The pump starts the water moving around the circuit of pipes. What can we say about the water circuit? No water is used as it moves around the circuit. The water needs a pump to make it move. For water to go around the circuit it needs pipes. The water can turn the water wheel because of the energy given to it by the pump.

Surprisingly none of the electricity is used up as it moves around the circuit. The electricity needs a battery or cell to make it move. Electricity needs metal wires to move through the circuit. The electricity lights the bulb because of the energy given to it by the battery The battery pushes the electricity around the circuit of wires. What can we say about the electric circuit?

The water model is useful for describing some of the properties of electricity. However, when you cut the wire water doesn't flow out so maybe the model is not as useful as we first thought. If it is not water going round the circuit, what is it? What is in the metal wire that flows, is not used up, and can carry energy from one place to another?

Inside any metal there is good evidence to suggest that it is made up of atomsatoms Each of these atoms consists of a nucleus which is surrounded by small moving particles called electrons. It is suggested that it is the electrons which move in the wire. They are the electricity.atomsnucleuselectrons

In metals some of the electrons are loosely attached to the nucleus. They can be made to drift through the metal structure. In the model opposite the electrons are moving much to fast. The battery or cell is a device which can persuade the electrons to start drifting. It is the pump of the circuit.

A circuit in which the ends of the battery are connected directly together with a length of wire is called a short circuit. There is no restriction to the flow of electrons around the circuit. The battery therefore does a lot of work pushing and pulling and quickly runs down. A short circuit like this can be dangerous when you use rechargeable batteries so they are not advised when there is a possibility of short circuits.

So why does the light bulb light up? The light bulb filament is a very thin wire, thinner than the wire from the cell to the light bulb.

The electrons being pushed by the cell have to go through the thinner wire of the filament. This slows the electrons down and also makes them jostle the metal atom nuclei more than they usually would. The metal atoms nuclei vibrate more and because of this the metal gets hotter and hotter. The filament of the light bulb eventually gets white hot and radiates white light.

The filaments are a type of resistor, the thinner they are the higher the resistance. There are types of resistor in other circuits which are different from the filament. For example there is a light sensitive resistor which changes its resistance when light fall upon it.

Putting two bulbs into the circuit restricts the battery push even more. This makes it even more difficult for the cell to move the electrons around the circuit. The light bulb filament glows less because of this restricted flow.

Sometimes you construct a circuit with two bulbs which you believe to be identical and you find one of them brighter than the other.

This is because the two bulbs are not identical. The filament in one bulb is either slightly longer or thinner than the other. This filament has a higher resistance than the other. The light bulb which has the smallest resistance therefore glows less