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PURPOSE: To demonstrate that the charge resides on the outside of a conductor.
DESCRIPTION: Charge the sphere several times by scraping charge off a rod, either positive or negative. Touch the proof plane several times to the outside of the sphere and then to the electroscope. The electroscope (at left in photograph) charges, indicating that there is charge on the outside of the sphere. Touch the proof plane several times to the inside of the sphere and then to the electroscope. The electroscope (at right in photograph) does not charge, indicating that there is no charge on the inside of the sphere. Repeat for the outside to demonstrate that the sphere is still charged.
SUGGESTIONS: See Question of the Week #187 for suggestions on using this demonstration to enhance class involvement.
REFERENCES: Available. (PIRA 5B20.10)
EQUIPMENT: Hollow conducting sphere, positive and negative charging materials, proof plane, and electroscope.
SETUP TIME: 10 minutes.
