Electromagetic field Definition and 61 Threads

No Wikipedia entry exists for this tag
  1. cianfa72

    I Do electromagnetic fields have momentum?

    Hi, reading Feynman's lectures on section 10-5 I came up with a question. He claims that electromagnetic fields have momentum. He gives an example of two charges A and B in a electromagnetic field. When the charge A is suddenly moved (as I understand by an external force w.r.t. the "A + B"...
  2. cianfa72

    I Video: 'How electricity actually works'

    Hi, I found this interesting video about How electricity actually works. The point he makes (see for example the video at minute 7:23) is that the energy in a light bulb connected to a battery is actually transferred by the electromagnetic field and not by electrons flowing through it. The...
  3. K

    Force Between 2 Coaxial Current-Carrying Loops

    I have attempted to solve it as follows: Using the Biot-Savart law, I found the flux density at the centre of the smaller coil due to the bigger coil as: $$\frac{\mu_0 I b^2 N_2}{2(a^2 + b^2)^{1.5}}$$ where a is the distance to the coil (10cm), N2 is the number of loops in the larger coil (50)...
  4. cianfa72

    I Macroscopic objects in free-fall

    Hi, very basic question. Take an object like a rock or the Earth itself. If we consider their internal constituents, there will be electromagnetic forces acting between them (Newton's 3th law pairs). From a global perspective if the rock is free from external non-gravitational forces, then it...
  5. user2539

    Magnetic equivalent circuit for a UU-core inductor

    Hello, I am trying to develop a magnetic equivalent circuit for a UU-core inductor with two parallel bus bars in the middle of the slot. I am not sure as to how to model the MMF in such problem. The logical way in my mind is to have two current sources to represent the fields of each bus bar...
  6. cemtu

    I How does the electrical field become bent instead of following a straight line?

    Why is electrical field bent like that rather than following a straight line across to the relevant point over there?
  7. R

    Engineering How to calculate the interference voltage?

    Hello everyone, I have this circuit and I need to determine the interference voltage. I am not sure, where the interference voltage is applied and how to determine it. I think the interference voltage is uv nad my equivalent circuit looks like this: Am I in heading into the right direction...
  8. Salmone

    I Two molecules with different polarizability in an EM field

    If I have two separated and non-interacting molecules with different constants polarizabilities ##\alpha_1## and ##\alpha_2## and I send an EM field of frequency ##\omega## first on the molecule no.##1## and then on the molecule no.##2## so that the two molecules will have a dipole moment...
  9. E

    B Virtual photons as force carriers

    (My multipart question is from a very naive perspective, so sorry if it is rife with misunderstandings. Please answer conceptually, with as few & as simple equations as possible. I think that all of the answers to these questions should be understandable to a high schooler, though maybe the...
  10. M

    Amplify ferrite core solenoid electromagnetic range

    Hello all, I'm playing around with a PIC + LCC Tank to send - at a 5MHz frecuency - some numeric data via BPSK. The receiver is a loop antenna placed in the ground. The sender antena (L) is a ferrite core solenoid (N=10). As having a larger core, or increasing the Number of coils around the...
  11. Narayanan KR

    A Question on Skin Effect and Eddy Currents

    When you try to create time varying magnetic fields in solid metals, there is severe heating due to eddy currents, when you increase the frequency, just like in NDT(non destructive testing) the magnetic field is pushed away from the core to the periphery due to eddy currents opposing the field...
  12. Narayanan KR

    An Interesting Question on Faraday's Law of Electromagnetic Induction

    On examining Maxwell's third equation which is about time varying magnetic fields (Faraday's electromagnetic induction) we find that time varying magnetic fields produce loops of electric fields in space irrespective of whether a coil is present or not, if any coil is present then these loops of...
  13. F

    Four-momenta trend as a function of proper time

    As a starting point I immediately thought about the equation: ##\frac{dp^\mu}{d\tau}=qF^{\mu\nu}v_\nu## From this I proceed component by component: ##\frac{dp^0}{d\tau}=qF^{0\nu}v_\nu=q\gamma E_yv_y## ##\frac{dp^1}{d\tau}=qF^{1\nu}v_\nu=q\gamma v_yB_z##...
  14. F

    Lorentz transformations for electric and magnetic fields

    Good evening, I'm trying to solve this exercise that apparently seems trivial, but I wouldn't want to make mistakes, just trivial. Proceeding with the first point I wonder if my approach can be correct in describing this situation. From the assumptions, the two fields are in this...
  15. E

    Waveform produced by a collapsing magnetic field

    A thought experiment: A electron is moving in a straight line at velocity v. It instantly stops dead. It doesn't move another femtometer. Obviously its magnetic field collapses and produces light. What is the waveform of the light produced? Is it something like this...
  16. P

