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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Purpose:A quantitative verification of Einstein's famous equation describing the photo-electric effect.
Procedure:An instruction manual for this h/e experiment is available here. This demo makes use of the PASCO h/e Apparatus AP-9368 and the Mercury Vapor Light Source OS-9286 (replacement lamp). Set up the apparatus as shown in the picture, connecting the output to a voltmeter. The detector consists of a vacuum photodiode connected to a unit gain amplifier. The photodiode and its associated circuitry have a small capacitance. When light falls on the photodiode, the capacitor is charged until the stopping potential is reached and the circuit stabilizes giving a direct reading of the stopping potential for that frequency.
A grating attached to the Hg lamp splits the light into its spectral components. Line up each of the lines with the opening of the detector and read off the stopping potential for each making sure to zero the circuit after each reading. A plot of stopping potential vs frequency will give a straight line, the slope of which gives the value of h/e.