p240_ct5_f07

# p240_ct5_f07 - Physics 240 Fall 2007 Lecture#5 Dr Dave Winn...

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Physics 240 Fall 2007 Lecture #5 Dr. Dave Winn 2405 Randall Lab [email protected]

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Quick review • Point charges interact through Coulomb’s law • We find the total electric force by taking the vector sum of the Coulomb forces from every point charge • Each charge is surrounded by an ‘electric field’ which fills space • We find the total electric field by taking the vector sum of the electric field from every point charge r r Q kQ F ˆ 2 2 1 21 = G r r kQ E ˆ 2 1 1 = G
Some important examples: 2 0 2 4 : charge Point r Q r kQ E πε = = r r k E 0 2 2 : Line Infinite λ = = 0 2 2 : Plane Infinite ε σ π = = k E

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This time: a powerful new approach to determining electric fields • In electrostatics, positive charges are ‘sources’ of electric field, negative charges ‘sinks’ • If we look at a volume containing excess positive charge, more field will come out than go in… • If we look at a volume containing excess negative charge, more field will go in than come out… • Gauss’ law will quantify this for us
The basic idea: If electric goes mostly out, there must be positive charge. If electric field goes mostly in, there must be negative charge. If it goes equally out and in, there must be no net charge inside.

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Quantifying this…. • How can we quantify
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## This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Fall '08 term at University of Michigan.

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p240_ct5_f07 - Physics 240 Fall 2007 Lecture#5 Dr Dave Winn...

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