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AP mag. problem

  1. Nov 16, 2004 #1
    A 2.0 keV positron is projected into a uniform magnetic field B of 0.10 T with its velocity vector making an angle of 89 degrees with B. Find
    a. the period
    b. the pitch p
    c. the radius of the helix

    We have never done a problem similar to this in class so i'm am not sure where to start........
  2. jcsd
  3. Nov 16, 2004 #2


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    Here's a hint:

    [tex] \v{F} = Q ( \v{E} + \v{u} x \v{B} ) = \frac{m v^2}{r}[/tex]
    Last edited: Nov 16, 2004
  4. Nov 16, 2004 #3

    Chi Meson

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    The 2.0 keV is the kinetic energy of the particle, from which you can get the speed (but remember to convert to joules).
  5. Nov 16, 2004 #4
    ahhh.........mag force = centripital force
  6. Nov 17, 2004 #5

    Chi Meson

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  7. Nov 17, 2004 #6
    "pitch"? :confused:
  8. Nov 17, 2004 #7

    Chi Meson

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    If you look at a spring that is hanging vertically, you can see that it winds "up" to the right or to the left with a certain angle to the horizontal. This angle is the pitch. THe path of a charged object travelling through a magnetic filed will also be a helix (like a spring).
  9. Nov 17, 2004 #8
    we went over it in class and i got the correct answers :smile:

    if u wanna know here they are:

    a. period is 3.6e-10 sec.
    b.pitch is 1.63e-4 m
    c.radius is 1.48e10-3 m

    Was easy once I figured that i needed to resolve the velocity vector in horizontal and vertical components :rofl:
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