# What is Electrodynamic: Definition and 33 Discussions

Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force.

Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which create molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. Electromagnetism is very widely used in modern technology, and electromagnetic theory is the basis of electric power engineering and electronics including digital technology.
There are numerous mathematical descriptions of the electromagnetic field. Most prominently, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905.

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1. ### A Finding potential of a dipole outside of a sphere

Hey guys! I am currently tackling the following problem: An electric dipole P is kept close to a conducting grounded sphere of radius A -assume a distance B between the center of the sphere and dipole. What is the potential of the dipole outside of the sphere when the orientation of the dipole...
2. ### Calculate the Magnetic Vector Potential of a circular loop carrying a current

Can someone explain what exactly happens at (4) ? I do not clearly follow, except that there is some cosine law going on? I also do not really understand why at (3), r' doesnt have a z hat component, but I can live with that.
3. ### A Radiation Friction: Solving Abraham-Lorentz Eq for Non-Physical Solutions

There is a well-known Abraham-Lorentz equation describing radiative friction. Suppose a particle moves in an electromagnetic field. ma(t)=q(E+vxB) + m(tau)a’(t) By solving this equation numerically, I get non-physical solutions(runaway solutions) Although, it would seem that an electron in an...
4. ### How does a current "know" where to go

Let's say we have a circuit, and in that circuit there's a resistor, and there's a wire that goes around it so that the current can flow freely without getting to the resistor. my question is this: how does the current "knows" to flow towards the around the resistor? how does it know not to get...
5. ### Electrodynamic tether on the Moon/Mars?

Moon and Mars have no magnetic field, but that they are immersed into solar magnetic field. If I place a long wire along north pole, perpendicular to Sun, while Moon/Mars moves along its orbit, the wire cuts magnetic field lines; this should produce a difference of potential between fare edges...
6. ### I Difference between electrodynamic suspension (EDS) & quantum levitation?

What is the difference between electrodynamic suspension (EDS) in maglev trains and quantum levitation? I'm having trouble distinguishing the difference between both.
7. ### Electrostatic self-force is zero

Homework Statement Consider a charged body of finite size, (\rho=0 outside a bounded region V). \vec{E} is the electric field produced by the body. Suppose \vec{E} \rightarrow 0 at infinity. Show that the total self-force is zero: \int_V \rho \vec{E} dV = \vec{0}, i.e. the charged body does not...
8. ### A Problem In Electromagnetic Phenomena

Homework Statement [/B] In a thin rectangular metallic strip a constant current I flows along the positive x-direction, as shown in the figure. The length, width and thickness of the strip are l,w and d, respectively. A uniform magnetic field B is applied on the strip along the positive...
9. ### Electrodynamic - Spherical cavity in dielectric

First, sorry if something is not totally clear, I'm translating physics term the best I can! 1. Homework Statement A sphere or radius a of permittivity ε2 is placed in a dielectric ε1. Without the sphere, we would have E = E0. We want to find the solution to this problem when ε2 = 1...
10. ### Why Does Rearranging an Inductor Yield Different Magnetic Fields?

I found two ways to solve this problem, but I get two different solutions, it's confusing because I can't see the flaw in wrong solution. 1. Homework Statement Long cylindrical inductor of diameter D1 and inductance L1 is connected to battery and creates magnetic field B1. Inductor is then...
11. ### Confusion about bound surface current of a cube

If the magnetization vector is in the z direction, is the bound surface current of a cube always 0, since z cross z is 0, and x and -x cancels and y and -y cancels out?
12. ### Electric Field in Conductor w/ Infinite Length & Density ƍ

Hello, I have a doubtaboutthe use of Gauss theorem in the presence of a coductor. If I have a infinite cylindric long shell with a charge density ƍ of radius b and inside of it a cylindrical conductor of radius a, also of infinite lenght, what will be the electric field in a point located...
13. ### Electrodynamic Combustion Control for Rocket Engines

A company called ClearSign says it can use electric fields to shape combustion flames to improve powerplant efficiency by upto 30%: http://www.technologyreview.com/news/520466/flame-shaping-electric-fields-could-make-power-plants-cleaner/...
14. ### Electrodynamic Tether experiement

I was reading about the electrodynamic tether experiments in low Earth orbits to generate electricity. I had a doubt regarding the mathematics that went behind calculating the emf across the tether. I read further and i realized they use the equation ε=Bvl, but the problem with this is that the...
15. ### Deriving electrodynamic equations

Hey all. I am taking my second college physics course (electromagnetic physics) and am looking for some help deriving the equations. I found it very helpful to know how to derive many of the equations in my first physics course. So far we have studied e fields, guass's law, capacitors...
16. ### What is the electrodynamic action and its energy-momentum tensor?

