Questions tagged [classical-electrodynamics]

Classical electrodynamics is the discipline that studies electromagnetic phenomena – such as electric and magnetic fields, radiation, and the dynamics of charged bodies – in classical terms.

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Does action at distance in electromagnetism violate energy conservation?

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 ...
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Net force on the northern hemisphere of a uniformly charged sphere, using the Maxwell stress tensor [on hold]

they start by a) wanting the E field in r
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Are Fresnel Equations with Complex Indices and Angles always valid?

This question-answer pair came after i was asked the following question and realized i had to do some research of my own to answer it fully, and to be sure that the answer is „yes“, in the sense ...
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How exactly is electric field produced and propagated? [on hold]

i wanted to know how does electric field exists in space, and how does a charge create it or how is force/energy transmitted to test charge through the source charge, does the charge produce some kind ...
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What's wrong with the theory of an electromagnet? [on hold]

Let's imagine we have a uniform magnetic field pointing directly upwards, filling the whole space, so $\mathbf B(\mathbf r)=B\mathbf k, B>0$ for all points in $\mathbb R^3$. This can be seen as a ...
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Problem: A infinite thin spherical shell with radius $r_0$, centered around the origin, is homogeneously charged with surface-charge-density $\sigma$ and rotates with the constant angular verlocity $\... 3answers 41 views 'Electrostatic field of a circuit' What does it mean? I've recently gotten into electrodynamics, I've studied electrostatics & magnetostatics, so far I know these facts: Electrostatic fields are produced by static charge configurations Magnetic ... 0answers 26 views Difference between monopole moment and charge or mass itself? I'm trying to understand the difference between monopole moment and charge or mass itself. What I found is related to magnetic monopole that is irrelevant. I want to know in multiple expansion of ... 2answers 55 views Deriving Current density of a Moving Point Charge Using the Continuity-Equation Problem: We know, a point charge at position$\mathbf{r}_q$has the charge density $$\rho_q(\mathbf{r})=q\delta(\mathbf{r}-\mathbf{r}_q) \tag{2}$$ if it moves with the velocity$\mathbf{v}$, we get ... 0answers 20 views 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 ... 4answers 365 views How is it possible for the induced emf to take negative values in Faraday's Law of induction? Faraday's Law of induction states that the work done per unit charge by the (induced) electric force along a loop of wire, or the emf, is minus the rate of change of magnetic flux through the loop/... 2answers 57 views How does alternating current provide energy? [duplicate] In my head, direct current makes complete sense; the electrons carry energy around the circuit to something being powered losing its potential and then return to the battery or whatnot to have their ... 1answer 18 views Effect of a current carrying wire on a point charge Given a point charge$q$near a wire carrying current as shown, what would be the effect of the magnetic field produced by the wire on this point charge$q$? I think the sign on$q$is important so ... 1answer 228 views The use of Helmholtz decomposition Examining the article on Wikipedia Helmholtz decomposition, compatible with the explanations of the book Introduction to Electrodynamics$4^{\mathrm{th}}$edition David J. Griffiths §1.6 the theory of ... 0answers 158 views Difficulty to understand a chain of equalities If we start with a functional or integral action \mathscr{F}(\boldsymbol{\mathcal{A}})=\iiiint_{D} L\Biggl(x_\nu, \mathcal{A}_\mu, \frac{\partial \mathcal{A}_\mu}{\partial x_\nu}\... 1answer 68 views Motion of a charged particle in a constant and uniform magnetic field Assuming the following relationship has been demonstrated $$r=\frac{m u_{0}\sin \theta_0}{qB\sqrt{1-\left(\dfrac{u_{0}^2}{c^2}\right)}}=\frac{p_0\sin \theta_0}{qB}$$ where$p_0=mu_0/\sqrt{1-\beta^2}$... 0answers 20 views Electromagnetic field with Dyadic Green's function in Non-homogeneous media I post a question about how to derive integral forms of electromagnetic fields with Green's function in non-homogeneous, isotropic media. The source paper is following; Poon, A. S., O'Driscoll, S., ... 1answer 72 views How Is Induction Energy Transferred From a Toroidal Solenoid To An External Conductor During Linear Current Change? It is widely understood that$\nabla \times \vec A =\vec B = 0$outside a toroidal solenoid with constant current,$I=k$($I = \vec J$in the below illustration). It is not so widely understood that ... 1answer 35 views Magnetic compression of plasma? What is the mechanism for plasma compression in the video below? I provide a still from the video and a link to the actual video on YouTube. https://www.youtube.com/watch?v=gsjWGz3YE5o BTW, is ... 0answers 9 views Charging mist particles I've used an aquarium mist maker to make mist of water and the mist comes out through a pipe (PVC) of ~ 4cm diameter and ~ 12cm length, I want to charge those mist particles using induction technique. ... 0answers 28 views Drift of a Positron's Position Between two Plates I am writing code for a 1D case where a positron with charge$e$and mass$m$is placed between a charged plate, and a grounded plate in the positive$x$direction, a distance$d$away . Let the ... 2answers 93 views What are change of frame and change of coordinates? What's the difference between a change of frame and a change of coordinates? I feel like both are transformations on the coordinates but change of frame changes also the vectors. 3answers 83 views How can the first Maxwell equation be valid in non-static cases? I am thinking in the framework of Classical Gravity, where the speed of the interaction is infinite. Now it is also known that there is a correspondence between Classical gravity and electrostatics, ... 1answer 33 views Particle deflection in a magnetic dipole field Consider a small magnetic dipole of magnetic moment$\vec{\boldsymbol{\mu}} = (\mu_x, \; \mu_y, \; \mu_z)$sitting at the origin. The magnetic field all around is \tag{1} \mathbf{B} = ... 3answers 78 views How to describe the unit vector for a complex wave vector? In optics, we often come across complex wave vectors that describe absorption, dispersion, etc. given as:$\textbf{k} = \textbf{k}_{real} + i\textbf{k}_{imag}$The electric field in phasor notation ... 0answers 24 views Negative real part AC conductivity I am reading this paper, where the authors are calculating the frequency dependence of the chiral magnetic effect, i.e.,${\bf J} = \sigma^{\text{CME}}(\omega) {\bf B}\$. The authors find, see for ...
We know that from relativistic Lagrangian for a charged particle is $$L = - m_0 c^2 \sqrt{1 - \frac{u^2}{c^2}} + \frac{q}{c} (\vec u \cdot \vec A) - q \Phi$$ leads to the Lorentz force equation, but ...