The stopping potential refers to the voltage difference required to stop electrons from moving between plates and creating a current in the photoelectric experiment. The minimum amount of energy that is required to eject an electron from the metal surface is known as the work function. Photons are electrically neutral. Photons have no mass, but they have energy E = hf = hc/λ. Here h = 6.626*10-34 Js is a universal constant called Planck's constant. The energy of each photon is inversely proportional to the wavelength of the associated EM wave.

Thumbnail: Stopping Potential and Energy of a Photon