SJSU EE 140 - ch27_B_force (67 pages)

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ch27_B_force



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ch27_B_force

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Pages:
67
School:
San Jose State University
Course:
Ee 140 - Principles of Electromagnetic Fields
Principles of Electromagnetic Fields Documents

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Chapter 27 Magnetic Fields A Brief History of Magnetism 13th century BC Chinese used a compass Uses a magnetic needle Probably an invention of Arabic or Indian origin 800 BC Greeks Discovered magnetite Fe3O4 attracts pieces of iron A Brief History of Magnetism 2 1269 Pierre de Maricourt found that the direction of a needle near a spherical natural magnet formed lines that encircled the sphere The lines also passed through two points diametrically opposed to each other He called the points poles A Brief History of Magnetism 3 1600 William Gilbert Expanded experiments with magnetism to a variety of materials Suggested the Earth itself was a large permanent magnet A Brief History of Magnetism 4 1819 Hans Christian Oersted Discovered the relationship between electricity and magnetism An electric current in a wire deflected a nearby compass needle A Brief History of Magnetism final 1820 s Faraday and Henry Further connections between electricity and magnetism A changing magnetic field creates an electric field Maxwell A changing electric field produces a magnetic field Magnetic Poles Every magnet regardless of its shape has two poles Called north and south poles Poles exert forces on one another Similar to the way electric charges exert forces on each other Like poles repel each other N N or S S Unlike poles attract each other N S Magnetic Poles cont The poles received their names due to the way a magnet behaves in the Earth s magnetic field If a bar magnet is suspended so that it can move freely it will rotate The magnetic north pole points toward the Earth s north geographic pole This means the Earth s north geographic pole is a magnetic south pole Similarly the Earth s south geographic pole is a magnetic north pole Magnetic Poles final The force between two poles varies as the inverse square of the distance between them A single magnetic pole has never been isolated In other words magnetic poles are always found in pairs All attempts so far to detect an isolated



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