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Photo electric effect problem

  1. May 21, 2015 #1
    1. The problem statement, all variables and given/known data
    A magnesium surface has a work.func of 3.68eV. El.mag. waves with wavelenght of 215nm strike the surface and eject electrons. Find the max Ek of the ejected electrons in eV.

    2. Relevant equations
    E=Ek-W <=> Ek=(hc/lambda) - W

    3. The attempt at a solution
    I convert eV to J and nm to m but i get -3.68*10^10eV, but the answer is suppoused to be 2.10eV.
    I even re did it but got the same answer, where em I going wrong?

    Thanks
     
  2. jcsd
  3. May 21, 2015 #2

    TSny

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    Homework Helper
    Gold Member

    Hello.
    In order to see where you are going wrong, we need to see your entire calculation.
     
  4. May 21, 2015 #3
    Ek=(hc/lambda)-W

    ((6.63*10^-34)*(3*10^8))/(2.15*10^-7) - (5.888*10^-9)

    (9.25*10^-19) - ( (5.888*10^-9) = -5.887*10^-9 J / (1.6*10^-19) = -3.68*10^10eV
     
  5. May 21, 2015 #4

    TSny

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    Check the power of 10 for the work function expressed in Joules.
     
  6. May 21, 2015 #5
    ah ye, there we go. thanks :)
     
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