# How Dangerous is Your Christmas – 5. Experimentin' around the Christmas Tree

Scientists Dave Porter and Fran Scott show Dick and Dom some festive science experiments. If you would like to try them yourself, here’s how!

The science of fairy lights, napkin tricks and indoor snow.

## Activity 1: Fairy lights and circuits

If you want to have a go at making a circuit yourself, you will need to enlist the help of a friendly science teacher, because you may not have the materials at home. But you could ask an adult to show you what happens to a string of fairy lights when you take a bulb out!

In the programme, scientist David Porter helps Dick and Dom and Dan and Amy build a circuit to show how the lights in a Christmas tree work. First, they create a circuit by attaching wires to a battery, and a bulb. They then use another wire to add a second bulb to their circuit. A circuit in one single loop like this is called a series circuit. But when the second bulb is added, both bulbs get dimmer. If you were to keep on adding bulbs, they would get dimmer still. And if you remove a bulb, the circuit breaks – and all of the bulbs go out. This used to be a problem with old-fashioned Christmas lights!

Today, fairy lights are made using parallel circuits – each bulb has its own loop of wire. They all stay bright, and if one bulb goes, the others will stay on.

## Activity 2: A Napkin Siphon

You will need 2 glasses, one full of water, the other empty, and a paper napkin.

How can you get water from the full glass into the empty one, without touching either of them?

The answer is to roll the napkin into a tube shape. Dangle one end in the full glass, and the other in the empty glass. And then wait... If you come back in about an hour, you should see that water has travelled through the napkin into the empty glass. It will stop when the water in the glasses is at about the same level.

What’s happening

This is something called capillary action. Water is being drawn up through the spaces in between the fibres of the napkin. Capillary basically means small tube, and a good example of where capillary action is important is in plants - it’s how water and nutrients move through their roots and around the plant.

## Activity 3: Instant Snow

This is a relatively new type of Christmas decoration that is become more and more popular. It looks very like real snow. It comes in powder form, and when you add water, the powder absorbs it, soaking up all the water until you have something which looks like snow.

What’s happening

The snow powder is made of a chemical called sodium polyacrylate, which is a super-absorbent polymer. It soaks up water a bit like a sponge, and as it takes in the water, all the long chains of the molecule stretch out so it gets bigger and bigger. A similar chemical is used in babies’ nappies – although thankfully nappies don’t swell to 100 times bigger than their original size when they get wet!