Em Definition and 1000 Threads

Can someone demonstrate how the momentum of a charged particle in a time-varying electromagnetic field is given by p - qA where A is the vector magnetic potential? I've always wondered :-) Cheers!

Homework Statement So, I'm asked to find how the fields (E, and B) transform by transforming the electromagnetic field tensor. The transformations are a) rotation around y axis, and b) boost along z. Homework Equations F'_{\mu\nu}=\Lambda^\mu_\rho \Lambda^\nu_\sigma F_{\rho\sigma} The...

The instantaneous energy density of a region of space of an EM wave is: u = \epsilon0E2 [J/m^3] hence the average energy density is: uavg = (1/2)\epsilon0E02 [J/m^3] uavg = <S> / c [J/m^3] Is this equal to the wave's average http://en.wikipedia.org/wiki/Radiation_pressure"...

Hello everyone, I'm a bit confused about electric dipole radiation. In my E&M book "Intro to Electrodynamics" by David Griffiths, it states that the electric field from an oscillating dipole is in theta hat direction. Mathematically I have the proof as to why in my book, but conceptually I'm...

I am a self studyer and I studied "Field and Wave Electromagnetics" by David K Cheng and "Introduction to Electrodynamics" by david Griffiths. Cheng is more for EE where it put a lot of effort in phasor, transmission lines, Smith Chart. Griffiths is more on the physics side that cover in more...

When I read about Fresnel equations, I see that it is based on boundary equations determined by Maxwell's equations. So I would think these equations only apply to EM waves. But is there a similar behavior in other waves like sound waves in water? Would I want to use or modify Fresnel...

If light is quantized, and is given out in packets, why are the EM wave spectrum and the black body spectrum continuous? I am very confused, can someone offer some explanation? Any input is greatly appreciated.

If you take a permanent magnet and wave it back and fourth, or even just move it along in one direction, this seems like it should create an electromagnetic wave. If so, how would one compute the frequency, and could you possibly detect it with a radio if you shielded it from other noise?

I keep looking at a sketch of the mutually perpendicular electric & magnetic fields in an EM wave. The sketch (and my text) says they are in phase, i.e. their maximum values occur simultaneously, ... ...but the discussion centers around the changing E field producing the B field and...

Homework Statement A star is moving away from Earth at a speed of 2.4 x 10^8 m/s. Light of wavelength 480 nm is emitted by the star. What is the wavelength as measured by an Earth observer?Homework Equations fo=fs(1 - vrel/c) I substracted because they the star is moving away from the earth...

According to this site http://quantummechanics.ucsd.edu/ph130a/130_notes/node453.html a good choice of Lagrangian for the electromagnetic field is L = - \frac {1}{4} F_{\mu\nu}F_{\mu\nu} + \frac {1}{c} j_\mu A_\mu where F_{\mu \nu} = \frac {\partial A_\nu}{\partial...

my question concerns electromagnetic (EM) wave propagation. consider a two layer medium where the first layer has constant conductivity $\sigma_0$ and the second layer constant conductivity $\sigma_1$. If a EM wave propagates from the first medium into the second one boundary conditions have...

Hello. I need an explanation for a strange phenomenon ... I use a fan (PC type) powered by mains (220 V / 50 Hz in my country). At a distance of about 3', I get a sin EM field (sure it is not by mains cords) at a stable frequency of 200 Hz synchronized on main frequency. Even during power on...

This is a theoretical question not a homework question, so if this is the wrong section to post this in please let me know. But my friend has this idea that if he sent an electromagnetic wave at a certain frequency at a surface it could create a current and this in turn could charge a battery...

What does it mean by "independent"(in gauge fixing of EM field) In my textbook, it gives the Coulomb gauge \phi = 0,\nabla A = 0 and says they will kill two degrees of freedom of the four potential and leave two independent components. I understand \phi = 0 will kill one degree of freedom...

