In a photoelectric experiment in which monochromatic light and a sodium photocathode are used, we find a stopping potential of 1.85 V for\lambda \cong3000Å and of 0.82 V for\lambda \cong4000Å. From these data, determinea) A value for Planck’s constant,b) The work function of sodium in electron volts, andc) The cutoff wavelength for sodium.