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Homework Help: True of False

  1. Feb 16, 2009 #1
    1. The problem statement, all variables and given/known data
    A parallel plate capacitor with plate separation d is connected to a battery. The capacitor is fully charged to Q Coulombs and a voltage of V Volts. (C is the capacitance and U is the stored energy.) Give all correct answers concerning a parallel-plate capacitor charged by a battery (e.g. B, AC, CDF). If none of the statements is correct, enter the word none.

    A) After being disconnected from the battery, inserting a dielectric with kappa > 1 will decrease V.
    B) After being disconnected from the battery, increasing d increases U.
    C) After being disconnected from the battery, increasing d decreases V.
    D) With the capacitor connected to the battery, inserting a dielectric with kappa > 1 will increase U.
    E) After being disconnected from the battery, inserting a dielectric with kappa > 1 will increase C.
    F) After being disconnected from the battery, decreasing d decreases C.


    3. The attempt at a solution
    ok so i had thought it was ACD but that was said to be wrong. dont know where i am going wrong
     
  2. jcsd
  3. Feb 16, 2009 #2

    Delphi51

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    I think C is false. Increasing d will decrease C, so V = Q/C will increase.
    I would say D is false, too. Using V = Q/C in U=.5CV^2 = .5Q^2/C means that when C increases, U decreases.
    E is true - the dielectric makes it a better capacitor with greater C
    F is true - greater capacitance with reduced D.
     
  4. Feb 16, 2009 #3

    LowlyPion

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    This should answer all your questions.
    A good presentation of the material.

    https://www.youtube.com/watch?v=E185G_JBd7U
     
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