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Lecture Demonstrations Laboratory


The Demonstrations Manual


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Electrostatics
Electric Fields And Potential
Capacitance
Parallel Plate Capacitor
Simple Properties of Dielectrics
Capacitor Discharge
Current and Resistance
Electromotive Force And Current
DC Circuits
Magnetic Materials
Magnetism
Inductance
Induction
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Semiconductors And Tubes
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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.

Comments:

If you have a suggestion for the use of this demo which might benefit others, you can enter it below.

Equipment:

  • 9 V battery pack
  • Capacitance meter
  • Metal and Plastic Dielectrics
  • Connecting Wires
  • Parallel Plate Capacitor
  • Electrometer