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. A

    Classical Prerequisites for Jackson's Classical Electrodynamics

    Hello, I have already studied Griffith's book, Intro to Electrodynamics. However when I try Jackson's book, I find it a bit hard for me. My question is, what Maths and Physics texts (or specifically, chapters of texts) do you recommend, so that I would be best prepared for a graduate course in...
  2. J

    Classical Cheng's or Lorrain/Corson's Electromagnetics book?

    Hello, I want a book on electromagnetics for my second course on electromagnetism. In my first course we used Griffith's "Introduction to Electrodynamics" with supplements like Morin and Purcell's "Electricity and Magnetism". I borrowed those from the university's library but now I want to step...
  3. ChrisVer

    Interesting Electrodynamics Problem

    I am not sure if this fits under this title, but oh well... I guess it goes for students but also for higher in hierarchy people (they also like some problems which can have an extension) What has been your favourite to talk-about problem in Electrodynamics ? I am looking for something that...
  4. SU403RUNFAST

    Electric Field of a square plate intro to electrodynamics

    nvm
  5. Dale

    Electrodynamics from Jefimenko's equations

    @vanhees71 are you familiar with anyone who teaches electrodynamics starting from Jefimenko's equations? What would you think about such an approach? I haven't thought it through carefully yet, but I wonder if it would be easier for students to grasp. The connection to relativity would be a...
  6. G

    Can QFT adequately describe the elusive properties of photons?

    What is the photon's equivalence of the electron's wavefunction? Can I measure qualities of the photon that will collapse into an eigenstate? What properties of the photon aren't fixed?
  7. H

    Classical Jackson's Electrodynamics: 1st edition vs 3rd edition

    Hello all. I am currently using Jackson's Electrodynamics book to study the subject and was wondering how different is the 1st edition from the 3rd. So far, I have read the first chapter and have done most of the problems from the first edition. My question is, how much will I miss out on if I...
  8. Prins

    Classical What best book for Electrodynamics/electromagnetics?

    Need a book to completely revise ED. Book not be of beginner level. Must be of Masters level. Thanks Attaching a list of topics that needs to be there in it. Electrostatics: Gauss’s law and its applications, Laplace and Poisson equations, boundary value problems. Magnetostatics: Biot-Savart...
  9. Pyrus

    Observer is moving &charge is stationary,magnetic field acts

    CASE I - Do magnetic field is felt by observer which is moving and charge is stationary? CASE II- Do magnetic field is felt by observer which is moving with same velocity as that of charge? Does it has some experimental proofs and explanations...
  10. G

    Hello I'm proud to be here.

    Decided to make this account in order to supplement my studies of QM by Griffiths and Electrodynamics by Jackson. I'm finishing my BS in chemical engineering soon and then it's onto grad school to study materials science :).
  11. M

    Proof of Gauss' Law for Electrodynamics?

    I’ve been searching for a proof, using the equation for the electric field due to a moving point charge – given, for example, on page 438 of the Third Edition of David Griffith’s Introduction to Electrodynamics (equation 10.65) – that Gauss’s law holds for a moving point charge. There is no such...
  12. vanhees71

    Electrodynamics in Robertson Walker spacetime

    I've a (perhaps somewhat stupid) question. Is there a good source, where one finds the plane-wave solutions (or what comes closest to it) for electrodynamics for the closed and open (non-flat) Friedmann-Lemaitre-Robertson-Walker metric. I try this myself for a while, because to my surprise I...
  13. A

    Biot Savart Law for Charged Particles: Fact or Fiction?

    Well, I am a bit confused. Griffiths himself writes in his book "Introduction to Electrodynamics" at one point in his book that this law is "simply wrong". In a footnote, he writes that it was wrong in principle wheras it is true for non-relativistic speeds, and later on in his book, he goes on...
  14. N

    Jackson 1.12 & 1.13: Prove Thomson's & Insulated Conductor Theorem

    Homework Statement 1.12 - Prove Thomson's theorem : If a number of conducting surfaces are fixed in position and a given total charge is placed on each surface, then the electrostatic energy in the region bounded by the surfaces is a minimum when the charges are placed so that every surface...
  15. C

    Given Ez, with Bz = 0, how to find other components?

    Hey there, I have a quick question, and it can be answered with a reference to a book chapter of article. If I'm given the z component of the electric field inside a resonant cavity, and furthermore, if it's set that Bz = 0, how do I determine the other components for both E and B?
  16. S

    Advice on my outline on undergraduate physics curriculum

    I have studied physics during my undergraduate years but I want to relearn everything as I came to my realization that I'm weak because of the quality of education I got. So far, I want to know if my order of study is good. Classical Mechanics: An Introduction to Mechanics by Kleppner and...
  17. C

    Total power radiated from two dipoles (electrodynamics)

    Homework Statement The retarded vector potential ##\mathbf{A}(\mathbf{r}, t)## in Lorenz gauge due to a current density ##\mathbf{J}(\mathbf{r}, t)## contained entirely within a bounded region of size d is $$\mathbf{A}(\mathbf{r},t) = \frac{1}{4\pi c}\int_V' \frac{\mathbf{J}(\mathbf r'...
  18. S

    Balancing magnetic force with gravity.

    I have been reading ahead in my course from Griffiths textbook and I have a couple of questions. I found this solution online to a question: http://glennrowe.net/physicspages/2013/09/23/balancing-magnetic-force-with-gravity/ It says: A square loop is cut out of a thick sheet of aluminum. It is...
  19. Y

    How do we eliminate the existance of luminiferous aether?

    According to Maxwell's equation, the speed of light, ##C_0 = \frac{1}{\sqrt{\epsilon_0\mu_0}}##, is a constant regarding to some form of medium, called luminiferous aether. Shortly after the death of Maxwell, Michelson-Morley Experiment shows that the speed of light is constant regarding to the...
  20. Jason Chen

    Shape of vortex electric field line in a rectangular metal

    We know that,the shape of electric field line in a cylinder under varying magnetic field is circle,and I wonder,what's the situation if it is a piece of metal with rectangular cross section? I think it might be something like superellipses.Can somebody tell me is it true or how to treat this...
  21. J

    Gauge Transformation Quantum Electrodynamics

    It's well known when if we are working on problems related to particles in presence of an electromanetic field, the way we state the problem can be done using the next Hamiltonian: H=\dfrac{(p-\frac{e}{c}A)^2}{2m} +e \phi where the only condition for A is: \vec{\nabla } \times \vec{A} =\vec{B}...
  22. J

    Gauge Freedom Quantum Electrodynamics

    It's well known when if we are working on problems related to particles in presence of an electromanetic field, the way we state the problem can be done using the next Hamiltonian: H=\dfrac{(p-\frac{e}{c}A)^2}{2m} +e \phi where the only condition for A is: \vec{\nabla } \times \vec{A} =\vec{B}...
  23. A

    Length of Wire Effect on Current and Inner Electric Field.

    >Two wires of the same material are both connected to a 9-V ideal battery. They have the same cross section area but wire 2 is twice longer than wire 1. Compare the following quantities by answering if the quantity for wire 1 is smaller, equal or greater than the same quantity in wire 2. > -...
  24. Ahmad Kishki

    Disappearing terms in electrodynamics boundary conditions

    In the derivation of the boundary conditions we apply the integral form of maxwell's equations, but once we take a very small volume we find that some terms disappear like the displacement current as well as the time derivative of the magnetic field. Why do these terms disappear? For reference...
  25. Futurestar33

    What is your reason for studying physics?

    What is your reason for studying physics and what do you want to do with it. I actually got thrown into my schools physics program by accident. I began at a community college studying nanotechnology and when i transferred schools it was supposed to be a two-plus two program meaning I would get...
  26. C

    Oscillating current along antenna, electrodynamics

    Homework Statement A thin linear antenna of length ##d## is excited in such a way that it carries the sinusoidal current ##I(t) = I_0 \sin(2\pi z/d)e^{ i\omega t}##, where ##\omega = 2\pi c/d##. (i) Beginning with the exact solution for the vector potential in Lorenz gauge, calculate the power...
  27. V

    Earnshaw's theorem and 'free space'

    I am trying to understand the proof for Earnshaw's theorem. Though the theorem states > that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges ([Wikipedia][1]) In the proof, Gauss's Law in...
  28. ELB27

    Evaluating an integral for an expanding, charged sphere

    Homework Statement An expanding sphere, radius ##R(t) = vt## (##t>0##, constant ##v##) carries a charge ##Q##, uniformly distributed over its volume. Evaluate the integral Q_{eff} = \int \rho(\vec{r},t_r) d\tau with respect to the center. (##t_r## is the retarded time and ##d\tau## is an...
  29. W

    Cavity quantum electrodynamics

    hi, i am studing cavity QED - but needs some comprehensive book on that - i will be very grateful if someone guide me in this regard.thanks
  30. D

    Problem 2.4 Griffiths E&M 3rd ed -- E-field above a square loop

    Homework Statement The problem states, "Find the electric field a distance z above the center of a square loop (sides of length a) carrying a uniform line charge λ. " The hint says to use the result of example 2.1. Example 2.1 is a similar problem, but instead of a square loop you are asked...
  31. Mr. Rho

    Question about mathematical equality

    Hi there, I am reading Chapter 9 of Jackson Classic Electrodynamics 3rd edition, and I don't see why this equality is true, it says "integrating by parts", but I still don't know... any help? http://imageshack.com/a/img673/9201/4WYcXs.png
  32. F

    Electrodynamics, multipolar development doubt

    Homework Statement In the XY plane there are two point charges +q at (0, -b, 0) and –q at (0, b, 0) and a ring of radius a centred in the centre of the plane: Find the electric field in all points of the z axis and study the field’s dominant behaviour at distances z >>a,b. Find the electric...
  33. R

    Calculating the Increase in Energy for a Capacitor with Concentric Spheres

    Homework Statement A capacitor consisting of two concentric spheres is arranged so that the outer sphere can be separated and removed without disturbing the charges on either. The radius of the inner sphere is a and that of the outer sphere is b, and the charges are Q and -Q, respectively a)...
  34. F

    Electrodynamics of a moving particle

    Homework Statement There is a charged particle (charge=q) moving on the x-axis such that x(t)=A\,sin(\omega t). Prove that: \int <\rho>\,dV=q Homework Equations We have the following equations: <\rho>=\frac{1}{T} \int_0^T \rho\, dt Where T=\frac{2 \pi}{\omega} The Attempt at a Solution So...
  35. F

    Where can I get some practice for Electrodynamics?

