Image intensifiers used in night-vision devices create a bright image from dim l
ID: 1378099 • 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 nm, in the infrared:
If light of wavelength 540nm strikes such a photocathode, what will be the maximum kinetic energy, in eV, of the emitted electrons?
Explanation / Answer
Kinetic energy of the emmited electrons is
KE = hc / 540 nm - hc / 900 nm
= ( 1240 eV. nm )/ 540 nm - ( 1240 eV. nm/ 900 nm )
= 0.918 eV