Distinguishing Electric Potential and Potential Energy Electric Potential Property of the source charges Present whether or not a charged particle is there to experience it Measured in J/C or V © 2010 Pearson Education, Inc. Electric Potential Energy Due to interaction of a charged particle q with the source charges Measured in joules J Electric Potential and Conservation of Energy: Charges in an Electric Field Recall: conservation of energy (isolated system) the total energy of the system is constant; i.e. the sum of the kinetic energy and the electric potential energy must be the same at any two points. Kf + (Uelec)f = Ki + (Uelec)i In terms of the electric potential: ½ mvf2 + qV f = ½ mvi2 + qVi Class discussion/handout: ΔK = -q ΔV © 2010 Pearson Education, Inc. Charged Particle Moving Through a Potential Difference © 2010 Pearson Education, Inc. The Electron Volt In terms of energy: 1J = (1 V)(1 C) A commonly used unit of energy comes from this relationship - the electron volt (eV) 1 eV = (1.60 x 10-19 C)(1 V) = 1.60 x 10-19 J Units: (C)(V) = C(J/C) = J 1 electron volt is the kinetic energy gained by an electron (or proton) if it accelerates through a potential difference of 1 volt. © 2010 Pearson Education, Inc. Potential of a Parallel-Plate Capacitor © 2010 Pearson Education, Inc. Graphical Representations of Electric Potential © 2010 Pearson Education, Inc. The Potential Inside a Parallel-Plate Capacitor units? Uelec Q V Ex x q 0 A © 2010 Pearson Education, Inc. Electric Potential of a Point Charge © 2010 Pearson Education, Inc. Connecting Electric Potential and Field Work done opposite to the E-field on a q W = ΔUelec = q ΔV ▬► To move the q at constant speed, the magnitude of the Fhand = Felec and Felec = q E W = Felec Δd = q E Δd Relating energy and field: ΔV = q E Δd = E Δd q Strength of E-field: E = ΔV Δd © 2010 Pearson Education, Inc. SI units: 1 V/m Connecting Potential and Field © 2010 Pearson Education, Inc. Potential and Field for Three Important Cases © 2010 Pearson Education, Inc. A Conductor in Electrostatic Equilibrium © 2010 Pearson Education, Inc.