Physics for Scientists and Engineers 8ed - ch29 - PowerPoint Slides

Physics for Scientists and Engineers 8ed - ch29 - PowerPoint Slides

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Chapter 29 Magnetic Fields
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A Brief History of Magnetism 13 th century BC Chinese used a compass Uses a magnetic needle Probably an invention of Arabic or Indian origin 800 BC Greeks Discovered magnetite (Fe 3 O 4 ) attracts pieces of iron
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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
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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
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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
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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
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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
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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
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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 magnetic pole has been unsuccessful No matter how many times a permanent magnetic is cut in two, each piece always has a north and south pole
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Magnetic Fields Reminder: an electric field surrounds any electric charge The region of space surrounding any moving electric charge also contains a magnetic field A magnetic field also surrounds a magnetic substance making up a permanent magnet
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Magnetic Fields, cont. A vector quantity Symbolized by Direction is given by the direction a north pole of a compass needle points in that location Magnetic field lines can be used to show how the field lines, as traced out by a compass, would look B r
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Magnetic Field Lines, Bar Magnet Example The compass can be used to trace the field lines The lines outside the magnet point from the North pole to the South pole Use the active figure to trace the field lines PLAY ACTIVE FIGURE
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Physics for Scientists and Engineers 8ed - ch29 - PowerPoint Slides

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