# Recent content by arlesterc

1. ### I Symmetry associated with current conservation

Dale - Thanks - that's very helpful. You write: " The Noether current and the Noether charge are related through a continuity equation which essentially defines a local conservation law. " What is the continuity equation? Where does the J I see so often come in? Aclaret's post as is is a...
2. ### I Symmetry associated with current conservation

As I understand it for every symmetry there is associated a conserved quantity - so for time symmetry there is energy conservation. I understand as well that charge conservation is associated with a 'mathematical' local symmetry - something turning in a mathematical space at a point so to...
3. ### I Poynting vector - uniform vs accelerated charge

I am trying to understand why an accelerating charge emits radiation/electromagnetic waves but a uniformly moving one does not. I saw one video on Youtube where it seemed that it was explained by the fact that with a uniformly moving charge the Poynting vector was pointing 'in to the volume' -...
4. ### I Duration of electromagnetic disturbance

Choosing to end this for now. Not getting very far. I will have to think about how to re-ask. Thanks for trying.
5. ### I Duration of electromagnetic disturbance

Nugatory/Davenn Thanks for the clarification. Those are the kinds of answers I was expecting to get and most always have gotten on PF. The articles I read prior to posting - many of them - did not make the critical distinction between accelerating and non-accelerating charges - you can see...
6. ### I Duration of electromagnetic disturbance

Google: +++++++++++++++++++ https://www.google.com/search?q=moving+charges+electromagnetism&oq=moving+charges+electromagnetism&aqs=chrome..69i57.10416j0j7&sourceid=chrome&ie=UTF-8 "Electromagnetic radiation, is a form of energy emitted bymoving charged particles. " "When a charged...
7. ### I Duration of electromagnetic disturbance

Let us say I have a moving charge. At each point x,y,z in it's path from understanding there is a transverse electromagnetic wave being radiated (could also be viewed as a photon). The electric field at any point x1,y1,z1 in the path is disturbed. The moving charge does the same thing all...
8. ### B Changing electric field generating magnetic field

Thanks for the quick and definitive response. This point was not made clear in a lot of material I saw - it always had reversal of direction - so negative and positive charges swapping repeatedly. That being said what difference does that particular scenario make as to the simply...
9. ### B Changing electric field generating magnetic field

I would very much appreciate a clarification on what is meant by a changing electric field in the context of statements such as 'a changing electric field creates a changing magnetic field'. My question is does the electric field actually need to reverse as a lot of examples show where two...
10. ### I Do electromagnetic waves have potential and kinetic energy

sophiecentaur: Thanks for quick reply. However I do not know what E and H are that you refer to? CWatters: Thanks for the link but I see nothing in there about potential and kinetic energy of an electromagnetic wave. I saw a video about a string wave on Youtube and with the string I understood...
11. ### I Do electromagnetic waves have potential and kinetic energy

Do electromagnetic waves have potential and kinetic energy like springs, strings, etc. If so how are they calculated, inter-related? What is the total energy? Are the energies fluctuating over time? I am a physics hobbyist so generally the first answers should come with the least mathematics...
12. ### I Gauge Symmetry

Thanks for the distinction between gauge symmetry and gauge invariance. I think however based on the amount that I see gauge symmetry used it will be a long battle to knock it out of use. Or is there such a thing as gauge symmetry apart from gauge invariance?
13. ### I Angular sector

Thanks. So what is the formula for calculating A using the parameters referenced? A picture or illustration would be great so I can see what exactly the variables refer to.
14. ### I Angular sector

In this article https://terrytao.files.wordpress.com/2008/03/ricci1.pdf the following is written: "Consider now an angular sector A(x, r, θ, v) inside a small disk B(x, r) of small angular aperture θ (measured in radians) centred around some direction v (a unit vector) emanating from x; this...
15. ### I Gauge Symmetry

I have reviewed the various posts on gauge symmetry in particular this one which is now closed. In this post there is the following link:http://www.vttoth.com/CMS/physics-notes/124-the-principle-of-gauge-invariance. This is a good read. However, there is some clarification I need. The...