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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.

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  video  - Kinds of Charge and Charging
  video  - Attraction and Repulsion Between Charged Objects
  video  - Charging by Induction
  video  - Lord Kelvin's Water-Drop Electrostatic Generator
  video  - Wimshurst Machine
  video  - Fun Fly Stick
  video  - Xerox
  video  - Fluorescent Bulb in Faraday Cage
 Electric Fields And Potential
 Current and Resistance
 Electromotive Force And Current
 DC Circuits
 Magnetic Materials
 Complex Circuits
 Semiconductors And Tubes
 Transmission Lines and Antennas

 video  - Kinds of Charge and Charging


To demonstrate the two signs of charge, attraction and repulsion, charging of electroscopes by contact and by induction.


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  DEMO VIDEO DOWNLOAD - HD - 1920x1080 / 27.4Mbps - 643MB size  

  DEMO VIDEO DOWNLOAD - LD - 854x480 / 5.69Mbps - 152MB size  

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  DEMO VIDEO DOWNLOAD - HD: 1920x1080 / 24.19Mbps - 1,758MB size  

  DEMO VIDEO DOWNLOAD - LD: 854x480 / 5.69Mbps - 411MB size  

  DEMO VIDEO DOWNLOAD - LD: 854x480 / 1.1Mbps - 79MB size  

  DEMO VIDEO DOWNLOAD - LD: 854x480 / 0.25Mbps - 17MB size  

The most effective way to charge a rod by friction is to hold the cloth vertically in one hand and "whip" it vigorously with the rod held in the other hand. Note that when rubbing a glass rod with cat's fur (silk), the rod becomes positive; the fur (silk) negative. Use the electroscope to show that the rod and cloth carry charges of opposite sign. This can be done after the electroscope has been charged with a known sign, either by contact or induction. Then investigate the sign of charge on rods of other materials which have been rubbed with all the available cloths. Show repulsion and attraction between hanging balls charged similarly and oppositely. Show effect of charged rods on small bits of paper or an inflated balloon.


Pith Balls: using them is tricky (they bounce around alot). Instead, you can use two balloons hung on fishing line - rub both in your hair, show like charges repel. Then, without touching balloon, bring your hand close to either one and show induced charge causes attraction.

Triboelectric Effect: when rubbing the following pairs of materials, one obtains a charge via friction.

Teflon Rod (neg) with Silk (pos).
Glass Rod (pos) with Cat Fur (neg).
Acrylic, Lucite or Glass Rod (pos) with Teflon Film (neg).

Some have suggested to use tinsel and helium filled conducting balloon. See


  • Teflon Tod
  • Silk
  • Rubber
  • Pith Balls
  • Lucite
  • Glass
  • Bits of paper
  • Electroscope
  • Balloon