Instructional experiment on Lenz's law


  • Juliane Teixeira de Moraes Universidade Federal de Viçosa
  • Bruno Ferreira Rizzuti Universidade Federal de Juiz de Fora
  • Bruno Gonçalves Instituto Federal Sudeste de Minas Gerais



Electromagnetic Induction, Lenz Law, LEDs, Classroom Activity.


We present a visual manifestation of Lenz’s Law. The setup is composed of two coils connected by a central linear metal nucleus. Each of them has a LED plugged in parallel to its terminals. The primary is fed with a pulsating external voltage. We recorded a slow-motion video (960Hz) of the two blinking LEDs. It is possible to observe a complete out-of-phase fade-in/fade-out behavior of them, which is a direct consequence of the minus sign present in the electromagnetic induction equation. We also discuss how to introduce the apparatus in a classroom activity. The mathematical modeling and the numerical results are instructively derived along with the text. There is also a review of the technical features that must be taken into account to study the observation of high-frequency blinking LEDs.


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