Van DeGraff Demos
Or, "How to put the fear of electricity into these little minds!"
Alrighty then! Let's get crankin' so to speak... A Van DeGraff generator, pictured below SOON, is a wonderful tool to demonstrate the properties of static electricity while introducing Coulomb's Laws and such. Here, for your edification and viewing pleasure, is a plethora of VDG Demos.
GENERAL CAUTION! DO NOT attempt these things for the first time in front of your students! There is nothing that will ruin a lesson quicker than doing something wrong, getting a big unexpected ZAP, and have your kids watch you writhing on the floor gasping for air... That's bad.
- Sparks : In a darkened room, just turn it on and watch the parks! This is the most demonstrative way of showing the power of a spark. Introduce the numbers. It takes a potential of 50,000 Volts PER INCH for a spark to be generated in air. On a good dry day, you can get 5 inch sparks! Blue, purple, white!
- Flying Pie Plates : Place several aluminum pie plates face down on top of the VDG dome and turn on. They fly off one by one! If you're lucky, you can even make one or more "levitate" for a few seconds before flinging into the air. Why? Repulsion since they are both picking up the same charge.
- Flying Peanuts : Secure one pie plate on top of the dome with a SMALL amount of tape. Place in a handful of packing "peanuts". Turn on. The packing peanuts levitate momentarily then fly off like popping corn.
- Light a Fluorescent Bulb : While on, hold a fluorescent bulb by the middle near the globe, pointing it like a...well, pointer. It will light from the point closest the dome to your hand!
Side note: If you do this with little kids, you know, ankle biters, have a kid who is wearing those annoying shoes that light up when they walk touch the dome and switch on. The little shoes light up!
- Blowing Bubbles : While the dome is charged and the VDG is running, blow bubbles at the dome. I use a battery powered bubble gun from WalMart since I have no coordination and a constant stream of bubbles is most effective. The bubbles will approach the dome and then be suddenly rejected and fly off away from the dome! This is a good demo for changing by induction.
- Floating Toupe : Obtain the typical cat or rabbit fur clump from any science supply house. Place it on the dome and switch on. The hair piece does a little dance as it becomes hugely negatively charged and tries to get away. As the edges rise, it creates a PD and sparks and falls back down.
- Chain of Death : CAUTION! DO NOT attempt this with anyone who has heart conditions or wearing electronic medical supplies like insulin injectors. The large shock CAN offset these things. With the VDG off and discharged, have one kid place and KEEP his hand on top of the dome. Then create a "daisy chain" of kids around the room by holding hands. Make sure no kid is near a grounding devise like an outlet or faucet. Crank up the VDG. After a minute or two, have the last kid in line touch a water faucet or the chalkboard. ZAP! The entire line gets discharges into the pipes and many of the kids at the end of the line will get a tremendous jolt.
- Screen Shielding : This one is GREAT! Get a large ALUMINUM screening roll from Home Depot or Loews. Large enough to make a screen "bag" that can fit over your upper body. This can be done by just sewing or even stapling the edges of two sides of a folded over sheet of screen. CAUTION: Don't be stupid or cheap and get the nylon screening! I did... Now, place the screen "bag" over your head and shoulders and approach a charged VDG. Sparks will jump from the dome to the screen. The audience will think you are getting zapped. But you aren't! The charges spread out over the metal of the screen and no charge enters where you are! From inside, all you see are little blue sparks that LOOK like they are coming for your nose.
- Stop a liquid in its proverbial tracks : This one is freaky! Mix up a thick cornstarch and water goop in a beaker; about the consistency of Elmer's glue. Now, while the VDG is running and charged, pour a small stream from above the dome like you are going to pour it so it falls right beside the dome. Watch. Go ahead! I'll wait.... As the goop comes out of the beaker and approaches the dome, you will notice the stream actually STOPS in midair! The pouring stops even though you have the beaker tilted!
Why, you ask? The goop is nothing more than long chain polymers that are electro-rheostatic. Whew! Big word that simply means "electrically reactive". So, as the polymers, long chain molecules, approach the Electric Field around the dome, they align to its presence and actually solidify the stuff like grabbing a a pile of pick-up-sticks! Cool!
- Coronal Discharging : Tape a thumb tack on the dome somewhere so the point is sticking diametricaly away from the dome and the base of the tack is in full contact with the dome. The dome, although charged, is fully safe to touch WITHOUT getting shocked! Why? The tack, being a point, is where ALL the charge wants to go. As the electrons pile up at the point, they jump off to their untimely death. This constantly discharges the dome. This is why many large buildings and jetliners have those pointy things sticking out from them. They discharge any built up charge.