Electromagnetic field Definition and 235 Threads

An electromagnetic field (also EM field) is a classical (i.e. non-quantum) field produced by accelerating electric charges. It is the field described by classical electrodynamics and is the classical counterpart to the quantized electromagnetic field tensor in quantum electrodynamics. The electromagnetic field propagates at the speed of light (in fact, this field can be identified as light) and interacts with charges and currents. Its quantum counterpart is one of the four fundamental forces of nature (the others are gravitation, weak interaction and strong interaction.)
The field can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. The way in which charges and currents interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. The force created by the electric field is much stronger than the force created by the magnetic field.From a classical perspective in the history of electromagnetism, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner. By contrast, from the perspective of quantum field theory, this field is seen as quantized; meaning that the free quantum field (i.e. non-interacting field) can be expressed as the Fourier sum of creation and annihilation operators in energy-momentum space while the effects of the interacting quantum field may be analyzed in perturbation theory via the S-matrix with the aid of a whole host of mathematical technologies such as the Dyson series, Wick's theorem, correlation functions, time-evolution operators, Feynman diagrams etc. Note that the quantized field is still spatially continuous; its energy states however are discrete (the field's energy states must not be confused with its energy values, which are continuous; the quantum field's creation operators create multiple discrete states of energy called photons.)

View More On Wikipedia.org
Recent contents Top users
  1. R

    Electromagnetic field from electric engine

    Physics is not my forte, but I need some answers re EMFs. I want to buy a 30-ft sailboat that has an electric engine. (I have attached a link to the exact model for reference.) Further, my intent is to live aboard. I have been planning on making my permanent bed right over the top of the...
  2. R

    Electromagnetic field strength

    hello world. it is know that electrostatic (coulomb's law) and magnetostatic (biot-savart law) fields lose their strength like 1/r^2. why do they say that electromagnetic field falls like 1/r ? is that true ? if yes how, can you explain please ? after all energy radiated from a point source must...
  3. C

    What kind of tensor is the electromagnetic field tensor?

    The covariant form of the Lorentz force can be written as m \ddot x^\mu =q F^{\mu \nu} \dot x_\nu and such a relation should prove by the quotient rule that F is indeed a tensor. But what kind of tensor is it? One can show that it transforms from an unprimed to a primed system like F'^{\mu...
  4. 1

    MATLAB [MatLab] Motion of Particle in a spatially varying electromagnetic field

    I have to simulate the motion of particle in an electromagnetic device which deflects particle using electric and magnetic field. Those field are arranged in such a way that the electric field is inside the magnetic one. Moreover the electrodes begin at the center of the magnetic field ad their...
  5. P

    Query on explanation for electromagnetic field - Feynman lectures on physics

    In 2-5, an analogy is given for electromagnetic field: two corks in water, and the effect of jiggling one cork on the other (probably the up and down motion). Now, that sounded more like water is a medium propagating the energy. But the electromagnetic waves require no medium for propagation...
  6. L

    Hamiltonian mechanics electromagnetic field

    Homework Statement Let (V(x,t) , A(x,t)) be a 4-vector potential that constructs the electromagnetic field (in gaussian Units) by E(x,t) = -∇V(x,t) - (1/c)δtA(x,t) , B = ∇xA , (x,t) elements of R3xRt Consider the lagrangian L=.5mv2 - eV(x,t) + (ev/c)(dot)A(x,t) a) compute and interpret the...
  7. Y

    Lorentz Transformations For Particle In Uniform Electromagnetic Field

    Homework Statement A charge q is released from rest at the origin, in the presence of a uniform electric field and a uniform magnetic field \underline{E} = E_0 \hat{z} and \underline{B} = B_0 \hat{x} in frame S. In another frame S', moving with velocity along the y-axis with respect...
  8. E

    Lagrangian for electromagnetic field

    Hi! In some texts (Sakurai - advanced qm and others) I found this expression for the lagrangian of an em field: L=F_{\mu \nu}F_{\mu \nu} but I'm a bit confused... L must be a Lorentz invariant, so I would write instead: L=F_{\mu \nu}F^{\mu \nu} \;\; Which form is the correct one? Or...
  9. J

    Mass of Dirac Electron increased by Electromagnetic field?

    The Dirac electron in the Higgs vacuum field v and an electromagnetic field with vector potential A_\mu is described by the following equation: i \gamma^\mu \partial_\mu \psi = g v \psi + e \gamma_\mu A^\mu \psi where g is the coupling constant to the Higgs field and e is the coupling...
  10. L

    Life on Europa vs. Jupiter's Electromagnetic field

    Hello everyone, First to preface I am not a scientist and have the heart of one (I purchased the heart from eBay... jk). Anyway I have a lingering question regarding Europa: Ok, I get the science about the tidal forces on Europa that flexes the rocky portion of Europa heating up the...
  11. M

    Quantization of electromagnetic field

    Instead of quantizing the vector potential A^μ why we do not directly quantize the B and E fields in electrodynamics.
  12. N

    Electromagnetic field( though could be any field) produced by a quantum particle

    A classical electromagnetic field requires you to know how far away from the source of the field you are, if this requirement is carried over to QED, how is the EM field of a particle known when we only know the probability of this particle being in a certain place?
  13. O

    Schroedinger's Equation for Electromagnetic field induced by charged wire

    Greetings all! I'm completely new to Quantum Mechanics (my PhD research is in Computer Vision) and I am planning to apply some concepts to my research. I would like to know whether it's possible to get the Wave Equation over the components of a \mathbf{B}=(B_\phi,B_r,B_z) field induced by...
  14. L

    Electromagnetic field strength tensor- Magnetic monopoles

    Hey! I stumbled across this problem while reading Wald's "General Relativity", but it belongs to Electrodynamics. In problem 3 of chapter 6 one has to find the general form of a static, spherically symmetric Maxwell tensor, which is clearly F_{ab}=A(r)(dt)_a \wedge (dr)_b+B(r)r(d\theta)_a...
  15. N

    Point charges in an electromagnetic field

    point charges in an electric field Homework Statement Problem: A +8.75 micro C point charge is glued to a frictionless table. It is tied to -6.5 micro C point charge by a 2.5 cm string (weightless and nonconducting). A uniform electric field of magnitude 1.85*10^8 N/C is directed parallel to...
  16. R

    Movement of lone electron in a plane-wave electromagnetic field

    I would appreciate some help regarding the movement of an electron in a plane-wave linearly polarized electromagnetic field. Its simple enough question, but I am not sure what approach to take. Let's say the electron is at rest in our frame of reference and the plane wave is continuous...
  17. D

    Which way is the electromagnetic field moving?

    Hi all I am wondering as this diagram shows. Which way is the electromagnetic field(s) moving? http://www.biophotonicsresearchinstitute.com/Picture1.png Thanks.
  18. T

    Inductor and electromagnetic field with voltage

    I'm having hard time understanding how exactly current that passes through inductor transforms energy into magnetic field and then into voltage, with 90° phase shift. I drew schemes representing sinusoidal imput current, its magnetic field and voltage relation. Is it correct? Would...
  19. A

    Can Earth's Electromagnetic field block asteroids?

    If it can block portions of anti-matter I am assuming. Could it possibly be true, that it can deflect asteroids?
  20. M

    Particle in electromagnetic field

    [PLAIN]http://img23.imageshack.us/img23/421/electromagneticquestion.png A positively charged particle, which charge q and mass m, reached an area with an electric field and a magnetic field. Electric field E is at y>0 and its direction is -y. Magnetic field B is at y<0 and its direction is...
  21. B

    What is the electromagnetic field?

    What is "the" electromagnetic field? I'm not a professional scientist, just a software engineer with a fascination for how our world works. I thought I'd plug into some of the smart minds here to see if I could make some sense of some things I'm not quite understanding. I've been reading...
  22. C

    Magnetic or Electric Field or Electromagnetic Field?

    Bob Reference Frame: A charged particle moves through a uniform magnetic field with velocity V. No electric field is present and gravitational forces may be neglected. The charge thus experiences a force due to this magnetic field equal to F = qV x B. B is the strength of the magnetic field...
  23. C

    Puzzled about electromagnetic field behaving like oscillators

    i am having some problem in unerstanding a concept explained in my book in the chapter harmonic oscillators. as an example of this, it says, is the electromagnetic field, where A (vector potential) plays the role of the co ordinate and its dot plays the role of velocity in the oscillator...
  24. S

    Electromagnetic field in vacuum

    hi, just to be sure, I believe that an electron in complete vacuum, that does not interact, carries an electromagnetic field, and that this electromagnetic field is mediated by virtual photons even when there is only one electron, in vacuum, that does not interact. is that statement correct?
  25. Z

    Poynting vector in static electromagnetic field

    There is a situation, we have an electric field and a magnetic field, both are static. And we know the density of energy is u=E·D/2+B·H/2, so dU/dt=0, but Poynting vector S=ExH is not zero, which means energy is flowing. This confused me. Static field also has energy flux?
  26. E

    Existence of electromagnetic field

    Do electric and magnetic fields occur simultaneously in the same spot anywhere around the globe? (other than during solar flares) If the field is named "electromagnetic" wouldn't that means exactly this simultaneity? Thank you.
  27. P

    Tensor of electromagnetic field

    F_{\mu\nu}=\frac{\partial A_{\nu}}{\partial x^{\mu}}-\frac{\partial A_{\mu}}{\partial x^{\nu}} F_{\mu\nu}=-F_{\nu\mu} F_{ii}\equiv 0 F_{11}=F_{22}=F_{33}=F_{44}=0 where A_{\mu}=(-\vec{A},\frac{1}{c}\varphi)(F_{\mu\nu})=\left(\begin{array}{cccc} 0& -B_z&B_y& -\frac{1}{c}E_x\\ B_z&0&-B_x&...
  28. P

    Impulse of electromagnetic field

    We have \vec{F}=\int_V\vec{f}dV=-\frac{d}{dt}\int_V(\vec{D}\times \vec{B})dV \vec{g}=\vec{D}\times \vec{B} \vec{F}=-\frac{d}{dt}\int_V\vec{g}dV \vec{F}=\frac{d\vec{p}_{mech}}{dt} \frac{d}{dt}(\vec{p}_{mech}+\int_V\vec{g}dV)=0 \vec{p}_{mech}+\int_V\vec{g}dV=\vec{const} In total field law...
  29. R

    Uncertainty principle and electromagnetic field

    hi, I have a question about the uncertainty principle. if an electron is in attractive OR repulsive electromagnetic field, is its uncertainty about its position lower than if it is a free electron? I believe particles are more random, with a higher entropy when there is less...
  30. B

    How to quantize electromagnetic field in media?

    How to quantize electromagnetic field in media? Especially in the case where the medium is dispersive and anisotropy.
  31. V

    What is the Electric Field of a Ring with Uniform Surface Charge Density?

    Homework Statement A thin, circular ring of inner radius a and outer radius b carries a uniform surface charge density \sigma (i) Find an expression for E at a point on an axis perpendicular to the plane of the disk, the axis passes through the centre of the disk. (ii) Keeping the surface...
  32. R

    Photons governing the electromagnetic field

    As I understand it photons govern the electromagnetic field. I don't have an intuitive knowledge of what that means. Does anyone have an explanation, link or reference for an intuitive interpretation? So if I rub a latex balloon against my clothes and then put it near my arm, I'll see all...
  33. P

    Is Biot-Savart law the only way to calculate energy density of magnetic fields?

    I wonder why we always assume that electromagnetic field energy density is w = \frac{1}{2}(E^2+B^2) . In fact energy of the filed can be any function w for which there exists such vectror field \vec{S} that continuity equation is fulfilled: \vec{E} \vec{J}+\frac{\partial w}{\partial...
  34. H

    Electromagnetic field question

    Homework Statement How would you find the magnetic field B inside the large field coil after you measured the induced emf on a test coil? Homework Equations i am not sure. The Attempt at a Solution i need some help in how to start this as i have 0 clue
  35. D

    Finding current in electromagnetic field

    A powerful electromagnet has a filed of 1.6 T and a cross-sectional area of .20 m^2. if we place a coil having 200 turns and a total resistance of 20 ohms around the eclectromagnet and then turn off the power to the electromagnet in 20ms, what is the current induced in the wire? R = 20 N =...
  36. A

    Electromagnetic field, Gauss’ Law questions

    Hey guys, help needed! Bad lecture, no idea what to do! The Q1 is: Q. 1 Three point charges are placed at the apexes of an equilateral triangle as shown in diagram. Calculate the net force on (a) the 5 μC (= 5 × 10‐6 C) charge and (b) the ‐6 μC charge. Give each answer in the form a i + b...
  37. H

    Is the electromagnetic field quantized?

    Hi! I'm not a physicist. Just trying to get a feeling og matter, space and time without having to do the math (How DO you understand it?!?) Still I have a question. Is the electromagnetic field of a particle quantized - except for either being there og not being there? Does - for example -...
  38. Q

    Electron in oscillating electromagnetic field

    Hi ! How one can calculate the spectrum of radiation emitted by the oscillating electron in the field of laser, the electric field of laser can be written as, E = Eo cos(w t) So, is the electron will emit the secondary radiation with same frequency 'w' or there will be a...
  39. T

    Electromagnetic Field Detector

    I am looking for an electromagnetic field detector that can detect use to detect the intensity of wave on a grid and return the results to a computer. the higher the resolution the better. does anyone know where this can be purchased? how could one be designed?
  40. Barbara.Ba

    A particle moving in an electromagnetic field

    Dear Friends A particle having charge q and mass m moves in a region where an electric field E = ( 0 , E_0 , 0 ) and a magnetic one B = ( 0 , 0 , B_0 ) exist. For t = 0 its position is R = ( 0 , 0 , 0 ) and its velocity is V = ( V_0 , 0 , 0 ). I have worked out the...
  41. M

    Gauss' Law as a derivative of the electromagnetic field tensor

    Homework Statement Prove \nabla \bullet E =4 \pi \rho from \partial_{\beta}F^{\alpha \beta}=4 \pi J^{\alpha} where J^{\alpha}=(\rho, J^{1}, J^{2}, J^{3}). Homework Equations We are given that F_{\alpha \beta} is 0~~~~E_x~~~E_y~~~E_z -E_x~~~0~~~~-B_z~~B_y -E_y~~B_z~~~~0~~~-B_x...
  42. Q

    Solve EM Radiation Homework: Compute E & B with Monochromatic Point Source

    Homework Statement We are given monochromatic point source of EM radiation which power is P=100W. The task is to compute E(r) and B(r). We can assume that r is large enough to treat wave as a plane wave. Homework Equations The Attempt at a Solution First of all - what for do we...
  43. M

    Rank 3 tensor created by taking the derivative of electromagnetic field tensor

    Homework Statement Show that the rank 3 tensor S_{\alpha \beta \gamma}=F_{\alpha \beta , \gamma} + F_{\beta \gamma , \alpha} + F_{\gamma \alpha , \beta} is completely antisymmetric. I just don't feel comfortable doing this stuff at all. Each of the three terms seems like they should be...
  44. Bob_for_short

    Electromagnetic field in a medium

    An electromagnetic field, as a plane wave, has a known space-time dependence: E = E0cos(ωt-kx). In a transparent medium it is the same except for involving the refraction indices n. Now, let us look at the field in a moving reference frame - that with v = c/n. What solution is for the...
  45. J

    Electromagnetic field, finding beta.

    Hi, I am not sure whether this falls into a math category or here, I hope you can help me. I came across a problem in a book [bare with me, please] (Fundamentals of engineering electromagnetics by Cheng) and asked my electromagnetics profesor, but his response did not help me into getting to the...
  46. J

    Behaviour of ionized air when subjected to an electromagnetic field

    Hello, my name is James Dallas and am new to this forum. I am a first year electromechanical engineering student in Ontario, Canada. While looking through the net I ran across this thread. https://www.physicsforums.com/showthread.php?t=80986&page=3 rather than necro post I thought I...
  47. D

    How to determin the momentum eA of electromagnetic field?

    I got a question when I was reading a paper, it describe a periodic structure composed of many infinite metal wire, and then try to calculate the momentum per unit length of the wire like these when there is current through wire: electrons in a magnetic field have an additional...
  48. Y

    How do moving electric fields create magnetic fields?

    I have a bit of trouble with understanding how electromagnetic fields. More specifically, how the magnetic and the electric component of the field interact. I am aware that a time-varying electric field will generate a magnetic field and vice versa. What I am having trouble understanding is how...
  49. P

    Homogeneization of physic formula of electromagnetic field and velocity

    https://www.youtube.com/watch?v= I have a little problem with a formula, that I think it's not ok. It gives to me the result of units of electric potential (\vec A ) and velocity \vec v . The result seems to be volts per velocity, and I don't know it there exists this unit, or is a mistake...
  50. M

    Effects of an electromagnetic field moving at reletavistic speeds

    before I go into this please allow me to explain I don't know where else to ask this, so I am asking here. I have had this idea for a few years now and I cannot figure out if I am correct, in what I assume will happen under these conditions Homework Statement Well the idea is this, if one...
Back
Top