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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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 Harmonic Motion
  video  - Transverse Waves
  video  - Longitudinal Waves
 Acoustic levitation
  video  - Standing Waves
 Soap Film Standing Waves
 Bell in a Vacuum
  video  - Doppler Buzzer
  video  - Diffraction & Interference in Ripple Tank
 Double Slit Interference of Microwaves
 Interference of Sound Waves
  video  - Tuning Fork Beats
  video  - Oscillator Beats

Bell in a Vacuum


To show that sound does not propagate in a vacuum.


Connect battery to bell "flashlight" apparatus leads and place under bell jar. Shine flashlight on photocell to show that the bell does ring. Connect vacuum pump and begin pumping while periodically making bell ring to show a decrease in sound level. A significant reduction in the sound level is heard although not total. This is due to some coupling through the jar and base.

The bell "flashlight" apparatus utilizes a #46 miniature light bulb, 6.3V and 0.25A.


An alternative set up with microphone mounted inside the vacuum bell jar is available (see 2nd picture).

To use this setup connect the power to the bell using 120->6v transformer black and red leads. Connect the microphone inside to the mini jack and take the output to the PA and/or amplifier/speaker system on yellow and green leads. Students will hear continuously reducing sound intensity even while the pump is pumping.


  • Plastic Bell Jar
  • Flashlight
  • Bell with photocell
  • 6 V Car Battery
  • Vaccum Pump
  • FM Wireless Microphone