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**Unformatted text preview: **Lecture 7 Lecture 7-1 Electric Potential Energy and Electric Potential positive charge High U (potential energy) Low U negative charge High U Low U High V (potential) Low V Electric field direction High V Low V Electric field direction Lecture 7 Lecture 7-2 Potential due to two (source) charges 1 2 () || | | q q Vx k k x xa = + 1 2 q q = > Lecture 7 Lecture 7-3 E from V x V E x = y V E y = z V E z = Expressed as a vector, E is the negative gradient of V V E = a a We can obtain the electric field E from the potential V by inverting the integral that computes V from E : () ( ) r r x y z Vr Edl EdxEdyEdz = = + + a a a a i E always points from high V to low V. (But high V is high U only for a positive charge.) Lecture 7 Lecture 7-4 EquipotentialSurfaces An equipotential surface is a surface on which the potential is the same everywhere. U V q = = For a displacement r of a test charge q along an equipotentital , E E q U W r = = = ca a i E an equipotentialsurface everywhere. Perpendicular...

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