What is Electromagnetic fields: Definition and 77 Discussions

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.)

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  1. M

    B Multiple frequency EMFs and capacitors

    In an RC low-pass filter, low frequencies pass through the filter, and only signals with high frequencies pass through the capacitor (where they are filitered out), and that happens because for low frequencies, the capacitor is charging, so they are blocked, while high frequencies don't allow...
  2. cianfa72

    I Confused about electromotive forces

    Hi, reading Griffiths - Introduction to Electrodynamics I'm confused about his claims in section 7.1 My point is that the job of electromotive force ##f## is actually produce the "movement/drift" of free charges against the electromagnetic field, so ##f## should not be given by the Lorentz...
  3. rudransh verma

    B Is the Kink in the Electromagnetic Wave Responsible for Delayed Motion?

    I was reading Six easy pieces from Feynman and I got stuck what is electromagnetism 2 years ago. Recently I came across a video and I think I have figured it out. The paragraph says like this: “ If we were to charge a body, say a comb, electrically, and then place a charged piece of paper at...
  4. Glenn Rowe

    I Lorentz Transforms of Electromagnetic Fields

    The Lorentz transformations of electric and magnetic fields (as given, for example in Wikipedia) are $$ \begin{align*} \bar{\boldsymbol{E}}_{\parallel} & =\boldsymbol{E}_{\parallel}\\ \bar{\boldsymbol{E}}_{\perp} &...
  5. sophiatev

    I Transformations of Electromagnetic Fields: Griffiths' Claims

    In Griffith's Introduction to Electrodynamics, chapter 12, he discusses how electromagnetic fields transform when we move from one inertial reference frame to another. On page 553, he claims He then considers how the electric field inside a conductor made up of two parallel rectangular plates...
  6. Ascendant78

    I Create Black Holes with Warping EM Fields: Feasible?

    As a prior physics major (had to stop at my 3rd year of undergrad due to children and financial difficulties), there was something I was always extremely passionate about - finding feasible ways to travel faster than light. Obviously, the only feasible way seems to be to bend space-time, but I...
  7. D

    I Electromagnetic Fields and the manipulation of Space-Time

    Summary: Mathematical and Physical queries in regards to Electromagnetic Fields and their manipulation of Space-Time. I recently started looking into Einstein's Field Equations, to get a better understanding of how mass distorts and curves the plane of Space-Time, however from doing this I...
  8. E

    Electromagnetic fields are polarised when leaving a dipole antenna....

    at a point they become plain waves, how much will they be attenuated when 'received' by a spiral log periodic antenna Vs another dipole? Would an H field created by a loop antenna have less attenuation?
  9. A

    What is the magnetic field generated by these two particle beams?

    A uniform beam of positively charged particles is moving with a constant velocity parallel to another beam of negatively charged particles moving with the same velocity but in opposite direction separated by a distance d. Then, how should be the variation of magnetic field B along a...
  10. ZuperPosition

    Abstract definition of electromagnetic fields on manifolds

    Hello, In the sources I have looked into (textbooks and articles on differential geometry), I have not found any abstract definition of the electromagnetic fields. It seems that at most the electric field is defined as $$\bf{E}(t,\bf{x}) = \frac{1}{4\pi \epsilon_0} \int \rho(t,\bf{x}')...
  11. R

    Generating electromagnetic fields with an electromagnet

    Hello, I am working on a science project to generate electromagnetic fields. From what I understand, the simplest way to do that is to coil copper wire around an iron core. My initial goal is to create a magnetic field with a maximum strength of 500 microtesla. Can this be accomplished if I...
  12. A

    Special relativity - transformation of electromagnetic fields

    Homework Statement In a reference frame ##S## there is a particle with mass ##m## and charge ##q## which is moving with velocity ##\vec{u}## in an electric field ##\vec{E}## and in a magnetic field ##\vec{B}##. Knowing the relativisitc laws of motion for a particle in an EM field, find the...
  13. CAT 2

    Problems with electromagnetic fields

    Homework Statement Copy the following diagram and draw field lines for both magnetic fields. Then, use them to determine the direction of the force acting on the conductor. HINT: Check your answer, using the right - hand rule for the motor principle. Their diagram: 2. Relevant equation n/a...
  14. V

    I Gravitational Waves Affecting EM Fields: Evidence & Implications

    Suppose a gravitational wave propagating through space encounters a strong magnetic field (for example the wave might pass through a magnetar with a B field strength of 10^{11} Tesla). Would there be any observable perturbation in the magnetic field itself? In other words would the gravitational...
  15. S

    B Electromagnetic fields of fundamental particles -- help please

    Hi, we know that the particles have intrinsic properties for them electric field and magnetic moment, but for what I mean particles, I mean quarks, the fundamental blocks of (protons, neutrons and mesons) with everything that nobody explained as electric and The magnetic field of a particle and...
  16. S

    What is the effect of electromagnetic fields on the Earth's

    What is the effect of electromagnetic fields on the Earth's magnetic field? Electric energy in the transmission and use of the process, will produce electromagnetic field, the electromagnetic field will have an impact on the Earth's magnetic field? I think it is possible to cause the...
  17. S

    What is an electrostatic/Coulomb barrier? How is it created?

