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Homework Help: Mass of a particle through a magnetic field

  1. Jun 18, 2013 #1
    1. The problem statement, all variables and given/known data

    In a mass spectrometer, the mass of charged objects is inferred from how much thier trajectory curves when passed through a perpendicular magnetic field. A particle has a charge of q=1.602x10^-19 C and is traveling at v = 2.00x10^5 m/s in a perpendicular magnetic field of B=100gauss. If the radius of the curvature is found to be 20.8 cm, what is the mass of the particle? & can you identify this particle?

    2. Relevant equations


    3. The attempt at a solution

    Fc=m(2.00x10^5 m/s)2/r

    I am guessing this is proton because of the positive charge.
  2. jcsd
  3. Jun 18, 2013 #2
    Actually, I believe the equation is r= (mv)/(|q|B)
  4. Jun 18, 2013 #3
    So, (0.208m)=(m*2.00x10^5m/s)/(1.602x10^-19*0.1 tesla)

    and m = 1.67 x 10^-26 kg

    Is this correct?
  5. Jun 18, 2013 #4


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    0.1 tesla is 1000 gauss, not 100. Fix the exponent.
  6. Jun 18, 2013 #5
    It would be 0.01 Tesla and the answer would be 6.49x10^14 ?
  7. Jun 18, 2013 #6


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    It would be 0.01 tesla but now your answer is WAY off. You were closer before. What happened?
  8. Jun 19, 2013 #7
    I think I made an algebraic error.

    Now I have m=1.67x10^-27
  9. Jun 20, 2013 #8
    And thanks for your help!
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