magnetism

magnetism - MAGNETISM History of Magnetism Sources of...

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MAGNETISM History of Magnetism Bar Magnets Magnetic Dipoles Magnetic Fields Magnetic Forces on Moving Charges and Wires Electric Motors Current Loops and Electromagnets Solenoids Sources of Magnetism Spin & Orbital Dipole Moments Permanent Magnets Earth’s Magnetic Field Magnetic Flux Induced Emf and Current Generators Crossed Fields
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History of Magnetism The first known magnets were naturally occurring lodestones, a type of iron ore called magnetite (Fe 3 O 4 ). People of ancient Greece and China discovered that a lodestone would always align itself in a longitudinal direction if it was allowed to rotate freely. This property of lodestones allowed for the creation of compasses two thousand years ago, which was the first known use of the magnet. In 1263 Pierre de Maricourt mapped the magnetic field of a lodestone with a compass. He discovered that a magnet had two magnetic poles North and South poles. In the 1600's William Gilbert, physician of Queen Elizabeth I, concluded that Earth itself is a giant magnet. In 1820 the Danish physicist Hans Christian Ørsted discovered an electric current flowing through a wire can cause a compass needle to deflect, showing that magnetism and electricity were related.
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History (cont.) In 1830 Michael Faraday (British) and Joseph Henry (American) independently discovered that a changing magnetic field produced a current in a coil of wire. Faraday, who was perhaps the greatest experimentalist of all time, came up with the idea of electric and magnetic “fields.” He also invented the dynamo (a generator), made major contributions to chemistry, and invented one of the first electric motors In the 19th century James Clerk Maxwell, a Scottish physicist and one of the great theoreticians of all times, mathematically unified the electric and magnetic forces. He also proposed that light was electromagnetic radiation. In the late 19 th century Pierre Curie discovered that magnets loose their magnetism above a certain temperature that later became known as the Curie point. In the 1900's scientists discover superconductivity. Superconductors are materials that have a zero resistance to a current flowing through them when they are a very low temperature. They also exclude magnetic field
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Magnetic Dipoles Recall that an electric dipole consists of two equal but opposite charges separated by some distance, such as in a polar molecule. Every magnet is a magnetic dipole. A bar magnet is a simple example. Note how the E field due an electric dipole is just like the magnetic field ( B field) of a bar magnet. Field lines emanate from the + or N pole and reenter the - or S pole. Although they look the same, they are different kinds of fields. E fields affect any charge in the vicinity, but a B field only affects moving charges. As with charges, opposite poles attract and like poles + _ - N S Electric dipole and E field Magnetic dipole and B field
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magnetism - MAGNETISM History of Magnetism Sources of...

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