Faraday’s law—Quantitative experiments Available to Purchase

A cylindrical bar magnet is dropped through a coil which encircles a glass tube. A Commodore 64 computer equipped with an analog to digital converter digitizes and stores the resulting voltage pulse. The magnet velocity and the number of turns on the coil are varied and simple measurements on the voltage pulse give quantitative tests of Faraday’s law. Integration produces the total flux through the coil. Flux integral calculations which treat the magnet either as a dipole or as a uniformly magnetized cylinder lead to equations for the voltage pulses which give a good fit to the experimental data obtained with a set of variable area coils. Either model is good for radial distances >40% the magnet length. Other results include determination of dipole separation and pole strength and surface current density. A versatile program for data acquisition and inspection is described. Suggestions are made for demonstrations and laboratory work for students in introductory noncalculus and calculus based courses and for advanced experimental work for majors.