I have studied Jackson, Landau, and Barut textbooks on electrodynamics, together with Weinberg's Gravitation and Cosmology textbook, and I find that the usual action S = S_f + S_m + S_{mf} is inconsistent and not well-defined. For instance, what is the meaning of S_f? A free-field term? Or...
17. ### Theoretical electrodynamic cycle 2

Here is a second thought experiment I designed to test if I understand certain concepts concerning electrostatics correctly. Help will be appreciated. There must be an error somewhere in the explanation below; I am giving the explanation as if “factual” only to explain how I understand it at...
18. ### Theoretical electrodynamic cycle 1

I am casually working through Introduction to Electrodynamics, 3rd ed. by David J. Griffiths and created some theoretical situations to test my understanding of the subject matter. I am having difficulty with some, and will appreciate input. Consider the following theoretical cycle (see the...
19. ### Retarded Time & Position: Exploring Electrodynamic Concepts

Hey everyone, Just a quick question about a few electrodynamic concepts: 1) retarded time: t = t_r - (curly)r/c. Is t = total time, t_r = time elspased since the electromagnetic 'news' reached the point in question, and r/c = time taken to reach the point in question? 2) I'm a bit...
20. ### Electrodynamic Question about Metal.

I am sort of having a brain fart about this, when sending electricity threw a metal it becomes negatively charged correct? |-------------------------------------------------< |-->(Positive)Power(Negative)-------->Metal-------^ The electrons leave the negative terminal, pass threw the...
21. ### Transmission Line - Electrodynamic Calculations

Two very large parallel conducting plates of very large length l, and width w are separated by a distance d. A current I=Jw flows to the right in the lower plate and to the left in the upper plate. Each of the two currents produces a magnetic field \frac{B}{2} between the two plates. (a)...
22. ### Melvin Schwartz's book on electrodynamic

Have anyone of you have listened about Melvin Schwartz's book on electrodynamic.https://www.amazon.com/dp/0486654931/?tag=pfamazon01-20. It is known to be inconventially written. Is this a good book for an undergrad. If not which book is better between David J. Griffiths and Purcell. Thank You.
23. ### Why is the electrodynamic Lagrangian E^2 - B^2?

Is there a simple way to understand why the Lagrangian of the classical electrodynamic field is (in SI units) E^2/2 e0 - B^2/2 mu0 ? Why is there a minus in it? Is there some simple, intuitive explanation for it? Heinz
24. ### Is Maxwell's Electrodynamic Theory Violated?

In Edward Collet's book "Polarized Light: Fundamentals and Applications", Chapter 3 states that: However, in recent years (as recent as 2008), I came across a paper published in Nature Photonics that a group of scientists, Haifeng Wang et al. from Data Storage Institute based in Singapore...
25. ### Electrodynamic checks of the equivalence principle

Hello, I would like to know if there are experimental tests of the Equivalence Principle in the realm of electrodynamics. The book by http://books.google.com/books?id=BhnUITA7sDIC&pg=PP1&dq=Theory+and+Experiment+in+Gravitational+Physics&lr=#PPP1,M1" contains a lot of material about the...
26. ### Electrodynamic vector potential wave equations in free space.

In David Bohm's "Quantum Theory" (an intro topic building up to the Rayleigh-Jeans law), he states: "We now show that in empty space the choice div a = 0 also leads to \phi = 0 ... But since div a = 0, we obtain \nabla^2\phi = 0 This is, however, simply Laplace's equation. It is...
27. ### What are some recommended books for studying Electrodynamics?

I would like anyone to reccomend good books on Electrodynamics. Any links to online resources for reading are also welcome.
28. ### Relativistic invaraiance of a simple electrodynamic quantity

Homework Statement Under what conditions is the quantity E^2+B^2 relativistically invariant? Homework Equations E\cdot B and E^2-c^2B^2 are invariant. (Also Lorentz transformation laws for E and B which I won't type here.) The Attempt at a Solution I think you can just...
29. ### Build Electrodynamic Trap:Camera,Voltage,Distance

I am new to physics. I am trying to build an electrodynamic trap using 2 ring electrodes to trap aerosol particles. I will be applying a voltage of 5 KV. What are the things that i need for example what camera do i use to visulaize the particles and what distance should i maintain between the rings
30. ### What are the FULL classical electrodynamic equations?

Most (or all) solvable EM problems are either (1) given a fixed static or periodically-varying EM field, find the motions of charged particles, OR (2) given a fixed static or periodically-varying charge distribution, find the resulting EM field. That is, either (1) solve the Lorentz force...
31. ### How Do You Calculate the Potential of an Electric Dipole at a Distance?

Can someone explain how to solve the following problem? A physical electric dipole consists of two equal and opposite charges (+/-)q separated by a distance d. Find the approximate potential at points far from the dipole.
32. ### Exploring Electrodynamic Forces Behind Painful Wounds

hit a wall,u feel pain,what kind of forces r involved,r they electrodynamic?
33. ### In an electrodynamic system, does the entropy of the field increase?

Consider an electric field throughout the region of an electrodynamic system: E [x,y,z,t] The function, E [x,y,z,t], is a macrostate. Corrresponding to it are all the ways the charge in the system could be arranged ( p [x,y,z,t])so as to produce this macrostate. The set of p [x,y,z,t]s...