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the drunken engineer

A system was set up and analyzed for the purpose of determining Plank's constant (in terms of electron volts) and to the work function and threshold frequency in terms of given wavelengths of light. By applying various voltages to the phototube, and measuring the resultant current flow due to the photoelectric effect, the stopping potential was determined from a graph of this data (for each wavelength). These values were then plotted against the frequency of the light emitted from the source, for the purpose of discovering values for the work function and threshold frequency. Using the stopping potential for each wavelength, their respective frequencies and the work potential, an averaged value for Plank's constant was calculated at 3.786x1014 J-s, a discrepancy of 75% from the accepted value. This can be attributed to inherent inaccuracies in the system; analog meters (ie the volt meter), additional resistance in the wiring and terminals, and the fact that calculations were based on the speed of light in a vacuum, not in air. Also, the presence of outside light sources (overhead lighting in the lab) would have also had a minor effect on the current produced by the phototube. It can not be said that Plank's constant was found to a sufficiently accurate level - in order to do so, the laboratory must be performed under more favorable conditions with more accurate equipment.