A mercury lamp is a convenient source for studying frequency dependence of photo electric emission , Since it gives a number of spectral lines rating 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 where used . $\lambda_1 = 3650 A^{\circ}, \lambda_2 = 4047 A^{\circ}, \lambda_1 = 4358 A^{\circ}, \lambda_4 = 5461 A^{\circ}, \lambda_5 = 6907 A^{\circ}$The stopping voltages respectively were measured to be : $V_{o1}= 1.28 \;v , V_{o2}= 0.95 \;v, V_{o3}= 0.74 \;v, V_{o4}= 0.16\;v, V_{o5}= 1.28 \;v$ Estimate the threshold frequency and work function for the material .

Question

$\begin{array}{1 1} 20.5 \;ev \\ 205\;ev \\ 2.05 \;kev \\ 2.05 \;ev \end{array}$