# Electrodynamics Definition and 86 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 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...
2. ### 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...
3. ### Classical Confusion between Electrodynamics texts

Hello everyone, I recently completed kleppner and kolenkow classical mechanics book. Next I am going to learn Electrodynamics. My brother is a EE major and he gave me his copy of "principles of electromagnetics" Matthew Sadiku 4th edition. But a lot of people here recommend Griffiths. So, 1.)...
4. ### Spin-Orbit Coupling

I was reading in the Book: Introduction to Quantum Mechanics by David J. Griffiths. In chapter Time-independent Perturbation Theory, Section: Spin -Orbit Coupling. I understood that the spin–orbit coupling in Hydrogen atom arises from the interaction between the electron’s spin magnetic moment...

14. ### 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...
15. ### A Canonical momentum ##\pi^\rho## of the electromagnetic field

In David Tong's QFT notes (see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , page 131, Eq. 6.38) the expression for canonical momentum ##\pi^0## is given by ##\pi^0=-\partial_\rho A^\rho## while my calculation gives ##\pi^\rho=-\partial_0 A^\rho## so that ##\pi^0=-\partial_0 A^0##. Is it...
16. ### Rotating and tilting charged disk induces a voltage inside a ring

As I m learning for an upcoming exam I found an electrodynamics problem I struggle with. In the first task I need to calculate the magnetic dipole moment of a uniformly charged,thin disk with the Radius R and a total charge Q which rotates with a angular speed omega round its symmetry axis...
17. ### A Canonical quantization of Electrodynamics: physical intuition ?

Hello, I am freshly retired and enjoy going back to the fundamentals. I followed the wonderful courses by Alain Aspect on Coursera on Quantum Optics 1 and 2 . The quantization of Electrodynamics is really easy stuff. Just follow the correspondence between Poisson brakets and Commutators ... and...

45. ### Classical Griffiths Electrodynamics vs Pollack Electromagnetism.

I try to learn electrodynamics as theoretical physicist, Now I study from Griffiths, I find it very good book and do the job! but the problem I need to learn electrodynamic to do future topics like Quantum Electrodynamics, and Pollack I find it good and modern, so my question is what is the best...
46. H

Homework Statement An infinitely long wire carries current I=I_0sin(wt). A distance a from this wire is an w by l loop with resistance R with induced voltage V and induced current i. Find the induced voltage and current in the loop. Homework Equations Faraday's law is given by \varepsilon =...
47. ### Sketch of the electric field of a laser beam

I am trying to sketch the electric field E in snapshot of a linearly polarized laser beam. Is it correct that the E vectors bend from vertical to longitudinal near the cylindrical surface of the beam, and that all field lines within a half wave segment are closed loops?
48. ### Propagation of EM Waves in metamaterials

We have materials that have negative effective permittivity and permeability. In such materials, when the product of permittivity and permeability is negative, solving the wave equation yields a wave with a purely imaginary wave number. Does this mean complete attenuation of the wave ?
49. ### I Original references for Hertz's experiments

There are many website about the apparatus of Hertz's experiments, i.e. http://www.sparkmuseum.com/BOOK_HERTZ.HTM http://earlyradiohistory.us/1901hz.htm http://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture6/hertz/Hertz_exp.html There are many pictures showing the apparatus of...
50. ### Why can't I use this equation for the magnetic field?

Homework Statement Homework Equations ##\oint \vec{H} \cdot d\vec{l} = I_{free,enclosed}## ##\vec{B} = \mu_0 (1+\chi _m)\vec{H}## The Attempt at a Solution I found the magnetic field inside to be ##\vec{B} = \mu_0 (1+\chi _m)\frac{Is}{2 \pi a^2} \phi##. But why can't I use the same equation...