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Electric circuits
1d. Basic circuits: energy and volts
British Energy logo page 5  
     
Graphic showing energy transfers
Picture 1.9. A cell transfers chemical energy to light by pushing an electric current through the lamp.
What gets used up?
Electric current is the same all the way around the circuit. It does not get used up. So what does get used up?

Answer: the cells. A cell contains chemicals which are a store of energy. They have to do work to push the current around the circuit. By doing this work, the chemicals get used up and, eventually, the cell will need to be replaced. Chemcial energy has been transferred to light.

On page 4, we saw that an electric current is like a moving bicycle chain. The cell is like your muscles. Your muscles use chemical energy (from food) to do work to push the chain round. Eventually, you would have to eat some more food to keep pedalling!

Cutaway of cell
Picture 1.10. A cell produces a voltage using a chemical reaction inside the casing.
CD player
Picture 1.11. A CD player takes a current from the mains supply. This means that more fuel has to be used up at the power station.
What about the mains?
When you plug a CD player into the mains supply, it takes an electric current which drives the motor. However, the current coming out of the CD player is the same as the current going in. It doesn't get used up. So what does get used up?

It is the fuel at the power station. The power company uses coal, gas or nuclear fuel to turn water into steam and drive huge turbines. These turbines are connected to generators which generate the electricity. When you switch on your CD player, the generators have to a work a little bit harder to generate the electricity. This means they need a bit more coal, gas or nuclear fuel to keep them going.

So, using electricity in your home, means thata fuel is used up in a power station.

Car battery photo
Picture 1.12. Measuring the voltage of a car battery.
What is voltage?
Different batteries have different voltages (usually 3 V, 6 V, 9 V or 12 V). We use a voltmeter to measure the voltage of a cell or battery.

The mains electricity is at 230 V. You should never try to measure this yourself.

The voltage is a measure of how hard the source pushes the electric current. A low voltage gives a small push. A high voltage gives a bigger push. The bigger the push, the bigger the current that will flow.

The mains gives a much bigger push than any batteries. That's why you need to be very careful never to touch a live mains cable. It can push a big current through your body - big enough to kill a you.

Circuit Challenge 4 - Try it now!
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Question 4
Look at the situations below. In each case, decide what the main energy transfer is. Choose the correct energy labels from the drop down list.

In some cases the source uses an electric current to carry the energy to where it is needed. Click the check boxes for these situations.

Situation uses
electricity
A. A torch circuit to
B. A cyclist speeding up to
C. A hi fi amplifier to
D. A model car to
E. A gas fire to
F. An electric fire to