Thomas M. Scaife

Student understanding of the direction of the magnetic force on a charged particle

We study student understanding of the direction of the magnetic force experienced by a charged particle moving through a homogeneous magnetic field in both the magnetic pole and field line representations of the magnetic field. In five studies, we administer a series of simple questions in either written or interview format. Our results indicate that although students begin at the same low level of performance in both representations, they answer correctly more often in the field line representation than in the pole representation after instruction. This difference is due in part to more students believing that charges are attracted to magnetic poles than believing that charges are pushed along magnetic field lines. Although traditional instruction is fairly effective in teaching students to answer correctly up to a few weeks following instruction, especially for the field line representation, some students revert to their initial misconceptions several months after instruction. The responses reveal persi...

The Effect of Field Representation on Student Responses to Magnetic Force Questions

We examine student understanding of the magnetic force exerted on a charged particle and report three findings from a series of tests administered to introductory physics students. First, we expand on previous findings that many students believe in “charged” magnetic poles and find that although students may answer according to a model where a positive charge is attracted to a south pole and repulsed by a north, these students may not believe that the poles are charged. Additional models produce identical answer schemes, the primary being magnetic force parallel to magnetic field. Second, the representation format affects responses: students answer differently when the magnetic field is portrayed by a field source vs. by field lines. Third, after traditional instruction improvement in student performance is greater on questions portraying field lines than for questions portraying field sources.

The dependence of instructional outcomes on individual differences: An example from DC circuits

In a study of student understanding of the power dissipated through simple networks of resistors, two consistent, contradictory response patterns were identified: a greater equivalent resistance always dissipates more power, and a lesser equivalent resistance always dissipates more power. After completing one of two sequences of practice-questions, the performance of students who had initially thought that less resistance meant more power improved, while the performance of the opposing group did not-despite one of the practice sequences specifically addressing the idea that more resistance means more power. Because one prior conception appears to be susceptible to practice while the other does not, specific attention must be given to interactions between differing ideas and the physical concept being taught. If an instructor only examines the performance of the entire class, an overall increase in performance might mask a misalignment between instruction and the understanding of a significant, pre-defined...