What it shows
A clear cover over a black plate lets sunlight in and slows heat from escaping. Testing zero, one and two layers shows the benefit and the point where extra layers stop helping.
The science
Sunlight (short-wavelength radiation) passes through clear plastic and is absorbed by the black plate, which re-emits heat as long-wavelength infrared. Plastic blocks much of that infrared and also stops warm air moving away. One layer helps a lot, a second helps a little more, but each extra layer also reflects a bit of incoming light.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three identical shallow cardboard trays
- Black paper and foil for lining
- Clear plastic sheets or a transparent file cover
- Three thermometers
- Water and a measuring cup
- Tape and a wooden board
Safety
For this project: Handle cut plastic edges carefully. An adult must supervise testing near a roof edge or a hot surface. Do not leave water in a sealed container; let air escape.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Line each tray with black paper and place equal volumes of water in a small black cup in each.
Cover tray A with no sheet, tray B with one clear sheet and tray C with two sheets separated by a small gap.
Seal the plastic edges to the tray with tape to cut air leaks.
Place the trays side by side facing the sun on the board.
Push a thermometer through a small hole into the water cup in each tray.
Record all three temperatures every ten minutes for an hour.
Repeat on a windy and a calm day and note the difference.
Draw a bar graph of the temperature rise for each tray.
What you should see
The covered trays heat more than the open one, and two layers give a small extra gain over one. Wind reduces the open tray more than the covered ones.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a glazing layer?
A clear cover that lets sunlight in and keeps heat from escaping.
2Why does wind cool the open tray?
It carries warm air away by convection.
3Why not use many layers?
Each layer also reflects some sunlight and costs more.
4Where is such a plate used?
In flat plate solar water heaters on rooftops.
Take it further
Place a layer of foil under the black paper and see if the extra insulation helps.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
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