Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
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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You have selected the following Demos:
Bell in a Vacuum
Purpose:To show that sound does not propagate in a vacuum.
Procedure: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.
Hints: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.