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Homework Help: Threshold frequency experiment

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data

    Out of Sodium (2.75 eV), Cesium (2.14 eV) and Silver (4.73 eV), which metal would be best suited to coat the cathode of the light meter such that it is sensitive to all colors of light? The range of wavelength for visible light is 700 nm to 400 nm.

    2. Relevant equations

    threshold frequency= work function/ planks constant 4.14x10^-15
    Hz= speed of light/ threshold frequency

    3. The attempt at a solution

    2.75/4.14x10^-15= 6.6x10^-16= 3x10^8/6.6x10^-16= 4.5 nanometers
    2.14/4.14x10^-15= 5.2x10^-16= 3x10^8/5.2x10^-16= 5.8 nanometers
    4.73/4.14x10^-15= 1.1x10^-15=3x10^8/1.1x10^-15= 273 nanometers

    silver is the closest to being sensible to colors of light.

    it seems to me like i did everything right but nothing goes to sensible light, and i dont know what im doing wrong
  2. jcsd
  3. Feb 5, 2009 #2


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    Homework Helper

    For the photoelectric effect isn't it:

    hf = φ + Ekmax

    where φ = h*fo
    and E is the kinetic energy of the electrons freed up.

    So then it seems that the energy of the incident light times Plank and the frequency of the light would be your budget and the closer your work function φ is to the visible light spectra then the less that is available for the Ekmax.
  4. Feb 5, 2009 #3
    alright. i got the calculations now,
    silver= 273 nanometers
    cesium= 576 nanometers
    sodium= 454 nanometers
    would cesium be the most sensitive one because it emits the least frequency?
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