Is it possible for an EM stress-energy tensor such as this: [PLAIN]http://www3.telus.net/public/kots1906/emtensor.jpg to exist, where \sigma_{xx} = \sigma_{yy} ?

EM response function of the "Phase Action" of a BCS superconductor Hello, I am looking for a paper in which people calculated the EM response of phase action of A BCS SC. In the book "Condensed Matter Field Theory" by Altland and Simons, on page 393 they mention such a thing in the discussion...

I understand application of Snell's law for transition from one medium to another but I have a question regarding this model. When an electromagnetic wave transitions from air into a conductive medium does the wavelength change instantaneously as the theory seems to imply or is there a boundary...

Hi yall, I was just wondering, seeing as how photons are massless, would there be a limit to the amount of electromagnetic energy you can fit in a given (finite) area? Of course excluding the practical reasons that would stop you. And if there is a limit, how come? Because black holes are...

For some reason I can't derive the Hamiltonian from the Lagrangian for the E&M field. Here's what I have (using +--- metric): \begin{equation*} \begin{split} \mathcal L=\frac{-1}{4}F_{ \mu \nu}F^{ \mu \nu} \\ \Pi^\mu=\frac{\delta \mathcal L}{\delta \dot{A_\mu}}=-F^{0 \mu} \\...

If you held frequency constant, and changed the amplitude of EM waves coming from a source, then would the distance into a material the EM waves would penetrate change?

I have been told that 1. EM fields contain energy. 2. EM fields can store energy, e.g. capacitors. 3. EM fields can transmit energy, e.g. via waves. How are 1. and 2. any different from each other?

why according to classical, electron circuling around the nucleus will emit EM wave and lose energy and collapse? I know electron undergoes circular acceleration, but why emit EM wave?

What's the most persuasive argument for using the potential phi and A as independent deegres of freedom in the electromagnetic Lagrangian instead of the more physical field E and B? Why does the cannonical approach break down for E and B?

I see everywhere the explanation that electromagnetic radiation self-propagates this way: a changing magnetic field induces a changing electric field, which in turn induces a changing magnetic field and so on and so on. I do not understand that. I do not have a problem with saying (it is a...

When a light wave enters a medium the electric field value of the wave is smaller in the medium. With the incident wave = transmission wave + reflected wave. If the E field of the reflected wave is known . Can the wavelength of the reflected wave be obtained from these relationships : E = Em...

In flat space time the Lagrangian for the EM potential is (neglecting the source term) \mathcal{L}_{flat}=-\frac{1}{16\pi}(\partial^{\mu}A^{\nu}-\partial^{\nu}A^{\mu})(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}) which is a scalar for flat spacetime. I would have expected the...

Electricity and magnetism had been unified under Maxwell's four famous equations. But I wonder if there any method to separate the this two components from an EM wave? Will there be any effects if this two components are separated? Hope you all can help me to solve this problem^^ Thank...

I am aware that the human body has electrical properties, But was baffled by what I witnessed Christmas Eve. I had a malfunctioning electric candle in the window. I picked it up to check the tightness of the bulb, and it immediately came on. I set it down and it went off. Three times this...

I'm taking Modern Physics in the spring semester (starts Jan 10). It's been over 5 years since I took Mechanics and EM. Which topics from these courses should I review in preparation for Modern Physics? I plan to review everything, however this will take me longer than the time available before...

I'm taking Modern Physics in the Spring semester (starts Jan 10). It's been over 5 years since I took Mechanics and EM. Which topics from these courses should I review in preparation for Modern Physics? I plan to review everything, however this will take me longer than the time available...

Hi, I have been reading my textbook and online but I'm not sure if I understand. An EM wave attenuates in a conductor but not in a dielectric? If that is correct what does the impedance of a dielectric represent, since I thought impedance would be associated with an energy loss...

Can someone please walk me through (or provide a link that does) the derivation of the EM stress-energy tensor? I get all the concepts I'm just a little confused on some of the details. Basically, you have the definition of the stress energy tensor in terms of the lagrangian, and the condition...

