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 - Photoelectric Effect in Zinc
Purpose:To show that ultraviolet (UV) light of sufficient energy incident on a Zinc plate will cause electrons to be emitted from the metal's surface.
Electrically connect the Zinc plate to the top of the electroscope via banana plug wire and charge (by touching plate) with the negative Teflon rod (rubbed with silk) so that there is a noticeable displacement of the electroscope leaves or arm. Place the UV light above the Zinc plate and turn it on. The loss of charge due to photoelectric emission can be seen by watching the electroscope leaves fall back to a vertical position. Note: the UV light source has short-wave (sw = 254nm) and long-wave (lw = 366nm) settings. Only at the sw setting electrons will be emitted from the Zinc plate).
Hints:The work function for zinc is approx. 4.31 eV which gives a cutoff wavelength of 288 nm.
Zinc surface should be cleaned with steel wool before use.