# Is it possible to calculate the work function of a metal with basic lab equipment?

ive been given a problem in physics, its to prove if a lump of metal we have been given is real gold or not. one way to to do it would be to work out its density, which is fairly easy, mass/volume. (its not real gold by the way, we just have to show it). But as this is the route that all the other groups are gonna go down, id like to do something more interesting, but im not sure if its possible with the equipment, which consists of, basic optics equipment like a ray table, lasers,(which would give us a known frequency of light), prisms, mirrors, rheostats, transistors, geiger counters, thermometers, diffraction gratings, and a few other things. Maybe its also possible to measure some absorbtion(fraunhoffer) lines? does any body have any ideas or know problems that i might come into?

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You'd need a pretty decent vacuum to do the photo-electric effect experiment. Is that possible with your "basic lab equipment"? – dmckee Nov 26 '11 at 18:52
@dmckee, this is not true! Hallwachs found the photoelectric effect (Zink) in air. You can't determine the velocity of the electrons in air, but the borderline light wavelength will be enough. The problem I see is that work funktion data are rather coarse, maybe some metals "overlap" with gold values. – Georg Nov 26 '11 at 19:03
@Georg: Hmm...I guess so. I didn't know that bit of history. We always did it in vacuum to get a good measure of the stopping potential. I assume you use a very short gap? – dmckee Nov 26 '11 at 19:06
No, You just measure the current from the Zink electrode into air. I have seen that experiment in this form in school (early sixties). The experiments maybe were induced by Hertz's observation that voltage sparked over air gap between Zink spheres at lower voltages when illuminated by light. Hallwachs had been Hertz'assistant. Vacuum technology for photo cells was not ready at that time. – Georg Nov 26 '11 at 19:17
For a high-precision measurement, the gold electrode will have to be extremely clean, and the measurement will have to be done in a light-tight box to keep out stray short-wavelength light. I teach a student lab where we measure stopping voltage as a function of frequency (with the electrode inside a vacuum tube) and use the slope to determine h/e. The y-intercept would be the work function. The results of that lab are not high precision, about +-20%. It seems unlikely to me that one could do much better than that on the work function, with the electrode exposed to air. – Ben Crowell Nov 27 '11 at 15:15