Image intensifiers used in night-vision devices create a bright image from dim l
ID: 1909806 • Letter: I
Question
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 A If the threshold wavelength is 900 , what is the work function of the photocathode? Part B If light of wavelength 600 strikes such a photocathode, what will be the maximum kinetic energy, in , of the emitted electrons?Explanation / Answer
(a)
Work function = 1240/900 = 1.37 eV
(b)
Energy of radiation = 1240/600 = 2.067 eV
So,
KE = 2.067 - 1.37 = 0.696 eV
Therefore, the answer is 0.696 eV