Demos: 5A-13 Gauss' Law--No Internal Field
An alternate version of 5A -12 that is projectable consists of a hollow metal cylinder, open at both ends. Pith ball detectors are attached both externally and internally as shown in the end view at the right. When the cylinder is charged, the balls on the outside separate, indicating a charge, whereas the balls on the inside do not separate, showing no field inside the cylinder.
Directions: Connect the electrostatic generator to the metal cylinder and turn the generator on. Leave it on until the pith balls on the outside stand apart visibly.
Suggestions for Presentation: Point out that the inner pith balls are connected to the metal, so that if if the cylinder is charged, the charges should conduct to each set of pith balls. Do the demo and capitalize on the unexpected, that is, that the inner pith balls dont diverge.