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Question

A mercury lamp is a convenient source for studying frequency dependence of photoelectric emission, since, it gives a number of spectral lines ranging from the UV to the red end of the visible spectrum. In our experiment with rubidium photo-cell, the following lines from a mercury source were used
λ1=3650˚A,λ2=4358˚A,λ3=4358˚A,λ4=5461˚A,λ5=6907˚A.
The stopping voltages, respectively, were measured to be:
V01=1.28V, V02=0.95V, V03=0.74V, V04=0.16V,V05=0V,
Determine the value of Plancks constant h, the threshold frequency and work function for the material.

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Solution

Obtain V0 versus plot. The slope of the plot is (h/e) and its intercept on the v-axis is V0. The first four points lie nearly on a straight line which intercepts the v-axis at V0=5.0×1014 Hz (threshold frequency). The fifth point corresponds to V<V0; there is no photoelectrice mission and therefore no stopping voltage is required to stop the current. Slope of the plot is found to be 4.15×1015 V s. Using e=1.6×1019C,h=6.64×1034Js (standard value h=6.626×1034Js),ϕ0=hV0=2.11V.

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