Microscopic models for bridging electrostatics and currents

A teaching sequence based on the use of microscopic models to link electrostaticphenomena with direct currents is presented. The sequence, devised for high schoolstudents, was designed after initial work carried out with student teachers attending aschool of specialization for teaching physics at high school, at the University of Pavia. Theresults obtained with them are briefly presented, because they directed our steps for thedevelopment of the teaching sequence. For both the design of the experiments andtheir interpretation, we drew inspiration from the original works of AlessandroVolta; in addition, a structural model based on the particular role of electrons aselementary charges both in electrostatic phenomena and in currents was proposed.The teaching sequence starts from experiments on charging objects by rubbing and byinduction, and engages students in constructing microscopic models to interpret theirobservations. By using these models and by closely examining the ideas of tension andcapacitance, the students acknowledge that a charging (or discharging) process is due tothe motion of electrons that, albeit for short time intervals, represent a current. Finally,they are made to see that the same happens in transients of direct current circuits.