Building simple electric motors is an intriguing activity for students that helps them understand important concepts and principles in magnetism and electromagnetism.1,2 So, we built a simple electric motor in the laboratory based on a problem from a high-stakes exam (i.e., The National College Entrance Examination in China). However, we found that the “incorrect” answer was actually correct! To explicate the discrepancies, we will first introduce the problem and its original solutions, then we will demonstrate our experimental results of the simple motor through videos, and finally, we will provide explanations. Although there have been discussions on simple electric motors,3–5 our hands-on investigations uncover that paying attention to the homogeneity of magnetic field, the symmetry of coil, and the ways of stripping the enamel of the coil axle can bring a whole new perspective in analyzing simple motors.
Figure 1 shows the test item on the National Entrance...
