Coulomb Gauge vs. Lorentz Gauge transformation

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Discussion Overview

The discussion revolves around the recognition and differentiation between Coulomb gauge and Lorentz gauge transformations in the context of electromagnetic theory. Participants explore methods for identifying these gauges based on the properties of electric fields derived from scalar and vector functions.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests a method for identifying the gauge by deriving an electric field and checking if it resembles a static Coulomb field, concluding that if it does, it is a Coulomb gauge; otherwise, it is a Lorentz gauge.
  • Another participant clarifies that Coulomb and Lorentz gauges are not transformations but rather conditions on the four-potential, emphasizing the need to show that the divergence of the four-potential equals zero for the Lorentz gauge.
  • A later reply questions how to demonstrate that a given four-potential satisfies the Lorentz gauge condition.
  • One participant simply states that the derivative should be taken to show the condition, without further elaboration.

Areas of Agreement / Disagreement

Participants express differing views on the nature of Coulomb and Lorentz gauges, with some emphasizing their role as conditions rather than transformations. The discussion remains unresolved regarding the initial method proposed for identifying the gauges.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about gauge transformations and the definitions of the gauges themselves. The method proposed by the first participant may depend on specific conditions that are not fully explored.

kthouz
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Given a set of a scalar function V and a vector function, how does one recognize that it is a coulomb gauge or lorentz gauge transformation?
Actually there is a method that i use but i am not sure if it is always true:
what i do is to make an electric field (from that set and using known gauge transformation) and see if it has the form a coulomb electric field (static field). If it does i conclude that it is a coulomb gauge, else it is a Lorentz gauge.
Am i right?
 
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You can find descriptions of the Coulomb and Lorentz gauge conditions here:

http://en.wikipedia.org/wiki/Gauge_fixing

(and probably in any E&M textbook at the intermediate level or above.)

If this isn't what you're looking for, please clarify...

Also note that there is in principle an infinite set of possible gauges, of which Coulomb and Lorentz are only two.
 
The Coulomb and Lorenz gauges are not gauge transformations. They are auxiliary conditions on the four-potential that we may choose because of the fact that there is gauge freedom. If you have a given four-potential Aµ, and you want to check if it satisfies the Lorenz gauge, all you have to do is show that ∂µAµ = 0.
 
Exactly. And how do you show this?
This is my question ...
 
You take the derivative.
 

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