# L09 - Lecture 9 Electrostatic Energy and Energy Density...

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LECTURE 9 slide 1 Lecture 9 Electrostatic Energy and Energy Density Sections: 4.8 Homework: D4.11, 4.31, 4.33, 4.34, 4.35

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LECTURE 9 slide 2 Energy of System of Point Charges – 1 any system of charged bodies held static in relatively close proximity contains potential energy the potential energy is the work done to build the system, i.e., bring charges together against the Coulomb forces if charges of the system were set loose, this energy would set them into motion, i.e., be converted into kinetic energy the potential of a point charge Q 1 1 1 1 1 1 ,V 4 R R Q Vd d R πε == = ∫∫ EL is the work done to bring a unit positive charge from infinity to a point which is R 1 (meters) away from Q 1
LECTURE 9 slide 3 Energy of System of Point Charges – 2 if a charge Q 2 is brought at a distance R 21 from the first charge Q 1 the energy spent is 1 21 2 2 21 21 ,J = C × V 4 Q WQ Q V R πε =⋅ = as long as Q 1 and Q 2 are held R 12 apart the system holds W 21 = W 12 energy 21 12 WW = it does not matter which charge is brought close to which

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## This note was uploaded on 02/29/2012 for the course PHYS 227 taught by Professor Rabe during the Fall '08 term at Rutgers.

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L09 - Lecture 9 Electrostatic Energy and Energy Density...

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