1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Circuit formula problem

  1. Jan 20, 2007 #1

    A 0.25 x 10^-6 F capacitor is charged to 50V. It is then connected in series with a 25 ohm resistor and a 100 ohm resistor and alowed to discharge completely. How much energy is dissipated by the 25 ohm resistor ?


    I found a formula in the textbook related to this question:

    The resistors dissipate energy at the rate:

    PR = I^2R = (Delta V)^2 / R

    I don't know what to do next .... and if I'm using the right formula. Please somebody help.:confused: :confused: :confused:
  2. jcsd
  3. Jan 21, 2007 #2


    User Avatar
    Homework Helper

    ok... conservation of energy
    ask yourself, how much energy was stored in capacitor initially, then how do u think the energy are dissipated between the 25 and 100 ohm resistor? remember everything is in series... and you already have [tex]P=I^2 R[/tex]
  4. Jan 21, 2007 #3
    Hi, Do you calculate the energy by this formula;

    Q= (0.25 * 10^-6) ( 50)
    Q = 0.0000125 C
  5. Jan 21, 2007 #4


    User Avatar
    Homework Helper

    Your Q means "charge" not energy

    formula for energy stored in a capacitor is given in most books or can easily googled....
    [tex]\displaymath{U = \frac{1}{2}CV^2}[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook