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ELECTROMAGNETISM

ELECTROMAGNETISM

The English physicist, Michael Faraday, discovered that electrical energy could be turned into mechanical energy (movement) by using magnetism. He used a cylindrical coil of wire, called a solenoid, to create a simple electric motor. He went on to discover that mechanical energy can be converted into electrical energy - the reverse of the principle of the electric motor. His work led to the development of the dynamo. You can make a powerful electromagnet by passing electricity through a coil of wire wrapped many times around a nail (see page 26). Electromagnets are found in many everyday machines and gadgets. A body scanner, like the one pictured here, contains many ring-shaped electromagnets. With a solenoid and a current of electricity, you can close the cage.

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1. Take a piece of polystyrene and edge it with cardboard. Stick plastic straws upright around three sides as the bars of the cage.

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2. Cut out another piece of polystrene of the same size for the roof of the cage. Fix a piece of plastic straw to the side above the door. Wind a piece of wire around a nail 50 times leaving two ends. Fix the nail to the roof, as shown.

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Insert a needle into the straw so that it almost touches the nail. Cut out a rectangle of plastic for the door. Make a hole at the bottom of the door for the needle to fit through.

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Stick a piece of card across the door to help hold it open, and make sure the end of the needle just pokes through the hole. Now attach one of the wires to one terminal on the battery. Leave the other free. Make sure it will reach the other terminal. Put the animal into the cage.

Why It Works

switched

When the current is switched on, the nail becomes magnetized as the current flows through the wire. The needle in the door of the cage is attracted to the electromagnet. As the needle is pulled towards the nail, the door closes to trap the tiger.



Bright Ideas
Wind more turns of wire on to the electromagnet. The magnetic effect will increase. What happens if you use a more powerful battery?
Make another electromagnet using a shorter nail. This will also make the magnetic pull stronger.
Make an electromagnetic pick-up by winding wire around a nail. What objects

can you pick up? What happens when the current is turned off?
Use an electromagnet to make a roundabout work. Attach paper clips around the edge of a circular card lid to be the roof. Make sure it is free to spin, and place an electromagnet close to the paperclips. The roundabout should turn as you switch the current on and off quickly.

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Now pick up the free wire. Allow the free wire to come into contact with the unconnected battery terminal. The needle should be pulled back towards the nail. The door will fall down, trapping the animal in its cage.