Reference: EM22
Category: Electromagnetism
Purpose: Shows distribution of charge.
Description: Charge the hollow brass sphere by flicking it with flannel (or rubbing it with rabbit skin). Touch it either inside or outside with a proof plane and transfer the charge to an electroscope. Show that charge can be picked up by touching the outside of the ice pail, but none from the inside.
A related demonstration is as follows: Stand the copper calorimeter (from the mechanics section) on the plate of an electroscope. Charge a small brass sphere on insulating handle (in the box of proof planes) by flicking it with flannel (or rubbing it with rabbit skin). Introduce the sphere into the calorimeter but without touching it internally. The leaves diverge on account of induced charges, but they collapse again when the sphere is withdrawn. Repeat the process, but this time, allow the sphere to touch the inside of the calorimeter. It should make an audible 'ping'. This time the leaves remain diverged when the sphere is removed because all the charge on the sphere was removed from it while it formed part of the inside of the calorimeter. It may be shown that the sphere now has no charge on it. (Pass the proof plane through the flame of a Bunsen burner to remove charge from it between each operation.)
