How to uniformly charge an insulating sphere?

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Discussion Overview

The discussion revolves around the problem of how to achieve a uniform charge distribution throughout the volume of an insulating sphere. Participants explore theoretical and practical aspects of charging such a sphere, considering the implications of its insulating properties and the behavior of electric charge.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants note that while insulating spheres can theoretically hold charge throughout their volume, excess charge typically migrates to the surface over time.
  • One participant suggests that using electron beams could allow for localized charging, but expresses doubt about achieving a uniform distribution.
  • Another participant proposes that uniformly heating the insulating sphere might release conduction electrons, potentially aiding in charge distribution.
  • Several participants discuss practical methods, such as using a charged wand to touch the sphere's surface or bombarding it with electrons while rotating, to achieve surface charging rather than volume charging.
  • One participant mentions the idea of using a plastic coating that could be removed to induce surface charge, but acknowledges that this method would not charge the entire volume.
  • There is a suggestion to consider constructing the sphere from smaller spheres or cubes, raising questions about the feasibility of achieving uniform charge distribution in such configurations.
  • Some participants reflect on the idealizations involved in the problem, questioning the assumptions of perfect insulation and perfect spherical shape.

Areas of Agreement / Disagreement

Participants express a range of views on the feasibility of uniformly charging an insulating sphere, with no consensus reached on a definitive method or solution. The discussion includes both theoretical considerations and practical suggestions, highlighting the complexity of the problem.

Contextual Notes

Participants acknowledge the limitations of their proposed methods, including the dependence on idealized conditions and the challenges of achieving a uniform charge distribution in practice.

amiras
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In my Physics book there was this problem of finding electric field produced by the sphere, such that electric charge is distributed uniformly throughout the volume of an insulating sphere.

I know that excess charge tends to distribute itself on the surfaces, but since this sphere is made from insulating materials excess charge cannot leave individual molecules to do so?

Anyway, how it is possible to charge an insulating sphere throughout the volume?
 
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Those spheres are just hypothetical objects - there are no perfect insulators, if you wait long enough the charge will be at the surface only.
You can place electrons at specific regions with electron beams, but I doubt that the result will give a uniform charge distribution.
 
is it not possible to uniformly heat the "insulating sphere" as to release conduction electrons?
 
Johnahh said:
is it not possible to uniformly heat the "insulating sphere" as to release conduction electrons?

You could take a charged 'wand' and touch the surface of the sphere at all points over its surface. Alternatively, you could put the sphere in a vacuum and bombard it with electrons whilst tumbling it at a steady rate. Electrons would then be spread (painted) over the surface. Of course, you would need to adjust the energy and focus of the electron beam because it would be deflected by electrons already on the surface. Woops - just read the previous post which says more or less the same thing.

What about covering the sphere with a plastic coating and ripping the coating off. You would then get a charge all over the surface as you do with a roll of cling film. That. I think, is a method that could actually deliver some sort of a practical result.
 
sophiecentaur said:
What about covering the sphere with a plastic coating and ripping the coating off. You would then get a charge all over the surface as you do with a roll of cling film. That. I think, is a method that could actually deliver some sort of a practical result.
As far as I know, those induced charges are quite unpredicable, and not constant.

In addition, it charges the surface only, not the full volume.
 
You're a hard man to please.
Could your big sphere be made of many smaller spheres?
 
I would use something more space-filling, like cubes (with special parts for the surface?), but that is possible, sure.
 
You're unhappy with perfectly insulating, but are fine with perfect spheres?

Like a lot of problems in physics, these are idealizations or approximations. Just like frictionless planes, massless and stretchless ropes, etc.
 
Perfect 'enough'?
 
  • #10
amiras said:
In my Physics book there was this problem of finding electric field produced by the sphere, such that electric charge is distributed uniformly throughout the volume of an insulating sphere.

I know that excess charge tends to distribute itself on the surfaces, but since this sphere is made from insulating materials excess charge cannot leave individual molecules to do so?

Anyway, how it is possible to charge an insulating sphere throughout the volume?

What physics book?
 

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