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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
\( \mathrm{P} \) spectrum. In our experiment with rubidium photo-cell, the following

W lines from a mercury source were used:
\[
\lambda_{1}=3650 \AA, \lambda_{2}=4047 \AA, \lambda_{3}=4358 \AA, \lambda_{4}=5461 \AA, \lambda_{5}=6907 \AA \text {, }
\]
The stopping voltages, respectively, were measured to be:
\[
V_{01}=1.28 \mathrm{~V}, V_{02}=0.95 \mathrm{~V}, V_{03}=0.74 \mathrm{~V}, V_{04}=0.16 \mathrm{~V}, V_{05}=0 \mathrm{~V}
\]
Determine the value of Planck's constant \( h \), the threshold frequency and work function for the material.
[Note: You will notice that to get \( h \) from the data, you will need to know \( e \) (which you can take to be \( 1.6 \times 10^{-19} \mathrm{C} \) ). Experiments of this kind on \( \mathrm{Na}, \mathrm{Li}, \mathrm{K} \), etc. were performed by Millikan, who, using his own value of \( e \) (from the oil-drop experiment) confirmed Einstein's photoelectric equation and at the same time gave an independent estimate of the value of \( h \).
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