    I learned that for nuclear fusion to take place, particles must overcome the electrostatic field but what exactly is it? And how is it created/formed?
  18. 9

    Total moment density of electromagnetic fields

    Homework Statement These is a problem from my textbook. You have an infinite solenoid with n turns per unit longitude, radius "a" and a stationary current I. In the axis there exits a uniform line charge with lineal density λ. Compute total electromagnetic momentum (lineal and angular)...
  19. peasqueeze

    E and B fields for charged particle's parabolic motion

    I am looking to find a combination of electric and magnetic fields that create something similar to the (d) crests Currently, I have the cracks flipped clockwise 90deg, so that the crests are concave up. And each crest can be defined by a parabolic function (which are uniform with each new...
  20. Y

    Electromagnetic Fields due to Accelerating Charge

    Homework Statement What are the electric and magnetic fields due to a charge that is moving with uniform acceleration? (Non relativistic) Homework Equations Retarded solutions for the vector and scalar potentials. The Attempt at a Solution My attempt might be an overkill because I'm using the...
  21. D

    Doubts regarding Electromagnetic fields

    I read in a book that Electromagnetic fields propagate at speed of light and carry energy and momentum. Let's take electric field for example. Electric field is none other than a force per unit coulomb.So 1.How could a force(here field) move as force has no property of moving as force causes...
  22. A

    Understanding Electromagnetic Field Propagation: Insights and Formulas

    Homework Statement Hi this is my first post I hope that my explanation is good. Now this is the explanation. Now I will provide the known values. So I start looking literature and some formulas to solve this and I found two different propagation constants. Gama and Beta. Homework...
  23. M

    Help with radio waves and electromagnetic fields

    I need help explaining that this assumption is not correct or correct: A product uses Radio waves to turn on a LED. Radio waves can be a form of electromagnetic fields therefore, a Hall Effect sensor could be used in this device to turn on that LED.
  24. B

    Electromagnetic fields derivation

    Homework Statement In a book I find the following derivation: \int (J \cdot \nabla ) \frac{\bf{r} - \bf{r}'}{|\bf{r} - \bf{r}'|^3} d^3\mathbf{r'}= -\sum_{i=1}^3 \int J_i \frac{\partial}{\partial r_i'} \frac{\bf{r} - \bf{r}'}{|\bf{r} - \bf{r}'|^3} d^3\mathbf{r'} \\ = -\sum_{i=1}^3 \int J_i...
  25. R

    Total energy and power of electromagnetic fields

    Homework Statement Consider the charging capacitor in problem 7.34 (A fat wire, radius a, carries a constant current I, uniformly distributed over its cross section. A narrow gap of wire, of width w, w<<a, forms a parallel-plate capacitor) a) Find the electric and magnetic fields in the gap, as...
  26. I

    Why do electromagnetic fields exist where there is no matter

    Wikipedia define EM field as "a physical field produced by electrically charged objects" But there are no electrically charged objects in between cosmic entities and yet Wiki states "The electromagnetic field extends indefinitely throughout space". What am I missing here?
  27. Domenico94

    Cancer Therapy - Electromagnetic fields

    Hi everyone. I'm an electronics eng. student, and, during my studies, and my life outside university, I've heard several times of how electromagnetic fields could affect our body, in a way or another. There are also various resources talking about how these fields can attack cancer...
  28. D

    Neutrons in electromagnetic fields

    Consider a moving neutron passing by an electromagnet, will a neutron be deflected? This video seem to show that the neutron would have to be charged in order for it to move
  29. Bassirou

    Wangsness book "Electromagnetic Fields"

    Hi guys! I was wondering if someone could me help to get a free electronic copy of R. Wangsness book "Electromagnetic Fields". I would like to point out that I am just looking for a book which does not violate copyrights.
  30. G

    Manipulation of Electromagnetic fields using curls clarification

    Homework Statement Question 1. General Plane Waves. We may represent a general electromagnetic plane wave by (real part of the complex exponentials) E=E_{0}*e^(i*k*r-iwt) B=B_{0}*e^(i*k*r-iwt) Show that Faraday's Law becomes iwB0=-ik x Eo Homework Equations dB/dt=- curl of E The...
  31. F

    How Do Magnetic Field Lines Behave Around a Long Current-Carrying Wire?

