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: Point Charge in an uncharged spherical conductor

  1. Mar 12, 2013 #1
    1. The problem statement, all variables and given/known data

    Consider a point charge q > 0 which is surrounded by a hollow metal sphere (uncharged) with inner radius R1 and outer radius R2. Use Gauss Law to determine the electric field E=E(r)er in the following regions:
    (i) 0 < r < R1
    (ii) R1 < r < R2
    (iii) r > R2

    2. Relevant equations

    ∫EdA = Q/ε

    3. The attempt at a solution

    (i) I believe the answer would be 0 because the electric field inside of an enclosed conductor is always zero
    (ii) This is where my troubles really lie, don't know what to do here
    (iii) I think that the electric field would be equatable to that of one where the point charge didn't exist outside the conductor as long as r is great enough, and i can solve for this
  2. jcsd
  3. Mar 12, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    What is the precise location of the charge in the hollow of the sphere?
    Is it at the center of the hollow?
    Is the center of the hollow coincident with the center of the sphere?​

    For items (i) & (ii):
    The electric field in the conducting material itself is zero. (This is useful for (ii) but not for (i). )
    Nothing says that the electric field must be zero In the hollow of a conductor. Gauss's Law confirms this.​
  4. Mar 12, 2013 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Not if there is charge inside it!

    Can there be an E field in a conductor?

    I don't understand this statement.
  5. Mar 12, 2013 #4
    yes everything is concentric, and I'm starting to see my erroneous thoughts.

    (i) would just be the field as if no conductor was present yes? because I am checking the field at which it hasn't reached the conductor

    (ii) would be zero because it is inside of the conductor which means the net electric field is zero

    (iii) i am now not sure on, but think that it may be the same answer as (i) because the charge (lets say positive) in the conductor would pull all the electrons to the inside, leaving the outside of the conductor positively charged just like it would be before. Is this correct in theory?
  6. Mar 12, 2013 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Pretty much correct.

    In (iii), it's not true that all the electrons are pulled to the inside. Gauss's Law tells us that just enough electrons are pulled to the inside so that the flux in the conducting material is zero. ...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted