PIRA 5C10.20 Capacitance: 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.
Last Update 04/18 - University of Texas at Austin Physics Dept.
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