Electromagnetic Induction and Lenz's Law Revisited

Many of the old demonstrations in electricity and magnetism can be performed more effectively and with greater visual appeal by using newly available neodymium magnets and color LEDs. For this reason several demonstrations, commonly used for teaching electromagnetic induction and Lenz’s law, have received renewed attention in recent years. In particular strong neodymium magnets have been used in several new demonstrations and experiments to help students learn the subtleties of eddy currents and magnetic braking. Here we describe several demonstrations that use a strong neodymium magnet, a coil, and a few LEDs to teach students in introductory physics the fundamentals of electromagnetic induction. More importantly the addition of LEDs provides a visual demonstration of Lenz’s law, with which many students have some difficulty. The demonstrations described here are quite simple to construct, fun to do, and visually appealing; they may be used either in the laboratory or in the classroom. © 2019 American Association of Physics Teachers.