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Unformatted text preview: Outline todays review Remind important concepts and important formulae Solve typical problems Simple calculations that give numbers Problems with variables (symbols) as answers Concept questions Suggestions for your studying Previous exams with simple numbers Previous exams where solutions have a formula (but you wont plug in numbers) Iclicker problems (or previous exam concept questions) Homework problems with either simple numbers OR solutions with a formula (before plug in numbers) Current and current density Current through area A depends upon Charge carrier: concentration n, charge q, and drift velocity Current density J=I/A Direction of current = Fow of positive charge Chapter 25 Summary: Current Resistance and EMF I = d Q d t = n q v d A J = nqv d Resistivity and resistors Resistivity defnition Resistivity Can depend upon T Property oF material Ohms Law Resistance R Depends upon cross sectional area A and length oF wire Resistor takes electrical energy out oF a circuit Power into a resistor Chapter 25 Summary: Current, Resistance, EMF and Power = E J where J = nqv d ( T ) = [1 + ( T T )] R = L A V = IR P = V ab I = I 2 R = V ab 2 R You are given an electric feld oF magnitude E in a copper wire oF radius r and length L that carries a current. What is the magnitude oF the driFt velocity v d oF the electrons in terms oF E, the charge oF the electron e and the resistivity and number oF charge carriers n oF copper? Example 1, Chapter 25: Current and Resistance v d = EL ne v d = E ne v d = E ne v d = E Lne v d = EL r 2 ne A....
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This note was uploaded on 01/03/2012 for the course PHYSICS 750:227 taught by Professor Ronaldgilman during the Fall '11 term at Rutgers.
 Fall '11
 RonaldGilman
 Physics

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