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Van de Graaff

The Van de Graaff apparatus allows for a variety of quick demonstrations that can be used to illustrate the charge and electric field interactions. Our's is a PASCO Van de Graff that can generate High voltages (up to 400kV). We typically use it in conjunction with several accessories. For instance, a discharge sphere is used to get the attention of the students: charge buildup on the Van de Graaff dome spark across the air into the discharge sphere. We can easily obtain sparks at least 10cm on a good dry day --the air's dielectric strength is about 30kV/cm. To illustrate that like charges repel, we can put the PASCO electrostatic plume on top of the Van de Graff dome. The plume's ribbons become charged and they will stand on. Perhaps a more vivid display of repelling of like charges is obtained with a stack of small aluminum cups put on top of the Van de Graaff dome. As soon as charges start getting into the dome, they will be transferred to the aluminum cups making them repel each other. Because gravity is holding the stack down, the cups will start flying off the dome, one by one starting from the top. We also have a PASCO electrostatic whirl accessory that can be used to illustrate variations in electric field due to curvature. Another attention grabber is the lighting of a fluorescent tube. When the tube is held close to (but not touching) the charged dome and is radially oriented with respect to the dome, it will light up. This is a good illustration of the electric field that is build up radially from the dome. The gradient in this field creates potential difference that is large enough to move charges inside the tube. Of course there are many more demos that can be done with our Van de Graaff apparatus, please share them.
ID: d0015
Set up time:
3 minutes in class.
Requires:
Electrical outlet. Components.
Notes:
You may need assistance the first time you use these demos.Check the weather: some of the demos may not be as dramatic or even work on very humid or rainy days. When using the discharge sphere, do not forget to connect it to ground. This is normally done with a 36in banana cable running from the discharge dome to the ground located on the base of the Van de Graaff
Figures:
Documents:
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Table of Components

Qty. name location notes
1 PASCO Van de Graaff apparatus W106; North Cabinets; U1
1 PASCO electrostatic Whirl (SE-7233) W106; North Cabinets; U2.
1 PASCO electrostatic plume(SE-7232) "
1 Stack of aluminum cups "
1 Florescent tube W106; Central Cabinets; U2-L1
1 36in banana cable keep by the Van de Graaff
1 Electrical extension cord W106; North Drawers; L2.