When light with a frequency above the threshold frequency is shone on the cathode photoelectrons will be emitted and will travel across the gap to the anode and a current will be registered on the ammeter.The potential difference across the photoelectric cell is increased slowly until the anode is sufficiently negative to repel the photoelectrons and no current will be registered.This potential difference is called the stopping potential and is related to the maximum kinetic energy of the photoelectrons by:e Vs = ½m v2maxUsing light of different frequencies and finding the stopping potential for each frequency of light a graph of maximum kinetic energy against frequency can be plotted.The graph is a straight line of gradient h. It does not pass through the origin: it cuts the frequency axis at the threshold frequency f0 and extrapolates to −φ on the energy axis.