Charge Distribution on a Conducting Surface 5B30.20
Brass ovoid is located in ElectrostaticsCabinet, B2.
Electrometer and Faraday Cage are located in ElectrostaticsCabinet, B1.
Charge producers (rods and fur) and proof plane are located in Electrostatics Cabinet, A1.
Hot air gun located in Thermodynamics Cabinet, B2.
Connect the Electrometer to the Faraday cage so that the outside cage is grounded.
Set the electrometer so that it measures 0V at the center of the scale.
Touch the brass ovoid to the outside cage to neutralize any charge on the brass ovoid.
Rub one of the rods with the fur, until it crackles if possible. Touch the rod to the brass ovoid.
Repeat these steps several times.
Touch the proof plane to the outside cage to neutralize the proof plane.
Lay a flat side of the proof plane against the blunt end of the charged ovoid.
Remove the proof plane and insert it into the inside cage, without touching the walls. Note the deflection of the meter.
Touch the proof plane again to the outside cage to neutralize it.
Lay a flat side of the proof plane against the pointed end of the charged ovoid.
Remove the proof plane and insert it in the cage. The needle should deflect more.
Note: The hot air gun may be used to fully discharge the rods, which cannot be fully discharged merely by touching them to the outside cage, or even by drawing them along the outside cage.
Discussion: The surface charge density on a curved surface with no external field varies inversely with the radius of curvature, being largest at the place with the smallest radius of curvature.