Em Definition and 1000 Threads

Claim: \nabla \cdot \frac{\hat{e}_r}{r^2}=4\pi\delta^3(\vec{x}) Anyone know of a proof of this? (or a reference which covers it?) We need to show that \frac{1}{4\pi}\int_0^R{(\nabla \cdot \frac{\hat{e}_r}{r^2})f(r)dr=f(0). The claimed identity can be seen in the solution for...

It is a well-known fact that Maxwell's Equations, along with Lorentz's Force Law, form a complete description of classical electromagnetism. But why is that? I mean, I can understand that Lorentz's Law is necessary for describing the interaction between matter and electromagnetic fields, and I...

Let's assume that electron is moving around the unit circle. Using Maxwell equations show what is the frequency of radiating EM waves. How to start with it? What's the form of known variables - current density and charge density?

How "bright" are radio and other EM signals? Greetings, I am wondering how "bright" man made EM signals such as radio are. That is, if they were in the visible range, how would they compare to visible light sources? Would they be barely visible? Would they be daytime sky bright in every...

What are the equations of motion for two charges where the two charges are the only sources for the EM field? (No background field) What I'm looking for is given two particles of mass m_1 and m_2 with respective position vectors x_1 and x_2, what are f_1 and f_2 such that...

Is it possible to polarize an EM wave in the time direction as you would in any of the spatial dimentions?

Please see the diagram attached, I don't understand how my lecturer is resolving the E-field in the perpendicular case. He obtains: E_i = \bold{y} e^{-i\omega(t - \frac{n_1}{c} (-xsin \theta_i - z cos \theta_i))} How has he obtained the (-xsin \theta_i - z cos \theta_i) part from that...

Vacuum polarization is when an EM field causes the virtual particle pairs around it to become polarized like a dipole. The most common example is with an electron in vacuum, but a transmitting radio antenna could do it as well. But, if this was with an oscillating signal, it would create waves...

The electromagnetic field is mediated by virtual photons according to QED. These virtual photons, by virtue of being massive, should respond to Gravity. Therefore, in the presence of strong gravity such as that of a black hole range of EM force should be affected because very few virtual photons...

I'm having some trouble understanding this module. It would be great if anyone could help. In a homogeneous nonconduction region where μr = 1, find εr and ω if E=30(pi)e[i(ωt-4/3y)] in z direction H=0.1e[i(ωt-4/3y)] in x direction I am to understand that for a homognous nonconduction region...

This is probably a product of how I was taught, but I am unsure of the status of conservation of energy in classical EM with point particles. Here is the background: When I was taught in undergrad, general arguments were used to show that there needs to be a back-reaction on a point particle...

Homework Statement http://i258.photobucket.com/albums/hh258/Plutoniummatt/Untitled-1-2.jpg Homework Equations Pwr Ref Coeff: (Z'-Z)/(Z'+Z) all squared I maybe made a mistake but i can't spot it. And its bugging me I did square the whole thing afterward for the power...but...

So in a DC current we have a relative uniform movement of electrons in one direction. If we would have a very narrow coil around the dc current carrying wire, (like an atom wide), every time an electron pass trough the plan of the coil, should induce a voltage in the coil, so theoretically we...

I am trying to solve the following equation using the variation of parameters method d2x/dt2-(q2Bz2/m2)x=qEx/m I have put x1=cos(t) and x2=sin(t) into the Wronskian method. Can someone tell me if these are the correct functions to use, or should I be using exponential functions. Any...

The electromagnetic energy density is well-defined through the square of the Maxwell Field tensor. Why cannot such a quantity be defined for the grav. field?

i read this "in electrodynamics, polarization characterizes em waves, such as light, by specifying the direction of the wave's electric field" in a book. i really didn't get it clear & does the magnetic filed nothing to do with polarization?

Everytime I try to work out the Lagrangian for EM in different gauges, it gets messy really quick. Maybe there is some trick to simplify the process that I do not know, but either way I'd appreciate some suggestions. Starting point: For a point particle a (non-relativistic) Lagrangian...

Can EM waves falling on a solid contribute towards lattice vibrations? If yes, then i)when is the energy used in lattice vibrations, ii)when is it used in excitation of electron into higher energy level, and finally, iii)when is the energy utilized for slight vibration of the electron...

Since light is a type of EM wave, wouldn't that mean that when you flash a beam of light on a system of charges, you're exerting electric and magnetic fields onto the system?

I'm wondering what happens (or if it makes sense) if in the formula \mathbf{F} = q (\mathbf{E} + \mathbf{v} \times \mathbf{B}) we replace v by Lorentz factor, that is \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}. I realize that in the new formula I'm cross-producting a scalar with a vector, but I could...

Even in simple circuit, there must be some "turning point", for example the electric wire is bent somewhere. Therefore when electron pass through there is centripetal acceleration. I have heard that accelearation of electrons emits EM wave, so will EM wave be emitted from these positions?

Studying EM Theory?? Hi All, Is it possible to study Electromagnetic theory without knowing the concepts of classical mechanics. I have studied Newtonian mechanics but does not have any idea about Lagrange and Hamiltonian mechanics. I am concentrating on the below topics in...

I'm having a lot of trouble with basic EM (calculus based) because for some reason, the material simply isn't clicking with me. We're using Ohanian/Markert's Physics for Scientists and Engineers and I'm finding it to be very lacking. I'm wondering if anyone has any better alternative suggestions...

Homework Statement "Polarisation" is defined as the cofinement of the vibrations of the wave in only one plane and the removal of the vibrations in the other perpendicualar plane of the electromagnetic wave. But the e.m. wave is defined as a wave in which the electic vetors are restricted...

