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Magnetism Notes Magnetism gets its name from Magnesia in Turkey where, over 2000 years ago, the ancient Greeks came across pieces of rock, which possessed mysterious powers. (This rock was called lodestone!) A magnet is the name for a substance (usually a metal such as iron or steel) that has been ‘magnetized’ so that it will behave like a magnet. Another characteristic of a magnet is that if it is left to float on the water, or suspended in air from a thread tied around its middle, it will always end up pointing in a north-south direction. The two ends of a magnet are described as northseeking and south-seeking poles. Magnetic objects entering the field area around a magnet are affected by the magnet’s forces of attraction and repulsion. This area is called a magnetic field. The larger the magnet the stronger the field. If you divide a magnet in half, it produces 2 whole fields. Although the field itself is invisible, there are ways of finding out what it looks like. Metal objects that are attracted by magnets become magnets too, although this effect dies away once the object has been moved from the magnetic field. You can create a magnet yourself by magnetizing something metal (such as a needle or a paper clip.) Rub it with a strong magnet in the same direction 30 or 40 times. Some metals are magnetized easily and some metals take longer. Electromagnets 7. An electric current flowing through a wire gives rise to a magnetic field whose direction depends upon the direction of the current. 8. Electricity through a wire creates a magnetic field. 9. Electromagnetism is the relationship b/t electricity & magnetism. 10. Electromagnets are temporary magnets made by wrapping a coil of wire around a soft iron core and passing an electric current through the wire. 11. Two ways to increase the strength of an electromagnet: a. more coils b. increase current or voltage 12. The advantage of electromagnets is that they can be turned on and off. 13. An electric motor converts electric energy into mechanical energy. It consists of an electromagnet free to rotate. It also has a permanent magnet in a fixed position 14. The current is reversed in the coil of wire in the electromagnet causing it to spin inside the permanent magnet. The spinning allows the motor to do work. A galvanometer uses magnetism to detect electric current. Uses for electromagnets: Earth’s magnetic field lines