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Parallel Plate Capacitor
# 5C10.20

Description: An electroscope is connected to the parallel plate capacitor to show how charge behaves on the capacitor.

When the capacitor plates are close together, its capacitance increases and more charge is present on the capacitor plates. This means there is less charge on the electroscope and the metal indicator tends to be vertical.

When the capacitor plates are moved farther apart, its capacitance decreases and less charge is present on the capacitor plates. This means that there is more charge on the electroscope and the metal indicator moves away from the vertical.

Instructions: Connect a wire lead from one plate to the top terminal of the scope (this is the plate that you will ultimately charge). Warning: this wire lead should "float" in the air, i.e. it should not touch the table or anything else, or the plate will lose its charge. Connect the other plate to the ground terminal at the bottom of the scope (it's alright if this lead touches the table, etc.).

Charge a PVC rod with fur, and rub the rod on the plate that should be charged. You can now adjust the spacing between the capacitor plates and observe the effect on the electroscope.

This demonstration does not work as well in high humidity. It works best in the winter months.

Purchased/Built: built

Setup Time: 5 min

Quant. in Demo Room: 1

Demo References
The Video Encyclopedia of Physics Demonstrations Disc 18-19 Charge parallel plates with a rod, watch the electroscope as the distance between the plates is changed. Animation sequence.
Hilton E-4d Separate charged plates while an electroscope is attached.
Freier and Anderson Ed-1 Vary the spacing of a charged parallel plate capacitor while the voltage is measured with an electroscope.
Sutton E-69 Charge a simple capacitor of two parallel movable plates and the divergence of electroscope leaves varies as the plates are moved.

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