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 electric field within the closed cage. The charge that was originally on the electroscope has flowed to the outside of the conductor. Note that if you then re-open the two hemispheres, the electroscope again deflects as the charge flows back into it.

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.