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ELECTROMAGNETISM A metal can be moved around a scrap yard or a factory with an electromagnet Many electric motors contain electromagnets, The recording head on a tape recorder is an electromagnet. A moving coil meter has an electromagnet at its centre. A relay is a simple electromagnetic switch Safes may be locked and unlocked with electromagnets. The picture on your TV screen is moved about with electromagnets Loudspeakers and bells work using electromagnets. Physicists also use electromagnets in accelerators in research and the structure of the nucleus. What is an electromagnet then? It is simply a coil of wire with a current going through it. The wire is usually wrapped round a piece of iron. ELECTROMAGNETS These experiments are to help you to understand something about electromagnetism and electromagnets. Before starting any experiment read through the instructions carefully. Remember: Always turn the power supply off when you are not using it and never use very short lengths of wire. Otherwise you may damage the power supply. EXPERIMENT 1 YOU WILL NEED A low voltage high current power supply, about 50 cm of insulated copper wire, some pins or paper dips, a 15 cm iron rod, cardboard (or plastic) tube that just fits round the rod and a plotting compass. WHAT TO DO Wrap the wire round the tube as shown in the diagram and conned it to the DC sockets of the power 1. Switch on the power supply and see if the coil has turned into an electromagnet by trying to pick up some pins (or paper clips) with it. Try both ends. Now put the plotting compass at one end of the rod and notice which way the needle points. Then try it at the other end and also along the side of the coil. 2. Put the iron rod into the tube and repeat the experiments - does it make into a better electromagnet? 3. Change the connections to make the current flow the other way. What difference does this make? Record your results with diagrams. 4. Now try the experiments again but this time use the AC sockets. Record your results. 1 EXPERIMENT 2. YOU WILL NEED A low voltage high current power supply, about 1 m of wire, two C shaped iron cores (we will call these C ones), a postcard and some iron filings. WHAT TO DO Wrap the wire round one side of one of the C cores as shown in the diagram. Connect the ends of the wires to the DC outlets of the power supply. Stand the C core on its curved side and put the post card on the top of the flat ends. Sprinkle some iron filings onto the post card. Is there a pattern? What does this prove about the C core? Now switch on the current. Draw the pattern that you see - it helps to tap the card gently. Repeat the experiment using the AC sockets. Switch off. Take away the post card and put the second C core on top of the first. Switch on the power supply using the DC sockets. Try to separate the C cores. Repeat the sane experiment using AC. Write up your results. If possible try using less current and/or less coils. What effect do these changes make to the strength of your electromagnet? THE ELECTROMAGNET These experiments should have shown you that an electromagnet: (a) is stronger when there is an iron core in the centre of the coil (b) works which ever way round the current is flowing (c) works with AC or DC (d) is stronger if it has more coils (e) is stronger if the current flowing in the coils is made bigger FURTHER INVESTIGATIONS Find cut how the following men helped our understanding of electromagnets. Maxwell Ampere Oersted Faraday N S 2