(a) If the wavelength of the light incident on a photoelectric cell be reduced from `lambda_(1)` to `lambda_(2) Å`, then what will be the change in the cut-off potential?
(b) Light is incident on the cathode of a photocell and the stopping voltages are measured for light of two different wavelengths. From the data given below, determine the work function of the metal of the cathode in eV and the value of the universal constant `hc//e`.
`{:("WavelengthÅ","Stopping voltage (volt)"),(4000, 1.3),(4500, 0.9):}`