What propagates changes of Coulomb force?

Click For Summary

Discussion Overview

The discussion revolves around the propagation of changes in the Coulomb force when a positive charge moves from one position to another. Participants explore the nature of the electromagnetic information that conveys changes in electric fields, particularly questioning whether this information propagates through electromagnetic waves or some other medium.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant posits that when a positive charge moves, the electric field at a distant point changes with a time delay, suggesting that something must propagate from the charge to that point.
  • Another participant describes this propagation as a kind of longitudinal E-wave, noting that it does not carry energy since the Poynting vector is zero.
  • A later reply questions the physicality of the original scenario, suggesting that it presupposes unphysical movement but hints at a related, more physical question involving the Liénard-Wiechert potentials.
  • One participant inquires about the substance that carries electromagnetic information, comparing it to how EM waves carry information in radio and television, and asks if there is a similar substance that follows a wave equation at speed c.
  • Another participant argues against the necessity of a substance, stating that the concept of aether is unnecessary and that the Liénard-Wiechert potential is a solution to Maxwell's equations.
  • Further questions arise regarding whether the Liénard-Wiechert potential is fundamentally linked to the speed of light and how it behaves in different media.

Areas of Agreement / Disagreement

Participants express differing views on whether a substance is required to carry electromagnetic information, with some arguing against the need for aether while others maintain that there may be something beyond electromagnetic waves involved in the propagation of information. The discussion remains unresolved regarding the nature of this propagation and the implications of the Liénard-Wiechert potentials.

Contextual Notes

Participants reference the Liénard-Wiechert potentials and Maxwell's equations, but there are unresolved questions about the assumptions underlying the discussion, particularly regarding the physicality of the scenarios presented and the nature of the propagation mechanism.

sweet springs
Messages
1,223
Reaction score
75
Hi.

Say a positive charge is at (x,y,z)=(0,0,0) at t<0 then (1,0,0) at t>0.
Electric field at (x,y,z)=(l,0,0) is (a,0,0) at t<l/c then (b,0,0) at t>l/c thus a<b.

With time delay of l/c, what propagates from (x,y,z)=(0,0,0) to (l,0,0) ?
I do not think it is electromagnetic wave because it is not transverse but longtitudinal.

Electromagnetic wave by accerelation necessary for charge position change has nothing to do with my question, I guess.

Not charge position but charge velocity change causes similar propagation question.

Best
 
Physics news on Phys.org
It is a kind of longtitudinal E-wave BUT it does not carry energy (the poynting vector for this wave is zero, because the resulting magnetic field doesn't cooperate with this longtitudinal wave).
 
Last edited:
sweet springs said:
Hi.

Say a positive charge is at (x,y,z)=(0,0,0) at t<0 then (1,0,0) at t>0.
Electric field at (x,y,z)=(l,0,0) is (a,0,0) at t<l/c then (b,0,0) at t>l/c thus a<b.

With time delay of l/c, what propagates from (x,y,z)=(0,0,0) to (l,0,0) ?
I do not think it is electromagnetic wave because it is not transverse but longtitudinal.

Electromagnetic wave by accerelation necessary for charge position change has nothing to do with my question, I guess.

Not charge position but charge velocity change causes similar propagation question.

Best
The specifics of this question are not answerable because it presupposes an unphysical movement.

However, with appropriate tweaking you could get a closely related question which would be physical. The answer to the closely related question would be the Lienard Wiechert potentials:

https://en.m.wikipedia.org/wiki/Liénard–Wiechert_potential
 
Thanks Dale. The linked document of your recommendation says, "The force on a particle at a given location r and time t depends in a complicated way on the position of the source particles at an earlier time tr due to the finite speed, c, at which electromagnetic information travels."

My question should be translated to : What substance carries this "electromagnetic information" ?
EM wave carries information as radio or television do. Are there similar substance following a wave equation of speed c that carry electro magnetetic information used in Liénard–Wiechert potential?
Best
 
sweet springs said:
What substance carries this "electromagnetic information"
Why should a substance be required? The aether is superfluous.

sweet springs said:
EM wave carries information as radio or television do. Are there similar substance following a wave equation of speed c that carry electro magnetetic information used in Liénard–Wiechert potential?
The Lienard Wiechert potential is a solution to Maxwells equations, just like any other classical EM field.
 
Dear Dale.
Your answer to my question "what propagates electromagnetic information e,g, displacement of distant source charges with speed of c and how does it?" was "the LW potential that satisfies Maxwell equation". I still cannot leave from idea that something other than EM waves keeps radiated from the source charges with speed of light telling the information of the charge position. Is the LW potential reduced to microscopic relation explicitly containing c? Is the LW potential is unchanged if EM media is inserted between ? I keep thinking about it by myself and ask again if it makes sense. Thank you so much for now.
 
sweet springs said:
I still cannot leave from idea that something other than EM waves keeps radiated from the source charges with speed of light telling the information of the charge position.
Please review the forum rules about personal speculation before pursuing this line of discussion here.

sweet springs said:
Is the LW potential reduced to microscopic relation explicitly containing c? Is the LW potential is unchanged if EM media is inserted between ?
You can read the derivation of the LW potential right there on the Wiki page, and in any halfway decent textbook. Including the online ones from MIT and UT.
 

Similar threads

Undergrad Coulomb gauge implies instantaneous radial electric field?
  • · Replies 5 ·
Replies
5
Views
1K
Graduate Electric and magnetic field lines in a plane wave of finite extent
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Griffith, Electrodynamics, 4th Edition, Example 4.8. (Second part)
  • · Replies 3 ·
Replies
3
Views
951
Undergrad Calculating the force on an electron from two positive point charges
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Voltage and current waves in a transmission line
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Modeling a ferromagnetic core moving inside a solenoid with scipy+FEMM
  • · Replies 1 ·
Replies
1
Views
2K
Direction of the magnetic field of an oscillating charge
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Query on Electromagnetic Theory (Dielectric Boundary Conditions)
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Instantaneous electric field solved by extended electrodynamics?
  • · Replies 1 ·
Replies
1
Views
1K
Graduate Interaction between a neutral atom and an external magnetic field
  • · Replies 2 ·
Replies
2
Views
2K