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!

Confusion to the solution of a MIT ocw problem

  1. Mar 15, 2014 #1
    1. The problem statement, all variables and given/known data
    My snipping tool is totally broken. So i'm going to leave a link :x
    It's problem 1.6
    http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/assignments/ps1a.pdf

    2. Relevant equations

    [itex]E_{sheet}[/itex]=[itex]\frac{σ}{2ε_{0}}[/itex]
    [itex]E_{slab}[/itex]=[itex]\frac{ρD}{2ε_{0}}[/itex]
    [itex]\frac{Q}{ε_{0}}[/itex]=[itex]\oint[/itex]EdA

    3. The attempt at a solution

    I got everything on the solutions page (http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/assignments/pss1.pdf) But I can't seem to understand why region I of Esheet is positive and Regions II and III are negative. If σ is a negative charge, shouldn't the signs be switched around?
     
  2. jcsd
  3. Mar 15, 2014 #2
    It's interesting that you have Gauss's Law as one of your equations. When taking a look at the plane, have you thought about it from a flux perspective?
     
  4. Mar 15, 2014 #3

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Welcome to PF !

    Here is an image of the problem:

    attachment.php?attachmentid=67685&stc=1&d=1394920480.png
     

    Attached Files:

  5. Mar 15, 2014 #4

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Post #2 is a good hint, follow it!
    3 equations, 3 unknowns, 3 gaussian surfaces.
    Hint: make sure two of them line up correctly!
     
  6. Mar 15, 2014 #5
    Thanks! My snipping tool makes it so that the screen turns gray and I snip black images >_<
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted