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Homework Help: Mass Spectrometer Question

  1. Oct 5, 2008 #1
    A mass spectrometer, sketched below, is a device used to separate different ions. Such ions with a well-defined velocity Vo enter through a slit into a region of uniform magnetic field B, where they follow a semicircular path until they strike the detector slit above the entry slit. The distance between the entry and the detector slits is d = 1.30 m.

    1. [1pt]
    Chlorine ions of mass 35 amu (1 amu equals 1.66x10-27 kg), carrying a charge of +1e, enter the spectrometer with initial speed of vo = 3.40E5 meters/sec. What value of B is required for these ions to hit the detector?

    Answer: Last Answer: -.095 T
    Incorrect, tries 4/99.

    I tried: r=mv/(qB) => B= mv/(qr)

    B= (5.81 x 10^-26 kg x 3.40 x 10^5 m/s) / (1.60 x 10^-19 C x 1.30 m)
    B= .0950 T

    where did i go wrong?
  2. jcsd
  3. Oct 5, 2008 #2
    If I'm picturing the situation right, d = 1.30 m is the diameter. The radius is explicitly needed in your equations.
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