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!

Magnitude of electric field near spherical shell

  1. Feb 8, 2017 #1
    1. The problem statement, all variables and given/known data
    A 10-nC point charge is located at the center of a thin spherical shell of radius 8.0 cm carrying -20 nC distributed uniformly over its surface.

    What is the magnitude of the electric field 2.0 cm from the point charge?
    upload_2017-2-8_13-23-15.png
    2. Relevant equations
    E = kq1q2/r^2

    3. The attempt at a solution
    I used k = 8.99*10^9 and the q charge with a distance of 0.08cm-0.02cm to get E = (8.99*10^9 C)(10*10^-9)(-20*10^-9)/(0.08-0.02)^2 = 9*10^5 N/C or 900 kN/C which is wrong. How do I go about doing this problem?
     
  2. jcsd
  3. Feb 8, 2017 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Your calculation is not in agreement with your relevant equation -- which is utterly wrong anyway (it calculates a force, not a field). Do you have a textbook with some relevant material you could study ?
     
  4. Feb 8, 2017 #3
    We dont use a textbook. Our professor has lecture notes instead.

    EDIT Am I not even using the correct formula? I feel as though I am, but I may be WAY off. Which is bad considering I have an exam tomorrow over this.
     
    Last edited: Feb 8, 2017
  5. Feb 8, 2017 #4

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Relevant equation is ##E=k{q\over r^2}##

    Did you learn about Gauss's theorem ? Tells you you can ignore the shell at 8 cm: it doesn't contribute to the field at 2 cm.
     
  6. Feb 8, 2017 #5
    OHHHH so then it should just be (8.99*10^9)(10*10^-9)/(0.02)^2 correct? And I still get confused on the uniform charge of sphere.
     
  7. Feb 8, 2017 #6

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Correct if you add units.

    What is the field inside a uniformly charged sphere (just from this sphere)?
     
  8. Feb 8, 2017 #7
    0 correct?
     
  9. Feb 9, 2017 #8

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

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

Have something to add?
Draft saved Draft deleted



Similar Discussions: Magnitude of electric field near spherical shell
Loading...