L21_Viet_Electromagnetic Induction

L21_Viet_Electromagnetic Induction - Physics 122...

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Unformatted text preview: Physics 122 Electricity and Magnetism Lectur e 21 Electr omagnetic I nduction 05/13/09 Physics 122 - Lecture 21 2 I n 1831, Joseph Henry, a Professor of Mathematics and Natural Philosophy at the Albany Academy in New York, discovered magnetic induction. I n July, 1832 he published a paper entitled On the Production of Currents and Sparks of Electricity from Magnetism describing his work. Because Henry published after Michael Faraday, his did not receive much credit for this discovery, which actually preceded Faradays. The H istor y of I nduction Joseph H enr y ( 1797-1878) M ichael Far aday (1791-1867) Michael Faraday's ideas about conservation of energy led him to believe that since an electric current could cause a magnetic field, a magnetic field should be able to produce an electric current. He demonstrated this principle of induction in 1831 and published his results immediately. The principle of induction was a landmark in applied science, for it made possible the dynamo, or generator, which produces electricity by mechanical means. 05/13/09 Physics 122 - Lecture 21 3 Far adays Discover y Faraday had wound two coils around the same iron ring. He was using a current flow in one coil to produce a magnetic field in the ring, and he hoped that this field would produce a current in the other coil. Like all previous attempts to use a static magnetic field to produce a current, his attempt failed to generate a current. However, Faraday noticed something strange. I n the instant when he closed the switch to start the current flow in the left circuit, the current meter in the right circuit jumped ever so slightly. When he broke the circuit by opening the switch, the meter also jumped, but in the opposite direction. The effect occurred when the current was stopping or starting, but not when the current was steady. Faraday had invented the picture of lines of force, and he used this to conclude that the current flowed only when lines of force cut thr ough the coil . 05/13/09 Physics 122 - Lecture 21 4 Far aday I nvestigates I nduction Faraday placed one coil above the other, without the iron ring. Again there was a momentary current when the switch opened or closed. Faraday replaced the upper coil with a bar magnet. He found that there was a momentary current when the bar magnet was moved in or out of the coil. Was it necessary to move the magnet? Faraday placed the coil in the field of a permanent magnet. He found that there was a momentary current when the coil was moved....
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L21_Viet_Electromagnetic Induction - Physics 122...

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