What is Electrodynamics: Definition and 416 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. F

    Classical Model Electrodynamics

    Hi, I am trying to gain a better understanding of the classical model of electrodynamics, so what I mean by this is, using the idea of dipoles and electron movement to understand electrodynamics. More specifically, I'm studying plane waves, and I can't understand why when a plane wave hits a...
  2. P

    Confirmation of understanding of electrodynamics

    Hi I'm trying to get my head round why Maxwell's equations fail for the electron going round the atom. The common sentence I see is along the lines of: "Accelerating charges emit electromagnetic radiation (EMR), and a point electron orbiting a point nucleus would continually accelerate...
  3. Logic Cloud

    Is there a concept of 'state' in electrodynamics?

    I have so far encountered the notion 'state' in classical mechanics, thermodynamics and quantum mechanics. I have, however, not seen this notion in the context of electrodynamics. Is there such a thing as a state in electrodynamics? My guess is it would be a pair consisting of an electric field...
  4. P

    Local Electrodynamics in higher dimensions?

    Local Electrodynamics in higher dimensions?? So I am an unexperienced undergrad but the other day I had a few thoughts which are most likely crazy. I'm just wondering why they don't work. And whether the questions I'm asking are answered elsewhere. So I've heard: (i) Maxwell's...
  5. S

    Deriving del cross A in Electrodynamics

    Hello, I am trying to derive the equation for the B-field due to a moving charge. ~ Griffiths Chapter 10, equation 10.66. I have been trying to “do” the del cross A and simplify . Things get messy and I am uncertain on some of my vector operations. In searching the internet I find...
  6. M

    Prerequisites for electrodynamics?

    Hi, I've had electrodynamics on my learning to do list for quite some time, but every time i start i get frustrated because it assumes prerequisite knowledge that i don't have. Last time it was integrals, so i learned integral calc, and i have vector calculus to learn as well, but I am still...
  7. A

    No drama quantum electrodynamics? (was: Local realism ruled out?)

    As the only thread I've ever started before (https://www.physicsforums.com/showthread.php?t=369328 ) attracted a lot of interest, became one of the most viewed threads in the forum, and was closed :-), I'd like to make a short update here. I have published a new article on the topic: "No...
  8. N

    Classical Electrodynamics: Explaining the Lorentz Gauge Condition

    what is physical meaning of Lorentz gauge condition in classical electrodynamics??
  9. S

    Griffiths Electrodynamics gradient of charge distribution

    I do not understand the following from Griffiths’ Electrodynamics – page 424 Equation 10.21. \nabla p = \dot{p} \nabla {tr} = … I’m not sure how much of this applies (I think my question is on the math) but p is the charge distribution, tr is the retarded time. Is this an...
  10. O

    Electrodynamics- combination of resistors

    Homework Statement What is the compensative system of this combination of resistors? http://img545.imageshack.us/img545/6610/circuitoi.jpg
  11. N

    Continuity conditions in electrodynamics.

    I have a question about the derivation of the boundary conditions at surfaces of electromagnetic fields. These conditions say, that the tangential component of the electric and the normal component of the magnetic field are continuous at surfaces. Their derivation goes as follows: To derive...
  12. S

    Griffiths Electrodynamics - Chap 5 clarification curl of B field

    Homework Statement This question is regarding clarifying some reading in Griffith’s Electrodynamics, page 224. “deriving the curl of B” In particular it’s less on electrodynamics and more on some vectors or vector calculus. The book states: we must check that the second term integrates to...
  13. G

    Multivariable calculus and electrodynamics

    Hi, I'm trying to learn physics and math on my own (I'm 16, bored with what I'm taught in school, and on vacation right now, so I have some free time). Over the past 4 months or so I've started more seriously learning, and I think I've been doing fairly well. To learn mechanics, I've been using...
  14. C

    Electrodynamics Continuity Equation

    Homework Statement I am currently studying for a quiz and then following a test in my Electrodynamics test. Right now I am struggling to define the following: Continuity equation and its physical meaningHomework Equations The Continuity Equation is given as the following: ∇J=-∂ρ/∂t The Attempt...
  15. S

    Griffiths - example 5.5 Electrodynamics - Calculate B Field

    Homework Statement Greetings, In Griffiths, Introduction to Electrodynamics, example 5.5 (page 216), calculating the B field a distance “S” away from a current carrying wire. l' (dl’) is the horizontal current carry wire – will be segmented to dl’ tan(\theta) = \frac{l’}{s} In the next...
  16. fluidistic

    Going through Jackson's book (electrodynamics, method of images)

    Homework Statement I would like to 1)Find the electric field in all the space in the following set up: There's an electric charge q in a region with dielectric constant ##\varepsilon _1## which is at a distance d from a plane that separates the space into 2 regions, namely the one of the...
  17. C

    Potential formulation of Electrodynamics with magnetic sources

    Hello! I am trying to construct (if it is possible) a potential formulation of an electromagnetic theory which permits the presence of magnetic sources, using as a starting point the equations referred here: http://en.wikipedia.org/wiki/Magnetic_monopole Although I think that I have make some...
  18. B

