1. Not finding help here? Sign up for a free 30min 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!

Calculating Energy (capcitor study)

  1. Jan 19, 2009 #1
    Study guide asked/stated: A 100 microF capacitor has 100 V across it terminals, A 100 ohm
    resistor is placed across these terminals. How much energy is lost when the voltage is dropped to 50V?

    I answered with w= 1/2 CV^2, 1/2*100*10E-6*100^2
    = .5 J
    Book says w = 25 * 10-6 * 10^4.
    = .25 J

    (next step is to calculate energy at 50V). Where did the 25 come from?

    Hope this is the right forum (and not already asked and answered).
     
  2. jcsd
  3. Jan 19, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    The delta energy should be a subtraction.... final E versus initial E. Does that help?
     
  4. Jan 21, 2009 #3
    Beckeman, thanks for your reply. I agree the final answer is computed from the difference
    of the two. My problem is in initial computation of energy.

    Alphonse
     
  5. Jan 26, 2009 #4

    berkeman

    User Avatar

    Staff: Mentor

    I agree that the book's answer appears not to be what the question is asking. Any chance you copied the question down wrong above? Your calculation looks correct to me, and the number you will get at half voltage does not seem to be related to the book's number. Maybe ask the prof?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Calculating Energy (capcitor study)
  1. Energy calculation (Replies: 1)

  2. Energy calculations (Replies: 4)

Loading...