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 end of the red visible spectrum. In our experiment with rubidium photocell, the following lines from a mercury source were used: `lambda_(1)=3650A^(@), lambda_(2)=4047A^(@), lambda_(3)=4358A^(@), lambda_(4)=5461A^(@), lambda_(5)=6907A^(@)` The stopping voltages, respectively were measured to be:
`V_(01)=1.28V, V_(02)=0.95V, V_(03)=0.74V, V_(04)=0.16V, V_(05)=0V`.
(a) Determine the value of Planck's constant h.
(b) Estimate the threshold frequency and work function for the material.

Explanation

Obtain `V_(0)` versus ν plot. The slope of the plot is (h/e) and its intercept on the ν-axis is `ν_(0)` . The first four points lie nearly on a straight line which intercepts the ν-axis at `ν_(0) = 5.0 xx 10^(14) Hz` (threshold frequency). The fifth point corresponds to `v lt v_(0)` , there is no photoelectric emission and therefore no stopping voltage is required to stop the current. Slope of the plot is found to be `4.15 xx10^(-15) v s`. Using `e=1.6xx10^(-19)C, h=6.64xx10^(-34)Js("Standard value h "=6.626xx10^(-34)Js), phi_(0)=hv_(0)=2.11V.`