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: Series capactors

  1. Mar 3, 2010 #1

    Linus Pauling

    User Avatar

    1. A battery with an emf of 60 V is connected to the two capacitors shown in the figure . Afterward, the charge on capacitor 2 is 540 uC.

    The capacitors are in series, with C1 = 12microFarads and C2 = ?

    Since series capacitors have the same charge Q, I used C1 and solved for Q in C = Q/V, obtaining Q = 720uC. I then solved C2 = 720/60 = 12microFarads, which is incorrect.
     
    Linus Pauling, Mar 3, 2010
  2. jcsd
    Phys.org - latest science and technology news stories on Phys.org
  3. Mar 3, 2010 #2

    ideasrule

    User Avatar
    Homework Helper

    The charge across each capacitor isn't 60 V because the 60V is divided across the two capacitors. However, you know what Q is across the first capacitor. It's 540 uC, because if you consider the two capacitors as one unit, it would have the same charge as the two individual capacitors.
     
    ideasrule, Mar 3, 2010
  4. Feb 8, 2011 #3

    jadenjaden

    User Avatar

    So.. what is C2 then? I got 18 and that was incorrec
     
    jadenjaden, Feb 8, 2011
  5. Feb 8, 2011 #4

    jadenjaden

    User Avatar

    So.. what is C2 then? I got 18 and that was incorrect
     
    jadenjaden, Feb 8, 2011
  6. Feb 8, 2011 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Old post

    Hey! The Original Post is over 11 months old!
     
    SammyS, Feb 8, 2011
  7. Feb 8, 2011 #6

    jadenjaden

    User Avatar

    I didn't realize that but this is a question I am currently working on
     
    jadenjaden, Feb 8, 2011
  8. Feb 8, 2011 #7

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    (What units?)

    Show how you got that.
     
    SammyS, Feb 8, 2011
  9. Feb 8, 2011 #8

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The capacitors are in series. If the charge on C2 = 540 μC, how much charge is on C1 ?

    What's the voltage drop across C1 ?
     
    SammyS, Feb 8, 2011
  10. Feb 27, 2011 #9

    danielcheung1

    User Avatar

    I am also working on this question, and I don't know where to begin. i know that the charge on both capacitors is equal
     
    danielcheung1, Feb 27, 2011
  11. Feb 27, 2011 #10

    gneill

    User Avatar

    Staff: Mentor

    If the charges are equal, and you know the value of C1, what does that tell you about the voltage across C1?
     
    gneill, Feb 27, 2011
  12. Feb 27, 2011 #11

    danielcheung1

    User Avatar

    i am not sure,
    but is it that Q = CV
    and so i can say C1V1 = C2V2
    and i think the voltage drop has to be different for the two capacitors..
     
    danielcheung1, Feb 27, 2011
  13. Feb 27, 2011 #12

    gneill

    User Avatar

    Staff: Mentor

    Yes, but the problem statement gives you the charge on one of the capacitors, right? You've also determined that the charges must be equal for both capacitors. The problem statement also gives you the value of one of the capacitors. Apply your Q = CV to find the voltage on that capacitor.
     
    gneill, Feb 27, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook