Em Definition and 1000 Threads

Hello, Is there any empirical evidence that electromagnetic radiation produces gravitational fields? I understand that as a form of energy it is expected to induce a spacetime curvature, but has this prediction of GR actually been tested? Is it at all subject to any controversy? Thanks, Armin

What are the ways (both natural and artificial) in which em radiation is generated? Here is one of the methods: We take a point charge (or more practically a charged sphere with uniform charge distribution) such that we can voluntarily fluctuate the amount of charge on it. We fluctuate the...

There is a EM radiation of frequency suppose x Hz.Let it has to travel a distance of y m.Now what's the time required for the radiation to travel the distance?The question seems to be very easy, but my confusion is in how can the frequency,distance,speed and time can be related? Can someone give...

OK so I'm familiar with the idea that EM radiation propagates through space in straight lines at a uniform speed, that of light. The idea that light moves in waves, that each wavelength carries a uniform energy and that the wavelength differs yet because the same speed is maintained each...

In short: Is a class based on the Jackson text necessary to truly understand electromagnetism? In length: I have heard many people (some on this forum) state that the Jackson text is more of an exercise in mathematical physics and/or is the “hazing” that one must endure to be a PhD in...

Hi, Something has been bothering me about deriving the wave equation for a plane EM wave. We were showed this derivation in class and had to reproduce it but something is not making sense to me... The derivation is as follows: Suppose you have a plane EM wave (in a vaccuum) traveling in the...

Hi, i was wondering Sorry if i don't have the right words, i study in France Why are Microwaves better for heating up food ? I mean since E=hv, these should contain less energy Right now, i know vaguely, that atoms absorb photons where the energy can make it go from one of its characteristic...

Hi I was wondering how can antennas capture + receive Electromagnetic waves I was thinking, in particular of FM Transmitters Antennas, and Fm receiver Antennas. And also, how come metals act as a shield to EM Waves I know that antennas have a resistance, and that they consume Energy by...

In GR, gravity is seen as property of the geometry of spacetime (curvature) as opposed to a force field. Does this theory extend to electromagnetics ,i.e. could EM be described as a property of spacetime, or is EM strictly dealing with fields? Do light waves and gravitational waves travel in the...

Hi, I understand that EM fields have energy and they travel at c. Light is an EM field so it travels at c as well. So say you run a current through a wire - an EM field is generated, propogating outwards at c. Since an EM field is generated, and EM fields have energy, that energy has to come...

Particle energy and momentum are obtained from the wave function as eigenfunctions of the spatial and time derivative operators. Is this true of ElectroMagnetic fields? In other words are E and B eigenfunctions of a differenial operator? I can see that E and B could be interpreted as a...

I have just read, in general, weak interactions, have the lowest Q values; meaning they have the smallest cross sections, which means they control processes in stars at some time in the early universe. What would be the next relative strength? Cheers

Homework Statement I've derived the EM wave equations from Maxwell's equations, and I now need to show that the E and B components are both perpendicular to each other and to the direction of propagation. The textbook I've been using attempts to show why this is, but it isn't particularly...

When playing poker at a 10 person table, each player obviously has a 10% chance of winning. This means that, when a person is the first player to act at the table, he should only play hole cards that are in the top 10%, in terms of non-losing percentage (ties count as wins here). [In any...

Another noobish question: Let's say there is an electromagnetic wave of constant wavelength and constant peak amplitude that travels a known distance. Let's say that we also know the total energy of this EM wave. Is there some formula that can tell us what the peak value of the electric field is...

Hi everyone, (nb: I posted this in the introductory physics section, but maybe it should be here? I'm not exactly sure how to divide physics into introductory and advanced. I hope this isn't against the rules - it's only my second post!) I am trying to understand my EM course again, and I...

can anyone help me derive the poynting vector from energy density of electromagnetic waves? and how we obtain average value <S> thanks

Helpppp please. EM Radiation doesn't make sense to me Hi. I don't see how you would get the answers to these questions. 1) A beam of light is shone on two sheets of paper, one of which is perfectly absorbing black and the other perfectly reflecting white. If the radiation pressure on the...

As I've been studying up on EM radiation, I've come to the conclusion that radio and light waves are not the same thing. Radio seems to be nothing other than a continuously flipping magnetic field (source: http://www.pbs.org/wgbh/aso/tryit/radio/radiowaves.html). In this way, there do not seem...

I'm bit confused about using terms temporal coherence and transverse/longitudinal spatial coherence when speaking about electro-magnetic radiation. I have understood that temporal coherence basically means how monochromatic light is. But I don't understand why temporal coherence is related...

This is a followup to the old thread What are the FULL classical electrodynamic equations? which never really provided a satisfactory answer. I have decided to phrase it perhaps in a more straightforward manner. Given that we have the EM field, or the equivalent potential field, and charged...

Didn't Einstein say that mass and energy were interchangeable quantities? Electromagnetic waves transport energy - Does this therefore mean they also transport mass? Could, therefore, all the radiation coming out of every decaying atom in the universe, every star and every accelerating...

can anyone help me with this problem? Thank you.

Maxwell's equations give that the electric and magnetic fields in E-M radiation are orthogonal. This is a classic equation, but can it be related to the orthogonality of, for example, the momentum and position operators which lead to non-commutivity?

I've been trying to better understand the relativistic origin of magnetism. I tried to do a slight variation on a common derivation and got an unexpected result. I'm hoping someone here can point to an error I made. The problem is to calculate the electric field a test charge would experience...

