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Homework Help: Magnetic fields and sodium ions

  1. Mar 30, 2007 #1
    1. The problem statement, all variables and given/known data
    Sodium ions (Na+) move at 0.851 m/s through a bloodstream in the arm of a person standing near a large magnet. The magnetic field has a strength of 0.254 T and makes an angle of 51 degrees with the motion of sodium ions. The arm contains 100 cm^3 of blood with 3 x 10^20 Na+ ions per cubic centimeter. If no other ions were present in the arm, what would be the magnetic force on the arm?

    2. Relevant equations

    [tex] F_{B}=qvBsin\theta[/tex]

    3. The attempt at a solution

    First I found charge by doing some mathematical operations:
    [tex] 100 cm^{3} * \frac{3*10^{20} Na+ ions}{cm^{3}}[/tex]
    [tex]= 3*10^22 Na+ ions * (1.60*10^{-19})[/tex]
    [tex]=4800 C [/tex] <--- I'm not sure if this procedure is right.

    If the charge is correct, then: [tex] F_{b}=4800 (0.851 m/s)(0.254 T)sin 51[/tex] [tex] =806.32 N[/tex]
  2. jcsd
  3. Mar 30, 2007 #2
    Also, although this is irrelevant and not associated with the problem above, what is the charge of a "singly charged ion" with mass= 2.18 x 10^-26kg? Thanks.
  4. Mar 30, 2007 #3
    The assumption is that the ion has a charge of the fundamental charge, [itex]e[/itex] (charge on a proton or electron). This has a value of 1.60 x 10^-19 C. [itex]Na^+[/itex] is a singly charged ion.
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