Ch24Sp09AGM

# Ch24Sp09AGM - C hapte 24 Ele r ctric Pote ntial Que stions...

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Chapter 24: Electric Potential Questions to Answer o How do you describe the energy stored in a system of charges associated with the electric force between them? o What is the relationship between electric potential energy and electric potential? o How do you calculate the potential energy for a system of charges? o How do you calculate the electric potential for any point in space due to a system of charges? o Why is calculating the electric potential for a system easier than calculating the electric field?

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Chapter 24: Electric Potential MORE Questions to Answer o How do you calculate the electric potential for any point in space due to a countinuous distribution of charge? o How can you calculate the electric field for any point in space from the electric potential? o What are equipotential surfaces? o How do you draw equipotential surfaces? o How much work do you do when you move a charge on an equipotential surface? o How much work do you do when you move between equipotential surfaces?
Ch. 24 Electric Potential So far we have learned about the electrostatic force, how to describe it in terms of an electric field and how we can more easily determine the electric field by using Gauss’ Law. Now we will see that the electric force is a conservative force and therefore energy is conserved. From this we will determine The potential energy associated with this force The electric potential, V , a physical characterisitic that is very useful in analysizing and understanding electronic systems. What equipotenital surfaces are and how to construct them.

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A B γ 1 γ 2 γ Forces Conservative (W AB does not depend on the path) Non-conservative (W AB depends on the path) Work B AB A W F dS = ur ur Along any path B B A A U U - = - The Coulomb force is conservative Thus we can define the potential energy U associated with it as follows:
Potential Energy U of two point charges Consider two point charges q and q o. The potential energy difference U b - U a between points a and b for these two charges is given by: Units for U: Joule = N.m Note: Since W ab does not depend on the path, it is only a function of r a and r b Along any path b b a ab a U U W F dS - ≡ - = - ur ur

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We will calculate the potential energy difference U b - U a as we move charge q o from point a to point b in the presence of charge q at the origin O. The calculation gives the result: 1 1 4 o b a o b a qq U U r r πε - = -
We divide the path from point a to point b into two segments. Segment 1( γ 1 ) is along the radius. Segment 2 ( γ 2 ) is along an arc. F 1 2 1 2 2 2 4 1 1 0 4 4 1 1 Thus 4 b a o b a o r o o o o b a r o b a o b a qq U U F dS F r qq qq dr r r r qq U U r r γ πε - = - - = - - = = - = - = - ur ur

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h m v A B In mechanics only changes in U have physical meaning.
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## This note was uploaded on 03/26/2010 for the course PHY 108 taught by Professor Iashvili during the Spring '08 term at SUNY Buffalo.

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Ch24Sp09AGM - C hapte 24 Ele r ctric Pote ntial Que stions...

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