Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

# Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

 Choose a Topic or Enter a keyword to search: I cannot find what I want! You have selected the following Demos: None Selected

Choose a subtopic:
Electrostatics
Electric Fields And Potential
Capacitance
video  - Parallel Plate Capacitor
video  - Simple Properties of Dielectrics
video  - Capacitor Discharge
Current and Resistance
Electromotive Force And Current
DC Circuits
Magnetic Materials
Magnetism
Inductance
Induction
Complex Circuits
Semiconductors And Tubes
Transmission Lines and Antennas

### video  - Parallel Plate Capacitor

#### Purpose:

To demonstrate the relationship between capacitance, charge, and voltage on a parallel plate capacitor.

#### Procedure:

DEMO VIDEO DOWNLOAD w/ sound / 1920x1080 / 24.19Mb/s / 789MB size

DEMO VIDEO DOWNLOAD w/ sound / 854x480 / 5.69Mb/s / 184MB size

This is a multi lecture demonstration.

1. Relationship between the capacitance and the capacitor geometry can be demonstrated. Simply connect a capacitance meter (Tenma 72-040) 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 capacitance meter and charge the plates to ~80V w/ a battery pack. Disconnect the batteries. Connect a high input impedance electrometer (either the digital Keithley 617 or analog Pasco ES-9054B) and demonstrate that the potential difference between the plates is changed by moving the plates together/apart. Note that the plates will slowly discharge over time.

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 meter to DISCHARGED plates, otherwise one will blow meter fuse.

#### Equipment:

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