    Domain of validity of classical electrodynamics

    i am currently reading griffith's book on electrodynamics, though he does an excellent job with the theory (along with all the sloppiness in math) he does not really answer the question, how well does this theory apply to the real world. i know Newton's theory is valid at v<<c, however in...
  19. micromass

    Classical Introduction to Electrodynamics by Griffiths

    Author: David Griffiths Title: Introduction to Electrodynamics Amazon Link: https://www.amazon.com/dp/0321856562/?tag=pfamazon01-20 Prerequisities: Calculus 1,2,3, Basic E&M Level: Upper-level undergrad Table of Contents 1. Vector Analysis 2. Electrostatics 3. Potentials 4...
  20. C

    Electrodynamics: Electrostatic field potencial in Cartesian coordinates

    Homework Statement It's given that absolute permitivity is a coordinate function: ε (x, y, z) = Asin(x)cos(y), where A=const Homework Equations We need to find an electrostatic field potential function \varphi in Cartesian coordinate system. The Attempt at a Solution I tired to solve, but...
  21. Greg Bernhardt

    Quantum Quantum Electrodynamics by Walter Greiner

    Author: Walter Greiner (Author), Joachim Reinhardt (Author) Title: Quantum Electrodynamics Amazon Link: https://www.amazon.com/dp/3540875603/?tag=pfamazon01-20 Prerequisities: Contents:
  22. Greg Bernhardt

    Classical Classical Electrodynamics by John David Jackson

    Author: John David Jackson Title: Classical Electrodynamics Amazon Link: https://www.amazon.com/dp/047130932X/?tag=pfamazon01-20 Prerequisities: Contents:
  23. J

    Feynman's Nobel classical electrodynamics action

    In his Nobel lecture Feynman describes an electrodynamic action between a set of particles (equation 1, one third way thru lecture): http://www.nobelprize.org/nobel_prizes/physics/laureates/1965/feynman-lecture.html The action is in 4-vector form. I wonder if someone could do me a favour and...
  24. G

    Understanding why Einstein found Maxwell's electrodynamics not relativistic

    I'm trying to understand exactly why Einstein considered Maxwell's electrodynamics to be non-relativistic. As I read Maxwell's paper, it seems to me that it is concerned only with relative motions. I'm thinking that the problem must be with the stationary ether proposed by Lorentz, for then...
  25. J

    Electrodynamics without fields?

    Can one describe electrodynamics without any reference to fields? I think you can. Using the Heaviside-Feynman expression for the electromagnetic field due to an arbitrarily moving charge, together with the Lorentz force law, one can write down an expression for the electromagnetic force...
  26. H

    Gauss's law for electrodynamics

    Gauss's law can be proved qualitatively by proving that the field inside a charged closed surface is zero. However Maxwells' equations says that gauss's law holds true even for electrodynamics. how can this be verified experimentally? Thanks in advance !
  27. W

    The Right Hand Rule: it's not just for electrodynamics anymore.

    Among its many other uses, it looks like you can use the right hand rule for screwing in a light bulb or screwing on the cap to a jug of milk! Who said learning physics was of no practical use?
  28. M

    Introduction to Electrodynamics: External Field & Induced Charge

    Homework Statement Introduction to Electrodynamics by Griffiths, 3rd ed. pg 141-2, Example 3.8: An uncharged metal sphere of radius R is placed in an otherwise uniform electric field E=(0,0,E). [The field will push positive charge to the northern surface of the sphere, leaving a negative...
  29. G

    Electrodynamics and vector calculus question

    Homework Statement 1) The magnetic field everywhere is tangential to the magnetic field lines, \vec{B}=B[\hat{e}t], where [\hat{e}][/t] is the tangential unit vector. We know \frac{d\hat{e}t}{ds}=(1/ρ)[\hat{e}][/n] , where ρ is the radius of curvature, s is the distance measured along a...
  30. S

    Electrodynamics, Need help with problem

    Homework Statement An infinitely long cylindrical volume of radius R contains a charge density ρ(s)=ks4 where k is a constant and s is the distance from the axis of the cylinder. Note that this is NOT a constant density. a) Find the electric field everywhere in space. b) From your result in...
  31. F

    Does QED reproduce classical electrodynamics? How?

    It seems to be a dumb question. But I haven't seen anyone making this connection between QED and Classical EM in a complete fashion. The only example I've seen is the connection between two particle scattering amplitude calculation in QED (Peskin's book), and the amplitude of a particle...
  32. M

    Is My Solution to Problem 2 in Electrodynamics Correct?

    Homework Statement I'd type this out but there's a bit too much formulae. http://www.maths.tcd.ie/~tristan/MA3431/Homework_1.pdf It's problem 2. I'm just wondering if my solution is correct. Thanks in advance! Homework Equations The Attempt at a Solution In this...
  33. N

    Basic requirements to start a course in electrodynamics

    I'm in my third year of undergraduate physics and I'm wondering what i'd need in order to start my course on electrodynamics on my own. thanks in advance.
  34. K

    A problem in Griffith's textbook of electrodynamics, P189.

