The fields outside a long solenoid with a time-dependent current

An instructive version of this well-known problem is the case of a current that is zero to t < 0 and varies as alpha t for t > 0. A generally excellent discussion of this case by Abbott and Griffiths features, however, a singularity in the fields at any point at the moment they first become nonzero, This singularity can be avoided by careful approximation, derived here using expressions for time-dependent fields rather than potentials. The result is that while the fields assume a quasistatic character for long times after the current has started to flow, they include a small amount of radiation at short times. Such an effect was observed in a simple experiment involving a kitchen appliance. (C) 1997 American Association of Physics Teachers.