8B - 8_Currents+magnet_11.ppt

8B - 8_Currents+magnet_11.ppt - Connection of Electricity...

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Connection of Electricity and Magnetism For thousands of years people had known about magnetic and electric effects: - Electric charges move other electric charges. - Magnets move other magnets. Until about 1800 there was no notable effect of charges on magnets -
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Breakthroughs - Øersted to Faraday In April, 1820 Hans Christian Øersted (Denmark) noticed the deflection of a compass needle by an electric current. (An earlier observation did not make an impression on scientists.) Moving charges pushed magnets . In 1831, Michael Faraday (England) discovered “induction”: Moving magnets pushed charges. This has revolutionized civilized life.
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Magnetic Fields from Electric Currents Although permanent magnets were known in antiquity, the fact that magnetism could be produced by electric currents was not discovered until 1820 by Hans Christian Oersted. One of the greatest discoveries in physics .
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Demo - Oersted’s Discovery
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Oersted’s Discovery Knew that magnets can move other magnets… Oersted had a FIXED current-carrying wire and a movable magnet. The key observation was that the current-carrying wire acted like a magnet !
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Quantifying Oersted’s Discovery Biot and Savart (1820, France) A current-length element produces a differential magnetic field, d B , at point P . The × (the tail of an arrow) at the dot for point P indicates that d B is directed into the page there.
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Example of Biot - Savart Magnetic field of a current in a semi-infinite straight wire
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Example of Biot-Savart - 2 Magnetic field of a current in a circular arc
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Sample Problem The wire in the figure carries a
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This note was uploaded on 05/02/2011 for the course PHYS 8B taught by Professor Catherinebordel during the Spring '10 term at Berkeley.

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8B - 8_Currents+magnet_11.ppt - Connection of Electricity...

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