    Homework Statement Exercise 1: Suppose a infinite plane z=0 divides the 3-dimensional space into two parts. The region below z=0 is filled with linear dielectric material of susceptibility \chi. The bound charge density at z=0 is \sigma. Find the electric field of the two regions...
  35. P

    Confusion regarding continuity equation in electrodynamics

    Suppose I have two charged particles with charge densities ρ1(r,t) and ρ2 (r,t) with corresponding velocity fields V1(r,t) and V2(r,t). Can I write continuity equation for the combined system? Wouldn't charges moving with different velocities would contribute differently to the current which...
  36. B

    Gauss's law in electrodynamics

    most(or all) proofs i have seen of gauss's law is based on coulumb's law. however coulumb's law is based off of electrostatics which certainly does not hold in electrodynamics. however gauss's law is used extensively in electrodynamics. is gauss's law derived otherwise or is it just a law like...
  37. M

    Griffiths, Electrodynamics Prob. 3.28a

    Homework Statement A spherical shell of radius R carries surface charge density \sigma=k \cos \theta. Whats the dipole moment of this distribution?Homework Equations The dipole moment is calculated as \bf{p} = \int \bf{r}' \sigma (\bf{r}') d\bf{a}' (Griffiths, Eq. 3.98).The Attempt at a...
  38. N

    Relative difference in laws of electrodynamics

    Consider a train moving at speed 's' and there is a charge particle at rest relative to the observer at train. The second observer on a ground see the charge particle and observer moving relative to him, and infer the existence of a magnetic field strong enough that its field is significant at...
  39. B

    Vector calculus questions in electrodynamics

    im reading introduction to electrodynmics by griffiths, the math techniques used is sloppy to the point of frustration. hence i have several problems with the math while reading the text 1) it introduces the dirac delta function in dimension 1 δ(X) = 0 if x≠0 and δ(x)= ∞ if x= 0 and ∫δ(x)dx...
  40. K

    What is the limit of classical electrodynamics?

    Hello everyone, I was wondering about the following question: Under what condition(s) could one say that the interaction between an electron and an electromagnetic wave is not governed anymore by the laws of classical electrodynamics? I would also be glad if someone could point out any...
  41. Q

    What's wrong with Weber's electrodynamics?

    Well, I was looking through electrodynamics, and I came across Weber's theory of electrodynamics. I was interested and looked further, but I couldn't find out what made Maxwell's theory better than Weber? Why is Weber's wrong?
  42. C

    Divergence questions from Griffith's Electrodynamics

    Hi all I basically have two questions that are very closely related to each other about divergence, specifically the divergence of a vector function 1/r2\widehat{r} First, I will be referencing pages 17, 18, and 45 from the 3rd edition of Intro to Electrodynamics. The first question...
  43. W

    How does special relativity follow from classical electrodynamics

    I'm trying to understand how one derives the relativistic treatment of the electromagnetic interaction from the classical one and which are the extra postulates made. We can start from Maxwell's equations and the Lorentz force. From the Galilean invariance of Newton's second law of motion...
  44. C

    Electrodynamics - I'm trapped in a stupid paradox - pleas help

    Homework Statement B = variable magnetic field, of constant direction (e.g B = b cos(wt) N, where N=const vect) A = magnetic potential vector of B R = vector from some origin O to a point M It is assumed that no exterior electric potential is present. Problem: to find the...
  45. B

    Jackson Electrodynamics syllabus

    Hi Everyone, I'm trying to go through Jackson this summer after having finished Griffith. However, it doesn't seem feasible to do all the problems in Jackson. So I'm wondering if any of you have a electrodynamics syllabus (with problems number on it) with Jackson's book and can give me the...
  46. TrickyDicky

    Textbook Electrodynamics May Contradict Relativity

    According to "physics today" www.physicstoday.org/daily_edition/science_and_the_media/em_science_em_magazine_news_report_textbook_electrodynamics_may_contradict_relativity the paper "Trouble with the Lorentz law of force: Incompatibility with special relativity and momentum conservation"...
  47. M

    Jackson's Electrodynamics. Question on Capacitance definition

    In Jackson's book he defines the capacitance of a conductor, "...the total charge on the conductor when it is maintained at unit potential, all other conductors being held at zero potential." I'm trying to get a more concrete definition in my head rather than the standard definition of...
  48. C

    Understanding Electron Mass in Classical and Quantum Electrodynamics

    Consider classical electron theory. Distinguish between the mechanical, electromagnetic, and observed electron mass. What is the degree of divergence of the classical electron self-energy? What are the roles of mass-renormalization, runaway solutions, and preacceleration in classical electron...
  49. M

    Dirac Delta Function (electrodynamics)

    I'm having a hard time grasping when I should use this little "function". I'm using Griffith's Intro to Electrodynamics and either he doesn't touch on it enough or I'm missing the point. From what I think I understand I'm to use it when there would be a singularity in a result or calculation(?)...
  50. K

    Easy Electrodynamics Question on Field Lines

    Homework Statement Explain why the electric field is perpendicular to any conducting surfaces in static situations. Is this true in general (i.e. even for changing electric or magnetic fields)? Are there similar conditions on the direction of a magnetic field at the surface of a...
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