The effect of electric fields in a classic introductory physics treatment of eddy current forces

A simple model of eddy currents in which current is computed solely from ma gnetic forces acting on electrons proves accessible to introductory student s and gives a good qualitative account of eddy current forces. However, thi s model cannot be complete; it ignores the electric fields that drive curre nt outside regions of significant magnetic field. In this paper we show how to extend the model to obtain a boundary value problem for current density . Solution of this problem in polar coordinates shows that the electric fie ld significantly affects the quantitative results and presents an exercise suitable for upper division students. We apply elliptic cylindrical coordin ates to generalize the result and offer an exercise useful for teaching gra duate students how to use nonstandard coordinate systems. (C) 2001 American Association of Physics Teachers.