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!

Question Relating Electric Field and Capacitance

  1. Feb 14, 2012 #1
    1. The problem statement, all variables and given/known data
    A parallel-plate capacitor has a plate area of 0.2 m2 and a plate separation of 0.1 mm. To obtain an electric field of 2.0 × 10^6 V/m between the plates, the magnitude of the charge on each plate should be


    2. Relevant equations

    Q=epsilon(E)(A)

    3. The attempt at a solution
    I keep getting half of the correct answer. Does anyone know why I am off a factor of 2? Cheers.
     
  2. jcsd
  3. Feb 15, 2012 #2
    Q=CV
    C=epsilon*Area/separation
     
  4. Feb 15, 2012 #3

    ehild

    User Avatar
    Homework Helper
    Gold Member

    No, without seeing your solution.

    ehild
     
  5. Feb 15, 2012 #4
    My guess would be that you are only considering the electric field caused by one of the plates. ?
     
  6. Feb 15, 2012 #5

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Without seeing your solution, my guess is that the correct answer is twice what your answer is.
     
  7. Feb 15, 2012 #6
    Sorry about that.
    Q=CV, C=(epsilon)A/d, V=Ed/ By substituting these last 2 equations into the first, the result is Q=(epsilon)A(E)-->8.85e-12(0.2)(2e6)= 3.54e-6. However, this is half of the correct answer. What am I doing wrong?
     
  8. Feb 15, 2012 #7

    ehild

    User Avatar
    Homework Helper
    Gold Member

    That is correct with the given data. But it is possible that the volume between the plates was filled by a dielectric, with dielectric constant of 2. Are you sure that the dielectric constant was not given?

    ehild
     
  9. Feb 15, 2012 #8
    Yes. The question I gave you was a copy paste from the document.
     
  10. Feb 15, 2012 #9

    ehild

    User Avatar
    Homework Helper
    Gold Member

    I have no more idea. It happens quite often that wrong solutions are given.


    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question Relating Electric Field and Capacitance
Loading...