What it shows
Foil reflects sunlight into the box, a clear cover traps heat, and a black cup absorbs it. The test shows how reflection, absorption and trapping of heat make a solar cooker.
The science
Foil on the flap reflects extra sunlight onto the cup. A black surface absorbs more of the radiation than a light one. The plastic cover lets sunlight in but traps the warm air inside, a small greenhouse effect. The temperature rises until heat lost equals heat gained. A good solar cooker can reach about 80 degrees Celsius or more on a bright day.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A clean pizza box or a shoe box
- Aluminium foil
- Black paper or paint
- Cling film or a clear plastic sheet
- A stick to prop the lid
- A thermometer
- A steel cup with water
Safety
For this project: The box and cup can become hot, so an adult must handle them. Never look at the reflected glare; wear sunglasses.
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.
Cut a flap in the lid of the box, leaving a hinge at the back.
Cover the underside of the flap with foil, shiny side out.
Cover the inside floor of the box with black paper.
Tape cling film tightly across the opening in the lid.
Place the cup of water on the black paper and close the box.
Prop the flap at an angle so it reflects sunlight into the box.
Record the temperature every 15 minutes.
Compare with a cup of water left in the open and make a graph.
What you should see
The water in the oven becomes 10 to 25 degrees warmer than the water in the open after an hour or two.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is the foil shiny side out?
A shiny surface reflects light well.
2Why is the inside black?
Black absorbs more heat radiation.
3What does the plastic cover do?
It traps hot air.
4Name an advantage of solar cookers.
They use free energy and no fuel.
Take it further
Change the tilt of the flap with the Sun and note the best angle.
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
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