The first time I saw this was at an AAPT meeting in Philly PA by Physics Legend, Harry Rheams, currently of Eastern HS in NJ. The procedure is simple:
Notice, "Plug in..." comes LAST! Keep in mind, you are dealing with LIVE AC! Use common sense and all possible caution! I grabbed ahold of one of the wires while discussing it infront of a group of Physics Pholks at Rutgers a few years back and got a rude awakening! Made the demo much more interesting for the audience, but ruined my day (not to mention my shorts...).
- Get a pickle.
- Jam electrical wires into opposite ends of said pickle.
- Plug wires into AC socket.
Lights should be dimmed to see the effect. I use a simple lamp cord ripped from an old lamp, duh... Expose the wiring at the ends of each wire. Wrap the wires around 16d (16 'penny') nails. Either clamp wires onto nails with aligator clips or tape in place. It's that simple.
Now, place the pickle on a non-metal platform. I use a hunk of 12"x12" pine shelving. This insulated the electrical stuff from any nearby metal on the table. Insert one nail into each end of the pickle. HINT: I inset the nails so they are perpendicular to each other. ie So if the pickle rolls, only one of the nails will contact the wood.
Now, step back and plug in the wires. Nothing will be immediately noticeable. About 15 or so seconds later, a loud buzzing sound is heard. Then, suddenly, the pickle lights up like a little green flourescent light bulb! It will also smoke a little and stink. Ignore these effects...
Harry did this with a hot dog and forks instead of a pickle and nails. Use your imagination!
EXPLANATION : For a detailed, much more detailed than I thought, go to Ask A Scientist Site. I removed my meager explanation of this after reading a few 'real' science explanations...