spontaneous-force optical trap,". Ketterle, K. B. Davis, M. A. BEC in many diff Joffe,. Martin, and D. E. Pritchard, Phys. Rev. Lett. 70, 2253(1993). A. Gallagher, and. Wieman, "Colli- trap,"Phys. Rev. Lett. 63, 961-964 C. Wieman, "Collective behavior of 64,408--411(1990);D Behavior of neutral atoms in a spon- Cornell, "Behavior of neto-optical trap, "J. Opt. Soc. Am. B 11, (North-Holl nd E. A. Cornell, "Stable ing of neutral atoms," U.P., Cambridge tom traps," in Pro- . Raab, M. Prentis Physics, edited neutral sodit cientific, Singapore, 2634(1987) C. Monroe, Einstein condensate in a phys.rev.a53,r1954-1957(1996 0. Mewes, N.. vanDruten, D. S. Durfe, D. M. Dyrn, of light-assisted collisic phys.rev.a50,3597-3600 atoms in Phys. Rev. Lett. 75, 3969(1995) Surface charges on circuit wires and resistors play three roles Unive. Jac niversity of Ca lifornia 94720-7300 (Received 11 Sept d 1 November 1995) The significanc s assciated with current-carrying circuits is often not apprec surface ctors of a current-carrying circuit ircuit must have nonuniforr orm ele in the potential around the circuit. (2) to provide the surface n vary greatly, depending on the location and orienta s with a circuit consisting of a resistor and a rmits solution with a four tor sizes and location of the batter res ow from the battery to the resistiv irtace charge densities around h the resistor removed. F lements, defined in terms of the surface the same as the capacitance of th oen circuit alone. The discussion is in terms of time-independent currents applies also to low-frequency ac circuits. 1996 American Association . INTRODUCTION A cursory inspection of some beginning undergraduate The ideas of electric charges and potentials of conducting texts-in the Berkeley Physics Library showed that only surtaces in electrostatics on the one hand and current flow in one (the new book by Chabay and Sherwood mentione d elementary physics textbook showing circuit has plus and minus signs next tricity and magnetism ther this is a hint charges, then cor charges presen face charge d treat a practic simple cir scribed as charges ments of the circuit, but able ex or ad into current densities c rrents obeying Ohm's law. In vanced texts15-18 are no better. My book does not even treat electrostatics, charges are always stationary; in circuits, circuits, except in a few pr charges are always in motion. ms associated with capaci- tance or inductance. It is very true that the amounts of charge 855 Am. J. Phys. 64(7), July 1996 1996 American Association of Physics Teachers 855