A Van DeGraaf Generator a ground wire, insulating blocks like Styrofoam.
Dry ice
a metal tray (large 20 cm x 30 cm and 4 cm or more deep)
warm water 

Assembly

Put the metal tray on top of 20 cm of Styrofoam insulators.
Fill the tray about 1/2 full with warm water.
Put the dry ice into the tray. The tray will fill with mist.
Connect the tray to the ground with a wire.
Stand on 20 cm thickness of Styrofoam blocks and put your hand on the Van deGraaf.
Turn on the Van deGraaf.

To Do and Notice

After you have become charged, this will take a minute, point a finger at the mist.

Watch the mist explode away from the place you point.

Turn off the Van deGraaf, reverse the connections, connect the tray to the Van deGraaf. You grab a ground wire. Turn on the Van deGraaf.

Point toward the tray.

Clear lines will appear in the mist. Write your name in the mist.

What's Going On?

An object covered with charge will be at a high voltage.

The electric field around such an object will be largest at points such as the ends of your fingers.

Charges will flow off the charged object at the points. These charges will strike air molecules and create a wind flowing away from the point. Thus when you point at the dry ice mist a wind strikes the mist and blows it away.

Going Further

Use other electrostatic generators and find their effects on the dry ice mist.

An Activity by Paul Doherty,

Thanks to Jan Sjokvist of The Xperiment Huset in Vaxjo for showing me this activity.

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Scientific Explorations with Paul Doherty

© 2000

1 Feb 2000