L15_a - ELECTRIC POTENTIAL(Chapter 20 In mechanics saw...

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ELECTRIC POTENTIAL (Chapter 20) In mechanics, saw relationship between conservative force and potential energy: dx dU F x Says: dependence of scalar quantity (potential energy) on position gives components of a vector quantity (force) Any connection to electric forces? Consider a spatial arrangement of charges: To directly calculate electric field at a point: o calculate contributions (vectors) from charges and add (vector sum) Will now see how to calculate electric potential (potential energy per unit charge) at a point by a scalar sum and then get components of electric field from derivatives o Avoids vector sum. Scalar sums are easier! Electric Potential is like a landscape. E is like a vector pointing down (or up) hill.
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WORK DONE ON A CHARGE MOVING IN AN ELECTRIC FIELD Electrostatic force on charge 0 q in field E is E q F 0 If charge moves through displacement s d , work ON charge BY electric field is: s d E q s d F dW 0 Notice scalar (dot) product But electrostatic force is conservative: Potential energy ( U ) decreases when a conservative force does positive work So: s d E q dU dW 0 dU is the change in potential energy of charge when it is displaced by s d If charge is moved from point A to point B, change in potential energy is: B A A B s d E q U U U 0 Important: because force conservative, ΔU independent of path from A→B
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This note was uploaded on 03/08/2012 for the course PHYSICS 1051 taught by Professor Michaelmorrow during the Winter '12 term at Memorial University.

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L15_a - ELECTRIC POTENTIAL(Chapter 20 In mechanics saw...

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