ElectricPotentialHongKongPolytechnicUniversityElectricalPotentialEnergy:Theelectrostaticforceisaconservativeforce.Thuswecandefineachangeoftheelectric potential energy U of a charged particle in an electric field to be,whereWistheworkdonebytheelectrostaticforceandispathindependent.If the potential energy is defined to be zero at infinity, the electric potential energy UofapointchargeisU=-W,whereW.istheworkdonebytheelectricfieldonthepoint charge as the charge moves from infinity to the particular point.Concept:In the figure, a proton moves from point i to point f in a uniform electric field directed asshown. (a) Does the electric field do positive or negative work on the proton? (b) Does theEelectricpotential energy of the proton increase or decrease?·iElectricalPotential:The electrical potential energy per unit charge is defined as the electric potentialdifference（电势差)：The electrical potential at apoint is;Theunitisvolt=joulepercoulomb
Hong Kong Polytechnic University Electric Potential Electrical Potential Energy: The electrostatic force is a conservative force. Thus we can define a change of the electric potential energy U of a charged particle in an electric field to be, where W is the work done by the electrostatic force and is path independent. If the potential energy is defined to be zero at infinity, the electric potential energy U of a point charge is U=W , where W is the work done by the electric field on the point charge as the charge moves from infinity to the particular point. Concept: In the figure, a proton moves from point i to point f in a uniform electric field directed as shown. (a) Does the electric field do positive or negative work on the proton? (b) Does the electric potential energy of the proton increase or decrease? Electrical Potential: The electrical potential energy per unit charge is defined as the electric potential difference (电势差): The electrical potential at a point is ; The unit is volt=joule per coulomb. f + i E
ElectricPotentialHongKongPolytechnicUniversityEquipotentialSurfaces（等势面）：Adjacent pointsthathavethe sameelectricpotentialformanequipotential surface,whichcanbeeitheranimaginarysurfaceorareal,physicalone(i) No work is done by theEquipotential surface-Ficld lineelectricfieldwhena chargeismovedonthatsurface(i)Theelectricfield Eisalways directedperpendicularlytotheequipotentialsurfacePotentialCalculatedfromtheField:45E9o+asInauniformelectricfieldE,thepotentialLdifference is
Hong Kong Polytechnic University Electric Potential Equipotential Surfaces (等势面): Adjacent points that have the same electric potential form an equipotential surface, which can be either an imaginary surface or a real, physical one. (i) No work is done by the electric field when a charge is moved on that surface. (ii) The electric field E is always directed perpendicularly to the equipotential surface. Potential Calculated from the Field: In a uniform electric field E, the potential difference is