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Mass spectrometer conceptual question

  1. Oct 10, 2009 #1
    1. The problem statement, all variables and given/known data

    It's not really a book problem, just a question I encountered in my reading.
    For a mass spectrometer, if r = mv / qb, then r is directly proportional to mass and inversely proportional to charge. However, my reading says that the higher the mass, the less deflection. I think I may be confusing deflection with r, then. What is deflection? Why is it different from r? I had formerly thought the amount of deflection referred to r.

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 10, 2009 #2

    Delphi51

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    Yes but r proportional to m means less deflection with higher m.
    An infinite mass would have infinite radius, meaning it goes in a straight line and has no deflection. A small mass will be deflected a lot into circular motion with small r.
     
  4. Oct 10, 2009 #3
    Yes but if r is directly proportional to m, if m goes up, then r must go up, according to the equation, no? And if q goes down, then r goes up? Am I making a conceptual mistake here?
     
  5. Oct 10, 2009 #4
    Unless r is not deflection, in that case, what is the difference?
     
  6. Oct 10, 2009 #5

    Delphi51

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    You have MORE deflection when r gets SMALLER.
    Zero deflection is when it keeps going in a straight line with infinite r.
    I guess r could be called the inverse of deflection.
     
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