Why do charged particles only produce magnetic fields while in motion?
11743
I'm tutoring high school students. I've always taught them that:     A charged particle moving without acceleration produces an electric as well as a magnetic field.   It produces an electric field because it's a charge particle. But when it is at rest, it doesn't produce a magnetic field. All of a sudden when it starts moving, it starts producing a magnetic field. Why? What happens to it when it starts moving? What makes it produce a magnetic field when it starts moving?
89534
If I wave around a bar magnet, the magnetic field in the space around it changes. Is this enough to go through the whole speed of light derivation implying that the motion creates an electromagnetic wave? If so how do I determine the wavelength and direction of the resulting wave?
7799
I learned that the force from a magnetic field does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets can stick to pieces of metal like a refrigerator?
10582
I know that Lorentz force for a charge $q$, with velocity $\vec{v}$ in magnetic field $\vec{B}$ is given by  $$\vec{F} =q \vec{v} \times \vec{B}$$  but there will exist a frame of reference where observer move at same velocity with that of charge $q$, so according to him $v=0$. hence he will see no magnetic force is exerted on charge $q$. I have work on this problem for a while and found that the special relativity predicts equivalent electric force will acting upon charge instead. I want to know the relationship between this equivalent electric force and magnetic force.  Thanks in advance
72770
What do we mean with  and ? I can not find a way to relate magnetic monopoles and dipoles with electric ones. I do not understand their outcomes. Also,what is their role in Gauss' law for magnetism (the net magnetic flux through a closed surface is zero)?  I read that the magnetic dipoles are essential for the meaning of this law. Why? If magnetic monopoles existed,then why would the law not be valid? Lastly,why do we say that the magnetic field is divergeless? Some physicists try to find a magnetic monopole (something Dirac tried to explain i think). So if they actually find one, what does that mean? For a classic magnet(N-S) we know that we have charges inside moving in a circular motion and they althogether form that magnetic field of the magnet. So how does finding a magnetic monopole change this? What does it mean for those small currents?    (I might understood something wrong here so enlighten me please!)
5045
Considering the fact that electrons tend to take the maximum conductance path to flow from A to B. This is justified by saying that $\vec{E}$ is larger in conductors. But once similarly it was thought for gravitation, that if in a region the gravity was stronger, the mass more likely took that path, then later it was found it is actually a geodesic in space time as gravity curves space time. So is there some underlying geodesic for motion caused by electromagnetic force?
12714
Can a magnetic field be induced without an electric field? Because, as far as I know, a time varying electric field induces a magnetic field an vice versa.  But in the case of conductors carrying currennt, it doesn't seem that electric field varies with time, then how is a magnetic field induced?
26103
When you release a magnetic dipole in a nonuniform magnetic field, it will accelerate.  I understand that for current loops (and other such macroscopic objects) the magnetic moment comes from moving charges, and since magnetic fields do no work on charges ($F$?perpendicular to $v$) it follows that the work done on the dipole (that caused its gain in kinetic energy)  must have come from somewhere other than the magnetic forces (like electric forces in the material).  However, what about a pure magnetic moment? I‘m thinking of a particle with intrinsic spin. Of course, such a thing should be treated with quantum mechanics, but shouldn't classical electrodynamics be able to accommodate a pure magnetic dipole? If so, when I release the pure dipole in a nonuniform B-field and it speeds up, what force did the work? Is it correct to say that magnetic fields DO do work, but only on pure dipoles (not on charges)? Or should we stick with "magnetic forces never do work", and the work in this case is done by some other force (what?)?  Thanks to anyone who can alleviate my confusion!
68709
According to electrodynamics, accelerating charged particles emit electromagnetic radiation.  I'm asking myself if the electron in an hydrogen atom emits such radiation. In , Murod Abdukhakimov says the total momentum of the electron is zero, hence it does not emit radiation. Could someone prove this statement ?  It may be an obvious question, but I can't figure out why the total momentum of the electron should always be zero, in any energy state.
38884
Despite being overall near-netural, I would expect the individual electrons and proton to radiate long EM waves as we accelerate around the Sun or rotate around our poles. Is the acceleration so small that the radiated energy is miniscule?  Or is it that somehow the macroscopic neutrality prevent radiation? If this is so, what mechanism causes single electrons or nuclei to fail to radiate?
