Analyzing high school students’ reasoning about electromagnetic induction

Electromagnetic induction is an important, yet complex, physics topic that is a part of Croatian high school curriculum. Nine Croatian high school students of different abilities in physics were interviewed using six demonstration experiments from electromagnetism (three of them concerned the topic of electromagnetic induction). Students were asked to observe, describe, and explain the experiments. The analysis of students’ explanations indicated the existence of many conceptual and reasoning difficulties with the basic concepts of electromagnetism, and especially with recognizing and explaining the phenomenon of electromagnetic induction. Three student mental models of electromagnetic induction, formed during the interviews, which reoccurred among students, are described and analyzed within the knowledge-in-pieces framework.

Figure 1

Experiment 1: the Oersted experiment. A wire was placed above the compass and current was then switched on.

Figure 2

Experiment 2: demonstrating the direction of magnetic field in various points around a current-carrying coil. A small compass was placed inside a coil and current was then switched on. Students could move the compass inside and around the coil during demonstration.

Figure 3

Experiment 3: demonstrating magnetic force on a current-carrying wire. The current-carrying wire jumped up or down, depending on the orientation of the magnet, when the current was switched on.

Figure 4

Experiment 4: demonstrating electromagnetic induction. The magnet was inserted in the coil, left for some time at rest inside it, and then again removed from the coil. Students were allowed to perform the experiment on their own to try different orientations or speeds of the magnet entering the coil. An additional experiment was shown using another coil with less windings than the first one.

Figure 5

Experiment 5: demonstrating electromagnetic induction using two coils. Primary coil with an iron core was connected to a dc supply and a secondary coil, with less windings than the primary, to the galvanometer. At first, the coils were positioned parallel to each other, and the current in the large coil was switched on and, after some time, off. The same was repeated for perpendicularly oriented coils and for coils at about 45 degrees to each other.

Figure 6

Experiment 6: demonstrating Lenz’s law. An aluminum ring was suspended from a string and put parallel to the large coil with an iron core, an electromagnet. The dc supply was turned on, and after some time, off.

Figure 7

Examples of students’ graphical representations of magnetic field lines around current-carrying wire. Note that the abbreviations are J for south (“jug” in Croatian) and S for north (“sjever” in Croatian).

Figure 8

Faith_4’s graphical representation of the magnetic field inside the coil indicating local reasoning. Note that the abbreviations are J for south (“jug” in Croatian) and S for north (“sjever” in Croatian).