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 900 , in the infrared:

Part AIf the threshold wavelength is 900 , what is the work function of the photocathode?

Part BIf light of wavelength 600 strikes such a photocathode, what will be the maximum kinetic energy, in , of the emitted electrons?