p240_ct11_w12_feb_9

# p240_ct11_w12_feb_9 - Physics 240 Winter 2012 Lecture#11 My...

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Physics 240 Winter 2012 Lecture #11 Dr. Dave Winn 2405 Randall My Office Hours (1416 Randall Lab) Monday 1pm-3pm Tuesday 1pm-3pm Thursday 2pm-4pm (Prof. Gidley) Learning Assistant Office Hours Tuesday 4-8pm Thursday 4-6pm Also in chat room Tue/Thu evening!

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In the circuit shown, the two bulbs A and B are identical. Compared to bulb A , A. bulb B glows more brightly. B. bulb B glows less brightly. C. bulb B glows just as brightly. D. answer depends on whether the mobile charges in the wires are positively or negatively charged Q25.6
Electrical resistance For many materials V = IR Units of resistance = Vs/C = Ohms (sym: ) Where the resistance R depends on resistivity and geometry, for example R = (L/A) Power dissipated in resistors P=I 2 R=V 2 /R Current Voltage I = (1/R)*V Symbol for resistors:

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Other materials… Ohm’s law is not a good approximation for the conductivity of some materials. For these the relation between I and V can be more complex Semiconductor diodes are an example An example: a “diode”, or one way current device. Demo: negative temperature coefficient
To maintain a current in a circuit, something must ‘pump’ positive charge from low to high potential This ‘electromotive force generator’, EMF device, must do work on charges to make this happen Some examples:

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p240_ct11_w12_feb_9 - Physics 240 Winter 2012 Lecture#11 My...

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