Electromagnetism Definition and 853 Threads

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. GeniVasc

    Work done via induced charges in a grounded conductor

    I'm currently studying Method of Images in Griffiths book and in section 3.2 he introduces the method of images for a point charge at a distance ##d## from a grounded conducting plane at potential ##V = 0##. In subsection 3.2.3, Griffiths compute the energy of the real system and the image...
  2. B

    Electromagnetism -- What do charges have to do to create EM waves?

    I am not sure, but I think the answer is between acceleration and velocity.
  3. A

    How to insulate an object with electromagnetism?

    Hi. I've got two questions. Is it true that waves with longer wavelengths are handled easier? Think of a scenario where radio-waves insulate a solid object (in a lab for example). How can this be done? Given my understanding, waves don't travel around the environment uniformly.
  4. P

    How Does Dipole Interaction Energy Vary with Orientation?

    Draw graphs showing how interaction energy depends upon the relative orientation of two dipoles if (i) p1 is parallel to r, (ii) p1 is perpendicular to r. I've done the first part and found the interaction energy as UInt = 1/(4*pi*epsilon0*r^3)*[p1.p2-3(p1.r^)(p2.r^)] which I know is correct...
  5. Mr_Allod

    Electromagnetic Induction of a Disk

    Hello I'm having trouble finding the right way to apply Faraday's law to this question. I've found the flux through the disc: ##\phi = \vec A \cdot \vec B = B_{0} \sin{\omega t} \left( \frac D 2 \right)^2 \pi ## and the EMF: ##\varepsilon = - \frac {d \phi} {dt} = -B_{0} \omega \cos{\omega t}...
  6. R

    Size of bremsstrahlung radiation fields generated by linear accelerators

    Hi everyone, sorry we are talking about pulsed power accelerators again. In this context, it is about the HERMES III again. According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf HERMES III, a 16 terawatt pulsed power accelerator at Sandia National Labs, which fired electron beams...
  7. Pi314227

    Electromagnetism: Determining Induced EMF

  8. B

    Electric Potential inside an insulating sphere

    I used the potential at the surface of the sphere for my reference point for computing the potential at a point r < R in the sphere. The potential at the surface of the sphere is ## V(R) = k \frac {Q} {R} ##. To find the potential inside the sphere, I used the Electric field inside of an...
  9. V

    Find the potential using a line integral (Electromagnetism)

    Sorry - I wish I had some way of writing equations in this forum so the "relevant equations" section is easier to read. The answer to the first part is (a) so the rest follows from using the electric field given in B. If anyone is interested this question comes from Griffith's 3rd edition...
  10. oondi

    Electromagnetism: Force between two charged plates

    Hello, I need to find the force between the two metal plates, one is charged positively, and another is charged negatively. I have to use surface integration, but then I get two surface integrations because of the two differently charged plates. Now I am confused. Please help me. Thank you in...
  11. Uchida

    Minimium diameter of an electromagnetic beam in terms of wavelength

    Is there a limit on the minimum diameter that a collimated electromagnetic beam must have (lasers or masers), in terms of its wavelength, or it is possible to create a beam with its diameter smaller than its wavelength? I'm considering a colimated planar wave directly from the source, and not...
  12. F

    Does the theory of electromagnetism have this fundamental problem?

    This is about possible problems with the equations of EM theory of Faraday and Maxwell. EM theory states that when an electron moves a magnetic field is generated. Does this field move with electron in the direction of the electron (if the electron is in motion)? Or, does it stay still in the...
  13. J

    I Falling EM system contradicts the equivalence principle?

    The following is an improved version of my previous post https://www.physicsforums.com/threads/falling-electric-dipole-contradicts-the-equivalence-principle.964594/ Consider the following system comprising a particle on the left with charge ##+q## that is a large distance ##d## away from two...
  14. anaisabel

    Magnetic field (correction term)

    Ampere´'s law with the correction term I have a infinite cylinder with radius R with a current density , and magnetic field . I have to proof that it is acceptable to discard the correction term of term of ampere's law, while calculating the magnetic field, as long as it obeys the following...
  15. K

    E&M: Field of a Wire with non-uniform current

    Summary:: Not sure if my solution to a magnetostatics problem is correct [Mentor Note -- thread moved from the technical forums, so no Homework Template is shown] I was trying to solve problem 2 from...
  16. I

    Wave propagation - Oblique Incidence

    Summary:: A plane wave incident upon a planar surface - determining polarization, angle of incidence etc. 𝐄̃i = 𝐲̂20𝑒−𝑗(3𝑥+4𝑧) [V. m−1 ] is incident upon the planar surface of a dielectric material, with εr = 4, occupying the halfspace z ≥ 0. a) What is the polarisation of the incident wave...
  17. C

    Parameterize Radial Vector of Electric Field due to Spherical Shell

    Homework statement: Find the electric field a distance z from the center of a spherical shell of radius R that carries a uniform charge density σ. Relevant Equations: Gauss' Law $$\vec{E}=k\int\frac{\sigma}{r^2}\hat{r}da$$ My Attempt: By using the spherical symmetry, it is fairly obvious...
  18. K

