Circuits
Why does a lamp go off the moment you flip a switch?
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Explain
Electricity flows in a loop.
Break the loop, and the light goes off.
A circuit is a complete loop that electricity can flow around. A switch opens or closes the loop.
A battery gives the push, called voltage. The flow of charge is called current.
Add more batteries, and the bulbs get brighter. Add more bulbs in the same loop, and they get dimmer.
Current (I) is the flow of charge, measured in amps. Voltage (V) is energy per charge, measured in volts.
In a series circuit, there is one loop, and the current is the same everywhere. Each bulb adds resistance.
Worked example: 2 cells make 3 V. With one 3 Ω bulb, I = 1 A. With two bulbs, I = 0.5 A.
- Battery pushes charge
- Charge flows in a loop
- The bulb lights up
Want the full story?
Real bulbs change resistance as they heat up, and the sim keeps it fixed. Conventional current is drawn from positive to negative, although electrons really move the other way. Homes use parallel circuits, so that one light can fail without the others going out.
Try it at home
Ask a grown-up to help
You need a torch.
You need: a torch.
Turn a torch on and off.
- Open a torch with a grown-up.
- Find the batteries, the switch and the bulb.
- Trace the loop that the electricity follows.
What's happening: the switch completes the loop, so that current can flow from the batteries through the bulb.
Only use small batteries. Never open mains plugs or sockets, and keep small batteries away from young children.
Physics is life
Your body
Your nerves carry signals.
Daily life
Switches turn lights on.
Nature
Electric eels make their own electricity.
Space
Spacecraft have circuits too.
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Words to know
Circuit: A complete loop that electricity can flow around.