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Homework Help: Quantum mechanics.

  1. Aug 22, 2010 #1
    Hi there.
    I am a student from Spain and I am about to join the University but I have to pass physics at High School.

    Here It is:

    The work of extracting an Eletron in a metal is 3.8 eV. Calculate the minimum frequency needed to start the electron.

    This is what I did.

    [tex]\[E = \phi + Ec\][/tex]

    Regarding to Einstein's equation of photoelectric effect:

    [tex]\[h\nu = h\nu _0 + \frac{1}{2}mv^2 \][/tex]

    When I got to this point, I assumed that the electron's velocity would be zero and then:

    [tex]\[\nu = \frac{{3.8}}{{6.63\cdot10^{ - 34} }} = 5.73\cdot10^{33}[/tex]

    Is everything alright?
    Last edited: Aug 22, 2010
  2. jcsd
  3. Aug 22, 2010 #2


    User Avatar
    Science Advisor

    No. You have to be more careful with units. You have used the energy in units of eV, and h in units of J-sec. You need to use a consistent set of units - either convert the energy in eV into J, or use h in eV-sec. Try again, and use dimensional analysis to check the units of your answer.
  4. Aug 22, 2010 #3
    lol, I didn't notice, [tex]\[
    1eV = 1.602\cdot10^{ - 19} J
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