1-31-08Lec08 - Lecture 8 Lecture 8-1 Again, Electrostatic...

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Unformatted text preview: Lecture 8 Lecture 8-1 Again, Electrostatic Potential Energy The electrostatic potential energy of a system ( relative to ) is the (external) workneeded to bring the charges from an infinite separation to their final positions. r 12 r 13 r 23 q 1 q 2 q 3 12 13 23 12 13 23 kqq kqq kqq U W r r r = = + + ( ) 2 3 3 1 1 2 1 2 3 12 13 23 12 13 23 11 22 33 1 2 1 2 kq kq kq kq kq kq q q q r r r r r r qV qV qV = + + + + + = + + Generally for n charges: 1 1 2 n ii i U qV = = The factor 1/2 comes from compensating for double- counting potential energy of each pair of charges. Lecture 8 Lecture 8-2 Electrostatic Potential Energy of Conductors bring dq in from q+dq, v +d v v kq U W dq dq R = = = Spherical conductor q, v R Total work to build charge from 0 up to Q: 2 1 2 2 Q kq kQ U U dq QV R R = = = = q v dq U Q V kq v r = Lecture 8 Lecture 8-3 Capacitors A capacitor is a device that is capable of storing electric charges and thus electric potential energy . => charging Its purpose is to release them later in a controlled way. => discharging Capacitors are used in vast majority of electrical and electronic devices. +Q- Q Q Q Q Typically made of two conductors and, when charged, each holds equal and opposite charges . Lecture 8...
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This note was uploaded on 04/07/2008 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue University-West Lafayette.

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1-31-08Lec08 - Lecture 8 Lecture 8-1 Again, Electrostatic...

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