Making motors go faster and slower
Listen carefully. You should be able to hear the fan of your computer. It should be making a high-pitched buzzing or humming noise. The fan spins round in your computer to keep the components cool. The fan spins due to the action of an electric motor. As you listen electricity is passing through a wire coil in the motor and turning it into a magnet to make it spin. The reason the coil spins is that there is a magnet around the coil and it pushes the coil round in the same way that two magnets push each other away when their north or south poles come close together. Nobody would guess that electricity and magnetism are related but an observant scientist made the connection way back in 1819.

In 1799 Alessandro Volta, an Italian scientist, invented the battery. Shortly after, scientists all over Europe began to use batteries to investigate the flow of electrical currents through wires. One day in 1819 Hans Christian Oersted, a Danish scientist, was giving a lecture to his students. He had some scientific instruments on his bench and was demonstrating how electricity could produce heat. In this demonstration he had a piece of wire held in two wooden supports. At one point in his lecture he moved a compass on his bench and put it under the wire. As he was about to continue with his demonstration he noticed that the compass needle had changed the direction in which it was pointing. At the end of his lecture he began an investigation to find out if the wire was affecting the compass.

A compass needle is a magnet. It is set on a pivot so that it is free to turn. The Earth behaves as if it has a huge magnet inside it and the force of the Earth's magnetism makes one end of the needle point north and the other end point south. When Oersted put the compass needle by the wire it did not point in the direction of the current flow but at right angles to it. Oersted checked the result by making the current go the opposite way through the wire and to his amazement he found the needle spun round and pointed in the opposite direction.

When scientists make discoveries they write up their experiments just as you may write up your investigations. As well as filing them away they send copies to be published in a scientific journal. This is like a magazine for scientists. It is full of investigations. Scientific journals are read by scientists all over the world. If a scientist sees an interesting experiment he or she may check it for themselves and then try and make up some other experiments from it to find out more. When scientists saw Oersted's work in a journal they became very interested in the link between the electric current and the movement of the magnet. One scientist, called Dominique Arago, who lived in France, showed that a wire carrying an electrical current attracted iron filings just like a magnet. Another scientist, Michael Faraday, who lived in England, made another discovery.

Faraday set up a bowl full of mercury with a magnet sticking up out of the middle. He hung a copper wire directly over the magnet so that it hung down into the mercury and rested on one side of the magnet. When he connected the wire and the bowl of mercury into a circuit with a battery, electricity flowed through the wire. This made the wire turn into a magnet and push away from the magnet in the mercury. In fact the push between the two magnets sent the wire round and round the magnet. Faraday had invented the first electric motor.

When you switch on an electric motor, you send a current of electricity through a coil of wire and turn it into a magnet. A push develops between the magnetic coil and the other magnet in the motor and this makes the coil spin. If you increase the current you increase the strength of the magnetic coil so a stronger push is made and the coil spins faster. If you decrease the current, you decrease the strength of the magnetic coil so a weaker push is made and the coil spins more slowly.

When you have finished at the computer you will switch it off. The current through the motor fan will stop immediately but the coil will spin on for a few moments as the force of friction slows it down to a halt. The coil no longer behaves like a magnet but next time you switch on the computer the coil will spin into action to help keep your computer working.

What kind of wire is used in an electric motor?
Copper wire.

Copper is not a magnetic metal is it?
No. However when electricity runs through the wire the electric current makes it behave as if it was a magnet.

Where are electric motors used besides computer fans?
They are used in CD players, cassette players and video recorders. An electric motor works the turntable in a microwave oven and tumbles the washing in a washing machine and spin dryer. An electric motor is used to work the fan in a hair drier. It is used in food mixers and electric drills and saws.

Are there any large electric motors?
Yes. They are used in the locomotives of trains. Vehicles which work inside buildings, such as forklift trucks, have electric motors. They do not produce smelly exhaust fumes like petrol and diesel engines.

Do any cars have electric motors?
All cars have electric motors in them but they do not provide the main power for movement. For example, when the ignition key is turned you can hear a starter motor whirring. It moves the pistons up and down inside the engine until the spark plugs make petrol vapour burn and the main engine takes over. Electric motors work the windscreen wipers and in some cars they also work the windows and move the seats. Scientists are working on cars that will have a motor that moves them instead of a petrol engine. Some electric cars have been made but they are not widely used - yet.

Are there electric motors on aircraft?
Yes, there are. They raise and lower the wheels and move the flaps on the wing so the aircraft can make a smooth take-off and landing.

Is there a real magnet inside the Earth?
There is not a huge bar magnet as some people once thought. The magnetic forces of the Earth are made by the way the metals in the centre of the Earth move. At the centre of the Earth is a ball of solid iron and nickel. Surrounding this ball is a layer of molten iron and nickel. Both these metals have magnetic properties. As the Earth spins the ball and liquid move at different speeds and scientists believe that this makes the Earth behave as if it had a magnet inside.

Was the link between magnetism and electricity made by accident?
In a way it was. When scientists make discoveries they try to link them to other discoveries. In Oersted's time some things were known about magnets and electricity so scientists were looking for links. Oersted just happened to have a compass close by a wire and see the change in the needle. This is a good example of a scientist making a careful observation - even though he was working on something else at the time.

Do scientists still report their investigations in journals today?
Yes, they do. There are many more journals today than in Oersted's time because there are far more scientists at work today than two hundred years ago. Scientists also have meetings where they present their results of experiments and discuss what they have found - just like you may have been doing at the end of some of your investigations.

Was Faraday's motor used to make anything work?
No. It was used to show that electricity could make something move. Other scientists found ways of making a motor which could do some work while Faraday investigated other ways in which magnetism and electricity could work together.