Image intensifiers used in nightvision 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 \(900 \mathrm{~nm}\), in the infrared.

a. If the threshold wavelength is \(900 \mathrm{~nm}\), what is the work function of the photocathode?

b. If light of wavelength \(700 \mathrm{~nm}\) strikes such a photocathode, what will be the maximum kinetic energy, in \(\mathrm{eV}\), of the emitted electrons?