Wax Photometer

Suitable for kids aged 6+ with parental supervision

CAUTION If you are unable to source your own paraffin wax blocks you will need to make your own. Wax blocks must strictly be prepared by an adult as they involve melting wax and pouring the hot wax into a mould.

You Need:

• Two small paraffin wax blocks (approx. 8 x 5 x 2cm). If you can’t source your own from a supermarket or candle supply centre then you will have to make your own. Instructions in the ‘What to do’ section.
• Aluminium foil
• Scissors
• Masking tape
• Torch (optional)
• Sheets of coloured paper (optional)

What to do:

1. Prepare two wax blocks of the same size. You might be lucky enough to source boxes of paraffin wax at your local supermarket or hardware store. If so, they often come in slabs that need to be cut in half with a sharp knife to get two blocks of roughly the size required. This must be done by an adult working carefully not to chip or break the slab. If you can’t source pre-made blocks, an adult will need to melt down some paraffin wax and pour the hot wax into an appropriate mould from around the house (juice containers, margarine tubs, even a double layer of thick aluminium foil can work). Paraffin wax has a low melting temperature of about 60 degrees celsius and a metal container that fits snugly inside your saucepan is a good option to melt the wax down for moulding.
2. With scissors cut a piece of aluminium foil to the same size as your two blocks, and place it in between the two blocks. Just like an aluminium sandwich (with the wax blocks being the slices of bread).
3. Wrap masking tape around the two blocks to keep them together and the aluminium foil in place.
4. You now have your photometer ready to read light intensity and colour. Hold the block horizontally. Which is brighter, the top or bottom block? If it is the top block, your photometer is telling you that the top half of the room is brighter than the bottom. Hold it vertically. Which half of the room is brightest? Spread out some different coloured paper on the floor or a table and run your block over the top. Don’t touch the paper with your block. You should see the bottom block turn a pale version of the colour of the paper underneath it.
5. As a further experiment, shine a torch light into one side of the block. In that way you can compare the intensity of the torch light to the light source on the other side of the photometer.

The wax is a translucent material, the light can enter and is reflected back through the block by the aluminium foil. Thus you can measure light intensity by the brightness of the block. You can compare the light intensity of two different light sources by placing each light source on opposite sides of the block, which ever block shines the brightest is indicative of the more intense light source. You can also read colour because the coloured light is also reflected back through the block by the aluminium foil.