Abstract

Field theory is used to analyze a simple circuit and to deduce the conditions for nonradiative and quasistatic fields. From the condition for quasistatic fields, which is the more stringent of the two, Kirchhoff's voltage equation and its range of validity are deduced. These conditions for the validity of circuit theory are not treated appropriately in the undergraduate curricula. A simple numerical problem is given to illustrate these ideas. (C) 2007 American Association of Physics Teachers.