    Clarification on field intensity (electromagnetism)

    Is the intensity of a general electromagnetic wave always the norm of its Poyinting vector? Or are there other notions of intensity?
  19. Amartansh

    I Intuition behind fields in Transmission lines

    How can traveling wave exist on transmission line if wires are perfect conductors (how voltages can be different at different positions on one perfect conductor)? I mean electric fiels should be zero on equipotential source. I know if length is too long compared to wavelength, we get phase...
  20. Adesh

    Classical Rigorous introductory books on Electromagnetism

    I need some rigorous introductory books on Electromagnetism, by rigorous I mean detailed and mathematical. Many books that I have found don’t actually work out the field produced by current carrying toroid, solenoid or even some other simple electrostatic situations. They just write “by...
  21. S

    Textbooks to be used as references for classical electromagnetism

    Summary:: I need to add references for several classical electromagnetism concepts, I would like to know which books deal with these concepts. Recently a paper about classical electromagnetism that I had submitted was rejected, among other reasons because it contained many references to...
  22. Adesh

    Why does the current have no ##\phi## component in a toroidal coil?

    These are images from the book Introduction to Electrodynamics by David J. Griffiths . . . My problem is that I'm unable to understand how the current has zero ##\phi## component (I have underlined it in the first image)? I do understand cylindrical coordinates, I know...
  23. K

    What topic in Electromagnetism do students find most difficult?

    Is there a topic in electromagnetism that students usually have most difficult understanding than other areas? I'm having a hard time studying diffraction. It's been the most difficult part.
  24. A

    Hello Reality Anyone familiar with the Davisson-Germer Experiment?

    Greetings, I'm happy to find such an enthusiastic community with an encyclopedic knowledge and mathematical rigor. I'm a Biomedical Engineering Researcher that's had to breach into the world of condensed matter physics to better understand the physical principles of the piezoelectric crystal...
  25. Blakely42

    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...
  26. T

    A Magnitude 4-Vector Lorenz Gauge: Klein-Gordon Eq.

    The Klein-Gordon equation is based on the relation (E-eΦ)2-(pc-eA)2=m2^2c2, which is the magnitude of the difference between the momentum four-vector and the four-potential. Since the magnitude of the momentum four-vector is given by E2-p2c2=m2c4, does it follow that the magnitude of the...
  27. M

    Inducing electric current in a wire (a comparison)

    Consider the following experiment: from a lacquered copper wire we cut off twenty to thirty pieces of about 10 cm. From them we form a bundle of parallel wires and connect the two ends with one more wire each. The other ends of these two wires are connected to a sensitive analog ammeter. We hold...
  28. V

    The difficulty of learning Electromagnetism vs Classical Mechanics

    There was an old thread comparing the difficulty of classical mechanics and electromagnetism. The consensus was that electromagnetism is more difficult, and substantially so according to some. The thread was no longer open for replies, but it got me suspecting that we're comparing apples to...
  29. Reneee

    What is the work done to move this Charge?

    I found two formulas to calculate the work done. One is with this path integral: ## W_{AB}## = W(## r_A,r_B ##)=q* ## \int_{r_A}^{r_B} E*dr ## but here is the one I tried to use: ## W_{AB}## = q*Δ U = q*(## \frac {kQ} {r_A} ## - ## \frac {kQ} {r_B} ## ) Now here's my problem, what are...
  30. P

    Solving Electromagnetism problems in 3 dimensions

    i am able to understand problems and solve electromagnetism problems, if the currents are given to be flowing in wires and circle loops in the xy axis. But if they provide similar problems in z axis i am finding it difficult to imagine and do the calculations. My question is any simple concepts...
  31. J

    Conventional current, magnetic fields and magnetic poles of different diagrams

    I need to do question 1. I understand the right hand rules but am lost on what to do here.
  32. K

    B Relativistic explanation of electromagnetism

    I am intrigued by the special-relativity explanation of magnetic force discussed here (linked from the physicsforums FAQ): http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Length_Contraction Naively, from this explanation, it seems that a test charge at rest in the lab...
  33. tworitdash

    A Dirichlet and Neumann boundary conditions in cylindrical waveguides

    The book of Balanis solves the field patterns from the potential functions. Let say for TE modes, it is: F_z(\rho, \phi, z) = A_{mn} J_m(\beta_{\rho}\rho) [C_2 \cos(m\phi) + D_2 \sin(m\phi)] e^{-j\beta_z z} There is no mention of how to solve for the constant A_{mn} . Then, from a paper...
  34. S

    The electric field of a piecewise uniform 1D charge distribution

    This is not really homework, but I'm having trouble understanding it intuitively. I came across this when learning about the space charge layer of a diode. The solution I know simply uses the 1D form of Gauss's law: ##\vec{\nabla} \cdot \vec{E}## = ##\dfrac{\rho}{\epsilon_0}## becomes...
  35. M

    History of the theories of electromagnetism

    I have lately been reading, with interest, the history leading up to Einstein's work as well as some of the debate that ensued after his theories were published. In particular, I was reading some of the ideas Ritz proposed and the disproof of his theories by de Sitter. A question occurred to me...
  36. F

    The Energy in an Electromagnetic Wave and the shape of the Wave

    no need of equations
  37. I

    Electromagnetism EMF induction calculations

    A square conducting loop of side length a is in a non-uniform magnetic field. The loop occupies the first quadrant of the xy plane, i.e. the space between the origin (x, y) = (0,0) and the point (x,y) = (a, a). The magnetic field is in the +z direction. Develop an expression for the magnitude of...
  38. M

    Show that the given Green Function is the propagator of a certain Lagrangian

    My fundamental issue with this exercise is that I don't really know what it means to "show that X is a propagator".. Up until know I encountered only propagators of the from ##\langle 0\vert [\phi(x),\phi(y)] \vert 0\rangle##, which in the end is a transition amplitude and can be interpreted as...
  39. S

    Conservation of energy when placing two inductors next to each other

    This is more like a theoretical question of my own than actual homework. Say there is a circuit with a current source and an inductor. There is a current ##i(t)=at## going through the inductor. We now place a new circuit with an inductor and a resistor next to it. The current ##i(t)## causes a...
  40. I

    Dipole moment from electrostatic potential equation

    Hello to everyone. The question or debate here is how you obtain the commonly known equation of dipole electric moment: from the electrostatic potential equation for a multipole of order n: I understand it is related with Dirac delta functions but a step by step solution might be helpful.Thank...
  41. joneall

    How does gauge invariance determine the nature of electromagnetism?

    In his book, "The greatest story ever told", Lawrence Krauss states: "Gauge invariance ... completely determines the nature of electromagnetism." My question is simple: How? I have gone back thru the math. Gauge invariance allows us to use the Lorenz gauge with the vector and scalar potentials...
  42. G

    How can I calculate the z-component of the magnetic field using the dot product?

    I thought I could replace r^ with z^ and |r|=z since it's only in the z-direction. Is it okay for me to do that? Also, do I need to consider the magnetic dipole moment, m, only in the z-direction as well? Or can I just keep it as m? So assuming that I can replace r^ with z^ and keep m as just...
  43. H

    Does action at distance in electromagnetism violate energyconservation

    Consider two charges A and B separated at distance D. charge B is attached on spring and can move towards and away from charge A. Now charge A is brought closer to charge B and then it is taken back to its original position. Work done in this process is zero because of conservative forces. If...
  44. Amartansh

    Simulating forward electromagnetic scattering for a dielectric

    I want to simulate 2D TM scattered fields (microwave range) for austria profile. Austria profile has 2 circles beside each other of certain dielectric and one ring below the circles. So basically I have three dielectric objects in the domain of interest and also positions of Tx and Rx are known...
  45. C

    Time-symmetry in electromagnetism: a simple puzzle

    All basic laws of physics are said to respect CPT symmetry, and Maxwell's equations in particular are time-symmetric. But here's a simple scenario I find very puzzling: Two particles of opposite charge attract each other. In the time-reversed picture, they'd repel each other, no? But they...
  46. jdou86

    A Understanding time invariant of EM

    on the conquering the physics gre book it says e.g. for time invariant "if you can see someones eyes in a mirror, they can see yours as well" so what the hell does that mean? isnt person A sending photons to person B and person B sending different sets of photons to person A? how does that...
  47. Amartansh

    Classical What Are the Best Resources for Learning Electromagnetic Scattering?

    What are the best resources (books/lectures/articles) to learn Classical Electromagnetic Scattering (forward and inverse modelling)? I am an Electrical Engineer so I would prefer some resource which is from an applied perspective. My specific research topic is related to modeling and analyze 2D...
  48. G

    Relativistic charged particle in a constant, uniform EM field

    I have to find pμ(τ) of a particle of mass m and charge q with v(0) = (vx(0), vy(0), vz(0)) in a electric field E parallel to the y-axis and a magnetic field B parallel to z axis, both constant and uniform, with E = B. Here follows what I have done (see pictures below): I wrote 4 differential...
  49. DamunaTaliffato

    Classical Electromagnetism Book: Find a Brief, Synthetic & Mathematical Guide

    Hi, I've just finished to study Griffith's book, and I would like to read something in order to do a review about electromagnetism. I would like to find a brief book that starts from Maxwell's equation and deals with the topic in a synthetic and mathematical way. A book of up to 150 pages, that...
  50. J

    Why don't electric motors use exciter coils like generators do?

    I remember (long ago, in college physics) learning about electric motors and generators, specifically about the "exciter" coils in generators which did a better job than permanent magnets, because of a sort of "turbo" or force-multiplier effect. I notice, however, that while basically ALL...
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