Canceling Magnetic & Electric Fields: An O Level Student's Guide

  • Context: High School 
  • Thread starter Thread starter Ahmed Abdullah
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Discussion Overview

The discussion revolves around the cancellation of magnetic and electric fields, specifically how to achieve this in practical scenarios. Participants explore concepts related to magnetic shielding, electric neutrality, and the behavior of charges in atoms, aiming for clarity suitable for an O Level student.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how to cancel the magnetic field from a magnet and the electric field from a charge, seeking a basic explanation.
  • Another participant suggests enclosing a magnet in a magnetic shield made of high magnetic permeability material to cancel its field, noting that the thickness of the shield depends on the magnetic flux.
  • They also propose enclosing a charge in a Faraday cage to negate its electric field, stating that any thickness of the conductive box would suffice.
  • It is mentioned that positive and negative charges do not cancel each other unless they are equal in total value and properly distributed in space.
  • Some molecules, like water, are electrically neutral due to having equal numbers of electrons and protons, but their charge distribution can still produce an electric field.
  • Full orbitals in atoms, containing electrons with opposite spins, are said to cancel out each other's magnetic fields, resulting in no net magnetic contribution from those orbitals.
  • Another participant asks for clarification on how a magnetic shield functions, comparing it to a Faraday cage.
  • A later reply explains that a magnetic shield conducts magnetic fields better than air or vacuum, allowing field lines to pass through it rather than around it.

Areas of Agreement / Disagreement

Participants express various viewpoints on the cancellation of fields, with some agreeing on methods like magnetic shielding and Faraday cages, while others raise questions about the conditions under which charges cancel each other. The discussion remains unresolved regarding the nuances of electric neutrality and the effectiveness of different shielding methods.

Contextual Notes

Participants highlight the importance of charge distribution and the conditions necessary for cancellation, indicating that the discussion is limited by these assumptions and the definitions of neutrality and shielding effectiveness.

Ahmed Abdullah
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Here is some very fundamental things troubling me. It follows...
How we can cancel
(1) the magnetic field produced by a magnet(so that there will be no magnetic field)
(2)the electric field produced by a charge (so that there will be no electric field)

Does same numbers of positive and negative charges cancel the field of each other in such a way that we have no electric field at all? Sounds silly but atoms are electrically neutral that way. If it is not that way then what is the definition of electrically neutrality? Is it not about having no net electric field?
In the same way, how two electrons in the same orbital having opposite spin cancel out the magnetic field of each other?

please explain in simple and basic terms (m An O level student) .
 
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Ahmed Abdullah said:
Here is some very fundamental things troubling me. It follows...
How we can cancel
(1) the magnetic field produced by a magnet(so that there will be no magnetic field)
(2)the electric field produced by a charge (so that there will be no electric field)

Does same numbers of positive and negative charges cancel the field of each other in such a way that we have no electric field at all? Sounds silly but atoms are electrically neutral that way. If it is not that way then what is the definition of electrically neutrality? Is it not about having no net electric field?
In the same way, how two electrons in the same orbital having opposite spin cancel out the magnetic field of each other?

please explain in simple and basic terms (m An O level student) .

(1) You can enclose the magnet in a magnetic shield. That is, a closed "box" formed by a high magnetic permeability alloy (as mu-metal) thick enough. How much thick depends on the magnetic flux that the shield has to "short-circuit".

(2) You can enclose the charge in a Faraday cage. That is, a closed conductive box. Any thickness work.

Positive and negative charges do not cancel unless they have the same total value and they have the good distribution in space. One "good" distribution is all positive or negative charge in the center surrounded uniformly by the charge of opposite sign (as an atom).

Some molecules (as water) are electrically neutral as they have as many electrons as protons. But the charges are not distributed in the "good" way, and they produce an electric field.

Full orbitals have each level filled with electrons of opposite spin, which cancel each other. These orbitals do not contribute to the magnetic field of the atom.
 
How does a magnetic shield work (in the simillar way a faraday cage does, I hope!)?
 
No. A magnetic shield is something that "conducts" the magnetic field much better than air, vacuum, etc. Lines of field "prefer" to pass through this material instead of traversing it, make a tour in the other side, and traverse the shield once again. But if you put a sheet of shield between the two poles of a horseshoe magnet, the field lines will happily traverse the shield to go from one pole to the other.
P.S. Do not tell anyone that I used the terms "conduct" and "prefer". It is not very scientific https://www.physicsforums.com/images/icons/icon12.gif
Wink
 
Last edited by a moderator:
Thx a lot. :)
 

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