I'm looking for a device that can record EM signals of unknown frequencies (unknown to me) emitted by devices. For example if I point my remote control at it and start pressing buttons it should record intermittent IR frequency surges. Or for example if I build an emitter to modulate an...

page 61 in Introduction To Electrodynamics (3rd ed, Griffiths) writes: " What exactly is an electric field? ... I encourage you to think of the field as a "real" physical entity, filling the space in the neighborhood of any electric charge. Maxwell himself came to believe that electric and...

How did maxwell derive the momentum of electromagnetic wave to be E/c ?

I have been trying to remember if in classical EM it is equivalent to describe magnetization through bound electric currents A. \vec{j_b} = \nabla \times \vec M \vec{k_b} = \vec M \times \vec{\hat{n}} OR bound magnetic charges B. \rho_b = -\nabla \cdot \vec M \sigma_b = \vec M \cdot...

Homework Statement Light from the sun arrives at the earth, an average of 1.5*1011 m away, at the rate of 1.4*103 W⁄m2 of area perpendicular to the direction of the light. Assume that sunlight is monochromatic with a frequency of 5.0*1014 Hz. (a) How many photons fall per second on...

Homework Statement An infinitely long wire contains a current I. A metal rod with length L moves with speed v. Determine the emf in the rod. http://img227.imageshack.us/img227/5149/52966616.jpg With \epsilon = -\frac{d\Phi_b}{dt}, I would have said emf = 0 at first. The current I generates...

Homework Statement A solid sphere of radius R carries a volume charge density \rho = \rho_0e^{r/R}, where \rho_0 is a constant and r is the distance from the center. Find an expression for the electric field strength at the sphere's surface. Homework Equations \int\vec{E}.d\vec{A} =...

Gravitation and Electromagnetic forces are independent, correct? That implies.. Gravitation would exist even if Electromagnetic forces didn't. But, electromagnetic forces are responsible for existence of atoms.. and atoms are what make up the mass, no? And Gravitation exists because of Mass...

While neutrinos have no electric charge they have magnetic moment and will interact with magnetic field causing precession of its spin.http://prl.aps.org/abstract/PRL/v45/i12/p963_1" So if neutrinos can interact with virtual photons what makes it impossible to interact with real photons...

Both Wikipedia and my educators called electromagnetic radiation a self propagating wave. I would suggest that the word self be removed from wikipedia at least. There is no self in a wave. Even the word "coupled" or "causally related" are risky WRT the grav and mag components as I don't...

I'm doing an electromagnetic fields and waves course. The first part of the course was mainly about transmission line's, using the Smith chart and a host of equations that comes with transmission lines...we had a mid semester exam and i got 13/30, which i wasn't happy about but i didn't put in...

Hello, How is a static magnetic or electric field understood in terms of QED. Is it correct to interpret them as a collection of photons? If so, would these photons be real or virtual? Thanks in advance.

Hi guys, If I have a \Sigma triplet of baryons, how do I calculate the EM and gravitational binding energy of these baryons? (assuming there is 1fm of distance between quarks and that each quark has 1/3 the mass of the \Sigma), I guess I have to use the EM and Gravitational Potential...

When an EM wave has a higher frequency, it is able to penetrate materials more easily. However, why does a microwave able to penetrate haze while visible light can't? Why visible light is able to enter our atmosphere while those of gamma can't?

I read somewhere that Thomson (1897) concluded that the electron was not an EM wave because it bended in a magnetic field and that it had been proven that EM waves did not do this. Is this true?

Is there any lower limit on the frequency of electromagnetic radiation? I imagine that beyond a certain frequency it becomes impossible to detect, but is there anything in the maxwell equations that establishes a maximum wavelength (besides the limits of the size of the universe)? Thanks

Hi Everyone! I'm new here and like this forum. Can anyone tell me how the electron moving roundly in atom doesn't emit EM waves while changing it's speed?