51030
There is no "action at a distance" in nature. Attraction of a piece of iron by a magnet, attraction between distant electric charges of opposite sign, have to be mediated by something. The  are proposed as an explanation.  If they have an observable effect, it seems like they must exist. If so, why do we call them virtual? It can't be that they have short lifetimes, as there are short-lived particles (resonances) that we don't call "virtual."  On the other hand, some people say that the so-called virtual particles only exist on paper, or that they are just a technique to help us handle our equations.  So what is the meaning of the word "virtual" here? Do these particles really exist, or not?
33024
I read this in my textbook: A charged particle or object is not affected by its own electric field.  Since I find this completely unintuitive and my mind is yelling "wrong! wrong! how could a particle even distinguish between its own field and the external fields?" I would really like to hear an explanation about why this is true, if it is.  (A corollary question that comes to my mind after thinking about this is... What about gravity and mass considering the analogous situation? And the other two forces?)
78804
I've seen some conflicted answers to this question in texts and on the web, in the case of a dipole, for example.   Do magnetic fields do work directly, or is it their induced electric fields that do work?
48139
A permanent magnet produces lines of magnet flux that we call a "magnetic field".  Those lines come from inside the magnet, come out of the N pole, loop outside the magnet, &amp; return back into the S pole to complete a magnetic circuit.  Using ferromagnetic materials, other magnets, &amp;/or test equipment, we feel &amp; measure forces that are caused by a magnet/s when other materials are placed within close enough proximity to the magnet/s (i.e. within their magnetic field/s).  We therefore conclude that the magnetic lines flow in a specific direction &amp; exert definite forces (i.e. magnitudes/strength) on some materials (ferromagnetic &amp; other magnets), depending on where those materials are placed within the magnetic field of a magnet/s.    We label those forces as "H Field" &amp; "B Field". We measure H in terms of Amperes/meter. We measure B in terms of Newtons/meter/Ampere (or Tesla). We also commonly defined B in terms of the force that it exerts on moving electric charges (i.e. the Lorentz force).  An "Ampere" is basic unit of electrical current in the SI system, which = 1 Coulomb per second--which is formally defined to be the constant current which if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 × 10 −7 newton per meter of length.  A "Coulomb" is the standard unit of quantity of electricity in the SI system, which = the quantity of charge transferred across a conductor in which there is a constant current of 1 Ampere/Second.  Consequently, those "magnetic lines" are currents (or flows) of charges that don't appear to need any external source of energy to continue generating their currents.  We also know those magnetic lines exist inside a vacuum, so they are independent of air molecules to flow outside of a magnet.  So now my questions:   Exactly what charged particles are flowing outside (and inside) a permanent magnet that create the magnetic "lines"?   Do those particles come from something inside the magnet or does the magnet do something outside of it to affect unknown particles to make the lines? If there is a current (i.e. a continuous flow of charged particles), then why don't we harness that current like a water wheel (instead of 'using energy' to rapidly move copper wires through magnetic fields--like we do with electricity generators?)  Shouldn't we be able to get the line currents to charge a capacitor (or or other device) &amp; then otherwise discharge the capacitor for the energy that we want?
104341
Faraday's law states that "Any change in electric field induces a magnetic field and vice versa". I don't see exactly where these fields are induced, but I assume that these fields are induced at each and every point in space.  Now, let us consider a charge Q, moving with a uniform Velocity V. Obviously this movement of the charge creates a change in the electric field everywhere. As such it should induce a magnetic field.  Subsequently, this change in the magnetic field should also bring about an electric field, an induced one, owing to further changes induced in the magnetic field.   Apparently this machinery seems to be similar to an EM radiation. But we know that an EM radiation can only be produced by charges in accelerated movement. Why this chain of events can't be seen as an EM wave propagation?
77972
So I learned that the bar magnet makes a magnetic field and the field lines have a certain shape which kinda resembles 2 semi-ovals.  And if we pass current through a conductor then it makes a  magnetic fields and the field lines are in the form of concentric circles around the conductor.  My question is- why? Why do magnetic field lines take the shape that they take? There must be a reason behind it. Why aren't the field lines of a normal bar magnet shaped like the field lines of a conductor carrying electricity? And vice-versa?   Please explain it to me..i know that it delves very deep into the fundamentals of the working of science but still...please tell me the reason if anyone knows it
77403
Are they working with motion of electrons?