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Linear/Surface/Volume Charge Density

  1. Jan 18, 2009 #1
    1. The problem statement, all variables and given/known data

    (a) A charge of -345e is uniformly distributed along a circular arc of radius 4.00 cm, which subtends an angle of 41°. What is the linear charge density along the arc?

    (b) A charge of -345e is uniformly distributed over one face of a circular disk of radius 1.90 cm. What is the surface charge density over that face?

    (c) A charge of -345e is uniformly distributed over the surface of a sphere of radius 1.90 cm. What is the surface charge density over that surface?

    (d) A charge of -345e is uniformly spread through the volume of a sphere of radius 1.90 cm. What is the volume charge density in that sphere?

    2. Relevant equations



    3. The attempt at a solution

    OK so this should be really simple right??

    Part a)

    CHARGE / DISTANCE
    (-345 * 1.602 * 10^-19)/((41/360)*2*pi*.04) = -1.9309*10^-15 C/m


    Part b)

    CHARGE / AREA
    (-345 * 1.602 * 10^-19)/(pi*.019^2) = -4.8733*10^-14 C/m^2


    part c)

    CHARGE / AREA
    (-345 * 1.602 * 10^-19)/(4*pi*.019^2) = -1.2183*10^-14 C/m^2


    part d)

    CHARGE / VOLUME
    (-345 * 1.602 * 10^-19)/((4/3)*pi*.019^3) = -1.9236*10^-12 C/m^3



    According to my WebAssign homework, all these are wrong. What am I doing?
     
  2. jcsd
  3. Jan 18, 2009 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Nothing that I can see. I get a different exponent for the first one, but that's probably just a typo. Wrong number of significant figures? Something nit-picky like that?
     
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