A simple motor/generator demonstration for use in interactive lecture
This apparatus is easy and inexpensive to construct and provides a clear and compelling demonstration of Faraday's Law of Induction and the Lorentz force. Two magnets are suspended from springs so that they are free to oscillate vertically. These magnets are placed inside two solenoids (coils of wire). The solenoids are connected. Moving one of the magnets induces a current in the solenoid. This current flows to the other solenoid where is generates a force on the other magnet, causing it to move. Connecting the solenoid leads in different ways produces different results. The instructor can ask students to predict the results of each connection.
If this is used as part of an interactive lecture demonstration, students can also practice using physics reasoning to make predictions of the outcome of the experiment.
Context for Use
Description and Teaching Materials
To download the video for use in class, use this Quicktime version: movie of motor/generator demonstration (Quicktime Video 6.7MB Aug20 10)
Teaching Notes and Tips
Next, ask them to predict what will happen if the coil wires are switched, that is, if they are connected out-of-phase (top of one coil connected to the bottom of the other). Ask then to use physics reasoning to defend their position and to persuade others to accept their prediction. The instructor should encourage discussion before giving in to students' requests to reveal the answer by performing the demonstration.
References and Resources
Animated generator simulation from PhET
Animated simulation of Faraday's Electromagnetic Lab from PhET