on the lighter background will always appear darker even though we know they’re the same colour as your square on the dark background.

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Pin-Hole Camera Experiment

This experiment is the most fun. Basically you are making a model of the human eye out of a tin can, black sugar paper, a pinhole and some tracing paper.

  1. Firstly, wash out a tin can (with the top cut off). Make sure the top is not too sharp.
  • Draw round the base of the tin can onto black sugar paper. (Draw near the corner of your paper, not the centre, as you will need the rest of your black paper to line the tin).
  • Cut out the circle carefully to make sure it is the exact shape. Put the black circle of paper into the bottom of the can and then line the rest of the tin with your remaining black sugar paper. For this model, the tin can represents an eye!
  • Hammer a small nail into the exact centre of the base of the can. Make sure the hole also goes through the black sugar paper circle that’s inside the can. This hole represents the iris within your pupil. The smaller hole the better, so don’t use a very large nail!
  • Draw again around the base of the can, this time onto the tracing paper. Allow a bit of additional ‘border’ on the tracing paper so don’t cut out the exact circle, allow an extra couple of centimetres so that you can then fold the edge of your tracing paper circle over the open end of the can.  Attach the tracing paper to the open end of the can to create the ‘screen.’ Use either sellotape, masking tape or an elastic band to attach the tracing paper to the can.
  • Roll up your large sheet of black sugar paper and wrap it round the can (like a telescope). The ‘telescope’ end of the paper should enable you to look through the sugar paper tube at the screen.

You now have your pin-hole camera. The screen represents the retina in your eye.

When we see objects we basically see EVERYTHING upside down on the retina. Our brain is remarkably clever and turns everything the right way up (otherwise life would be very confusing!) LIGHT TRAVELS ONLY IN STRAIGHT LINES, so any light that comes in from higher up will travel to the bottom of our retina, and light that comes in from lower down will travel to the top of our retina. Have a look at the diagram below. This is how our retina would capture the image of a person.

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You can now go outside and look through your sugar paper tube at lots of things in the garden. They’ll all appear upside down on your tracing paper screen. This is EXACTLY how our eyes work.

Pin-hole cameras (like the ones that you have made) can actually take photographs but you’d need special photographic paper (in place of the tracing paper), photographic chemicals and a dark room. In Victorian times they used this pin-hole camera idea with giant boxes that people could sit inside. The boxes had a screen inside and were based on exactly the same principles as your model. People paid to sit inside (in the dark) and the entertainers would do things like juggling on the outside.  Their moving images would be captured (upside-down) on the screen inside the box. This was called a ‘camera obscura.’ They were basically giant models of the eye and Victorians thought that they were great fun!

If you’ve enjoyed these simple experiments and want to investigate the science of light further, there are lots of things you could do, such as make a simple periscope or kaleidoscope. If you search for ‘How to make a simple periscope’ or ‘kaleidoscope’ you’ll easily be able to find some instructions and advice through The Internet.

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