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Homework Help: Long selenoid please help!

  1. Oct 14, 2009 #1
    1. The problem statement, all variables and given/known data
    A long solenoid has 100 turns/cm and carries current i. An electron moves within the solenoid in a circle of radius 2.20 cm perpendicular to the solenoid axis. The speed of the electron is 0.048 c (c = speed of light). Find the current i in the solenoid.

    2. Relevant equations

    i= mv/e*mu*n*r

    3. The attempt at a solution
    i= (9.11E-31kg)(.0480)(3.0E8)/ (1.6E-10 C)(4*pi E-7 Tm/A)(100/.01 m) (2.2E-2) = .266 A
    this answer is wrong...
    what am i doing wrong? thank you!
  2. jcsd
  3. Oct 14, 2009 #2


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    Homework Helper

    Probably a typo but you wrote 1.6E-10 for the charge on the electron.
    Of course you need brackets around all the factors in the denominator.
    I ran your calc through my calculator and got .297 A.
  4. Oct 14, 2009 #3
    yeah, that's right! i must have messed up on the calculations somewhere!
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