Em Definition and 1000 Threads

I was reading Einstein's seminal work: http://hermes.ffn.ub.es/luisnavarro/nuevo_maletin/Einstein_1905_relativity.pdfGo to this part: II. ELECTRODYNAMICAL PART § 6. Transformation of the Maxwell-Hertz Equations for Empty Space. On the Nature of the Electromotive Forces Occurring in a Magnetic...

Homework Statement The problem deals with a charged (Q) rotating sphere around its axis (Ω_0) z^^ (z hat) of radius a. I'm asked to find the total angular momentum of the EM fields. 2. The attempt at a solution There is a solution posted to this question and I was just wondering why my...

My textbook says that the trough of the electromagnetic wave cancels out when it meets a crest. Okay, that makes sense, but if the crest is the actual photon/wave of energy, what is this trough that can cancel out the energy? It seems to mean that there are "negative energy photons" in between...

In Ballentine's Quantum Mechanics book, as part of a discussion of pure states vs non-pure (mixed) states, he says Polarized monochromatic light produced by a laser can approximate a pure state of the electromagnetic field. Unpolarized monochromatic radiation and black body radiation are...

The E and B field lines of a dipole radiating EM waves looks like that (sorry for the poor quality) : What I wonder is how can we see that the amplitude of the fields decrease as 1 / r? When you look as such a picture it actually feels likes the amplitude should rises. The E field gets...

I was looking around for information on the electromagnetic spectrum, but I have found some sources saying there is a new part of it called "terahertz", which would be between infrared and microwave. I have found some sources, but I don't really believe them so. Here are some sources of what I...

Sources : paper here and http://www.quora.com/What-is-the-phase-of-the-EM-waves (fifth paragraph). This is beyond my knowledge so I am not looking for an explanation of the phenomenon. But I thought nothing could go faster than light so I am very surprised. Are there exceptions to the speed...

When EM waves interfere, what happens to the energy?

I've recently learned about EM waves. One thing I find hard to really get, is how the E and B fields are constantly "generating" each other. I think maybe the key for this is in the following equations, obtained from Maxwell’s equations in vacuum : (source...

For a good conductor, an incoming plane electromagnetic wave will be attenuated exponentially as it penetrates a distance ##z## into the conductor, ##|\vec{E}(z)| = |\vec{E_0}|e^{-z/ \delta}##. ##\delta## is called the "skin depth". The current generated by this incoming electromagnetic wave is...

Why do we say gravity [GR] is a theory about ‘spacetime curvature’ and gravitational waves are ‘ripples’ but nobody uses such a description for electromagnetic fields? Don't EM waves 'ripple' spacetime? For example, one might imagine different types of spacetime curvature associated with each...

I'm so puzzled right now (sorry if I'm being stupid or something) , we can clearly see that EM waves oscilate the electrons in a conductor,they start vibrating and create EM waves again and these EM waves oscilate some other electrons and again they create another EM wave. All EM waves are...

Hey this isn't so much a homework problem but one I have just had an exam over. I have absolutely no idea how to calculate it and in all past papers/tutorial questions and the notes, makes no mention of the sort of problem. I'm not bothered over the exact answer, just how you go about it...

basic question- neutrinos pass through matter because they are only subject to the weak interaction whereas photons interact with matter because they are subject to EM? Does the small mass of the neutrino contribute to this - if there was a neutrino with the mass of a proton how differently...

For electromagnetic wave if it's reflected from a perfect conductor standing wave can be form. I wonder why Poynting vector can be used to describe the intensity of standing EM wave. (see p.19 of http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide13.pdf ). From some textbooks...

According to Max planks equation, E=h*f, the more is the frequency the more is the energy of the EM waves. So why UVC (shortest uv ray or high frequency uv ray ) is absorbed by the ozone and UVA and UVB rays ( longer uv rays than UVC penetrate the ozone and reach the Earth's surface?

I know that we have a free parameter in the relativistic potential for electromagnetism. I also know that we can introduce this as a scalar field ψ which gives this free parameter. I understand that this can be related to U(1) by mapping ψ: ---> e^iψ, which is the U(1) group. It just seems a...

