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Archived Energy of a RC circuit

  1. Nov 4, 2008 #1
    A 0.25mu F capacitor is charged to 50 V. It is then connected in series with a 25ohm resistor and a 100ohm resistor and allowed to discharge completely.How much energy is dissipated by the 25ohm resistor?

    I know that Q=CV
    and U=.5CV^2=.5 * Q^2/C

    Now U is the energy released over both resistors. So the energy that is discharged over the 25 ohm resistor relates to the total energy dissipated over the two resistors equaling 125 ohm. But how do I use the total energy dissipated over both resistors and the total resistance of 125 ohm to find the energy dissipated over the 25ohm resistor?

    Thanks.
    Stephen
     
  2. jcsd
  3. Feb 7, 2016 #2

    gneill

    User Avatar

    Staff: Mentor

    One approach is to imagine that the two resistors are combined into a single resistor (no change to circuit behavior will result from this). Knowing the total energy dissipated and assuming that the energy dissipation is uniform over the whole resistor, apportion the total energy according to the relative portion of the whole resistor.

    upload_2016-2-7_13-50-3.png

    So if R1 is 100 Ω and R2 is 25 Ω, then R2 represent 25/125 = 1/5 of the whole.
     
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