Read about electrodynamics | 78 Discussions | Page 1

  1. C

    I Is the Configuration of Magnetic Fields Only a Convention?

    If I understand correctly, the concept of electric and magnetic fields originated with Faraday and was developed by reconceptualizing forces acting at-a-distance. For example, the electric field concept was developed by looking at the force on a test charge in the presence of a source charge...
  2. AndreasC

    Going through Jackson's Electrodynamics as an undergad who "hates" E/M

    Summary:: Not entirely sure if this is the appropriate board, if I'm mistaken feel free to move it somewhere better. I decided to slowly go through Jackson's infamous Classical Electrodynamics book as a challenge to myself, solving as many exercises as possible. I will document my progress...
  3. Amitkumarr

    To find the Acceleration of a Pentagonal metallic plate

    In order to find force( and hence the Acceleration) on the Pentagonal plate,we must find the Resistance of the plate.But to find the resistance we must know how the current is flowing through the given plate(see attached figure). My question is how is the current flowing through the Pentagonal...
  4. K

    EMF shielding using a conductor

    So I've been trying to figure out how EMF shielding works. More specifically, I've seen videos where placing a metal conductor in front of a circular coil (with AC running through at radio frequencies) apparently shielded anything behind it. After searching online, I repeatedly saw Eddy...
  5. J

    I Does direct interparticle action imply advanced inertial forces?

    In his Nobel lecture (https://www.nobelprize.org/prizes/physics/1965/feynman/lecture/) Richard Feynman states that by varying the Schwarzschild-Tetrode-Fokker direct interparticle action $$A=-\sum_i m_i\int\big(\mathbf{\dot X_i}\cdot\mathbf{\dot X_i}\big)^{1/2}d\alpha_i+\frac{1}{2}\sum_{i\ne...
  6. 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...
  7. 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...
  8. K

    Rotating and tilting charged disk induces a voltage inside a ring

    As I`` m learning for an upcoming exam I found an electrodynamics problem I struggle with. In the first task I need to calculate the magnetic dipole moment of a uniformly charged,thin disk with the Radius R and a total charge Q which rotates with a angular speed omega round its symmetry axis...
  9. maajdl

    A Canonical quantization of Electrodynamics: physical intuition ?

    Hello, I am freshly retired and enjoy going back to the fundamentals. I followed the wonderful courses by Alain Aspect on Coursera on Quantum Optics 1 and 2 . The quantization of Electrodynamics is really easy stuff. Just follow the correspondence between Poisson brakets and Commutators ... and...
  10. U

    I Current induced from a changing magnetic field

    This question is motivated by Problem 7.12 in Griffiths Electrodynamics book. I have not included it in the homework section, because I have already solved it correctly. However, I question whether my solution which agrees with the solution's manual is correct. Relevant Equations: $$\Phi =...
  11. Amartansh

    Classical 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...
  12. Aryamaan Thakur

    Electric potential at the edge of a thin charged circular plate

    My question might sound stupid to you but please clear my confusions. I'm taking an circular arc like element on the plate. That arc has a radius of 'r' (AB) and the radius is inclined at an angle 'θ' with OA (∠OAB). The area between arc of radius r and r+dr is dA. dA = 2θr.dr The charge on...
  13. JD_PM

    I Arguing about the magnetic force vector

    I am writing about the nature of force in classical mechanics and what does really imply, in terms of change in motion. I am using as an example a circuit, on which we exert a force. I am trying to justify the following scheme (concretely, ##f_{mag}##): The thing is that I am wondering...
  14. A

    I What is Current? I know it is a scalar but I found something weird...

    While I was going through "Introduction to Electrodynamics" by David J. Griffith I see the line "Current is a vector quantity". But we know it doesn't obey the vector algebra (addition ). Then how it can be a vector?... Please help me
  15. ubergewehr273

    B Doubt on an EM problem regarding gauss law

    There's this problem 2.18 in the book "Introduction to electrodynamics" by Griffith. The problem says the following, "Two spheres, each of radius R and carrying uniform charge densities ##+\rho## and ##-\rho##, respectively, are placed so that they partially overlap (Image_01). Call the vector...
  16. W

    Retarded time calculations: Electrodynamics

    Homework Statement A positive charge ##q## is fired head-on at a distant positive charge ##Q## that is held stationary. It comes in at speed ##v_0## and comes to an instantaneous halt at distance ##r_f## away from Q. What is the amount of energy radiated due to acceleration in this time...
  17. W

