Physics 121: Electricity & Magnetism – Lecture 4 Carsten Denker NJIT Physics Department Center for Solar–Terrestrial Research

February 7, 2007Center for Solar-Terrestrial Research Electric Potential Energy Gauss’ and Coulomb’s law are identical  electrostatic force is a conservative force! Electric potential energy Reference configuration (initially infinite separation  U i = 0)

February 7, 2007Center for Solar-Terrestrial Research Electric Potential Potential differencePotential defined Electric potential is a property of an electric field, regardless of whether a charged object has been placed in that field. It is measured in J/C or V. Electric potential energy is an energy of a charged object in an external electric field (or more precisely, an energy of the system consisting of the object and the external field. It is measured in J.

February 7, 2007Center for Solar-Terrestrial Research Equipotential Surfaces Imaginary or real, physical surface where adjacent point have the same electric potential. No work is done by the electric field on a charged particle while moving the particle along an equipotential surface. Equipotential surfaces are always perpendicular to electric field lines.

February 7, 2007Center for Solar-Terrestrial Research Calculating the Potential from the Field Potential differencePotential difference with V i = 0 at infinity

February 7, 2007Center for Solar-Terrestrial Research Potential Due to a Point Charge Point charge Ensemble of point charges A positively charged particle produces a positive electric potential. A negatively charged particle produces a negative electric potential.

February 7, 2007Center for Solar-Terrestrial Research Potential Due to a Continuous Charge Distribution Line of charge Charged disk The component of in any direction is the negative of the rate of change of the electric potential with distance in that direction.