Ethan conducted a photoelectric effect experiment to calculate Planck's constant. The experiment involved measuring the stopping potential of electrons emitted from a metal surface under monochromatic light of varying wavelengths. Plotting average stopping potential versus the reciprocal of wavelength produced a straight line, from which Planck's constant could be calculated using the slope. Ethan's calculated value of Planck's constant had a 36% error compared to the accepted value, which was within an acceptable range for the experiment.