How is energy dissipated in a traveling electromagnetic wave ? Will there be any dissipation if it were to travel through vacuum ?

Please forgive me if I am posting in the wrong forum. Also the board limits the length of the title. I wanted to ask about Effect of high intensity electric and magnetic fields on spacetime. To begin, 15 years ago this was published...

Homework Statement There's a uniform EM field given by ##\vec E=E\hat y##, ##\vec B=B\hat z## with respect to an inertial reference frame K. A charged particle with rest mass m and charge q>0 moves in the field with an initial velocity orthogonal to ##\vec B##. 1)Write down the equation of...

I am curious on what is meant by amplitude in an EM wave. From all the searching I have done the amplitude has something to do with the density of photons in the EM wave, and the frequency with energy of the photons. The part I am confused about is the fact that the wave is oscillating. I...

This started with me trying to read up how static electric/magnetic fields are described with photons, but it quickly evolved into the realization that I don't really know how the photonic viewpoint describes *any* changing EM field that isn't a neat monochromatic wave. Some sites mention...

Hello folks. This is Sandeep. I have many lingering doubts in physics that I am here to get cleared. This has become more of an issue ever since I decided to teach physics to my young nephew. My first question pertains to electromagnetic waves and the conservation of energy. Consider an AC...

In the thread about EM waves, the EM wave equation \left(c^2\nabla^2 - \frac{\partial^2}{\partial t^2} \right) E = 0 got me pondering. The term \frac{\partial^2}{\partial t^2} E is the second derivative of the field. In a solid-body wave equation, that same term (not with E, but the...

nothing in the universe moves without force, so what does makes em waves move through space?

In my lecture we were discussing the Lagrangian construction of Electromagnetism. We built it from the vector potential ##A^\mu##. We introduced the field tensor ##F^{\mu \nu}##. We could write the Langrangian in a very short fashion as ##-\frac{1}{4}F_{\mu \nu}F^{\mu \nu}## In the end we...

I understand that sinusoidal EM waves result from charged particles in harmonic motion, e.g., up and down an antenna. But what if the charge is undergoing some more complicated periodic motion? Wouldn't the EM waves be non-sinusoidal? I saw in a textbook a hypothetical EM wave with infinite wave...

I have a question about complex reflection and transmission coefficients. For example, I am modeling a wave in air (medium 1) ## \varepsilon = \varepsilon_0 ## reflecting on, and transmitted to, a medium 2 with ## \varepsilon = \varepsilon' -j \varepsilon'' ## If the wave would have traveled...

I am reading through my course guide and problems worked out and something bothers me. I think at this point we are working with classical waves, moving towards QM eventually. The idealization we work with is this. We have a light source creating a wave ψ(x,t)=Acos(ωt+kx) . The light beam...

A Science Daily report discusses observations of cosmic gamma rays that suggest that magnetic fields in the universe disproportionately have left handed rather than right handed helicity. It goes on to suggest that under a 2001 theory of another physicist that this could explain...

With ω/k = 2π/T / 2π/λ = velocity for both transverse mechanical waves and EM waves. I can understand velocity as distance over time in mechanical wave. But how is the ratio Em/Bm = ω/k = c. That is the maximum amplitudes of the E and B fields in the y and z planes corresponding to c in...

Homework Statement A sphere with dielectric constant ##\varepsilon## and radius R is placed inside a homogenous external electric field ##\vec E_0##. The sphere is divided in 2 hemispheres such that their common interface is orthogonal to the external field. Using the energy-momentum tensor...

Homework Statement Consider a particle of charge q and mass m, free to move in the xy plane in response to an electromagnetic wave propagating in the z direction (might as well set δ to zero) a) Ignoring the magnetic force, find the velocity of the particle, as a function of time. (Assume the...

I was studying my notes and specifically for the ##e^+e^- \rightarrow \mu^+ \mu^-## process, cross section is given by \sigma = \frac{4\pi}{3} \left( \frac{\alpha \hbar c}{W} \right)^2 where ##\alpha = \frac{g_{EM}^2}{4\pi}## and ##W## is the centre of mass energy. Is this the same for...

