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Force due to a line charge

  1. Feb 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A 10-cm long thin glass rod is uniformly charged to +50 nC. A small plastic bead, charged to - 5.2 nC, is 4.1 cm from the center of the rod. What is the magnitude of the force on the bead?

    2. Relevant equations
    dF = (k dq)/r[tex]^{2}[/tex]

    3. The attempt at a solution
    I've gotten to this point:

    dF sin [tex]\theta[/tex] = k[tex]\lambda[/tex] * (dx/(h[tex]^{2}[/tex] + x[tex]^{2}[/tex])[tex]^{3/2}[/tex]) * (h/[tex]\sqrt{h^{2} + x^{2}}[/tex])

    and I understand fairly well how and why. But now I have no idea where to go from here, aside from the fact that I have to integrate at some point. I know the two halves of the rod are equivalent so I can integrate from 0 to 5 and double (right?).

    What do I do? :grumpy:
     
  2. jcsd
  3. Feb 17, 2008 #2

    Hootenanny

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    I'm not quite sure what you've done here as you haven't posted your initial steps. Furthermore, your initial equation should involve a distance element (dz), rather than a charge element (dq). The usual way to solve such problems is to consider the electric field
     
  4. Feb 17, 2008 #3
    Isn't he using the line charge concept ? I guess so : dq = pdz, where the p denotes the charge per unit of distance.


    marlon
     
  5. Feb 17, 2008 #4

    Hootenanny

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    Now you mention it, yes it does :redface:. I'll go and put another coffee on...
     
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