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: What is the charge on the capacitor after the wire is connected?

  1. Oct 3, 2007 #1
    assume an 80 mF capacitor is initially connected to a 9V battery. The battery is then removed and a wire is connected between the 2 terminals of the capacitor. What is the charge on the capacitor after the wire is connected?
  2. jcsd
  3. Oct 3, 2007 #2
    Theoretically, it is zero. Practically speaking, it depends on several things:

    The internal resistance of the battery and how long you hold it to the capacitor.
    The resistance of the wire and how long you hold it on the capacitor.
    The residual energy stored in the dielectric (this is exemplified in electrolytic caps--you can short them out but they'll apparently regain a little charge after removing the short. Its becasue of the way the electrolyte works).

    BTW, mF means millifarad, which isn't used very often--not sure if that's what you meant. Microfarad is more common, typically notated by MFD or uF (that's suppose to be a mu symbol--I don't know how to insert it in a post). You can tell if its an electrolytic if it has polarity marked (plus and/or minus)--since electrolytics only work when forward biased.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook