Image intensifiers used in night-vision devices create a bright image from dim light by letting the light first fall on a photocathode. Electrons emitted by the photoelectric effect are accelerated and then strike a phosphorescent screen, causing it to glow more brightly than the original scene. Recent devices are sensitive to wavelengths as long as 900nm , in the infrared:
If light of wavelength 720nm strikes such a photocathode, what will be the maximum kinetic energy, in eV, of the emitted electrons?