Em Definition and 1000 Threads

Since I couldn't find any reference on the subject of Poisson bracket formalism of classical field theory, I'm posting a few question here: A) What are the Poisson brackets of the source-less EM field? B) Does the law that the Poisson brackets between a dynamical variable and its conjugate...

Hello all, I had a question about Electromagnetic waves. Although it isn’t homework (just to settle something in my own mind) I thought this would be the best place to put it. Perhaps it would be best if I could explain a situation I could understand and then hopefully someone could bridge...

Hi all, I was just wondering if there has been research into computing using electromagnetic waves. It seems to me like a sealed off box with internal EM pluses could be used to mould waveforms through interference, which would act as logic gates to provide useful computational results. Would...

For free EM field: L=-\frac{1}{4}FabFab Then the stress-energy tensor is given by: Tmn=-Fml∂vAl+\frac{1}{4}gmnFabFab The author then redefines Tmn - he adds ∂lΩlmn to it, where Ωlmn=-Ωmln. The redefined tensor is: Tmn=-FmlFvl+gmv\frac{1}{4}FabFab It is gauge invariant and still satisfies...

The situation is messy so I'll avoid details. I absolutely must do one module this February that is listed as 'level 3' at the Open University without formally taking the prerequisites. I have to teach myself the required mathematics, in two months, to give myself a decent chance of passing. If...

I did pretty bad in undergrad EM and remember nothing. However, my advisor says that since I'm doing well in my mathematical physics class, and if I get an A, I should directly take the grad EM course to not waste time. However, he acknowledges that I had difficulties with EM in the past, so...

A metal box will block most EM waves. Is this because the oscillating E field will be canceled when in contact with the conductor. And because the oscillating E field is the source of the changing B field does this then kill the B field.

Homework Statement A rectangular metal plate measures 0.20 m long and 0.3 m wide. The plate is heated to a temperature of 1,433 K by passing a current through it. Assuming that it behaves like a blackbody, how much power does the plate radiate under these conditions? Homework Equations...

Hello all, I'm not all too familiar with the electromagnetic spectrum, nor generally with physics but there is something that keeps me up. I learned, and also read now everywhere that visible light (to humans) lies in the wavelength range of about 400-700 nm. No I have a science book here...

I've been thinking of 2 point charges separated by some distance in static equilibrium. When one charge is moved from rest, the EM field would change the way it looks at the location of the other point charge. This "changing in the looks" of the EM field as I understand propagates from the...

Homework Statement Moving in negative x-axis: E1 = E sin(wt + kx) Moving in right axis: E2 = Esin(wt-kx-θ) moving to right write complex representation The Attempt at a Solution E1= E Im(exp[i*(wt+kx)]) E2= E Im(exp[i*(wt-kx-θ)]) are these correct or do I have to take into...

What is the difference between the two, in that EM calorimeter will stop photons and electrons effectively wheras hadronic calorimeters stop hadrons effectively (but both do not seem to affect much muons)? What materials are used in each type? One usually hears that the EM calorimeters...

My community college physics instructor thought a certain textbook would be a good supplement to Lorrain and Corson's Fundamentals of Electromagnetic Phenomena. I was looking at something at the time and didn't pay enough attention, so now I don't remember exactly any of the authors, although I...

Homework Statement 6. S1 and S2 in the diagram are effective point sources of radiation, excited by the same oscillator. They are coherent and in phase with each other. Placed 4.0 y m apart, they emit equal amounts of power in the form of 1.0 m wavelength electromagnetic waves. (a) Find...

Homework Statement Consider a charged particle of charge e traveling in the electromagnetic potentials \mathbf{A}(\mathbf{r},t) = -\mathbf{\nabla}\lambda(\mathbf{r},t)\\ \phi(\mathbf{r},t) = \frac{1}{c} \frac{\partial \lambda(\mathbf{r},t)}{\partial t} where \lambda(\mathbf{r},t) is...

then how can you tune into, say, 101.1 when its not at 101.1 MHz all the time given the frequency change?

When the mic hears the noise, it creates an alternating current electrical signal right? So how does that translate to em waves? Is it just that a higher frequency radio wave length would resemble a higher pitch? If so, is it impossible to hear the pitch "produced" by, say, visible light?

So far the best general physics book for EM I've found has been Alonso and Finn. The problem is that I just spent too much time trying to understand electric displacement using the hand-wave magic mathematical definitions they give. The rest of the book seems fine (it gives vector forms for...

Let's say we have a radio wave coming into a receiver. When the phase is near 0, does this mean that fewer photons are being absorbed by the receiver compared to when the phase is near 90? (Hope I'm using the right terms here)

Homework Statement Two astronauts are at rest in outer space, one 15.3 m from the Space Shuttle and the other 30.6 m from the Shuttle. Using a 123.0-W laser, the astronaut located 30.6 m away from the Shuttle decides to propel the other astronaut toward the Space Shuttle. He focuses the laser...

For a simple harmonic oscillator, the creation and annihilation operators can be expressed as linear combinations of the position and momentum operators, \hat {a} = \sqrt { \frac {m \omega} {2 \hbar} } ( \hat {x} + \frac {i \hat {p} } { m \omega } ) \hat {a} ^{\dagger} = \sqrt...

Other than nearby light pollution. Or is that the only reason?

Recently a device invisible to a static magnetic field was described. The device features a cylinder with two concentric layers. While the inner layer consists of a superconducting material that repels magnetic fields, the outer layer is a ferromagnetic material that attracts them. Placed in a...

Hi ,does anyone know a good book in advanced EM radiation and it contains more information on velocity EM field , I have already finished Griffith's book

Title pretty much says it all. In EM waveguides (rectangular, circular, what have you), I understand there are various "modes." I'm gathering that these represent specific, discrete solutions to the Hemholtz equation, and therefore there are only specific frequencies that will propagate? What...

