VanDeGraaff Generator

Age

Elementary School, Middle School, High School

Format

Stage Show

Materials

   Van de Graaff Generator
   Extension cord
   Metal rod with copper ball on end
   2 grounding wires (one with a clamp and one with a wrist band)
   Wig
   Bell contraption
   Metal cup
   Plastic cup
   Packing peanuts
   Tape (any type that won’t block the charge)
   Fluorescent light
   Check box for additional items 

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

   Produces an electric field – no electronic devices should be near it
   Produces a shock – can hurt
   Maintain appropriate distance
   Make sure anything you are touching it with is grounded
   Ground self when using light
   Always discharge when you turn it off
   Discharge before changing settings (i.e. power, speed, turning it off)
   Make sure you have appropriate training before using – This can hurt you!! 

Preparation

Make sure the generator is turned off and the speed is turned all the way down. Plug it in and use the extension cord if necessary. Remove the supplies from the storage container. Test demonstrations before the show at the site to ascertain atmospheric conditions. If doing the bell demonstration, you may want to test it now.

Demonstration

Make sure the generator is turned off before starting each demonstration. See the end of “Demonstration” for instructions on how to discharge properly. Choose the demonstrations you would like to perform.

Standard Discharge

   Plug the metal rod into one of the holes on the generator to ground it. Turn the generator on. Bring the metal rod close to the top ball of the generator. You can show various jumps by holding the stick at varying distances.

Wig – Like Charges Repel

   Turn Place wig on the top of the generator. Turn the generator on. Discharge before turning off.

“Airplane People” – Like Charges Repel

   You will need the metal cup, plastic cup, and packing peanuts. Place the metal cup on the generator. Place peanuts inside the cup. Turn the generator on. Observe the lack of flying peanuts. Discharge and turn the generator off. Remove metal cup from the generator and replace it with the plastic cup. You will need to tape the plastic cup onto the generator. Transfer the peanuts into the plastic cup. Turn the generator on. Observe the flying peanuts. Discharge and turn off. Clean up your mess.

Bell – Transfer of Charges

   Place bell contraption on top of the generator. Make sure the ball is the correct distance away. (The correct distance will change from day to day. You want the ball close to the bell connected to the generator but not quite touching.) Turn on the generator and observe. The ball should go back and forth between the two bells. If it doesn’t, you need to discharge everything and move the ball accordingly. (You may want to do this prior to show time.) Discharge everything before turning it off.

Fluorescent Light – Induced Charge

   Place the grounding wrist band on whichever arm you plan on holding the light with. Plug the wrist band grounding device into the generator. Turn on the generator. Making sure you are holding the light with your grounded hand, bring the light close to the generator but don’t touch it (or it won’t work). Preferably, have it discharge through the wires on the end and not the glass because it might damage the light. Discharge and turn the generator off.

Van de Graaff Generator (in general)

This is an explanation only. The way it is described will depend on audience age.

How to Properly Discharge

The metal rod should always be plugged in to the generator. Discharge by placing the metal rod on the generator and holding it there to prevent further build up of charge. Turn off the generator.

What to Say

Standard Discharge

   This is the same principle as lightning and static electricity. A charge builds up on the generator and transfers/jumps to an area with less charge. (You can use a diffusion analogy such as people moving out of a crowded room when the door opens.) You can talk about how electricity likes to move toward the ground. (It is like a mole.) It will take the path of least resistance (the easiest way to get to the ground). This is the how lightning works and why lightning rods are attached to the ground.

Wig – Like Charges Repel

   Each of the hairs becomes charged. Since they all have the same charge, they repel each other and stand up. (You can compare to magnets or any other situation in which there are two of the same objects that don’t “get along”.)

“Airplane People” – Like Charges Repel

Metal cup – The metal cup, being a conductor, gets the charge and spreads it out over its surface. So, the peanuts don’t get a charge on them.

Plastic cup – The plastic cup, being an insulator, gets a charge only on the bottom, which is touching the generator. Then, the charge moves to the peanuts. The like charges of the peanuts repel. So, they try to move away, and the only way to go is up. You can now tell how this relates to airplanes. The airplane picks up a charge from the air (through friction) like a cloud does. This is why planes are made of metal.

Bell – Transfer of Charges, Like Charges Repel, & Conservation of Charge

   The charge first moves from the generator into the closest bell. It then moves from the bell and into the ball. The like charges then repel, and the ball moves and hits the second bell. Upon striking the bell, the ball loses its charge. It is no longer repelled by a charge, so it falls back and strikes the first bell. It picks up another charge and repeats. This will continue long after the machine is off. This happens because the bell holds onto its charge. You can make an analogy to a hitchhiker. A hitchhiker (the charge) will move from place to place but doesn’t go away.

Fluorescent Light – Induced Charge

   The fluorescent light will pick up a charge from the surrounding electric field created by the generator because it is the faster way for the electricity to reach the ground. The electric field acts like the plug in your house. When the light is connected to it, the electricity can flow through and light it up.

~ High School and older –

At the bottom of the generator, there is a piece of wire mesh. The wire mesh is connected to the internal mechanics (the motor) of the machine. So, it basically is getting the charge from the electricity in the wall. The rubber belt, being an insulator, picks up the charge (not just any old charge) from the wire mesh and carries it to the top. At the top, the charge is transferred to yet another wire mesh which is connected to the large metal ball. The charge can then disperse over the surface of the ball.

~ Middle School and under –

At the bottom of the generator, there is a piece of metal connected to a motor. The metal picks up a charge and puts it on the belt. The belt carries the charge to the top where it spreads out over the large ball. (Put in analogies if you think they are necessary for comprehension. Most likely this would happen with very young audiences.)

Why It Is

Grounding/Discharge –

   Electricity likes to diffuse throughout its surroundings to create a uniform charge. Grounding works because the planet is big (really, really, really, big) and the charge can spread out easily.

Like Charges –

   A charged state is an unnatural state; all things like to be neutral (zero charge). A negative and a positive charge cancel each other out. This is why positive and negative charges are attracted to one another, and like charges repel.

Transfer of Charge –

   This is based on diffusion. The charges want to spread out. When the charged ball strikes the uncharged bell, the charge vacates the ball and moves into the “empty” bell. When the ball receives a charge from the first bell, the same thing is happening.

Conservation of Charge –

   Charge is neither lost nor gained in a closed system; it is only transferred or transformed.

Induced Charge via an Electric Field –

   At a specific distance from the center of your field, there is a specific amount of electrical potential energy. (The further you get away, the less the potential is.) When you put an object into this field, the potential energy acts on it. In the case of the light-bulb, the electrical energy is transformed into a charge which runs through the tube. (This is an electrical current.)

Real Life Examples

Static electricity

Lightning / lightning rods

Electromagnets

Monorails

Really cool roller coasters