Chapter 17 - Dr. G. Antar 1 Chapter 17 Current and...

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Unformatted text preview: Dr. G. Antar 1 Chapter 17 Current and Resistance And Ohms Law Dr. G. Antar 2 Outline 1. Electric Current 2. Current and Drift Speed 3. Resistance and Ohms Law 4. Resistivity 5. Temperature Variation of Resistance 6. Electrical Energy and Power 7. Superconductors Dr. G. Antar 3 The total charge is equal to the sum of the charges on the capacitors Motivation: Capacitors in Parallel and the need for more precise description of what is happening 2 1 V V V = = + + = 2 1 C C C eq 1 V 2 V Q = Q 1 + Q 2 Q Q 1 Q 2 Dr. G. Antar 4 Electric Current and Current Density 1 2 Q Q Q- = I is the amount of charges passing through A per unit time ( 29 s C I t Q I = = A Ampere is of unit The ( 29 2 m A density Current the called is A I J = Q 1 Q 2 Dr. G. Antar 5 Current Direction Convention (!) Conventional current was defined early in the history of electrical science as a flow of positive charge . In solid metals, like wires, the positive charge carriers are immobile, and only the negatively charged electrons flow. Because the electron carries negative charge, the electron current is in the direction opposite that of the conventional current (or the electric ). Currents can be positive or negative. Dr. G. Antar 6 A microscopic view of the current: Charge Carrier Motion in a Conductor Sites of e- collisions with atoms in the conductor. While traveling inside a conductor, subject to an electric field, free electrons make a number of collisions with atoms....
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This note was uploaded on 01/06/2012 for the course PHYS 205 taught by Professor Antar during the Spring '09 term at American University of Beirut.

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Chapter 17 - Dr. G. Antar 1 Chapter 17 Current and...

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