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: Couple of quick q's

  1. Jan 28, 2009 #1
    ok if you could just tell em if this sounds alright.

    (i) A large horizontal sheet of surface charge density [itex]\sigma[/itex] has a hole of radius b cout out of it. Find the electric field directly above the centre of the hole.

    I already have expressions for the electric field due to the sheet and the disc of radius b on their own - can i just use the principle of superposition to subtract the field of the disc of radius b from the field of the sheet to get the total electric field?

    (ii) By applying a Gaussian pillbox to an infintely large charged sheet of surface charge density [itex]\sigma[/itex], I obtained [itex]\vec{E(z)} = \frac{\sigma}{2 \epsilon_0} \vec{z}[/itex] for the electric field. I am now asked why this field would double if the same charge were placed on the surface of a conductor.

    I have a feeling this is because in the conductor the charges inside arrange themselves to give a net internal field of 0 and then this arrangement of the charges would cause a field to be generated outside the conductor equal to the initial external field, hence doubling it as a result of the superposition principle.

    How do these ideas sound?
  2. jcsd
  3. Jan 28, 2009 #2


    User Avatar
    Homework Helper

    Of course you can.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook