Bicycle Generator | Pūngao Paihikar
Faraday’s Law of electromagnetic induction demonstrated with a coil and magnet.
Moving a magnet near a conductor or moving a conductor in a magnetic field induces a voltage in the conductor that causes a current to flow.
Te Reo Māori Version
This demonstration is easy to set up and very valuable. You’ll need a galvanometer, coil (which you can make by looping wire of almost any kind), leads with crocodile clips, and a reasonably strong magnet.
Electromagnetic induction is very general. A voltage is generated and causes a current to flow when a conductor is moved in a magnetic field or anytime a magnet is moved near a conductor. Several demonstrations illustrate this. See Eddy Current Tubes, Eddy Current Vanes, Eddy Current Drag. The easiest geometry to use for a Faraday’s Law demonstration is probably a coil of wire (which you can make yourself) connected to a galvanometer via leads with crocodile clips, and a strong magnet.
Note that moving the magnet faster induces a larger voltage and a larger current.
Key points to get across using this demonstration
If there is no relative motion between the coil of conductor and the magnet no voltage and no current are generated even for a very strong magnet. You can generate a voltage that causes a current to flow by moving either the magnet or the coil. The more rapidly the magnet or coil are moved the larger the induced voltage and current (not shown in the video, a good extension of the demonstration for teachers to set up).
Advanced: Direction of Current Flow
Moving the magnet into the coil causes a current in one direction, pulling it out causes a current in the other direction.
Flipping the coil or flipping the magnet reverses the directions of the current.
Much More Advanced
This demonstration can be done every year with an increasing depth of analysis. Finally, at scholarship level, students can be asked to apply Faraday’s Law and Lenz’s law: Knowing the orientation of the magnet and direction of windings on the coil, to predict the direction of current flow.
Increasing the current flow requires moving the magnet faster. This gives rise to a larger drag force and means you have to work harder to move the magnet. In other words, you don’t get the electrical energy for free. Unless you have an exceptionally strong magnet and/or a coil with many turns, you probably cannot feel the drag. This is best observed with the Papa Konukura (Eddy Current Drag), Haukapo Rā Aurere (Eddy Current Vanes), and Ngā Ngongo Aurere (Eddy Current Tubes) demonstrations among others.
Nearly all commercial electricity production is based on moving magnets in coils. But the magnets are usually electromagnets rather than permanent magnets. See the Pūngao Paihikara (Bicycle Generator) demonstration for more about this.
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
This teaching resource was developed by the Te Reo Māori Physics Project with support from
- Te Puni Kōkiri
- The MacDiarmid Institute
- Faculty of Science, Victoria University of Wellington
- School of Chemical and Physical Sciences, Victoria University of Wellington