Electric field of point charge within spherical shell.

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Discussion Overview

The discussion revolves around the electric field generated by a point charge located inside a spherical shell, considering different charge distributions on the shell. Participants explore the behavior of electric field lines in scenarios involving both negative and positive charge densities on the shell, as well as the implications of these configurations on the field lines from the point charge.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that electric field lines from a positive point charge inside a negatively charged shell would radiate outward towards the shell.
  • There is uncertainty regarding the behavior of field lines when both the shell and the point charge are positive, with one participant expressing difficulty in conceptualizing the situation.
  • One participant questions whether the electric field inside the shell from the shell's charge is zero, suggesting that only the point charge's field would be present.
  • Another participant confirms that the field from the shell is zero inside, but raises the question of whether the fields from the shell and the point charge need to be summed.
  • Concerns are raised about the behavior of field lines from the point charge, particularly regarding their density and the implications of the shell's positive charge repelling them.
  • It is noted that outside the shell, the electric field would be the sum of the fields from both the point charge and the shell, with the shell's contribution being zero inside the shell but not outside.

Areas of Agreement / Disagreement

Participants generally agree that the electric field from the shell is zero inside the shell. However, there remains disagreement and uncertainty about the behavior of field lines in different charge configurations, particularly when both the shell and the point charge are positive.

Contextual Notes

Limitations include assumptions about the uniform distribution of charge on the shell and the conditions under which the electric field is evaluated. The discussion does not resolve the implications of field line density or the conceptualization of field behavior in the presence of repelling charges.

malignant
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If there was a spherical shell with negative charge density and a positive point charge inside the shell, the electric field lines from the point charge would just be radially outward towards the shell right?

What about the case where there's a positive charge density and a positive point charge? I'm having trouble conceptualizing what happens to the field lines from the point charge then.
 
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malignant said:
If there was a spherical shell with negative charge density and a positive point charge inside the shell, the electric field lines from the point charge would just be radially outward towards the shell right?
Do you mean a hollow shell with a uniformly distributed negative charge? Then yes.

malignant said:
What about the case where there's a positive charge density and a positive point charge? I'm having trouble conceptualizing what happens to the field lines from the point charge then.
Ask yourself: What field does the shell's charge contribute inside the shell?
 
Isn't the field inside from the shell's charge zero leaving just the field from the point charge? Or would the field from the shell and the point charge have to be summed?
 
malignant said:
Isn't the field inside from the shell's charge zero leaving just the field from the point charge?
Yes.

malignant said:
Or would the field from the shell and the point charge have to be summed?
Yes. (But the field from the shell is zero. ;))
 
Ok but where do the field lines go from the point charge? If it doesn't escape the shell due to the positive charge on the shell repelling, and no lines can intersect, it sounds like the field would end up being infinitely dense.
 
malignant said:
Ok but where do the field lines go from the point charge? If it doesn't escape the shell due to the positive charge on the shell repelling, and no lines can intersect, it sounds like the field would end up being infinitely dense.
Outside the shell, the field will be the sum of the fields from the point charge and from the shell. (The field from the shell is zero within the shell, but not outside the shell.)
 

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