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Homework Help: Energy stored in capacitors

  1. Aug 30, 2007 #1
    Two capacitors, C1 = 20 µF and C2 = 5.0 µF, are connected in parallel and charged with a 150 V power supply

    A.) Energy Stored I found to be is 2.81*10^-1 J

    B.)What potential difference would be required across the same two capacitors connected in series in order that the combination store the same energy as in (a)?

    Delta V= sqrt of (2*Energy stored/C) This eqn can b used to solve for delta V

    I have no idea what im doing wrong! I have used the capcitor in parallel combo of C= C1+C2..... Then I have converted the microFaraday charges of these sums to Faraday but no success

    Any Suggestions??
  2. jcsd
  3. Aug 31, 2007 #2


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    Staff Emeritus
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    You know that the effective capacitance of capacitors in series is given by:

    [tex]\frac{1}{C}=\frac{1}{C_1} + \frac{1}{C_2}...... [/tex]

    You also know that the energy stored is given by:


    So you have rearranged perfectly well but the problem could just be that you are using the parallel combination rather than the series combination to find the effective capacitance.
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