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Magnetism

 Electromagnetic Devices and Inventions The discovery of electromagnetism led to a large number of inventions and devices. Being able to turn magnetism on and off, the great strength of electromagnets, and being able to vary the magnetism by varying the electrical current are characteristics of electromagnetism used in many inventions. Some devices reverse the characteristics to create another class of devices. Questions you may have include: How is the strength of an electromagnet used? How is moving something though varying magnetic strength used? How can some inventions be reversed? Lifting and dropping objects The magnetic strength of an electromagnet depends on the number of turns or wire and the current through the wire, and the size of the iron core. This allows electromagnets to be made much larger and stronger than a natural magnet, such that they can pick up very large objects. Also, when you turn off the electricity to an electromagnet, the magnetism is also turned off. Thus, an electromagnet can be used to pick up a piece of iron and then drop it someplace else. Crane uses electromagnet to pick up junked car Strong electromagnets are often used in areas of heavy industry to move large pieces of iron or steel. They are commonly employed in junkyards, where a crane with a huge electromagnet is used to pick up, move and drop old, junked cars. Creating motion Changing the electrical current through an electromagnet changes its strength and even direction of its magnetic field. This effect can be used to create controlled motion of objects, which in turn can result in some interesting results. Loudspeaker The loudspeakers in your radio, TV or stereo system use varying electric current through an electromagnet to create sound. The electric current varies at a fast rate, causing the strength of the magnetic field to vary. This results in moving the loudspeaker membrane or cone back and forth rapidly, resulting in sound and even music. Cut-out of a loudspeaker Take a look at a loudspeaker and see the coil of wire and electromagnet in its back area. Some loudspeakers use a solenoid instead of an electromagnet. Electric motor An electric motor is an even more clever application of electromagnets. Suppose you put some electromagnets on a wheel and put some permanent magnets around the wheel. The electromagnets could be made to attract and repel the surrounding magnets, causing the wheel to turn. Look at an electric motor and see the internal wheel made of electromagnets and the outer shell made of permanent magnetic material. Creating electricity You can reverse many of these inventions. You have seen that changing an electric current can change the magnetic field and cause varying motion of an object. By reversing that, you can move a magnet to create an electrical current. This is a result of an amazing duality principle that you will see many times in science, in that you can reverse ideas or inventions. Loudspeaker becomes microphone Suppose you took a loudspeaker or an earphone and vibrated its membrane with sound? The movement of the coiled wires or solenoid in the magnetic field would work just the opposite of a loudspeaker, and a varying electrical current would be created. You would now have a microphone. Creating electricity with a magnet Now if electric current moving though a wire creates a magnetic field, could just the opposite—a wire moving through a magnetic field—cause electric current? The answer is yes. If you take a N and S magnet and pass a wire through their magnetic field, electric current will flow through the wire. Moving a magnet through coils of wire creates electricity Electric motor creates electricity If you took an DC electric motor and spun the rotor, its wires would cut through the magnetic fields and create electricity. An electric generator is simply an electric motor that you are spinning. Phonograph The grooves in a phonograph record cause the needle to vibrate. Electronic amplifies the signal and rapidly turns the current to the loud speaker on and off. This results in playing of the sound that was previous recorded into those grooves. In conclusion Electromagnetic devices and inventions include a large magnet to lift up and drop automobiles, the loudspeaker, electric motor, microphone, electric generator, and phonograph. Some devices use the opposite effects as others. The loudspeaker and microphone are examples of this.