The Photoelectric Effect: Determination of Planck’s Constant

We test Einstein’s theory of the photoelectric effect, which predicts a linear relation between the energy of light incident on a metal surface and the energy of the emitted electrons. We determine the electron stopping voltage as a function of frequency of incident radiation by illuminating a potassium cathode and constraining the wavelength of incident radiation using several optical band-pass filters. From this, we calculate the constant of proportionality h/e as well as the constant offset, known as the work function. Our analysis included two different selection criteria to determine the stopping voltage, Vcutoff, each of which led to a different estimate of Planck’s constant and the effective work function, φeff. Our final results for both methods are h = (7.12 ± 0.88) × 10−34 J·s and φeff = 2.20± 0.32 eV and h = (4.08± 0.88)× 10−34 J·s and φeff = 1.28± 0.32 eV .