    I Irreducible Representations of EM-Tensor Under Spatial Rotations

    Can we consider the E and B fields as being irreducible representations under the rotations group SO(3) even though they are part of the same (0,2) tensor? Of course under boosts they transform into each other are not irreducible under this action. I would like to know if there is in some...
  17. 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} &...
  18. Pyter

    A Help on some equations in Einstein's original papers

    Studying Einstein's original Die Grundlage der allgemeinen Relativitätstheorie, published in 1916's Annalen Der Physik, I came across some equations which I couldn't verify after doing the computations hinted at. The first are equations 47b) regarding the gravity contribution to the...
  19. 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...
  20. M

    Suggest a geometry for headphone's speaker system

    Summary:: Suggest a geometry Hello! I have difficulties with this question. It is translated from Swedish so if something's weird tell me. The speakers in headphones often work with the help of magnetism, when a varying voltage is applied across a coil attached to the speaker membrane. The...
  21. E

    Create a method to measure a varying voltage from a power line

    I feel like i am spinning my wheels at the start here. so I figured that i would start with some type of wire loop that I could change its diameter. This would allow there to be a change in flux through the loop creating a current through the wire. i could then read the current through the...
  22. stanley

    Impact of frequency on Faraday cages

    I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0. Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able...
  23. Bernardtai

    Possible to connect two electromagnets perfectly together?

    Mission: create a pair of electromagnets which always connects (angel) perfectly together. Initially, I design with the following 3 ideas, could any design possible to achieve? 1) First idea is to separate 5 iron core, all close to the edge and connect to the battery source. this attempt is...
  24. E

    TE and TM modes in optical fibers

    In a step-index optical fiber, considering Bessel functions of order ##\nu = 0## and no ##\phi## dependence, it is possible to obtain two separate sets of components, which generate respectively TE and TM modes. In the former case, only ##E_{\phi}##, ##H_r##, ##H_z## are involved; in the latter...
  25. Riotto

    A Canonical momentum ##\pi^\rho## of the electromagnetic field

    In David Tong's QFT notes (see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , page 131, Eq. 6.38) the expression for canonical momentum ##\pi^0## is given by ##\pi^0=-\partial_\rho A^\rho## while my calculation gives ##\pi^\rho=-\partial_0 A^\rho## so that ##\pi^0=-\partial_0 A^0##. Is it...
  26. N

    Formula to calculate the pull force between a magnet and a steel plate

    i have a neobydium magnet of grade n40 , the diameter of magnet is 15mm and thickness is 10 mm , now i want to calculate the pull force between this magnet and a steel plate when there is no gap between them ; & in second case i want to calculate the pull force when i put a 0.15mm copper plate...
  27. H

    Calculating the final velocity of a simple electric train

    I am currently in grade 12, and for a physics project (a huge project, which gets assigned to you at the start of the semester and needs to be completed just before exams. You think up your project, make a proposal for it and you prove your hypothesis to be right after a presentation and lab...
  28. O

    I Does a conductor E field include a tangential component?

    Background: an ordinary wire supports an external radial electric field proportional to voltage, and an internal axial field equal to current times resistance per unit length. The present question is whether the internal axial field has an external counterpart. The original question that...
  29. T

    Can a Copper Coil Harvest Power from Power Lines for an FM Radio Receiver?

    I had an idea of building an FM receiver that is powered from the electromagnetic fields generated by power-lines. My question is , how can I make the electromagnetic field receiving antenna? Will a simple copper coil work? If so, can the same coil be used as the RF antenna or will that have to...
  30. AdrianHudson

    I Particle Focusing using EM fields

    Good day all! I have a question that has been in my head bouncing around for a while and I figured the best resource would be here as I can't find anymore related information (Or I am just looking in the incorrect spot). My apologies if this is in the wrong section I wasn't too sure where to...
  31. Irl495

    Rotating magnetic field effect on aqueous mixing (opinions?)

    This is question that can't really get a precise answer without significant modeling or experimentation, but I'm wondering what folks' intuition might be on an answer to the following setup + question: Suppose there is a steel tank made of steel pipe with walls about 0.25 cm thick, internal...
  32. 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...
  33. S

    How an electric field is absorbed by a dielectric

    when a em waves strikes a dielectric the atoms vibrate in response to the electric field and if the frequency matches the resonant frequency the Lorentz oscillator the electric field is absorbed how a field can be absorbed we know the em field contain energy how is the em field destroyed is some...
  34. T

    Is Magnetism Both Energy and Force?

    My question is magnetism energy or force? On the one hand, it is energy because it can be transformed to say electricity, on the other hand is the force because, say, in the alternator, it transfers the mechanical to the electric energy .
  35. E

    Gauss' Law for electromagnetic radiation?

