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Capacitors & Dielectrics

  1. Mar 8, 2009 #1
    1. The problem statement, all variables and given/known data

    Two capacitors are identical, except that one is empty and the other is filled with a dielectric (κ = 3.20). The empty capacitor is connected to a 11.0-V battery. What must be the potential difference across the plates of the capacitor filled with a dielectric such that it stores the same amount of electrical energy as the empty capacitor?

    2. Relevant equations

    q = cV
    C = EoA/d
    C = kEoA/d
    U = 1/2qV
    U = 1/2cV^2

    3. The attempt at a solution

    I'm not sure which form of the equation to use exactly. I know that since everything in the capacitors is equal except the dielectric I should be able to set them equal to each other some how and since I only know the voltage of the battery most of the terms will cancel out but I'm unsure of where to start. If someone could point me in the right direction that would be great!
     
  2. jcsd
  3. Mar 8, 2009 #2

    lanedance

    User Avatar
    Homework Helper

    you know the equation for C1 & C2, only differ by k term

    you want to fiond V2 in terms of V1

    and you know
    U1 = U2

    so equate the energy, subtitute for the C's & solve in terms of for V2 in terms of V1...
     
  4. Mar 8, 2009 #3
    got it! Thanks a lot!
     
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