My PBL Project

• Electric Whirl

• Discharge Sphere

• Electric Plume

• Van de Graaff Generator

Procedure:

• In the Van de Graaff Generator the motor makes the belt moves in a rotating motion causing the fabric from the belt to create a type of friction

• As the belt rotates it is brushed with the top brush and as this occurs the electrons from the top are removed causing the dome to become positively charged.

• Since the belt is a good insulator the negative charge does not move from it and its carried down.

• As the charges at the top accumulate the voltages of the pulley increase until the electrons are able to escape and jump the gap to the electrode brush were they are now free to go to the surface of the dome.

• In time the charges on the dome will build up to a point in were electrons will begin to escape by ionizing the surrounding air or connecting to a nearby ground, in any case a balance will be reached and the voltage of the dome will not increase once it reaches that point.

• When the generator is in action it produces high voltage, this voltage can be dangerous if touched without precaution. When the Van de Graaff is in action DO NOT touch the dome.

Scientific Principal:

• When two different materials in close contact are separated there is usually a transfer of free electrons from one to the other. The result is that one becomes charged negatively and one becomes charged positively. This charges may accumulate to higher voltage, but the charges neutralize over time and both material go back to having core of charge.

Safety:

• • Do not allow students to use the Van de Graaff generator unsupervised.

  • People with cardiac pacemakers should never operate the generator or come in contact with it.

  • Obviously, we are dealing with high voltage here. Stay about three feet away from the collector while it is charged. Full intensity, white-hot sparks can jump as far as 15 inches, less intense, red-purple sparks can jump 20-30 inches. While the current is too low to injure you, a surprise spark is no fun. Keep the generator at a safe distance from the outlet where you plan to plug it in. If you're too close, you won't be able to turn it off safely.

  • Always discharge the collector dome between experiments and when you are finished. Use the discharge wand for this. Connect the alligator clip to a gas main or similar grounded object. Hold the discharge wand by the handle. Do not touch the grounding strap when discharging the generator. The voltage is so high that the current can pass through the insulation into your hand.

  • The motor produces a lot of heat that could damage the belt or the motor itself. Do not run the generator continuously for long periods of time. Turn it off when not in use. This is an expensive device and we should try to keep it operating perfectly for a long time.

  • Leave the upper and lower combs alone. They are not supposed to touch the belt. Do not bend them or mash them. They were working fine when last tested and do not require any adjustment.

  • Keep the entire device clean and dry. Dust and moisture degrade the generator's performance.

  • Handle the aluminum parts with care. The collector, housing, and discharge wand are easily dented. The collector already has a sizable ding in it from and accidental drop of only three inches!