Electric field inside a cavity

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Discussion Overview

The discussion revolves around the electric field generated by a charge placed at the center of an empty cubic box, with the external potential considered to be infinite. Participants explore the implications of the box's shape and material on the electric field and potential, as well as the physicality of infinite potentials.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant describes a scenario with a charge at the center of a cubic box and questions how the box's shape influences the electric field around the charge, referencing Coulomb's law.
  • Another participant questions whether the box is made of material and states that infinite potentials are unphysical, suggesting that the field would be a superposition of the charge's field and the fields from the box and external environment.
  • A later reply emphasizes that the charge and its field cannot penetrate the box, reiterating the idea that the box defines the universe for the charge.
  • One participant proposes that a visual representation might clarify the situation and questions if the electric field around the charge adheres to Coulomb's law, particularly if the box's shape changes.
  • Another participant suggests that a new physics framework may be necessary to consistently describe the scenario where nothing can penetrate the box, implying that the electric field may not conform to Coulomb's law under these conditions.

Areas of Agreement / Disagreement

Participants express differing views on the physicality of infinite potentials and the influence of the box's shape on the electric field. There is no consensus on whether the electric field follows Coulomb's law in this scenario.

Contextual Notes

Participants highlight the limitations of using infinite potentials in this context and the need for a consistent physical description of the scenario presented.

jonjacson
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It is a simple arrangement. Imagine that we have an empty cubic box. Outside the box the electric potential is infinite. Imagine that you put an electric charge at the geomectric center of the box. What is the field around this charge? In other words, the tool I have to calculate the field generated by a charge is the Coulomb law, and according to this law the only parameters that influence the field are the distance to the source and its charge, but I guess the shape of the box must have an influence too.

Let me know your thoughts.
 
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Is the box made out of some material?

Infinite potentials are unphysical, especially if you want to look at fields as their derivatives.

The field will be the superposition of the field by the charge and the fields of box and whatever is outside.
 
mfb said:
Is the box made out of some material?

Infinite potentials are unphysical, especially if you want to look at fields as their derivatives.

The field will be the superposition of the field by the charge and the fields of box and whatever is outside.

Well, I want to mean that outside the box neither the particle nor its field can cross it. In other words, the entire universe for that charge is simply the empty box.
 
Maybe a picture will help. In the black space neither the charge nor its field could penetrate.

The question is: Does the field around the charge follow the Coulomb law? If we change the shape of the square, Doesn't that have an influence on the field around the charge?

ob08li.jpg
 
You'll need some new physics to describe "nothing can penetrate the box" in a consistent way, and your answer will depend on this description.
 
mfb said:
You'll need some new physics to describe "nothing can penetrate the box" in a consistent way, and your answer will depend on this description.

:)

So your answer is that it may be different to Coulomb law, interesting.!
 

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