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Energy required to charge up a capacitor

  1. Jun 12, 2012 #1
    The energy required to charge a capacitor is:

    W = ½εrCV2

    From this we see that a capacitor with a linear dielectric in between its plates requires a bigger energy to charge up to a given potential. My question is: Should this be intuitive?
    My teacher said that it is because the parts of the electric field is cancelled off by the bound charges. I guess I can understand that since you then have to pull in more charge overall. However - wont these charges being pulled in also experience a weaker repulsion due to the cancelled off charges?
     
  2. jcsd
  3. Jun 12, 2012 #2

    berkeman

    User Avatar

    Staff: Mentor


    Welcome to the PF.

    Your equation does not look correct. See for example this thread:

    https://www.physicsforums.com/showthread.php?t=170393

    If you want to include non-linear dielectric effects, then it seems like you would write the capacitance as a function of voltage, like:

    [tex]W = \frac{1}{2}C(V)V^2[/tex]

    And use an integral to calculate how much energe is stored in charging up the cap...
     
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