The Magnetic Field Along the Axis of a Short, Thick Solenoid

We commonly ask students to compare the results of their experimental measurements with the predictions of a simple physical model that is well understood. However, in practice, physicists must compare their experimental measurements with the predictions of several models, none of which may work well over the entire range of measurements. The following describes an experiment we use in the second semester of a two-semester course designed for chemistry, biochemistry, and biology majors as an example of this situation. There are three parts to the experiment. In the first part the students, working in groups of two or three, calibrate a search coil. In the second part they position the coil at various distances from the center of a thick, finite solenoid and measure the field at each position. In the third part they use three models to predict the magnetic field at each of those positions. The students must then decide if one model best predicts the results of the measurements. If no single model can do so, they must decide which model works best over which range.