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Homework Help: Capacitor (is this correct)

  1. Mar 1, 2007 #1
    Two capacitors, C1 = 25 µF and C2 = 6.0 µF, are connected in parallel and charged with a 150 V power supply.

    (a) Calculate the total energy stored in two capacitors.

    energy stored = 1/2C(deltaV)^2 or Q^2/2C

    I been doing this and its marking me wrong.

    first i found both charges which is

    Q = VC

    C1 = 3750 uC
    C2 = 900 uC

    then i did

    3750^2/2(25) = 281250

    900^2/2(6) = 67500

    i add both up and get 348750 J

    It is saying my answer is incorrect and i did this problem 3 different way getting the same number.

    does this look like a system error or is my number really off.
  2. jcsd
  3. Mar 1, 2007 #2
    Simple error in the units.

    You need to take into account that the units of capacitance given are MICRO farads. Do the sums again but this time dividing first by a million before you square the terms.
  4. Mar 1, 2007 #3
    Thanks for the correction.
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