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Homework Help: Find max kinetic energy

  1. Dec 19, 2013 #1


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    1. The problem statement, all variables and given/known data
    The electric field associated with a monochromatic beam becomes zero 1.2*10^15 times per second. Find the max kinetic energy of the photoelectrons when this light falls on a metal surface whose work function is 2.0 eV.

    2. Relevant equations

    3. The attempt at a solution
    K(max)=hv-W where W=work function.
    I have to find frequency from the given information which I don't know. But I guess it should be 1.2*10^15. Not sure about that.
  2. jcsd
  3. Dec 19, 2013 #2


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    I believe your interpretation that ##f = 1.2 \times 10^{15} Hz## would be the case.

    Convert your work function into Joules before you use it.

    Your equation also seems to be a bit off, it should read:

    ##E_k = hf - W##
  4. Dec 19, 2013 #3
    Think about a sine function (or even better draw it).
    How many times does it go through zero in a period?
    It is easier to see if you take a period from a maximum to the next maximum in the sine wave.
  5. Dec 19, 2013 #4


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    I got that. Thanks!
  6. Dec 19, 2013 #5
    Then what is the frequency of the light, in the problem?
    Or you solved the question already?
  7. Dec 20, 2013 #6


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    I solved that.
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