Plastic vs. Solid Resources In Upper-division E&M

Abstract: The ability of juniors in physics at Oregon State University to solve for the magnetic vector potential of a spinning ring of charge is analyzed using Sayre and Wittmann’s model of resource plasticity. None of the 17 students, working in groups of two or three, was able to solve the problem in the given time. Those students who used geometric reasoning to connect to something they solidly understood did not accept incorrect answers and knew they had not yet achieved a solution, whereas many other students were willing to connect their answers to more tenuously understood “plastic resources ” and their answers contained errors. We discuss these results and their instructional implications concerning the degree to which students are encouraged to connect to solid resources as they solve problems, compared to being encouraged to consider connection to plastic resources as being “good enough”