    For the proof I've read that verifies transverse electromagnetic waves are consistent with Gauss' Law, there seems to be the suggestion that the magnetic and electric field at a given small length c(dt), along which the waves travel, propagate infinitely backwards and forwards in their...
  36. C

    Application of Biot-Savart Law for Finite Wire: Exploring Point P and P_1

    Hi, I've got a question regarding application of the Biot-savart law along finite wire. There is a great explenation of this problem in the MIT paper but this does not cover one case. 1. Homework Statement My question is: does the equation defining magnetic field in point P(x,y) also applies...
  37. C

    A Question about derivatives of complex fields

    https://arxiv.org/pdf/1705.07188.pdf Equation 5 in this paper states that $$\frac{\partial F}{\partial p_i} = 2Re\left\lbrace\frac{\partial F}{\partial x}\frac{\partial x}{\partial p_i}\right\rbrace$$ Here, p_i stands for the i'th element of a vector of 'design parameters' \mathbf{p}. These...
  38. A

    Why is del(E_t) zero in TEM mode of transmission lines?

    I was going through MIT opencourseware https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-013-electromagnetics-and-applications-spring-2009/readings/MIT6_013S09_chap07.pdf and I didnt understand exactly why in equation 7.1.37 and 7.1.38 in page 192 the divergence of...
  39. A

    What is a magnetic field "made" of?

    I have looked this up on several occassions and never satisfied. It seems that either the answer keeps repeating magnetic or electromagnetic field over and over. Or the answer discuss the properties of electromagnetism. Is the field a wave/particle like a photon ? Is it emitted like a photon...
  40. infi

    Does an electromagnetic shield reflect?

    Let say a nanoparticle (graphene) is electromagnetic shield. If we send a pulse of magnetic wave will it get reflected back. If it reflects can that be interpreted. And what happens if there going to be infinite EM shielded nanoparticles. Is that any kind signal which will reflects back from...
  41. F

    Physical degrees of freedom of an Electromagnetic field

    As I understand it, the classical source-free electric, ##\mathbf{E}## and magnetic, ##\mathbf{B}## wave equations are solved by solutions for the electric and magnetic fields of the following form: $$\mathbf{E}=\mathbf{E}_{0}e^{i (\mathbf{k}\cdot\mathbf{x}-\omega t)}$$...
  42. cluelessGUY

    Electromagnetic Coil 2 SS Rods Converging

    Howdy all, I'm looking at having two (preferably) stainless steel rods inside a plastic tube (for insulation and so they don't touch) with a push spring inside and between the two rods pushing each other away from one another, when not activated inside of an electromagnetic coil. When the coil...
  43. R

    Capacitor with uniform space charge between them

    Homework Statement 2 large plates are separated by a distance d and a space charge of uniform charge density p is placed between them and a potential difference V is applied across the plates. Find the electric field stength at a distance x fromt the positive plate The answer is -V/d...
  44. ThunderLight

    What composes the E Field of the Electromagnetic Wave?

    What composes the E Field of the Electromagnetic Wave where "disturbances" for propagation occurs? If electromagnetic waves cause disturbances in the Electric Field… what “is” in this E Field which photons Interact with? I ask because in Vacuum, there are no electrons to excite. So what is...
  45. SunRay-dvsh

    A Why is the Matter wave analogous to photon and derived from it?

    The electromagnetic wave derivation uses the fact that charge enclosed is zero and it goes to obey plane wave equations. Lets say we were deriving a wave equation from maxwell's equations for electron wave motion, but we assume that charge enclosed is not zero, and come up with some...
  46. S

    Particle in an Electromagnetic Field

    Using the Lagrangian : L = ½mv^2 - qφ + qAv What is the physical intuition of Av ? I know that A is the magnetic vector potential and that v is the velocity of the charged particle. I just don't know what their dot product means physically .
  47. iHaveQuestions88

    The Decay Rate of a Hypothetical Antimatter Container

    Hi All, First time poster here, and I've got a couple questions. Straight up, I'm writing a sci-fi story where antimatter is utilised as fuel (feel free to laugh at the cliche), and I want to portray it as realistically as possible. To that end, I've come up with a storage method and I want to...
  48. Z

    Prove that a capacitor driven by an AC voltage radiates EM

    Homework Statement When the capacitor driven by DC voltage ##V_0##,it has the electric field distribution ##f(x,y,z)## When ##V=V_0e^{iwt}##,how to show the EM travel in the space forever like the light? Homework Equations ##-{\nabla}^2E-u{\epsilon}\frac{{\partial}^2{E}}{{\partial}t^2}=0...
Back
Top