My book seems to not go into a lot of details as to how EM-waves are created. More or less they just state that they are created by accelerated charges. I guess that somehow makes sense since an accelerated charge is clearly altering the electric field everywhere in space and that is as far as I...

Homework Statement This is an EM waves class, but we are given the following problem, which seems deceptively simple. I'd like some feedback to see if this is done correctly. Homework Equations Consider a parallel plate capacitor connected with a resistor with resistance R, as shown in the...

Ok, I've been reading up on the EM field and how it exerts force on charged particles. By exerting this force it creates 'ripples' in the EM field and this is felt by other charged particles as a force (either of attraction or repulsion). We say that the two particles exchanged a virtual photon...

In the light that QED suggests the speed of interaction is infinite, are there any experiments which makes it clear that mediating fields are retarded in classical electrodynamics ? Whereas, on the theoretical grounds the causality requires time assymetric interaction, but do we have any...

Hi eveyone, I am new to this forum and I hope that I can gain lots from this forum. Recently, one question comes into my mind, that is about the possibility of splitting the electric component and magnetic component of EM wave. This two components seem to always stick together. However, if...

Touch of background, about half way through a mechatronics engineering degree, I found that I love fluid mechanics and from previous studies I know I enjoy EM. To throw a curve ball in I also am fascinated by the concept of randomness and the associated mathematics. Now for the question, could...

In wikipedia's description of transmitter, if an alternating current is given to an antenna, then the antenna radiates off em wave. But why this happens so?

Homework Statement How do I classify modes? If there is a rectangular waveguide how can I show it is operating in TE10, TE20 or TE11 mode. Homework Equations Could someone help clarify how the 10, 11 or 20 comes about? Is it due to the dimensions of the guide or something else?

the energy of em radiation (or photon) is proportional to the frequency of the radiation. the em radiation (or photon) is composed of oscillating Electric and Magnetic fields. as such this energy must be stored in the oscillating electric and magnetic fields constituting the radiation...

I have been reading different articles about EM wave modes, it is said that in TE waves the E_z is zero, similarly for TM H_z is zero, and TEM both E_z and H_z are zero. How about the E_x and E_y in TE wave? Someone said E_y is also zero and only E_x exists in TE...is this true? Is it...

Hello all! I am trying to understand ER on a more intuitive level. I can see the relationship between energy and frequency. The relationship between amplitude and photon number is less clear. So far I have E = hf. I understand that the intensity of light is a function of the number of...

I'm reading my course book on ELectromagnetism and it is talking about a wave moving in the y-z plane but with polarisation in the x-direction, and it says that the equation $$\mathbf{E}=E_0 2i sin(k_0 z\ cos \theta) exp[i(k_0 y\ sin \theta - \omega t)]\mathbf{e}_x$$ Shows that there is no...

Visible light propagates at less than c in water. What about other wavelengths of EM? Do they all travel at the same reduced speed? I think not, but am not sure. If they travel at different speeds then Suzanna can be seen comin' round the mountain in certain wavelengths before others.

Hey all. I don't really understand how the fields of an EM wave have a vector. I think I understand the vector of a static EM field, but I'm having trouble understanding it when it comes to an EM wave. Could someone help me out a bit? Thanks. (I'm sure it's something simple that I just don't...

Consider a lens of diameter d and a focal length f >> d. Let the cross-section area of the lens be S = N*λ^2. Let a plane wave be focused from S to an area S1=λ^2. Then, by the linear superposition principle the electric field intensity in the area S1 will be N times greater than it was in...

Hi all, So quarks are given fractional charges, which then add to the total charge of the particle they constitute. My question is if the electromagnetic forces between quarks are taken into account? I was thinking that such things might be automatically taken care of via Feynman diagrams...

If photons emit virtual gravitons (but gravitons don't emit virtual photons) why isn't gravity considered to be a more fundamental force?

i was studying incidence of EM wave at a plane dielectric boundary and encountered equations in the attachment . I just want to know if n2 > n1 then electric field amplitude at the boundary increases . So from where does this extra value comes ? n1 and n2 are intrinsic impedances of 1st and...

How are stellar EM radiation formed?? I've read this in many books and sites... Any object above 0 K will emit EM radiation of all wavelengths... Now this is confusing me a lot... I mean, how for example a sun emit wavelength s of a Radio and it is the same sun which emits ultra violet and...

Hello everyone! This is my first posting. According to Maxwell, an accelerating charge emits a EM wave. All the books I have referred to, talk about the frequency of oscillating charge. How can we determine the frequency of EM wave emitted by a charge that is accelerating linearly? Thank you...

Hello, I have a question about the charge, q, that appears in, say, Coulomb's Law, Lorenz Force, etc. Can you use the charge associated with various ions? Say I wanted to find the force on aluminum by fluoride (I don't know why, those are just the first two off the top of my head)...

I understand that em radiation (light) will be produced if you cause a charge to oscillate. Does this happen at all frequencies? If I charged a comb by running it through my hair and then shake it up and down, am I sending out light waves?

I read that speed is directly proportional to wavelength in a medium. so does it mean that gamma is the slowest in air compared to the rest of the waves?

Is it possible (and practical) to use electromagnetic waves to heat copper (or other metals such as iron, steel or an aluminium alloy) over long distances (such as 1km)?

Homework Statement I'm given a charge density rho (\rho (r) = r^2 \sin ^2 \theta e^{-r}) and I'm asked to find the multipole expansion of the potential as well as writing explicitely all the non vanishing terms. Homework Equations Not sure and this is my problem. The Attempt at a...