# What is Electrodynamics: Definition and 411 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. ### I Coulomb gauge Lorenz invariant?

Hey, What is meant by Coulomb gauge not being Lorenz invariant? The Coulomb gauge is just a constraint on \mathbf{A} and \phi and thus it is independent of inertial frame. I posted the question in the wrong section. This question is in the context of QFT. The notes says: A disadvantage of...
2. ### Classical Griffiths or Jackson for Electrodynamics?

I'm looking to brush up on my knowledge of electrodynamics and am trying to decide between Jackson and Griffiths. I have a fairly advanced math background and am comfortable with differential geometry, special and general relativity. I'm leaning toward Jackson but wanted to get input from...
3. ### I Bent Electrical Field How?

Why is electrical field bent like that rather than following a straight line across to the relevant point over there?
4. ### 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.
5. ### Einstein's Electrodynamics of moving Bodies

Okay I’m assuming I have to use √1- v^2/c^2 multiplied by some coefficient of length but I don’t understand any of this and could really use help understanding the process and/or reference material that might point me in the right direction
6. ### A Radiation back reaction in classical electrodynamics

I've been doing some research on the topic of radiation reaction force/self force in classical electrodynamics and although there are some discussions on the internet I would like direct answers to these following questions: Is there a rigorous and universally accepted treatment of radiation...

8. ### I Follow Up on M. LeBellac & J.M. Levy-Leblond's "Galilean Electromagnetism

In https://www.physicsforums.com/threads/what-assumptions-underly-the-lorentz-transformation.1015982/post-6657920 a discussion evolved from the basic assumptions of the Lorentz transformations, to a paper M. LeBellac, J. M. Levy-Leblond, Galilean electromagnetism, Nuovo Cim. 14B, 217 (1973)...
9. ### What chapters can I skip when self-studying Griffiths electrodynamics?

I'm currently studying Griffiths electrodynamics on my own and I want to be done with it once and for all. I however don't know if all the chapters are important for the rest of physics and which ones can be skipped without loss of continuity. Can someone give me some insight?
10. ### A Variation of Energy for Dielectrics (Zangwill's Electrodynamics)

Hello PhysicsForums community, I have been reading through Zangwill's Modern Electrodynamics all on my own, and I've just joined here hoping I can post some questions that come up for me. To start, I am confused about something in section 6.7.1, concerning the variation of total energy U of a...
11. ### Zangwill Modern Electrodynamics Lectures?

Summary:: Courses in electrodynamics Any online lectures or courses keyed to this book? Thanks very much
12. ### I Measurement of charge in motion

In Purcell's E&M Section5.3 "Measurement of charge in motion", he said when a charge is in motion, the force on test charges may not be in the direction of radius vector r. And in next paragraph, he defined Q by averaging over all directions. However, he just measured the radial component of...
13. ### Classical Electrodynamics Recommendations

I'm currently studying quantum mechanics from MIT opencourseware, just about to finish 8.05, quantum physics 2. I have little knowledge of electrodynamics, but I want to learn enough to be comfortable studying quantum electrodynamics in the future. My math background is pretty strong, so I've...
14. ### A Compactness and complexity in electrodynamics

As human beings, we tend to act and observe and think over time periods spanning a few milliseconds to several decades (or even centuries.) Essentially all phenomena that we directly engage with in everyday life are electrodynamical (with quantum electrodynamics over reasonably short time and...
15. ### I Visual Interpretation of Advanced Electrodynamics

Hello! I am a junior undergraduate physics major and I am very confused on how to visualize things in my electrodynamics class. Specifically, I am having issues with dielectrics and spheres with constant potentials etc. I usually notice that I am lost in a class when I can no longer draw out a...
16. ### Electrodynamics: electrostatic potential

Hi! I tried to solve it by using the equation of the electric potential above and as we see it requires the electric field, but the electric field at the center of the ring is zero. Then I tried by using the equation [text] V = \frac{1}{4\pi\epsilon_0r} \int \lamda dl [\text] and I got [text] V...

