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Homework Help: The Atom: wavelength, energy, kinetic energy, etc. of photons

  1. Sep 13, 2010 #1
    here are the problems that I need help with:


    I am afraid that I know not much information about the questions. Sadly, I am enrolled in a poorly written Physics class online. I am not looking for the answers, but just how to go about finding them. The book never explained what eV was, but gave be basic equations like: E = hf, KE = hf + work function, and wavelength = h/mv

    h is always Planck's constant.

    It would be great to know the equations, units, etc. I can use. Because I am confused with Jules and Hz and nm and eV, etc.

    Help? I am stuck. Thanks in advance!
  2. jcsd
  3. Sep 13, 2010 #2


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    Homework Helper

    ok so we have three equations:

    E=hf ; E=Φ+KEmax and λ=h/mv

    The first question is asking for wavelength 'λ', so in the three equations which do you think you have to use? What is the mass of an electron and what is the speed of electron in the question?

    For the second question, you are given the energy of the electron, so you have 'E' and you want to get 'λ'. What is the frequency of the photon?

    Joule and eV (electron-volts) are two units used to represent energy. For energy sometimes dealing with electrons or photons, eV is used.'e' is the elementary charge of an electron which is 1.6x10-19C.

    so 1 eV= 1.6x10-19CV = 1.6x10-19 J.

    Hz is a unit of frequency.

    nm is a measure if length, it means 'nanometer'. The prefix 'nano' means 10-9. S0 200nm is the same as 200x10-9m.
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