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!

Capacitor problem - Calculate the heat in connecting wires

  1. Apr 18, 2014 #1
    Capacitor problem -- Calculate the heat in connecting wires

    1. The problem statement, all variables and given/known data
    A [itex]5.0[/itex][itex]\mu[/itex][itex]F[/itex] capacitor is charged to [itex]12 V[/itex] . The positive plate of this capacitor is now connected to the negative terminal of a [itex]12 V[/itex] battery and vice versa. Calculate the heat developed in the connecting wires.


    2. Relevant equations
    [itex]W = QV[/itex]

    [itex]E = 0.5CV^2[/itex]

    3. The attempt at a solution

    I know from the above 2 equations that half of the energy supplied by the battery should be lost as heat . But I don't know how to proceed with this problem ?
     
  2. jcsd
  3. Apr 18, 2014 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    That statement is incorrect since there is an initial charge on the capacitor.
    In this particular case, what is the capacitor stored energy before (t<0) and after (t=∞)? Which says what about the fraction of battery energy lost to heat?

    So, back to fundamentals:

    You need to write the KVL around the loop including consideration of the initial voltage on C.
    This starts as an integral equation in current i but you can make it a 1st order differential equation in i with the appropriate initial condition, getting you i(t), then integrate R∫(i^2)dt from 0 to infinity for the total power dissipation where R is the wire resistance.

    There may be a shortcut here using only initial and final capacitor stored energy but I don't see one.
     
  4. Apr 18, 2014 #3
    Hello rude man...

    Do you get 2CE2 as the heat dissipated as well as the work done by battery ? Here C is the capacitance and E is the EMF of the battery .
     
  5. Apr 18, 2014 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    It is right.

    ehild
     
  6. Apr 18, 2014 #5

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Yes I do Tanya.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Capacitor problem - Calculate the heat in connecting wires
  1. Connected capacitor (Replies: 11)

  2. Connected Capacitors (Replies: 1)

Loading...