What is electricity?

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. 

Here is a closed water circuit.

The pump in action!

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

Here is an electrical circuit.The battery  pushes the electricity around the circuit of wires. What can we say about the electric circuit?

You can also switch electricity on and off like you can switch the water flow on and off.

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?

Another model

Inside any metal there is good evidence to suggest that it is made up of atoms

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.

Atoms

Make those Atoms Move!

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.

Electrons in a wire… a short 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.

Short Circuit

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.

Let there be Light

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.

Two Light Bulbs

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.

Two Light Bulbs

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

Two bulbs

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