Image intensifiers used in night-vision devices create a bright image from dim l
ID: 1899265 • 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:If light of wavelength 680 strikes such a photocathode, what will be the maximum kinetic energy, in , of the emitted electrons?
Express your answer using two decimal places and include the appropriate units
Please give me a correct answer
Explanation / Answer
A) hf = work function = 6.63 . 10^–34 . 3 . 10^8 / 900 . 10^–9 = 2.21 . 10^–19 J = 1.38eV
B) KE = photon energy – work function
KE = ( 6.63 . 10^–34 . 3 . 10^8 / 680 . 10^–9 . 1.6 . 10^–19 ) – 1.38 = 0.44eV