    Hey all! I'm taking a higher level electrodynamics course this semester and next. We are using Introduction to Electrodynamics fourth edition by Griffiths. I was just wondering where I could get some practice problems outside of the book to work and boost my skills. Thanks
  36. C

    Understanding Dipole-Loop Interactions in Electrodynamics

    Hi Guys I have hards time doing a question in electrodynamics, i have uploaded the problem and i can't figure out how to do question a), i have hard time understanding what coordinat system i should use, cartesien og cylendrical. I have tryed to draw the field lines, its a bit messy, but its...
  37. I

    Electrodynamics (Lorentz to Faraday)

    Electrodynamics (Lorentz Force & Voltage) [edited] Two part inquiry PART I Situation: I have a B-field and I'm pulling a straight piece of wire through that B-field You pull the wire perpendicularly through the B-field at velocity v; charges between points a and b will...
  38. P

    Electrodynamics text study guide?

    There is a book with very briefly theory, showing the essentials for make the exercices of electrodynamics, and also with solved exercices? Similar to Kubo of Statistical Mechanics (but of electrodynamics). Jackson and Griffits are very good books, but i am looking for a book with the...
  39. Rugile

    Electrodynamics problem (circuit with two sources)

    Homework Statement In the circuit (see attachment) we have 2 sources. If we decrease the EMF of the first source (ε1) by 1.5V, the current changes in every branch of the circuit. How does the EMF of the source ε2 has to be changed, so that the current through the ε1 source would be the same...
  40. S

    Electrodynamics for a rotating ring

    Homework Statement A thin copper (resistivity 1.7 x 10-8 Ωm, density 8.9 g/cm3) ring rotates about an axis perpendicular to a uniform magnetic field B0. Its initial frequency of rotation is ω0. Calculate the time it takes the frequency to decrease to 1/e of its initial value, under the...
  41. DocZaius

    A Figure in Griffith's Intro to Electrodynamics

    A Figure in Griffiths' Intro to Electrodynamics I am really loving this book. But I have come across a figure whose purpose I just don't understand. It is shown when Griffiths is introducing the concept of self-inductance. He talks about how a changing current not only induces an electromotive...
  42. A

    Two-photon physics/quantum electrodynamics

    In a Wikipedia article about two-photon physics it is stated: "From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but half wavelength is a positive charge and the next half wavelength is a negative charge." This is the...
  43. V

    Alternative to Griffiths Introduction to Electrodynamics

    I hope I am posting this question in the correct forum. I am in the second course in an upper level Electricity and Magnetism sequence (E&M II). We are using Griffith's Introduction to Electrodynamics as in the first course in the sequence. We covered chapters 1-3, 5, 7, and some of 8 in the...
  44. D

    Full Lagrangian for Electrodynamics: Find ##\mathcal{L}_\textrm{matter}##

    The full Lagrangian for electrodynamics ##\mathcal{L}## can be expressed as ##\mathcal{L}=\mathcal{L}_\textrm{field}+ \mathcal{L}_\textrm{interaction}+\mathcal{L}_\textrm{matter}##. Practically every textbook on relativity shows that...
  45. S

    Boudary conditions, rough interface (Electrodynamics)

    Hello. I'd like to know, does anybody know any information about finding boudary conditions for E, H vectors in case of rough interface, if phi(x) function is set. Maybe such kind of case ( 2D or 3D case) has been considered somewhere. Thank you in anvance.
  46. O

    Classical electrodynamics problem

    Homework Statement suppose every charged particle carried electric and magnetic charge in the universal ratio Gk/Ek=a. is there another way of looking at this situation in which we would be unaware of magnetic charge?
  47. L

    Method to learn electrodynamics?

    Dear friends, can some one tell me the method to learn electrodynamics??(iam a postgraduate student). Thank you
  48. M

    Electrodynamics question - Induced EMF

    > A very long straight wire carries a current I. A plane rectangular coil of high resistance, with sides of length $a$ and $b$, is coplanar with the wire. One of the sides of length $a$ is parallel to the wire and a distance $D$ from it; the opposite side is further from the wire. The coil is...
  49. M

    Jackson - Electrodynamics guidance (for the ones who used it)

    How did Jackson arrange his set of problems in this famous book Electrodynamics? I mean, does he move according to the course? Or the problems are mixed up?
  50. P

    Electrodynamics Potential from charged sphere. I am lost :/

    ~Electrodynamics~ Potential from charged sphere. I am lost :/ Homework Statement A sphere of radius R, centered at the origin, carries a charge density ρ(r,θ)=κ/r^2(R-2r)sin^2(θ). κ is constant. Find exact potential. Homework Equations 1/4∏ε∫ρ∂t/r The Attempt at a Solution Question and...
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