The classic problem of determining the force on a current-carrying wire in a magnetic field is
critically analysed. A common explanation found in many introductory textbooks is to represent the
force on the wire as the sum of the forces on charge carriers. In this approach neither the nature
of the forces involved nor their application points are fully discussed. In this paper we provide an
alternative microscopic explanation that is suitable for introductory electromagnetism courses at
university level. By considering the wire as a superposition of a positive and a negative
cylindrical charge distributions, we show that the electrons are subject to both magnetic and
electric forces, whereas the ionic lattice of the metal is dragged by an electric force.
Furthermore, an analysis of the orders of magnitude involved in the problem gives counterintuitive
results with valuable educational potential. We argue that this approach allows one to discuss
different aspects of the physical …