    I Electrodynamics: Derivatives involving Retarded-Time

    Hi all, I have ran into some mathematical confusion when studying the aforementioned topic. The expression for retarded time is given as $$t_R = t - R/c$$ ##R = | \vec{r} - \vec{r'} |##, where ##\vec{r}## represents the point of evaluation and ##\vec{r'}## represents the source position. I...
  18. W

    A Maxwell's equations and exterior algebra

    Maxwell's equations in differential form notation appeared as a motivating example in a mathematical physics book I'm reading. However, being a mathematical physics book it doesn't delve much into the physical aspects of the problem. It deduces the equations by setting dF equal to zero and d(*F)...
  19. W

    I Volume current densities

    Hi all, I have been reading Griffiths' book on Electrodynamics and have come across a point (image attached below) where he states that volume current densities are 0 on the surface of the current-carrying objects. He then uses these properties in pretty-important integrals. However, I...
  20. W

    I Quantum Mechanics and Electrodynamics/Electrostatics

    Hi all, I have a question relating to the title above. The uncertainty relation tells us that an electron that is localised (in terms of its PDF) is space has a large uncertainty in momentum space. However in classical electrostatics/dynamics we seem to make attempts to do things like...
  21. AwesomeTrains

    Effective refractive index of a stratified medium

    Hello PF, I'm reading a paper for a project. In the paper they derive an equation for the effective refractive index ##n=\sqrt{\epsilon^{e} \mu^{e}}## of two stacked layers ##(n_1^2 = \epsilon_1 \mu_1, a)## and ##(n_2^2 = \epsilon_2 \mu_2, b)## where ##a,b## are the lengths and in my case...
  22. omega_minus

    I Getting Maxwell's Equations from Field Tensor (Griffith 4ed)

    Hello, I am reading Griffith's "Introduction to Electrodynamics" 4ed. I'm in the chapter on relativistic electrodynamics where he develops the electromagnetic field tensor (contravariant matrix form) and then shows how to extract Maxwell's equations by permuting the index μ. I am able to...
  23. W

    Lagrangian Field Theory - Maxwell's Equations

    Homework Statement $$ L = -\frac{1}{2} (\partial_{\mu} A_v) (\partial^{\mu} A^v) + \frac{1}{2} (\partial_{\mu} A^v)^2$$ calculate $$\frac{\partial L}{\partial(\partial_{\mu} A_v)}$$ Homework Equations $$ A^{\mu} = \eta^{\mu v} A_v, \ and \ \partial^{\mu} = \eta^{\mu v} \partial_{v}$$ The...
  24. CDL

    Studying Higher Year Physics Studies with a Shaky Foundation

    I have just finished my first semester of third year undergraduate physics, and have a 3-4 week break before my next semester, in which I will be taking a third course in electromagnetism (classical electrodynamics). It is my second course with a full focus on electromagnetism, since in first...
  25. W

    Phase relation between the electric & magnetic fields in a plasma

    Homework Statement So I have got the question below. I am asked to find the phase difference between the electric field and magnetic field of electromagnetic waves traveling in a plasma, using the electrical conductivity expression. Now I have found the frequency of the waves and I know that...
  26. U

    Studying What do I need before starting to learn electrodynamics?

    I am a high school sophomore and I want to take part in Physics Olympiads which is exactly why I want to learn electrodynamics. I have ordered 'An Introduction to Electrodynamics' by D.J. Griffiths. I am halfway through MIT OCW mechanics course and I know Calculus equivalent to standard Calculus...
  27. ubergewehr273

    B Case of a charged capacitor

    It is given that an uncharged capacitor is connected with a battery. Clearly, it gets quickly charged and flow of current stops in the circuit. What is the reason behind a charged capacitor in completely restricting the flow of current ?
  28. ubergewehr273

    B Non symmetric case of Ampere's law

    When we use Ampere's law, the most basic case that of an infinite current carrying wire is taken whose magnetic field is evaluated at a distance r from the wire. However there's nothing wrong in using the law for non symmetric scenarios. If this is the case how do you explain the B field at a...
  29. ubergewehr273

    B A Doubt about Ampere's law

    When we try to find magnetic field due to a set of current carrying wires in a region we draw an imaginary amperian loop and using ampere's law find the magnitude of the magnetic field. ##\oint \vec B \cdot d\vec l = \mu_{0}i_{enclosed}## The RHS involves only the enclosed current inside the...
  30. sams

    I Finding Real and Imaginary Parts of the complex wave number

    In Griffiths fourth edition, page 413, section 9.4.1. Electromagnetic Waves in Conductors, the complex wave number is given according to equation (9.124). Calculating the real and imaginary parts of the complex wave number as in equation (9.125) lead to equations (9.126). I have done the...
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