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Circular Magnetic Field and direction problem

  1. Feb 25, 2012 #1
    1. The problem statement, all variables and given/known data
    A certain commercial mass spectrometer is used to separate uranium ions of mass 3.92 10-25 kg and charge 3.20 10-19 C from related species. The ions are accelerated through a potential difference of 140 kV and then pass into a uniform magnetic field, where they are bent in a path of radius 1.10 m. After traveling through 180° and passing through a slit of width 1.00 mm and height 1.00 cm, they are collected in a cup.


    2. Relevant equations
    r = mv/abs(q)B

    v = sqrt(2qV/m) (where V is potential)

    3. The attempt at a solution
    What is did was first find for velocity using the equation given and I got 478091.4438 then I used the radius equation above and massaged it to B= mv/abs(q)r plugged in my velocity and got .486 this is incorrect why? Also in general when I am ding problems involving magnetic fields how can I easily determine the direction of it I struggle with that.
     
  2. jcsd
  3. Feb 26, 2012 #2

    ehild

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    What is the question? What quantity have you calculated? You got 0.486, what is it? What is the unit?


    ehild
     
  4. Feb 26, 2012 #3
    The unit I got was suppose to be tesla
     
  5. Feb 26, 2012 #4
    sorry I just realized I didnt put the whole question on their so here is the rest I was solving part a.

    (A) What is the magnitude of the (perpendicular) magnetic field in the separator?


    (b) If the machine is used to separate out 50 mg of material per hour, calculate the current of the desired ions in the machine.


    (c) In that case, calculate the thermal energy produced in the cup in 1.00 h.
     
  6. Feb 26, 2012 #5

    ehild

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    The 0.486 T is a bit inaccurate. Try again, and do not drop significant digits. ( I got a bit more than 0.5 T.)

    And what about the other questions?:smile:

    ehild
     
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