Electricity: Circuits and their Components
Switches and circuit diagrams
Make your own switch, and learn to draw circuits with symbols.
How does a switch turn a torch on and off? Make one (Activity 3.8). Fix a safety pin to a piece of cardboard with a drawing pin through its ring, so it can swing. Fix a second drawing pin where the free end of the safety pin can reach it. Join a wire to each drawing pin.
Put it in a circuit with a cell and a lamp (Activity 3.9):
| Safety pin | Gap? | Circuit | Lamp | Switch |
|---|---|---|---|---|
| touches both drawing pins | no | closed | glows | ON |
| touches only one | yes | open | dark | OFF |
A switch is a simple device that completes or breaks a circuit. It can go anywhere in the circuit. The switches on your walls at home work the same way: inside, two metal pieces touch when it is ON and move apart when it is OFF.
Drawing real pictures of every circuit is slow, so we use symbols. A circuit drawn with symbols is a circuit diagram.
- Cell: a long line and a short line. The long line is positive, the short line negative.
- Battery: two or more cell symbols in a row.
- LED: a triangle points the way the current can flow; two small arrows show it gives out light.
- Switch: a line with a gap when OFF, no gap when ON.
Groups like the IEC, ANSI and IEEE set standard symbols, so an engineer in any country can read anyone else's diagram.
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