As a rule of thumb, we might say that quantum theory becomes essential when we're analyzing systems at small distances (of the order of atomic sizes or less) and few enough particles (suppose particle number is conserved, as in QM); however, the world as a whole is quantum, and even a system...

Hi, so I've just started learning about physics and I get the gist of most of it. I understand motion, torque, energy, light, radioactivity. But there is one topic that absolutely stumps me. Electricity. Can someone explain to an absolute moron like me what it is? It seems like everyone around...

I might have learned what I am going to ask during my electrodynamics class long time ago but just that do not remember it now. I always wonder why does an electron moving in space with EM radiation have Hamiltonian of the form ## H = \left( \mathbf{p}-e\mathbf{A}/c \right)^2/2m +e\phi## where...

this is theoretical (and possibly stupid) question; accelerating protons would create an EM wave equivalent to an EM wave generated by electrons at same frequency but the amplitude would be opposite, is that possible. has anyone made a communication circuit from accelerating protons? are...

Which of the following of a wave can be affected by the medium it travels through? (i) wave crest velocity, (ii) wave frequency, (iii) wavelength

When trying to explain reflection through the EM treatment of light waves, how do we account for the fact that the electric/magnetic field of the incoming light would penetrate into the medium from which it is reflecting off of? Diagrams like these: show the 'reflection point' on the axis of...

Hi, The reflection coefficient (R) of an EM wave is, as far as I know, 1 if there is total reflection and -1 if there is total reflection AND the phase changes by 180º. However, we also know that the transmission coefficient is given by T = R + 1 (or by its own formula, which should give the...

Homework Statement Given the Lagrangian density \Lambda = -\frac{1}{c}j^lA_l - \frac{1}{16 \pi} F^{lm}F_{lm} and the Euler-Lagrange equation for it \frac{\partial }{\partial x^k}\left ( \frac{\partial \Lambda}{\partial A_{i,k}} \right )- \frac{\partial \Lambda}{\partial A_{i}} =0...

Hello, I've been reading a book on particle physics for the general audience, and as you might expect, I was left with a slew of nagging unanswered questions. There was a chapter on gauge symmetry where the author described that the weak and the EM forces are the same force at some energy...

Homework Statement We have an infinite plane of width 2b made of a magnetic, conducting material (μr >> 1, σ >> 1). Two monochromatic electromagnetic plane waves, with magnetic excitation vector amplitude Hs approach it, each one traveling towards one of its two faces. Find the current density...

hi, everyone I didn't know where to post this thread so I posted it here. I have read many articles about EM wave to find what I'm searching for and nothing still. I have seen many pictures, animations and videos about EM wave, and about oscillating charge, but still nothing. What I am really...

Homework Statement Hey, I've been given this EM-wave: (-2\vec{e}_x+2\sqrt{3}\vec{e}_y+3\vec{e}_z)E_0e^{i[\omega t-a(\sqrt{3}x+y)]} with a∈ℝ 1) Describe the wave and how it's polarized. 2) In what direction does the wave propagate? 3) What is the phase velocity of the wave? 4) What is the...

I know that in a vacuum, speed of light is constant. My question is more about the speed of light in a material like air. Dispersion of light in a prism tells us that the speed of light or the material index depends on the wavelength ( or frequency which is constant ) so I thought that air...

Hello, There is an omni-directional and coherent light source rotating at the frequency of EM waves. If you think of the wave model, there will be nothing unexpected that you can imagine the space is rotating around the source. However, if it is quantized I can't tell what happens since photons...

I have 2 questions about EM radiation produced by an occilating electric charge. Q1: With graphs of electromagnetic fields, you can see that it contains an electric and magnetic component. What does these mean or give information about? Q2: By occilating the charge, you will get such a graph...

So I have some big speaker amplifiers at home, and they sometimes pick up radio interference from the CB enthusiast next door (he uses AM, so I'm guessing this is inducing a signal inside my amplifier which amplifies it into my speakers). It isn't really a big problem so I'm not looking for a...