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# lecture5 - Physics 2102 Jonathan Dowling Physics 2102...

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Electric Potential I Electric Potential I Physics 2102 Jonathan Dowling Physics 2102 Physics 2102 Lecture 5 Lecture 5

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Electric potential energy Electric potential energy Electric potential energy of a system is equal to minus the work done by electrostatic forces when building the system (assuming charges were initially infinitely separated) U= - W The change in potential energy between an initial and final configuration is equal to minus the work done by the electrostatic forces: U= U f U i = W What is the potential energy of a single charge? What is the potential energy of a dipole? A proton moves from point i to point f in a uniform electric field, as shown. Does the electric field do positive or negative work on the proton? Does the electric potential energy of the proton increase or decrease? +Q –Q a +Q
Electric potential Electric potential Electric potential difference between two points = work per unit charge needed to move a charge between the two points: V = V f –V i = - W/q = U/q 0 0 0 f f i i f f i i dW F ds dW q E ds W dW q E ds W V V V E ds q = = = = = - = - = - r r r r r r r r

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Electric potential energy, Electric potential energy, electric potential electric potential Units : [U] = [W]=Joules; [V]=[W/q] = Joules/C= Nm/C= Volts [E]= N/C = Vm 1eV = work needed to move an electron through a potential difference of 1V: W=q V = e x 1V = 1.60 10 –19 C x 1J/C = 1.60 10 –19 J
Equipotential surfaces Equipotential surfaces

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## This note was uploaded on 11/18/2011 for the course PHYSICS 2102 taught by Professor Dowling during the Fall '10 term at LSU.

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lecture5 - Physics 2102 Jonathan Dowling Physics 2102...

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