Lecture14

# Lecture14 - Physics 132 Introductory Physics: Electricity...

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1 February 6, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 1 Physics 132 Introductory Physics: Electricity and Magnetism Winter Quarter 2008 Lecture 14 February 6, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 2 Conductors in Electrostatic Equilibrium - + - + - + - + - + Where are electrons in an isolated piece of copper wire in a static electric field? Simple view: Copper is a conductor, so electrons are free to move. They move until E=0; then motion stops. Reality: Electrons are ‘hot’, so they move at 10 6 m/s at room temperature! Frequent collisions randomize their directions. On the average, E=0.

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2 February 6, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 3 Non-Electrostatic Conductors 0 +V E I v e Connect a battery to create a potential difference across a copper wire. Then E 0 in the wire. As electrons move to try to cancel the field, the battery supplies more electrons to maintain it. The average motion of electrons turns out to be a slow drift much less than their random velocities. Electron drift leads to current (a net flow of charge) I = dq dt q = Units : Coulomb second = Ampere Note sign convention. February 6, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 4 Current So far we have dealt with charges in electrostatic equilibrium . In electrostatic equilibrium all charges are at rest. Now consider charges in steady motion. Current The amount of charge moving through an object per unit time Units: Coulombs/second= Amperes Symbol:
3 February 6, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 5 Current Density Current is like a flowing fluid.

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## This note was uploaded on 04/18/2008 for the course PHYS 132 taught by Professor Beatty during the Winter '08 term at Ohio State.

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Lecture14 - Physics 132 Introductory Physics: Electricity...

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