@Make #Electronics Experiments 26-28--Fun with Coils

These three experiments, like #25, are pretty short. Since they're related, I decided to do them all together.  I thought of doing this starting with 25, but I did not have all the parts I needed (lacking the spool of magnet wire).  Now that I have what I need, I'm ready.

Here's a video of the three experiments.  Following is a discussion of each part and links to individual (shorter) videos.

Experiment 26: Tabletop Power Generation

This one is neat. It's in two parts:

1. Use a 3/4-inch neodymium magnet to generate alternating current
   By stripping the ends of a 100ft coil of 26-gauge magnet wire on a spool, connecting the ends to an LED, and then moving the magnet up and down through the spool, we generate electricity to light the LED. The LED flashes only on one direction--reverse the connections and it only flashes in the other (alternating current).
   Video.
2. Use a diode to rectify AC current and store in a capacitor
   Using the same coil as in part 1, we use a 1N4001 signal diode and 100uf electrolytic capacitor in series to replace the LED.  We connect a multimeter across the leads of the capacitor to measure volts.  When we move the magnet up and down through the coil, it generates electricity, but the diode blocks one direction, so it's DC.  The capacitor charges up until we stop moving the magnet (I got it to about 2.5V), then it slowly discharges.
   Video.

Experiment 27: Loudspeaker destruction
I fudged this a little because I did not have a 2" speaker. The 1 1/4" Radio Shack cheapie was good enough for demonstration.  The whole point is that there's a coil and a magnet and the inputs to the speaker causes vibrations which are received as sound.
Video.

Experiment 28: Making a Coil React
In this experiment , we power a circuit from 12V DC, passing through a momentary tactile switch, a 220 Ohm resistor, two low-current LEDs oriented in opposite directions, and on through a coil.  When the button is pushed, the coil initially blocks flow so the circuit finds a path through one of the LEDs.  Once the coil;s self-inductance is overcome, it accepts current and the LED goes out.  When we release the button, the current that was stored in the coil releases and lights the other LED.
Video.