Conductors & Fields: Feynman's Argument Explained

In summary, the conversation discusses a proof by Feynman that the electric field inside an empty cavity of a conductor is always zero. It is then mentioned that this argument can also be used to show that if there is a charge inside the cavity, the electric field outside must also be zero. However, there is a doubt raised about the net charge not being zero when the conductor is considered as a whole. It is explained that this is due to a mistake made by Feynman and that the concept of grounded-ness helps preserve the argument. In the case of a grounded conductor, the charges rearrange themselves such that the net charge inside a Gaussian surface containing the conductor is zero, leading to a zero electric field under electrostatic conditions.
  • #1
atavistic
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I had been reading Feynman lectures , and in it he has shown an argument which proves that E field inside an empty cavity of a conductor is zero_OK. Now he says a similar argument can be used to show that if there is some charge in a cavity of a conductor than the field outside must be zero. Electrostatic shielding works both ways. Doubt: But then if we consider a gaussian surface containing the conductor , then the net charge is not zero => integral(E.da) is non zero, but E is zero. HOW?
 
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  • #2
Feynman made a mistake. See the comments by Thorne at the bottom of http://www.feynmanlectures.info/flp_errata.html.
 
  • #3
How does grounded-ness preserve the argument?
 
  • #4
If the conductor is grounded, an amount of charge equal and opposite to the amount in the cavity can come into the conductor and the net charge inside a Gaussian surface containing the conductor would be zero. Of course this doesn't necessarily mean E must be zero, but it turns out that under electrostatic conditions the charges always rearrange themselves such that it is.
 
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Related to Conductors & Fields: Feynman's Argument Explained

1. What is the significance of Feynman's argument in the study of conductors and fields?

Feynman's argument, also known as the "shielding argument," is important because it helps us understand how charges are distributed on conductors in the presence of an external electric field. This is crucial for analyzing the behavior of conductors and fields in various applications, such as in electronic devices.

2. How does Feynman's argument explain the distribution of charges on conductors?

Feynman's argument states that charges on a conductor will rearrange themselves in such a way that the electric field inside the conductor is zero. This means that any charges on the surface of the conductor will redistribute themselves to cancel out the external electric field, resulting in a net zero electric field inside the conductor.

3. Can Feynman's argument be applied to all types of conductors?

Yes, Feynman's argument can be applied to both perfect and imperfect conductors. For perfect conductors, the charges will redistribute themselves instantaneously, while for imperfect conductors, there may be a delay due to the resistance of the material.

4. How does Feynman's argument relate to the concept of electrostatic shielding?

Electrostatic shielding is the phenomenon where an electric field is blocked or reduced by placing a conductor in its path. Feynman's argument explains this concept by showing that the charges on the surface of the conductor will rearrange themselves to cancel out the external electric field, effectively shielding the inside of the conductor from the field.

5. Are there any limitations to Feynman's argument?

Feynman's argument is based on the assumption of a steady-state system and does not take into account any changes in the external electric field. It also assumes that the conductor is a perfect conductor, which may not be the case in real-world situations. Additionally, it only applies to static electric fields and does not consider the effects of changing magnetic fields.

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