241-29_Lec-17

241-29_Lec-17 - Physics 241 Lecture 17 Y. E. Kim October...

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Physics 241 Lecture 17 Y. E. Kim October 26, 2010 Chapter 29, Sections 4 7 October 25, 2010 University Physics, Chapter 25 and 26 1
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October 25, 2010 University Physics, Chapter 29 2 Induced Voltage (motional emf) on a Moving Wire in a Magnetic Field (1) Consider a conducting wire of length L moving with constant velocity v perpendicular to a constant magnetic field B as shown The magnetic field exerts a force F on the conducting electrons in the wire, causing them to move downward This motion of the electrons produces a net negative charge at the bottom of the wire and a net positive charge at the top of the wire This charge separation produces an electric field E that exerts a force F on the conduction electrons that tends to cancel the magnetic force
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October 25, 2010 University Physics, Chapter 29 3 Induced Voltage (motional emf ) on a Moving Wire in a Magnetic Field (2) After some time the forces on the electrons are in equilibrium and we can write Thus we can express the induced electric field as This electric field produces a voltage between the two ends of the wire given by We can then write the voltage between the ends of the wire as BE F qvB F qE E vB V vB L V vLB
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October 25, 2010 University Physics, Chapter 29 4 Application of Faraday’s Law of Induction Generators and Motors Faraday’s Law of Induction can be applied to the generation and use of electric current A device that produces electric current from mechanical motion is called a generator A device that produces mechanical motion from electric current is called a motor
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October 25, 2010 University Physics, Chapter 29 5 Generators and Motors (2) A simple generator consists of a loop forced to rotate in a fixed magnetic field The driving force that causes the loop to rotate can be supplied by hot steam running over a turbine Or the loop can be made to rotate by water or wind in a completely pollution-free way of generating electrical power Direct current generator split ring commutator Alternating current generator slip ring commutator
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October 25, 2010 University Physics, Chapter 29 6 Direct and Alternating Current Generators In a direct current generator the rotating coil is connected to an external circuit using a split commutator ring Direct voltage/ current Alternating voltage/ curre nt The voltages and currents produced by
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241-29_Lec-17 - Physics 241 Lecture 17 Y. E. Kim October...

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