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Homework Help: How to calculate the work function of a metal?

  1. Jul 14, 2013 #1
    HI im doing this equation : 14. When a certain metal is illuminated at 3.50x10^2nm the maximum kinetic energy of the ejected electrons is 1.20 eV. Calculate the work function of the metal.
    I did this:
    W=hc/Lambda -Ek

    That answer is wrong the correct one is 2.35 eV. what did i do wrong, PLS help me ty and show me what I should of done so i Dont repeat this mistake again.
  2. jcsd
  3. Jul 14, 2013 #2
    Hello madayag1
    Look again at the figure you've used for the wavelength - you forgot the nm.
    Also, the first part of the calculation is in J, but you've subtracted a value in eV from it.
  4. Jul 14, 2013 #3
    Did you convert the units, Joule to eV?
  5. Jul 14, 2013 #4
    The result of 'W=hc/Lambda " is in joules is it not? You cannot subtract ev from joules wiothout a unit conversion.

    Also, you have ente3red your wavelength incorrectly.
  6. Jul 14, 2013 #5
    srry it should be W=( (6.63E-34J.s)(3.00E8m/s) / (3.50E2nm) ) - 1.9E-19J = -1.9E-19
    still the wrong answer tho.
  7. Jul 14, 2013 #6
    You've written the nm part for the wavelength, but did you include it in the calculation?
  8. Jul 14, 2013 #7
    Check your math. The answer is not negative. Also, what units are reque3sted?
  9. Jul 14, 2013 #8
    book doesn't say what units is requested
  10. Jul 14, 2013 #9
    I think work function is normally in ev. Check your math however.
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