    Hello, I'm stuck on this question, and it's really annoying me. I scanned the page so it has a bit more context. It's question 3.7: "A long wire carrying a steady current is placed in a uniform magnetic field parallel to it's own length. What is the shape of the magnetic field lines...
  32. J

    Electromagnetism Electromagnetic fields

    Hi all, can the angular frequency of a electric waves be used to determine the wavelength using the following; ω=2πf rearranging for the frequency, and using the following; E=hf=(hc/λ) or can this formula no be used as it is dealing with photons?
  33. H

    Coplanar Electromagnetic Fields

    Homework Statement The permittivity of a given medium is given by the equation ε = \begin{pmatrix} ε_1 & 0 & 0\\ 0 & ε_1 & 0\\ 0 & 0 & ε_2 \end{pmatrix} A wave is traveling in the \hat{k} direction in this medium where the unit vector \hat{k} is defined as \hat{k} =...
  34. P

    Evidence of Electromagnetic fields causing spacetime curvature?

    Hi All, Just wanted to know, is there any experimental or observational evidence today, that electromagnetic fields can cause spacetime curvature? Either direct or indirect?
  35. Astronuc

    Time-Harmonic Electromagnetic Fields by Roger Harrington

    Author: Roger Harrington Title: Time-Harmonic Electromagnetic Fields (IEEE Press Series on Electromagnetic Wave Theory) Amazon Link: https://www.amazon.com/dp/047120806X/?tag=pfamazon01-20 Prerequisities: Undergraduate degree in Electrical Engineering or Physics, with appropriate...
  36. S

    Modify crystallization process by electromagnetic fields?

    Has anyone come across an example where electromagnetic fields have been applied during crystallization processes. For example to modify crystal properties like magnetization or to change the polymorphism. In principle the use of electric / magnetic fields should change the formation of a...
  37. M

    Needing Tips for Electromagnetic Fields Class

    Just posting to ask if anyone has any tips to give for a student in a Junior level Electromagnetic fields class. We usually get about 10-20 problems/week and I manage to only get 6-7 of them done every time. Also, though I generally do well with it, I'm struggling to find the energy to read...
  38. F

    Electromagnetic fields of a rotating solid sphere: total charge inside

    Homework Statement A solid sphere of radius a rotates with angular velocity ω\hat{z} relative to an inertial frame K in which the sphere's center is at rest. In a frame K' located at the surface of the sphere, there is no electric field, and the magnetic field is a dipole field with M=M\hat{z}...
  39. iVenky

    Electromagnetic fields and Maxwell's equations

    Basically I couldn't understand Maxwell's equations during my college days mainly because I didn't understand divergence and curl intuitively. I need some good book on Electromagnetic Fields (such as Gauss Laws and so on) and also I want to learn about Maxwell's equations. I want to...
  40. A

    Biot-Savart's law of magnetic field electromagnetic fields

    Biot-Savart's law of magnetic field " electromagnetic fields" Homework Statement A rectangular loop carrying 10 A of current is placed on z=0 plane as shown in figure . Evaluate H at a) (2,2,0) b) (4,2,0) c) (4,8,0) d) (0,0,2) Homework Equations the used...
  41. E

    Electromagnetic fields and microwaves

    I need some help with properties of electromagnetic fields in the presence of microwaves. specifically will a electromagnets field, powered by an external power supply, function normally in a microwave chamber? Will the magnetron induce a current in the copper coil? Would the external power...
  42. M

    [Electromagnetic Fields] Electrical conductivity of a material

    Homework Statement Two inflnitely long, straight, parallel Wires are embedded in an infmite medium of conductivity 2 Sm-1. The wires are identical, with a round cross-section of radius 0.25 cm. The centres of the wires are 1 cm apart. Find the conductance per metre between the wires. A)...
  43. T

    Explaining Electromagnetic Fields: Mass and Distance

    I have skimmed relevant links in wikipedia, and some external links regarding electromagnetic fields, but would like a simple (I'm no physicist) answer to the following question that I have. When one, for example, takes two strong permanent magnets and aligns so that there is repulsive/or...
  44. S

    Electromagnetic Fields and Effects of Oscillation

    The electrical circuits in a house run on alternating current. This is a current of electrical charges that oscillates back and forth at a frequency of 60 Hz. Do these currents produce magnetic fields? Explain. Do these circuits radiate electromagnetic waves? Why or why not? I don't have any...
  45. S

    Photons vs. Neutrinos in electromagnetic fields

    I have been wondering why photons can't go through matter and electromagnetic fields mostly unaffected while neutrinos can. Neither of them have an electric charge as a particle, and the basic description I see about neutrinos is always that "they are unaffected because they have zero electric...
  46. V

    Problems with electromagnetic fields inside matter

    Homework Statement see attachment/picture im having problems with fields inside matter. i get the left side of gaussian surfaces/ampere loops. but for example this first equation's right side i can't understand. The Attempt at a Solution i would think the right side should be I since...
  47. N

    Electromagnetic fields and empty space

    is it possible for electromagnetic field to exist without matter?
  48. G

    Electromagnetic fields: Eletric potential inside a non conductive sphere

    Homework Statement Hello all; i am trying to calculate the potential, inside a non conductive sphere of radius equal to a, in a point at a distance r from the center of the sphere. Homework Equations i know that: where E and s are vectors; and that the Eletric field inside the...