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Parallel Plate Capacitor
Purpose:To demonstrate the relationship between capacitance, charge, and voltage on a parallel plate capacitor.
Procedure:This is a multi lecture demonstration.
1. Relationship between the capacitance and the capacitor geometry can be demonstrated. Simply connect a capacitance meter (multimeter) to the plates (w/out charging them) and demonstrate that pushing the plates together/apart or sliding parallel to each other (thus changing the area) changes the capacitance.
2. Disconnect the multimeter and charge the plates to ~80V w/ a battery pack. Disconnect the batteries. Connect a high input impedance electrometer (either Keithley or our Gauss law one) and demonstrate that the potential difference between the plates is changed by moving the plates together/apart.
3. Electric permeability demonstration. Slide a piece of dielectric between the plates to see capacitance and/or voltage change.
Hints:Regular voltmeters have too low input impedance and quickly discharge the capacitor.
Do not connect the electrometer and capacitance meter at the same time. Electrometer has input capacitance comparable with the one of the plates.
Always connect capacitance meeter to DISCHARGED plates.
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