5C10.20 • Capacitors : Parallel Plate Capacitor

Photo Shows the Demonstration Apparatus Used by the University of Texas at Austin

Set Up Instructions / Notes:

• Demo includes a Wimshurst machine, an adjustable parallel plate capacitor and an open electroscope.
• (Step 1) A red wire is attached connecting the electroscope to the non-moving plate of the capacitor.
• (Step 2) A second red wire is then attached to the first red wire and one of the electrodes of the Wimshurst electrostatic generator.
• This second red wire will be pulled of the fixed plate of the capacitor after charging the demo with the Wimshurst.
• Therefore, the second red wire must fit loosely into the first red wire, if it is to be easily removed from the circuit.
• (Step 3) A double set of black wires are connected to the adjustable plate of the capacitor, electroscope and the second Wimshurst electrode.
• Note: This demo uses static surface charges - which require very dry air conditions in order to work effectively.
  • If the air in the classroom is humid - then the surface charges will bleed away rather quickly.

Photo Shows the Demonstration Apparatus after charging and subsequent removal of the second red wire from the circuit.

Operating Instructions:

• Prior to charging the capacitor - adjust the spacing between the plates so that they are separated as far as possible from each other.
• To charge the apparatus - turn the crank on the Wimshurst machine clockwise until the Electroscope needle deflects upwards.
• Quickly remove the red wire lead from the Wimshurst to the parallel plate capacitor, taking care not to disturb the red wire between the electroscope and the capacitor plate.
• To vary the strength of the E-field - decrease the spacing between the plates and observe the transfer of electric charge from the electroscope to the large parallel plate capacitor.
• Increase the spacing between the parallel plates and observe the needle on the electroscope as it returns to its prevous position.
• A set of dielectric plates are provided with the demonstration to show the effect of inserting a dielectric material.

The 5 minute video below is intended for staff use.

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5C10.20 Parallel Plate Capacitor Backup:

Photo Shows the Demonstration Apparatus Used by the University of Texas at Austin

Concept:

• This Parallel Plate Capacitor is used to illustrate capacitance and charge with air acting as an insulation medium.
• Since the charge stored in a capacitor depends on the area of the capacitor plates, different plates are also provided with alternative insulation materials, with the distance between the plates playing an important role as well.

Instructions/ Notes: This will serve as a backup to the 5C10.20: Capacitors: Parallel Plate Capacitor

Procedure: Same as the demo listed above

Last updated on November 5, 2025