Hello, is it possible to create a pressure wave from any form of electromagnetic radiation that travels inward to a central point emanating from a spherical surface. Also, the pressure wave must not be produced from explosives that are imploding.

I understand that according to Maxwell's equations time-varying EM fields cannot exist in a perfect conductor (but static magnetic fields can). Also if you have a time-varying magnetic field you also have time-varying electric field and vice versa. And this knowledge is used to solve EM wave...

hey..while looking into the consequences of the invariance of light...we see that time needs to be slowed down in order to incorporate it in all the appropriate condtns..normally every body( in most of the books) gives an example...if we are in a space ship(moving horizontally with a speed of v)...

http://www.youtube.com/watch?v=5wnk6FVXCmc&feature=related That is one of several parts, 4 or 5 I believe. So is there any real science or truth to what he is saying? If he is correct it could quite possibly be the most important discovery in human history. Mind you, I'm not talking so...

1. If you took a positively charged antenna and shook it up and down 500 million times a second, would it emit a radio wave. If so, why? If not, why not? I would say, the EM wave that it emit is heat due to friction with the air. anyone have any other suggestion. 2. Electric charges are...

I read that em waves get generated by oscillating and/or accelerating charges. I am confused on how this occurs. Doesn't this violate energy conservation? Say 2 charges( a +& a -) are separated by a certain distance. So they have potential energy. Then you let them go. The potential energy is...

Hi All, I've been recently reading a thread, and a question keeps popping up there. Its not very difficult, it just requires a simple yes or no answer...in a single photon emission, is the energy of the photon distributed evenly on the sphere r=ct, or does this sphere represent the...

Another thing that I've never really understood... As fas as I'm concerned, waves need a medium to travel through, but electromagnetic waves seem not to need one at all. I just can't visualise them as oscillations in anything. It sort of helps if I visualise EM waves as photons, because then...

How does the exchange of photons/virtual photons give rise to the electrostatic or electromagnetic force? Why do like charges repel and opposite charges attract?

If a conductor connects your nose with the computerscreen with electricity going through it (allways in the same direction), the magnetic fieldlines will allways surround the conductor with one direction. Obviously nature prefers one direction more than the other. Is there some very important...

what kind of sources of light generate sinusodially varying electric field that is solutions of the form E(x,t)=E_{o}(x,t) \sin(kx-\omega t)

# Hi # My instructor of EM course wrote two formulas on the blackboard and asked whether they are correct and what their names are. (He does not know the answers too) # These formulas give V and \vec{A}, given \vec{E} and \vec{B} V(\vec{r},t) = - \vec{r} \cdot \int_{0}^{1} d\lambda...

Numerous BBC and Daily Mail articles ( yeah, trustworthy sources 8-| ) keep bringing this up, stating that there might indeed be a link between cellphone/radio waves and disease (usually cancer). My mother has informed me that at the latest Romanian Neurology Convention they stated that too...

2 infinite parallel plates separated by a distance s are at the potentials zero and V0. find the surface charge densities on the plates. I got the answer that it first calculate E and then as 1. x=o, Ex = σ / ε, then could know σ 2. x=s, Ex = - σ / ε ---> here's what I don't know. why...

I got this : 1 - z / (R^2 + Z^2) ^1/2 = 1- (1+ (R/Z)^2) ^-1/2 = 1 - 1 + (1/2) ( R/Z )^2 I'm confused why it got all these steps. it seems like taylor expansion ? or ? Thank you.

This paper which just appeared on arxiv http://arxiv.org/abs/0709.2365 Loop quantum gravity corrections to gravitational wave dispersion Martin Bojowald, Golam Mortuza Hossain 27 pages (Submitted on 14 Sep 2007) "Cosmological tensor perturbations equations are derived for Hamiltonian cosmology...

Inertial frames of reference ( IFRs ) and Electromagnetic ( EM ) waves. What would happen if you move at c velocity ? ( at the same velocity of a EM wave ) Maxwell equations are valid ? No relativity, please.

Sorry if its a simple question but I was wondering what EM waves are composed of. Is it like an electron beam traveling through the air and the magnetic field a consequence of the moving electrons? Another thing that's been really confusing me and no matter how many radio circuit tutorials I...

Why microwave frequencies are more affected due to rain? How does water actually affect microwaves?And lower frequencies have more diffraction.Why is it so?

Amplitude of EM waves in vacuum~~~ As we know, amplitude of waves decreases with distance due to energy loss. But what if EM waves in the space?? Since there's no matter around, I was wondering if there is any energy loss when EM waves travel through vacuum.

i need to have some scientific papers about this. I understand the massive ones but i can't understand it when it comes to a EM wawe. Can anyone advice me a book or a paper ?

Hello All, this is my first post, and while I'm a newb to the forums I'm not a newb to Optics. However, I have a very light background in low level electromagnetics, I'm more of a network design person. I'm working on a very very long term personal project to understand optics better and I've...

Does anybody know of free 3-D EM software so that I can model a transformer? In particular, I'm interested in mapping Poynting vectors. Thanks.

Hi, in my notes for the Hertzian Dipole I have a derivation of the vector potential A, and the scalar potential (phi). However, I'm missing the derivation of the E and B fields from these potentials. It seems that only the theta component of the E field exists, and I have ... well, I can't write...

Homework Statement A square coil of wire has sides of length 10mm, consists of 2000 turns and has a resistance of 250\omega. The coil is placed in a magnetic field such that the normal to the plane of the coil is parallel to the direction of the field. When the coil is rotated through 180...