Faraday Ice Pail (5B20.10)
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Shows that charge resides only on the outside of a hollow conductor. A metal trash can is charged using a Wimshurst machine, then the charge distribution on the can is investigated using a metal ball on an insulating rod.
1) Let the class see you drop the metal ball into the can so that it makes contact with the interior bottom of the can. Drape the chain loop over one terminal of the Wimshurst Machine. Important: Drop the extra chain into the can so that there is no chance of arcing between the chain and the can lid.
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2) Crank the Wimshurst Machine about 10 to 15 turns to charge the interior of the can.
3) Use the insulated hook to unhook the chain loop from the Wimshurst Machine and carefully drop it into the can. Important: Do not let the chain arc to the can lid or you will have to start over.
4) Discharge the Wimshurst Machine!
5) Remove the plastic centerpiece and post. Touch the insulated probe to the interior of the can and then touch it to the electroscope.
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6) Touch the insulated probe to the exterior can lid and then touch it to the electroscope.
NOTE: This is usually the first demo that fails during Summer Quarters because of the humidity.
1) In his original 1844 paper, Faraday also investigated the effect of using several conducting containers one inside the other. He found that the induction effect works through multiple containers the same way it does through one container. He used four pails, each supported on a nonconductive pad inside the next. If a charge is lowered into the innermost pail, an exactly equal induced charge will appear on the outside of the outer pail. The charge on the outside of each pail induces an equal charge on the next. If one of the pails is grounded, the charge on all the pails outside it goes to zero. [Faraday's Ice Pail Experiment, Wikipedia]
2) Faraday, Michael (March, 1844). "On Static Electrical Inductive Action." Philosophical Journal. UK: Taylor and Frances. 22 (144): 200-204.