Between driving the weather, making plants grow and helping generate an ever-increasing amount of the electricity we use via photovoltaic cells, the sun does a pretty important job. There are plenty of kits available that can help bring solar power into the classroom, but if the equipment budget is a bit stretched, or your pupils are not especially electronically inclined – or just a bit young to deal with wires and fiddly components – here are a couple of really cheap and simple experiments you might like to try.
1. Making Your Own ‘Rain’
Here’s a really useful way to help children understand how the sun makes the world’s water cycle work. It’s very easy to do, and by the end of it, they’ll have made their very own fresh-water “rain” from seawater – albeit on a very small scale! This experiment works well individually, in small groups or as a class demonstration, depending on the availability of resources, age and ability of the class and preferred teaching style.
Before you start, you’ll need to collect a few things together:
- A large glass or clear plastic kitchen bowl
- Some see-through plastic food wrap
- A small stone or child’s marble
- A clean jam jar (small enough to fit completely inside the bowl)
- Some water-soluble ink or paint
You will also require a supply of water.
- Sit the jam jar in the middle of your bowl.
- Add some water to the bowl, ensuring that the jar doesn’t start to float.
- Add a few drops of ink to the water to colour it, and gently mix it in.
- Cover the top of the bowl securely but slightly loosely with the food wrap; there should be a little ‘give’ left in the top – but not too much.
- Place the stone directly above the jam jar; if you’ve got the tension of the cover right, this should mean that the weight of the stone makes a little depression in the plastic film, centred over the open mouth of the jam jar.
- Stand everything in direct sunshine, wait and watch.
What Should You See?
As the sun warms the bowl, the water inside begins to heat up and as its temperature rises, it starts to evaporate. The water vapour produced condenses on the internal surface of the plastic film, forming tiny droplets, and once they get large enough, they run down the underside of the film, to the low point created by the weight of the stone. As more and more collect, eventually the drops become too heavy to stick onto the film any longer, and “rain” falls into the open mouth of the jam jar.
A careful look should also reveal that the water collecting in the jar is clear, not coloured – the ink being left behind in just the same way as salt is left behind in the sea. The experiment can also be done with salty water rather than ink, but it doesn’t make the point quite so obviously – and you’re hardly going to want to encourage your class to taste what they’ve made to prove the point!
2. What’s the Best Colour for a Solar Panel?
This experiment looks at the way colour affects the rate at which solar heat is absorbed and it’s a good way to start exploring some of the science behind solar water heaters. Very little equipment is needed – just some ice cubes and a selection of different coloured sheets of cardboard. Black and white card are essential, but you can use as many other different colours as you like, so long as you can supply enough ice cubes! Like the previous experiment, this can be done individually, in pairs/groups or as a class demonstration.
- Cut your cardboard into equally sized squares; about 10cm / 4 inches is ideal.
- Stand your squares in full sunlight.
- Place an ice cube in the middle of each square (making sure that all the cubes are the same shape and size).
- Watch – and possibly time – how quickly they melt, to see which is quickest and which slowest.
What Does That Tell Us?
The black card/ice cube combination should always melt quickest because it absorbs the sun’s heat most efficiently, while the white one, which reflects much of the energy will be the slowest, which, of course, explains why solar collectors are typically painted matt black. By recording how well other colours absorb the sun’s heat – and melt their ice cube – the kids can put them in order too, and decide what they think would make the second best colour for a solar panel, and so on.
If ever there was a pair of experiments to prove that you don’t need a vast amount of expensive equipment to do good science, it’s these two. Now all you need to do is wait for a really sunny day!