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What is the voltage across the capacitor plates

  1. May 30, 2006 #1
    Am I overthinking this problem?

    A 15uF capacitor is connected ot a 55V battery and becomes fully charged. The battery is removed and the circuit is left open. A slab of dielectric material is inserted to completely fill the space between the plates. It has a dielectric constant of 4.8. What is the voltage across the capacitor plates after the slab is in place?

    I'm thinking that I just use V = Vo/k = 55/4.8 =11.5V

    This seems too easy and doesn't use the value for the capacitor.

    Can anyone tell me if I'm totally off in my thinking?
     
  2. jcsd
  3. May 30, 2006 #2

    chroot

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    Other way around.

    The introduction of a dieletric increases the capacitor's capacitance by a factor of k.

    Q = CV and Q remains constant. As a result, if C increases by a factor of k, V must decrease by a factor of k.

    You are correct that the actual value of the capacitance is irrelevant, as it cancels out.

    - Warren
     
  4. May 30, 2006 #3
    Sorry I'm confused, you said "Other way around" but based on what you wrote I have it correct that the voltage decreases by k, ie V = Vo/k
     
  5. May 30, 2006 #4

    chroot

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    Woops, sorry, I read your response incorrectly and thought you had increased the voltage across the capacitor. Your answer is correct.

    - Warren
     
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