Electricity: Circuits and their Components
The LED and its one direction
Investigate the LED, and find out what is special about the way it lights up.
Most torches today use an LED, a Light Emitting Diode, instead of a filament bulb. LEDs use much less electricity for the same light.
Look closely at an LED (Activity 3.5). There is no filament inside. It has two wires, and one is longer than the other:
| Wire | Terminal |
|---|---|
| longer | positive (+) |
| shorter | negative (−) |
In Activity 3.7 you join an LED to a two-cell battery, then swap its two wires. It glows one way and not the other. Current can pass through an LED in one direction only.
The rule, in one line: long wire to the battery's positive, short wire to the battery's negative. Then it glows. Join it the other way and nothing happens.
An incandescent lamp is different. It does not matter which of its terminals goes to which end of the cell; it glows as long as the circuit is complete.
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