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Homework Help: Bohr model of atom

  1. Jul 19, 2005 #1
    Hi; Could someone please help me with this question: By what fraction does the mass of an H atom decrease when it makes an n=7 to n=5 transition? How would I go about this question? Thank you.
     
  2. jcsd
  3. Jul 19, 2005 #2
    There's a mass change?
     
  4. Jul 19, 2005 #3
    Re:

    I guess so. That's what confuses me about the question. I don't know how to incorporate the mass into it. Does anyone know how to do this? Thanks.
     
  5. Jul 20, 2005 #4

    James R

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    What's the energy change?

    Next, use [itex]E=mc^2[/itex].
     
  6. Jul 20, 2005 #5
    Re:

    Ok, so I find the energy change by doing E of upper state - energy of lower state right? So I get (-0.2) - (-0.5) = 0.3 After I find this energy change, how do i find the decrease in mass? If I use E=mc^2, I plug in 0.3 into E and 1.00794 into m? What am I solving for? I'm confused. Thanks for your help.
     
  7. Jul 20, 2005 #6
    As per [itex]E=mc^2[/itex] , Mass is the condensed form of energy . So whenever energy is released from particle , it is accompanied by a small mass change. So calculate the energy change from one state to another , and then equate the energy change with [itex]mc^2[/itex].

    BJ
     
  8. Jul 23, 2005 #7

    James R

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    You're trying to find m. c is the speed of light, which is [itex]3 \times 10^8[/itex] m/s. If you want m in kilograms, you need E in Joules. Your 0.3 is not in Joules, so you'll need to convert it.

    If your energies are in eV, the conversion is: [itex]1 eV = 1.6 \times 10^{-19} J[/itex]
     
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