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!

Energy stored in a Capacitor derivation

  1. Jun 29, 2011 #1
    Electric potential difference is defined as the potential energy difference (work difference) per unit charge, when this charge q is moved between points b and a.
    so Ub - Ua = qVba

    Said in other words, if an object with charge q is moved through a potential difference Vba then its potential energy changes by an amount qVba


    How do you relate those equations to this one concerning Electric energy storage in a capacitor? U = 1/2 QV

    Why is W = U = 1/2QV for a capacitor
    instead of W = U = qV as above?
     
  2. jcsd
  3. Jun 29, 2011 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    That's a very good question.

    It is addressed here:

    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capeng2.html

    The work done by the battery, let's say, in moving ALL of the charges from plate to the other is not the same for all the charges. The first one doesn't encounter much resistive force, but as more and more charges accumulate on one plate, more work has to be done to do the charge transfer. The total amount of work done at the end is the store energy and the capacitance voltage V.

    So when you move a charge at the end against the potential V, you are doing work against the "full field", which is different than the stored field.

    Zz.
     
  4. Jun 29, 2011 #3
    thanks youre brilliant!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Energy stored in a Capacitor derivation
Loading...