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Homework Help: Frequency of photons emitted from electrons

  1. May 12, 2012 #1
    1. The problem statement, all variables and given/known data
    The energy of the electron in the first and forth levels in a hydrogen atom are: (21.76*10^-19), (-0.85) e.V.. the electron moved from the forth level to the first level with one leap. Calculate:
    The frequency of the emitted photon from the atom

    2. Relevant equations
    ΔE = hf

    3. The attempt at a solution
    f = ΔE / h
    f = [(-0.85) - (21.76*10^-19)] / 6.6*10^-34
    f = -1.2878*10^33 Hz ..
    I get that answer while the answer given in the book is 3.09*10^15 Hz, I'm confused..
  2. jcsd
  3. May 12, 2012 #2
    i think that energy in the first level is given in Joule (-21.76*10^-19) and the second is in eV.so you have to convert both energy levels to Joule.since electron's charge is negative, it's energy in presence of positive charge's potential is negative. so f=(-.85*1.602*10^-19--21.76*10^-19)/(6.6*10^-34)=3.09*10^15 Hz
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