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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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 Electric Fields And Potential
 Current and Resistance
 Electromotive Force And Current
 DC Circuits
 Magnetic Materials
 Magnet collection
  video  - Magnetic Fields w/ Iron Filings
  video  - Magnetic Fields w/ Matrix of Iron Rods
  video  - Magnetic Fields Associated with Current Carrying Wires 1
  video  - Magnetic Fields Associated with Current Carrying Wires 2
  video  - Solenoid w/ Iron core
  video  - Magnetic Deflection of an Electron Beam
  video  - e/m Tube Lorentz Force Demonstrator
 Magnetohydrodynamic Motor
  video  - Forces Between Current Carrying Wires
  video  - Vibrating Lamp Filament
  video  - Force on a Current Carrying Wire in a Magnetic Field
 Hall Effect
  video  - Galvanometer Movement
 Complex Circuits
 Semiconductors And Tubes
 Transmission Lines and Antennas

 video  - e/m Tube Lorentz Force Demonstrator


The electron beam of an e/m tube in Helmholtz coils is shown under various electric or magnetic field configurations.


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  DEMO VIDEO DOWNLOAD - LD - 854x480 / 5.69Mbps - 117MB size  

Turn ON 5 minutes before use. Even if beam is visible, it takes 5 minutes before it is bright enough to resolve on a camera!

A Pacific Science Supplies Model P63412 e/m Lorentz Force Demonstrator can be shown with the aid of a video camera in a darkened room. It is possible to bend the e- beam in a circle and spiral by adjusting the orientation of the tube and the current of the Helmholtz coils. The electron beam is visible due to the tube vacuum containing a trace of inert gas (argon?). Ionization of the gas around the electron beam creates a glowing discharge marking the path of the electrons.


  • Make sure all voltage & current controls are minimized and off before turning on the main power to the unit.
  • Wait 5 minutes before turning up the accelerating voltage for the electron beam. Do not exceed 200V.
  • Turn selector to "clockwise" or "counter clockwise" before turning up current to Helmholtz coils.