When sodium metal is illuminated with monochromatic light with a wavelength of 420 nm, the maximum potential difference developed between the
plates in the experiment shown in figure Q3.1b is found to be 0.65 V; when the wavelength is 310 nm,this voltage is found to be 1.69 V. Check that these
experimental results are consistent with a value of 1240 eV • nm for hc, and find the value of W for sodium.