Electricity: Circuits and their Components
Inside an incandescent lamp
Look inside an old-style light bulb and see how it is made.
Many older torches use an incandescent lamp, the old kind of light bulb. With your teacher's help, look closely at one (Activity 3.4).
Inside the glass bulb is a very thin wire, often coiled. Switch the torch on and it is this thin wire that glows. It is called the filament.
Parts of the lamp:
| Part | What it does |
|---|---|
| filament | the thin wire that gets hot and glows |
| two thick wires | hold the filament up |
| metal tip at the centre of the base | one terminal |
| metal case at the base | the other terminal |
The two terminals are fixed so that they do not touch each other. The current has to go in at one, through the filament, and out at the other.
When current passes through the filament, it gets very hot and glows, and that gives light. These old yellow bulbs waste a lot of electricity as heat, which is why most homes now use LEDs.
Sometimes a lamp will not glow even when connected properly. We say it has fused. Usually the filament has broken. A broken filament leaves a gap, so no current can flow, and the lamp stays dark.
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