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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video - Electron DiffractionPurpose:To show the wave nature of the electron by diffraction of an electron beam by a carbon foil anode (polycrystalline graphite). The de Broglie hypothesis can be verified by observing that the diffraction angle changes as a function of the beam momentum (acceleration voltage).Procedure:The electron beam appears as concentric rings around a bright center. The pattern looks like a one-dimensional diffraction pattern of bright spots rotated about its center. For an explanation as to why one sees a concentric circle pattern when accelerating electrons thru a graphite foil as in our demo apparatus, take a look at Matter Waves (1961) video (especially starting at 9:00 minutes as measured by your media player).  For a schematic on setting up the circuit click here. Turn the high voltage control to minimum, apply power to the filament and wait 30 seconds. Bring up the high voltage to about 2500 volts and diffraction circles will appear on the tube. The anode voltage can then be increased and the rings will move inward showing that the wavelength of the electron has decreased as the momentum increased. One can use a bar magnet to deflect the beam to convince the students there are electrons creating the image on the phosphor screen and not light. Equipment:
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