(5C10.20) Parallel Plate Capacitor

In the figure above, the capacitor has two vertical circular aluminum plates whose separation can be adjusted by moving the track. Place the electroscope on the overhead projector or Elmo projector. The connections from the capacitor plates to the electroscope (via “BNC” cable) are not obvious; they are red-to-red and black-to-metallic sheathing. After turning on the HV generator (about 3000 V) charge the capacitor by briefly touching either plate with the leads to the side of the plates, giving an electrometer response. Use of two sets of alligator clips leads gives more transparent electrical connections, but the electrometer reading is susceptible to change if the leads are shaken. Move the plates of the capacitor closer together and apart and observe the reading of the electroscope, which shows the potential increases with the plate distance. Because the electroscope does not give a quantitative response we cannot test the predicted linearity of voltage with distance.