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Chapter 12 Lesson 5-Magnetism Vocabulary 1. Magnetism 2. Magnetic field 3. Electromagnet 4. Generator 5. Alternating current 6. Magnetic levitation Notes What is magnetism? Magnets apply forces to certain metals like iron or nickel. Magnets have two poles: north (N) and south (S). o Like poles repel one another o Opposite poles attract one another. Magnets always exist in north-south pairs. o If you cut a magnet in half, each half will form a new magnet with two poles. Compass needles point toward Earth’s North Pole. Geographic North Pole and magnetic north pole are in slightly different places. Atoms act like magnets. In most materials, the north and south poles of atoms point in random directions. o The forces from the random poles cancel each other out. If the poles of many of the atoms line up in the same direction, a permanent magnet is formed. o The forces from the aligned poles of atoms add up and give a magnet its strength. o Ex: bar magnets Iron, nickel, cobalt, and a few other metals are attracted to magnets. When small pieces of these metals are sprinkled over a magnet, they form lines. The closer the lines appear, the stronger the magnetic forces are in that area. The magnetic forces around Earth are similar to those of a bar magnet. What are electromagnets? The moving electrons in electricity generate magnetic fields. When the current stops the magnetic field disappears. o The simplest electromagnet is a straight wire. o The magnetic field circles around the wire when current is flowing. o When you wrap a wire into a loop, you increase the strength of the magnetic field. o Many loops together can make a coil. o The magnetism from each loop adds up to make the coil a stronger electromagnet. Placing a rod of iron in a coil will magnetize the iron. o This adds to the strength of the electromagnet’s magnetic field. An iron rod in an electromagnet’s coil is pulled toward the center of the coil. o This means the magnet can turn on and off. If you try to pull it out, it will spring back. A voice coil operates audio speakers. o Voice coil sits in a permanent magnetic field. o Current changes in the coil alter its magnetic field. o Causes the forces of the permanent magnet to move it back and forth. o Coil is connected to a cone of paper or metal. o The coil’s vibrations make the cone move back and forth, creating sound waves in the air. o If several voice coils were placed in a circle, changes in electric current would cause them to rotate back and forth. An axle is attached to many coils which are between two permanent magnets. Forces between the permanent magnets and the coils acting as electromagnets cause the coils to rotate. Electric motors are used in many devices, from ceiling fans to cars. How can magnets produce electricity? Energy is used to turn the axle of the generator. As the coil moves through the magnetic field, forces push on its electrons and create an electric current. Wires attached to the loop allow the current to flow as the loop rotates. Whenever a loop moves past the pole of a magnet, the direction of the magnetic forces changes. o This causes changes in the direction of the electric current. In real generators, there are several coils of wire that spin past many magnets. U.S. generators produce alternating current that changes directions 120 times each second. Devices called transformers use magnetism to lower the voltage used in homes. What is magnetic levitation? When two poles of magnets face each other they feel a pushing force. If you balance this pushing force against the force of gravity you have magnetic levitation. Scientists and engineers have designed trains that use magnetic levitation (maglev for short) to travel on a track. Electromagnets in the track and in the train have alternating north and south poles. By aligning the right type of poles in the track and in the train, electromagnets push the train a few centimeters above the track. The train moves forward by switching the poles in the track back and forth. Maglev trains have no touching parts between the track and the train. o This means little to no friction. o Still air resistance. o Able to provide very efficient means of traveling from city to city.