By Robert Allen | Updated Mar 24, 2022
Michael Faraday’s discovery of electromagnetic induction underpins every electric motor and generator. When the axle of a motor spins, the changing magnetic field turns it into a simple generator that produces current from motion.
For a hands‑on demonstration, a model generator—often called a “dynamo”—can be assembled with just a magnet and a spool of insulated copper wire. The result is a small but effective illustration of the physics behind modern power systems.
Cut two circles, 3–4 inches in diameter, from cardboard using a hobby knife.
Wrap half of a 60‑D nail with electrical tape, starting at the head and working toward the point. The tape will keep the nail in place while allowing the magnet to move freely.
Poke a hole through the center of each cardboard circle with the nail, pressing the nail’s head into the first circle and its taped end into the second.
Let a hot‑glue gun heat up. Apply glue to the exterior of the cardboard circles where they meet the nail, being careful to avoid the inside of the spool. This keeps the structure rigid without interfering with the winding.
Start winding magnet wire around the nail between the two circles. Tight, uniform turns produce the strongest magnetic flux. Continue until you have about 10 inches of wire left on each end.
Use a small amount of glue to hold the coil in place so it won’t unwind when you release it.
Trim any rough edges of the cardboard with the hobby knife.
Attach the bar magnet to the axle of a crank with strong adhesive. Precise alignment ensures the magnet spins smoothly around the nail.
Secure the wound spool to the mounting surface, keeping it steady.
Carefully scrape insulation off both ends of the coil with the hobby knife.
Place the crank so that the magnet is as close as possible to the coil while spinning on the same axis as the nail.
Glue the crank to the mounting surface once the magnet’s position is confirmed.
Turn on a digital voltmeter and select the most sensitive DC range.
Wrap one free end of the coil around the meter’s black (negative) probe, and the other end around the red (positive) probe.
Spin the crank to rotate the magnet and observe the voltage reading.
If the meter shows no voltage, reverse the polarity of the connections.
Keep roughly 10 inches of wire free at both ends for easy connections. A pencil can replace the nail if needed, and a homemade crank will work fine. For quick demos, simply glue a magnet to a pencil’s tip and spin it by hand.
Because the output of this model generator is unregulated, never use it to charge batteries or power electronic devices.
