Electric field inside a uniformly charged insulator

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  • #1
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Homework Statement


ok here's the problem: find the magnitude of the electric field inside uniformly charged insulating sphere of raduis R.


Homework Equations


application of gauss's law..but...


The Attempt at a Solution


should i use
[tex]\phi[/tex] = q[tex]_{encl}\epsilon_0[/tex]
or
[tex]\phi[/tex] = q[tex]_{encl}[/tex]/[tex]\kappa[/tex][tex]\epsilon[/tex]
???
 

Answers and Replies

  • #2
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It becomes slightly different inside a sphere. Electric fields are vectors, and a point inside a sphere is being affected by an electric field in every direction. Heres what you need to know: Any point inside a spherical shell of any thickness receives a net electric field of 0N/C. Same concept applies to electric force and gravity.
Here is a site to help you out on this:
http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elesph.html
Using that, if a point is a radial distance a from the center of the sphere (while inside the sphere), the net electric field at a point inside a sphere would be due to only the the charge within the radial distance (the charges outside the radial distance contributes to the 0N/C).
 
Last edited:
  • #3
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So, are you in space or a material? Would you want to use the electric constant for free space or not?
 
  • #4
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So, are you in space or a material? Would you want to use the electric constant for free space or not?
that is what I'm confuswed about...if the insulating sphere is made of a material other than air, which one should I use on the righthand side of the flux equation? [tex]\epsilon_{0} [/tex] or [tex]\epsilon[/tex]. that is should I take the permittivity constant ([tex]\kappa[/tex]) into account or not?
 
  • #5
dynamicsolo
Homework Helper
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Since you are solving for the electric field strength E, you would just use [tex]\epsilon_{o}[/tex]. If you were asked for the electric flux density D, you would need to be concerned with the electric permittivity of the material. (The hint is that you aren't given a value for [tex]\kappa[/tex] in the problem...)
 
  • #6
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The Attempt at a Solution


should i use
[tex]\phi[/tex] = q[tex]_{encl}\epsilon_0[/tex]
or
[tex]\phi[/tex] = q[tex]_{encl}[/tex]/[tex]\kappa[/tex][tex]\epsilon[/tex]
???
Out of curiosity, what volume are you using for the enclosed charge?
 
  • #7
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a sphere
 
  • #8
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thanks dynamicsolo. I'm starting to see how things are now
 
  • #10
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If a charge were distributed uniformly on the surface of the balloon(insulator). A point particle with charge q inside is greatest when it is anywhere inside the sphere because the force is zero?

or when it is near the inside surface of the balloon?
 

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