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Photons of energy 12 eV are incident on a metal. It is found that current flows from

  1. Apr 20, 2012 #1
    1. The problem statement, all variables and given/known data

    Photons of energy 12 eV are incident on a metal. It is found that current flows from the metal until a stopping potential of 8.0 V is applied.
    If the wavelength of the incident photons is doubled, what is the maximum kinetic energy of the ejected electrons?

    2. Relevant equations

    I am absolutely clueless. I feel like I'm supposed to use KE = hf - W but how am I supposed to know the frequency if it isn't given? So I don't think I'm supposed to use this one.
    Please just lead me towards the right direction. I don't have a clue as to which equation to use.

    3. The attempt at a solution

    This question is gibberish to me and I don't know how to even approach it. Please help.
     
  2. jcsd
  3. Apr 20, 2012 #2
  4. Apr 20, 2012 #3
  5. Apr 20, 2012 #4
    Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

    Fair enough, did you look at the third link on Google? The Yahoo Answer one?
     
  6. Apr 20, 2012 #5
    Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

    Yes but it doesn't say how you get wavelength. Although E = hf and f = c/wavelength.
    E = h(c/wavelength). In which case what is E?
     
  7. Apr 20, 2012 #6
    Re: Photons of energy 12 eV are incident on a metal. It is found that current flows f

    It does. What that person did was used the relevant equations and formulated an equation that related the wavelength to the maximum energy.

    Ekmax = (h×c/λ) - (e×Vs-E)

    Now plug in the data you know, and use two variables for the wavelength and solve for the ratio.
     
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