Faraday's Ice Pail

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Faraday's Ice Pail

A ball on a string held over a metal cup

PIRA 5B20.10

Charge the metal cup shown at left with the Van de Graaff generator. Use a pith ball on a thread to show that the excess charge all lies on the outer surface. Identical proof planes touched to the inside and outside will also show this when the charge they pick up is compared with an electroscope. The insulating disc separating the can from the metal base may not be enough to prevent arcing. If this is a problem, separate the base from the table with a styrofoam slab as shown.