I just need help with Part B, Part A is answered. Image intensivers used in nigh

Question

I just need help with Part B, Part A is answered.

Image intensivers 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: Part A If the threshold wavelength is 900 nm. what is the work function of the photocathode? Express your answer with the appropriate units. Part B If light of wavelength 620 nm strikes such a photocathode, what will be the maximum kinetic energy, in eV, of the emitted electrons? Express your answer using two decimal places and include the appropriate units.

Explanation / Answer

energy = work funcion + KE

KE = hc/lambda - workfunction

KE = hc/620 - hc/900

KE = 2 eV - 1.38 eV

KE = 0.62 eV

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