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Capacitor and dielectric

  1. Jan 1, 2015 #1
    • 1. The problem statement,
    Dielectric plate is placed in capacitor to the half(picture) and it can freely move. Capacitor consists of two parallel plates and is isolated. Consider two cases:
    a)charges on plates are constant,
    b)voltage is constant.
    What happens in each case?

    2. Relevant equations

    $$W=\frac{1}{2}CV^2=\frac{q^2}{2C}$$
    $$F=\frac{dW}{dx}\\ \text{(1)}$$
    $$C=εεr \frac{A}{d} $$

    3. The attempt at a solution
    I know that the answer is that the dielectric will be moving inward in both cases and I even have written solution but I don't understand it. I guess that I should find force on dielectric from (2) but before that i need to determine C which I don't know how to do since dielectric is in wierd position.
     

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    Last edited: Jan 1, 2015
  2. jcsd
  3. Jan 1, 2015 #2

    ehild

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    Gold Member

    How does the capacitance depend on the geometry of the capacitor and the dielectric partially between the plates? Write it in terms of x.

    capdiel.JPG
     
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