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lecture16 - PHYS 272 Matter and Interactions II Electric...

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Fall 2010 Prof. Yong Chen ( [email protected] ) Prof. Michael Manfra ( [email protected] ) Lec16 Slide 1/24 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ PHYSICS 272 Lecture 16 Electric Fields and Circuits [EMI Ch.19] Prof. Chen is giving both sections’ lecture today
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Fall 2010 Prof. Yong Chen ( [email protected] ) Prof. Michael Manfra ( [email protected] ) Lec16 Slide 2/24 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ (macroscopic) observables do not change with time Take copper as an example: Drift speed = 5 × 10 -5 m/s; Mobility = 4.5 × 10 -3 (m/s)/(N/C) E-field ~ 10 -2 N/C (small ) but adequate to push a sizable current through the copper wire
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Fall 2010 Prof. Yong Chen ( [email protected] ) Prof. Michael Manfra ( [email protected] ) Lec16 Slide 3/24 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ E nAu i n is assumed the same everywhere (same material) 1. There must be an electric field in the wires. 2. The magnitude of the E-field must be the same through- out a wire of uniform cross section and material. 3. The direction of the E-field at every location must be along the wire, since current flow follows the wire.
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Fall 2010 Prof. Yong Chen ( [email protected] ) Prof. Michael Manfra ( [email protected] ) Lec16 Slide 4/24 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ Remember this picture High V Low V What provides the E-field that drives electrons in wires in circuits? emf
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Fall 2010 Prof. Yong Chen ( [email protected] ) Prof. Michael Manfra ( [email protected] ) Lec16 Slide 5/24 PHYS 272: Matter and Interactions II -- Electric And Magnetic Interactions http://www.physics.purdue.edu/academic_programs/courses/phys272/ Potential difference across connecting wires Connecting wires: thick copper wires Light bulb: resistive, low mobility Even for long connecting wires nAuE v nA i bulb wires E E  bulb bulb wires wires L E L E  0 emf 0
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lecture16 - PHYS 272 Matter and Interactions II Electric...

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