What it shows
Some materials let electric current pass and some do not. A bulb lights up when the circuit is complete and a conductor is in the gap.
The science
Electric current flows in a closed loop from the cell through wires and the bulb and back to the cell. If the loop has a gap, the bulb stays off. When a conductor, like a metal key, fills the gap, the current flows and the bulb lights. Insulators, like plastic and wood, do not let current pass.
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.
- One 1.5 V cell (AA) (under Rs 50)
- One 1.5 V torch bulb and holder
- Three short pieces of insulated wire with bare ends
- Sticky tape
- Items to test: coin, key, pencil lead, eraser, plastic spoon, cloth, paper clip, wooden stick
Safety
For this project: Use only a small cell and never touch mains sockets or plugs. An adult must strip the wire ends and stay with you while you test.
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.
Fix the cell and bulb holder and connect one wire from the cell to the bulb holder.
Connect a second wire from the other side of the bulb holder and leave its end free.
Tape a third wire to the other end of the cell and leave its end free.
Touch the two free wire ends together and check the bulb lights.
Place the key between the free ends and see if the bulb lights.
Test each other item in turn and note lit or not lit.
Write the results in two columns: conductors and insulators.
Guess what kinds of materials are conductors and check with your table.
What you should see
The bulb lights for metal items like the key, coin and paper clip, and for the pencil lead, but not for plastic, wood, cloth or eraser.
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 conductor?
A material that lets electric current pass.
2What is an insulator?
A material that does not let current pass.
3Why does the circuit need to be a loop?
Current flows only in a complete path.
4Why are electric wires covered in plastic?
Plastic is an insulator that protects us.
Take it further
Test a steel spoon, a pencil and water, and a tap-water bowl, but only with an adult.
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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