When we use wires to connect a battery with a bulb (or buzzer etc) and the bulb lights then we have a circuit
The inside of a wire is made of COPPER (which is a good conductor of electricity)
The copper wire is covered with coloured plastic (which is an insulator).
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| The bulb |
  Circuit symbol (Either symbol can be used) |
The BULB |
A light bulb has a thin metal filament, often made out of tungsten, which glows very hot when an electric current flows through it.
If we use a higher voltage more current will flow and the filament gets hotter and glows brighter. Too much current makes the filament melt (and the bulb ‘blows’). |
Two bulbs joined end to end (in series) This is how christmas tree lights are joined together |
Two bulbs joined side by side (in parallel) This is how the lights in a house are wired together. |
Changing the brightness of a bulb
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Two bulbs (in series) makes the bulbs dimmer |
 Making the wire longer will make the bulb dimmer |
Two cells and two bulbs is the same brightness as one cell and one bulb
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All the switch does is to break the circuit and switch everything off (or on) A switch like this is sometimes called a SPST switch (you dont have to have two cells, one will do) |
Sometimes a circuit does not work.
The three main causes for a circuit not working are:
- A wire not connected (or broken)
- The bulb ‘blown’. This is when the filament has melted.
- The batteries are dead (flat)
- The wires are not in the correct place
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There is something wrong with each of the circuits below. can you see what it is?
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