PURPOSE: To demonstrate that the electric field within a closed surface is zero.

DESCRIPTION: Charge the two wire strainers, which are connected electrically to the electroscope indicator. With the two meshes separated, the electroscope deflects. When they are placed together, forming a closed sphere, the electroscope deflection is zero, indicating zero potential within the closed cage.

SUGGESTIONS: See Question of the Week #189 for suggestions on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 5B20.30)

EQUIPMENT: Double wire strainer Faraday cage with electroscope, charging materials, and projection point source.

SETUP TIME: None.