Fields of Permanent Magnets and Straight Wires

# Fields of Permanent Magnets and Straight Wires - ends?...

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Fields of Permanent Magnets and Straight Wires We begin looking at the sources of magnetic fields by looking at the most simple cases: permanent magnets and straight wires. Permanent magnets Permanent magnets are the most familiar sources of magnetic fields. A compass needle is a permanent magnet, which itself reacts to the permanent magnet in the earth's axis. Unfortunately, the fields of permanent magnets are very hard to calculate, and require an understanding of complex ferromagnetic phenomena, belonging as much to atomic theory as to electromagnetism. Here we will simply give a qualitative description of the magnetic fields of permanent magnets. In essence, a permanent magnet is a piece of metal with a "North Pole" and a "South Pole". Any magnetized piece of metal has both poles; no magnet can exist with only one pole. Since magnetic charge does not exist, there is no isolated concentration of magnetic charge in an object. So why not simply take a magnet and split it in half, thus separating the north and south

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Unformatted text preview: ends? Well, when we try it, two smaller, identical magnets are produced, shown below. Again, the north or south end of a magnet cannot be isolated. Figure %: a) A permanent magnet, with a north and south pole, is broken up into two pieces in b). Each piece becomes its own permanent magnet, with north and south poles Even though we cannot describe quantitatively the field of a permanent magnet, we can show its shape: Figure %: The field of a permanent magnet The field lines always point away from the north end, and toward the south end, in a shape similar to the electric field between two oppositely charged particles. As we will see, this field is quite similar to the field created by a coil of wire with a current running through it (see solenoid ). Permanent magnets are often used to create magnetic fields; these magnets are usually oriented in a manner that causes a uniform field, so we do not have to concern ourselves too much with their field shape....
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