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:
`lambda_1 = 3650 oversetcircA`, `lambda_2=4047 oversetcircA`, `lambda_3=4358 oversetcircA`, `lambda_4=5461 oversetcircA`, `lambda_5=6907 oversetcircA`
The stopping voltages respectively were measured to be
`V_0=1.28 V`, `V_0.95V`, `V_0=0.74V`, `V_0=0.16`, `V_0=0V`
The threshold frequency and work function for the material.