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Homework Help: Conceptual Parallel Plate Capacitor

  1. Sep 28, 2008 #1
    1. The problem statement, all variables and given/known data
    Which statements are correct/incorrect for two oppositely charged, isolated parallel plates: (C=capacitance, U=stored energy, +Q and -Q = charge on the plates).
    Correct Incorrect When the distance is doubled, U is unchanged.
    Correct Incorrect Inserting a dielectric increases Q.
    Correct Incorrect When the distance is doubled, C is halved
    Correct Incorrect Increasing the distance, decreases the E field.
    Correct Incorrect Inserting a dielectric increases C.
    Correct Incorrect When the distance is halved, Q is halved.
    Correct Incorrect Inserting a dielectric decreases U.


    2. Relevant equations
    Below in my answers


    3. The attempt at a solution
    Now I don't know if I am misunderstanding the concept of Dielectrics or what, but this is what I believe:

    A - I thought that this is false because PE = 1/2QV. And I know that the potential difference is dependant on r.
    B - False because inserting a dielectric will not increase a charge.
    C - True because C = (A/d)*constant
    D - True because E = -Change in V/Change in X
    E - True because the formula includes multiplying by a constant k.
    F - False because Q = V*A*constant/d. Halving distance doubles Q
    G - False. A dielectric is only an insualtor that can allow the capacitance to increase.
     
  2. jcsd
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