25. ### I Calc QED Charge Particle Repulsion/Attraction

Maybe this will help.
26. ### Problem on induced electric field, electrodynamics

The problem is shown above, the hint to solve the problem is below. See the hint if it is difficult for you to imagine what is going on. I am assuming the diagram in the hint shows what's happening when the mass is falling at terminal velocity. I have quite a few questions. 1. How do the wheels...
27. ### Calculating the force on an electron from two positive point charges

So this is more of an intuitive question rather than a mathematical one. I present the problem. Assume I have 2 charges of charge +q at a distance r from each other on the z axis. Position of two charges is (0,0,r/2) and (0,0,-r/2). Assume now that I want to calculate the force these two...
28. ### Energy paradox in classical electrodynamics?

Consider two massive charged objects at rest with a large horizontal distance ##d## between them (object ##1##: mass ##m_1##, charge ##q_1## and object ##2##: mass ##m_2##, charge ##q_2##). I apply a constant vertical force ##\vec{f_1}## upwards to object ##1## so that it gains an acceleration...
29. ### A charged particle entering a magnetic field -- find the position

I am computing the radiation pattern for that I have to calculate the power per solid angle I found $$m( magnetic moment)=I(t)A$$ where then i took the cross product with $n=sin(\theta)cos(\phi)i+sin(\theta)sin(\phi)j+cos(\theta)k$ After that I moved towards computing the E and B which I know...
31. ### Electrodynamics and the Poynting theorem

In my opinion the field momentum is the field's intrinsic momentum which it will give to charges(if any present)...
32. ### Electrodynamics problem -- Calculating the resistance of ocean water

A return path for the current was provided by the ocean itself. Given that the resistivity of seawater is about 0.25 ohm-meter, see if you can show that the resistance of the ocean return would have been much smaller than that of the cable. (Assume that the electrodes immersed in the water were...
33. ### Electrodynamics regarding volume charge density behavior

In this explanation we need to involve the Dirac delta functions(maybe) but I clearly have a difficulty in understanding it can some one explain me the whole concept of constant or non constant volume charge density.
34. ### I Electrodynamics of Dielectrics: 4D to 3D

Hi, so the four-dimensional generalization of $$\vec{B}=\mu\vec{H}$$ is $$F_{\lambda \mu}u_{\nu} + F_{\mu \nu}u_{\lambda} + F_{\nu \lambda}u_{\mu} = \mu (H_{\lambda \mu}u_{\nu} + H_{\mu \nu}u_{\lambda} + H_{\nu \lambda}u_{\mu})$$ From these four-tensors and four-vector I should be able to...
35. ### Separation of Variables: Find the potential b/w concentric hemispheres

I'm having troubles setting up this problem. I know we are to use boundary conditions to determine An and Bn since in this case (a<r<b) neither can be set to 0. I don't know how the given potentials translate into boundary conditions, especially the V3 disk.
36. ### Electrodynamics flux calculation question

I don't really know how to find it mathematically as I am really confused in finding the normal vector and finding the electric field as well. pls help
37. ### Is the Configuration of Magnetic Fields Only a Convention?

If I understand correctly, the concept of electric and magnetic fields originated with Faraday and was developed by reconceptualizing forces acting at-a-distance. For example, the electric field concept was developed by looking at the force on a test charge in the presence of a source charge...
38. ### Jackson Classical Electrodynamics: page 35 expansion of charge

Could anyone explain how did Jackson obtain the Taylor distribution of charge distribution at the end of section 1.7 (version 3)?

48. ### Learning Nothing from my E&M Course

Summary:: Griffiths' Electrodynamics Text is Worthless for Teaching It seems like Griffiths just makes things up as he goes along. There's no reasoning. Sometimes he does things one way, sometimes another. Solutions are never really explained, whether I look up homework solutions online or...
49. ### Electric field Difference between Electrostatics and Electrodynamics

Hello everyone, I have been pondering on the behavior of the E field in conductors. In electrostatics (where the charges are not moving): a) Electric fields are time- independent but position-dependent b) Electric fields are always zero inside a charged or uncharged conductor. At the...
50. ### Griffiths Introduction to Electrodynamics (Stokes Theorem Corollary)

Although Stokes Theorem says that the line integral of a closed surface equals to zero why do we get a non-zero value out of this question 1.11 (and figure 1.33) in the Griffits Introduction to Eletrodynamics Book?