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).



Here is a circuit where a battery (sometimes called a cell) is connected to a bulb using wires.

Below is a circuit diagram of the same circuit using the correct symbols circu1image2

The Cell ks2_circuits_clip_image006
Circuit symbol

The cell has a voltage which makes an electric current flow around the circuit.

The higher the voltage the greater the current

A ‘battery’ of cells
Symbol for a battery

Several cells joined together form a battery.

The bulb
Circuit symbol
(Either symbol can be used)


 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’).

How to connect a bulb:




Circuit diagram

Two bulbs joined end to end (in series)

This is how christmas tree lights are joined together
If one bulb is unscrewed the other bulb will also go out





Circuit diagram

Two bulbs joined side by side (in parallel)

This is how the lights in a house are wired together.
If one bulb is unscrewed the other bulb will stay alight


Changing the brightness of a bulb

Circuit diagram

Two cells makes the bulb brighter
because there is a higher voltage





Circuit diagram

Two bulbs (in series) makes the bulbs dimmer
because it is more diffcult for the electricity to flow



Making the wire longer will make the bulb dimmer



Circuit diagram
Two cells and two bulbs is the same brightness as one cell and one bulb

Using a switch


Circuit diagram

All the switch does is to break the circuit and switch everything off (or on)
It does not matter where we put a switch in the circuit.

A switch like this is sometimes called a SPST switch
( SPST=Single Pole Single Throw)

(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


There is something wrong with each of the circuits below. can you see what it is?
  The bulb is connected incorrectly. The wire should not be touching the glass.
There is a break in the circuit
The cells are pointing in opposite directions. One cell needs turning around.
The bulb is connected wrong. There is a short circuit.