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Homework Help: Some more basic homework help

  1. Oct 28, 2003 #1
    some more basic homework help!!

    can you guys point me in the right direction, where to start? (grrr, so freakin lost in this class)

    11. A 22.5-eV positron (positively charged electron) is projected into a uniform magnetic field B = 455[mu]T with its velocity vector making an angle of 65.5 degrees with B (vector). Find (a) the period (b) the pitch p, and (c) the radius r of the helical path.

    ill try and scan the diagram too



    im "learning" magnetic fields for this chapter.

    here is the scan of the problem, and a figure to go with it:

    http://storage.whiteazn.com/phy181_pr11.jpg [Broken]
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Oct 28, 2003 #2
    was reading the chapter..and they had a section on circulating charges ... it had an equation relating qvB to centripetal acceleration of:


    problem is, in the question, to find r, we have to know v, which isnt given ?? and also, dont know the mass ?


    any help!1??!
  4. Oct 28, 2003 #3
    I think you can find v from the energy of the positron by using the kinetic energy formula, since E = 22.5 eV << the positron rest mass (0.5 MeV). The mass is equivalent to the electron mass.
  5. Oct 29, 2003 #4

    is the kinetic energy formula:

    K=(1/2)mv^2 ?

    and still lost on this part:

    since E = 22.5 eV << the positron rest mass (0.5 MeV). The mass is equivalent to the electron mass.
  6. Oct 29, 2003 #5
    Yeah, that should be the right formula.

    A positron basically is just an electron with a positive charge, so they have the same mass.
  7. Oct 29, 2003 #6
    so whats the mass? 22.5 ??
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