I am trying to code a java applet to give a physical representation of an EM wave, and how it will react in a resonant cavity. However, I am having a very hard time finding a good physical representation of what an EM wave actually looks like. For example, If I take a 2 meter wave, place it...

Does string theory predict additional long range forces gravity EM? One of the most touted features of String theory is that it correct predicts and even requires 2 infinite long range forces, gravity and E&M. I've heard that string theory though also predicts additional non-observed long...

Why does the strength of an electrical field diminish with distance from its source whereas the amplitude and frequency of a beam of light do not vary, regardless of distance?

I am generally an "artsy" person, though I am interested in science, too. I am curious about EM waves, particularly how they get started and what determines their amplitude and direction. I've read that an oscillating charge can generate a magnetic field, though I'm a bit confused about what...

Hey guys and gals, Here are two of a vast sea of sources that say a passing EM wave will disturb charged particles: http://books.google.com/books?id=jC4...age&q=&f=false "...a wave passing over a row of electrons; the arrows indicate the magnitude and direction of the electromagnetic...

Homework Statement Problem: 2 spheres each one of them with a radius R and uniformly charged with ro+ and ro-, are situated in a way they superimpose partially ( see figure). Let be "d" the vector from the positive center to the negative center...

Do only electrons emit a photon when accelerated in EM field? Do protons, for example, radiate?

Hi, Let E(r,t) = E(r)exp(-ikz)exp(iwt) be a plane wave in time domain, propagating along Z direction. I wonder how to find the spectral representation of it (i.e. E(r,w))?? I know, for a finite intensity field (i.e. |E(r,t)|^2 < infinity), we can give...

This is not actually a homework question, just something I am wondering about. A specified charge density dependent on /theta is glued over the surface of a spherical shell and you are asked to find the potential inside and outside the sphere, which is done in the example using separation of...

The path taken by a ray of light, from an event E1 to event E2, follows a zero arc length curve such that E2 ∫ds = 0 1. E1 Where S is the interval along the null geodesic path between the...

Can anyone provide a brief explanation what an EM mode is? I've read some EM theory, but still have problems understanding what a mode really is! I know for some EM waves, the medium supports only certain modes, but is the 'mode' a property of a medium? Or is it something that should be...

I have some basic doubts regarding how the energy is transferred (e.g. transmission of radio waves) as EM waves. As I know, the wave is not anything that can be practically seen in the space, but it is a model that we use to describe how energy is transferred. But if we think practically, how...

AC Circuits II: AC Power Generator Homework Statement A An AC generator supplies an rms voltage of 110 V at 60.0 Hz. It is connected in series with a 0.300 H inductor, a 5.80 μF capacitor and a 236 Ω resistor. What is the impedance of the circuit? B What is the rms current through the...

As grotesque as the title may appear to suggest, I basically want to understand just that. Why is it that EM radiation of each group of wavelengths (visible, IR, UV etc.) manages to penetrate materials with varying ease. From what I've seen so far - and I haven't studied this directly, I'm just...

The equation widely used to calculate the force on a projectile in an electromagnetic launcher, more specifically a railgun, is: F = 0.5 * L' * I^2 where: --> F is the force in Newtons --> L-prime is the inductance gradient of the rails in henries/meter (H/m) --> and I is the current...

Can anyone please tell me that if for Electric charge we have its unit Coulomb what would be unit of Magnetic charge ? (if they exist)

Does light exhibit any type of dispersion in a vacume?

"Life" after Griffiths EM Hi, I need a textbook on electrodynamics. I have already finished Griffiths electrodynamics, a wonderful book but it does not cover the things I need now from an EM book (i.e. research on photonics). Therefore, I need a book which covers the mathematical methods...

In the classical picture of an electromagnetic wave, the wavelength is specified along the direction of travel. However, with EM shielding that is using a grid (microwave, chicken wire), I've heard that so long as the spaces are less than the wavelength, you will achieve electromagnetic...

My notes say that Heinrich Hertz was the first to generate and detect EM waves in the lab. ... Uhhh, this might seem really basic to you guys, but what exactly are EM waves? Because I thought they were any type of wave that appears on the electromagnetic spectrum, including visible light...

What exactly is tempertaure? As far as I know it represents the average vibration of atoms. How it relates to EM wave? because I have read in many Physics texts saying that 'the temperature of this wave is X Kelvin'. How do they find the temperature of individual EM wave? Correct me if I...

I've read in a few places that the energy and momentum of the electromagnetic field will itself induce a curvature of spacetime, much like the presence of matter. I'm not very familiar with general relativity, but does this imply that particles with mass and zero charge will still be affected...

Hi everyone I am teaching myself QFT, and am currently learning Lagrangian Field Theory. Here is a question I am trying to solve, and I am not absolutely sure if my solution is correct because I am new to this notation and material. I would be grateful if someone could go over it and let me...

So I am trying to work through the proof why why the direction of proporgation, the E field and B field are all orthogonal to one another. What i have is... E=E_{0}e^{i(k\ \bullet \ r-\omega t)} B=B_{0}e^{i(k\ \bullet \ r-\omega t)} \nabla \times E= -\frac{dB}{dt} \Rightarrow k...

I have a simple question about reflecting EM waves at dielectric boundaries. To best illustrate my question, consider normal incidence. The incident wave has the wavevector k positive, and the reflected has k negative. Since B = k x E , and k has changed sign, B must also change sign. This is my...

Will the frequency of EM waves produced by oscillating current in an LC circuit be the same as the frequency of the current? Thanks!