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Homework Help: Help - webassign due tonight - need some help

  1. Feb 13, 2008 #1
    help -- webassign due tonight -- need some help

    1. The problem statement, all variables and given/known data

    A parallel-plate capacitor has a plate area of 160 cm2 and a plate separation of 0.0400 mm.

    A). Determine the capacitance.
    which i got to be 3.54e-9 F

    B). Determing the potential difference when the charge on the capacitor is 450.0 pC.

    2. Relevant equations

    C= ɛo A/d

    3. The attempt at a solution

    i got part a using that equation, and i know that i should use it for part B, but i'm confused as to how to incorporate the 450pC....
  2. jcsd
  3. Feb 13, 2008 #2
    Do you by chance go to NTHS?I have the exact same problem for my web assign except I have a 180 cm^2 and I need help getting that. For B I think you get the A answer and divide by the charge.
  4. Feb 13, 2008 #3
    haha yea i do go to NTHS.

    by the way what IS the charge??
  5. Feb 13, 2008 #4
    Can you tell me how you got A.? for B you do C=Q/change of V, change of V you get by = -E(Change of d) because it's in a uniform electric field. The pC number, I think.
    I was wrong on the previous post. it's asking for the potentical difference. I thought C, was the capacitors
    Last edited: Feb 13, 2008
  6. Feb 13, 2008 #5
    for A you do ɛo A/d

    ɛo is a constant, which is 8.85E-12
    A is your centimeter number, but watch out cause it's squared so for me 160cm^2 = 160E-4

    and d is your mm to meters, for me it's .04E-3

    by the way i still cant get B
  7. Feb 13, 2008 #6
    is the unit for potential difference in volts?
  8. Feb 13, 2008 #7
    it's supposed to be in volts, but i honestly have no friggin idea what is C and Q and -E(change of d) ?
  9. Feb 13, 2008 #8
    I got it! change of V = Q/C.
    Q= the pC thing
    C is the answer for a

    Do you have
    11. b/c
    3. a/b
    by any chance?
    Last edited: Feb 13, 2008
  10. Feb 13, 2008 #9
    it worked! awesome.

    did you get 3b?? the angle thing?
  11. Feb 13, 2008 #10
    I have no idea on how to do any of 3
  12. Feb 13, 2008 #11
    thanks anyways
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