Faraday’s Law: A Little Generator Using Magnets and Coil

Be Safe! Please educate young children about the properties and risks of strong neodymium magnets.

How about a little STEM project exploring Faraday’s Law about electromagnetic induction? When a magnet moves in relation to a coil, it induces a voltage (electromotive force or emf), which is a function of the number of turns of a coil and the rate of change of the magnetic flux.
The present design has three parts: a coil spool, a magnet holder (rotor), and a hexagonal bar. With a few round button-sized neodymium magnets and some enameled copper wire, one can make a small generator that can light up a LED, exploring the effect of spinning speed, turns of the coil, number of magnets. Please note that the voltage induced is AC (alternating current). The LED lights up for only one half of the cycle. Two LEDs could be used in opposite ways.

Materials Needed

1. A magnet holder that fits the diameter of the magnets.
2. A spool.
3. A handle bar.
4. Enameled copper wire: 30 to 36 AWG.
5. A LED. Its forward voltage is between 1.7 V to 3.2 V. That is why we need a large number of turns for the coil.

How To

1. Clean the magnet holder and the handle bar, once printed, so that the hex bar can slide into the hex holes without being too loose.
2. Snap a round magnet on both sides of the magnet holder, adding more on both sides in a balanced manner.
3. Wrap the copper wire 500-100 turns around the spool and fasten the two ends with tape. Make sure to leave enough at both ends for LED connection. It works with 200-300 turns; but one needs to spin fast!
4. Remove the insulation on both ends of the wires and solder, if possible, them to the LED. Otherwise, twist the wire ends to the pins of the LED. Please make sure the insulation is removed with sandpaper or scraped with a small blade. It doesn’t matter which goes to which, as we are dealing with AC voltage.
5. Spin the magnets in the coil and see if the LED lights up.
6. A multimeter can be set to AC Voltage mode and used for estimating the voltage induced.

Math Questions

1. The external diameter of the spool is about 29mm. How much wire, in mm, do we need for one turn?
2. To wrap 1000 turns of copper wire around the spool, how much, in feet, wire do we need?

References

1. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html
2. https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction