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: Capacitors with switch

  1. Feb 8, 2009 #1
    1. The problem statement
    The capacitors in the figure are initially uncharged and are connected, as in the diagram, with switch S open. The applied potential difference is Vab = + 210 V.

    What is the potential difference Vcd?


    2. Relevant equations
    (series) 1/C = 1/c1 + 1/c2 + ...
    (parallel) C = c1 + c2 + ...

    3. The attempt at a solution
    Trying to find Vcd:
    I first found the equivalent capacitance of the series, which is 4*10-6 F. I calculated the charge on the capacitors using Q = CV, which was 8.4*10-4. Then, I tried to find Vad and Vac by using V=Q/C. I don't think this is the right way to do this problem though.
    Last edited: Feb 8, 2009
  2. jcsd
  3. Feb 8, 2009 #2


    User Avatar
    Homework Helper

    That looks like the way to do it as far as you went.
  4. Feb 8, 2009 #3
    Ah, I figured it out. The upper and lower series each have half the value of the charge that I calculated. Then using V=QC, Vad=140V and Vac=70V, so Vad-Vac=70V.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook