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ahmed osama
Joined: 18 Jul 2004
Posts: 289
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 21 Jul 2004 18:48 Does the ElectroMagnetic Wave have cross-section area !! |
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I will till you how this question come to my mind ,Now we all know the square law of the light
A2 r2^2
------ =------------
A1 r1^2
A1:area of radiating surface
A2: area of illuminated surface
r: distance from the origin
from the above equ. it is impossible that the origin area of the light to be zero !! So it must have a certain area !!!
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flatulent
Joined: 19 Jul 2002
Posts: 4867
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Location: Middle Earth
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21 Jul 2004 20:01 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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| These equations are for a mathematical model which can have a point source. Frequently in physics an idealized model is used on real world situations because the results are close enough to measured ones for the intended situation.
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bibo1978
Joined: 01 May 2004
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25 Jul 2004 21:52 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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| Electromagnetic Wave is quite a complicated model for the wave equation of the photons best described by maxwell's equations, so it may have cross-section area,but the photon it self doesn't have a cross sectional area or so I think.
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sifeddin
Joined: 28 Sep 2003
Posts: 40
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24 Aug 2004 17:33 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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Dear Ahmed
right now your question seems meaningless because it is based on the very old geometric optics which is outdated by the electromagnetic theory. However it also contains so deep meanings if you are asking about the origin of the EM wave and from where it eminates. Since till now ,even to my latest knowledge, no one really SAID if the electron or the so called Photon or the fictous other many particles have the VOLUME of so and so. And in Amr M. Selim's Unity Theory, as I know it for the time being, the electron is modeled as a point particle that may interact with the EM radiation in region around it. Yet from my very own point of view it may turn out that the electron can have a volume of its own to remove the energy density singularity at its position in space.
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djalli
Joined: 10 Nov 2001
Posts: 887
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Location: 1600 Pennsylvania Avenue, Washington DC 20500
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29 Aug 2004 5:53 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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He is asking a valid question.
In a wire (let say round wire just for sake of simplicity) a signal travels at 1GHz (still for example!!!) acording to skin effect formula EM wave travels to some 2mm let say in depth from the surface inwards center of conductor.
Now let say increase frequency to 9GHz. What will happen? The skin depth will be less. So the cross-section area of EM wave in conductor wire is less.
I have attached pictures. Do not be mad at me. I am not an artist but hopefully should clear what is meant by skin effect.
Everything is a wire. Black is the area where EM wave is not traveling there. Blue is the area (cross-section) EM wave is traveling and as frequency increases this area decreases.
djalli
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sifeddin
Joined: 28 Sep 2003
Posts: 40
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03 Sep 2004 21:06 Does the ElectroMagnetic Wave have cross-section area !! |
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Dear djalli
You seem to be drifted very much away from "the valid question ahmed osama is asking" the question is not about the depth of penegtration in a metal or its "non-artistic" images in a "finite cross section wire" but if there exist an atomic level radiation cross section of emission.
In fact there is a quantity used in the analysis of many kinds of lasers has that name but it does not mean that the radiation has a cross section area (or any area of its own at all esp. when emitted)
Do not get mad at me but I think either you are not getting the essence of the question or you are deceiving who asked it
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wlcsp
Joined: 16 Aug 2004
Posts: 179
Helped: 14
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03 Sep 2004 23:00 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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| It is determined by the radar cross section
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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04 Sep 2004 5:45 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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Dear sifeddin
ahmed osama asked quoting "Electromagnetic Wave is quite a complicated model for the wave equation of the photons best described by maxwell's equations, so it may have cross-section area".
EM wave in guided medium for example a simple TEM wave (lets not complicate with light for now) does for sure have a cross-section area. Pictures are valid for that matter.
I honestly apologize I started to read thread from the above question while question was for something else.
I hope I clarify this. Come on sifeddin why should I get mad. My pictures are okay. Kidding.
| ahmed osama wrote: |
I will till you how this question come to my mind ,Now we all know the square law of the light
A2 r2^2
------ =------------
A1 r1^2
A1:area of radiating surface
A2: area of illuminated surface
r: distance from the origin
from the above equ. it is impossible that the origin area of the light to be zero !! So it must have a certain area !!! |
Square law is something belonging more to ray-optics area instead to what truly light should be studied. Why would I say that?
No matter of what intensity,polarization,etc think of the source an antenna radiating EM wave that would be light wave in our case.
What ray-optics domain under-estimates is the fact origin of light radiation source. Is it monopole, dipole, horn, a flat patch antenna, helical source of radiation? Pattern of radiation is "a lot" different for all these sources.
Quoting you: "it is impossible that the origin area of the light to be zero" actually study of antennas start with radiating intefinitisimal point-sources of having cross-section area zero and these are valid.
ahmed osama I hope a clarify something. Others have added very valuable information.
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sifeddin
Joined: 28 Sep 2003
Posts: 40
Helped: 2
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07 Sep 2004 19:13 Does the ElectroMagnetic Wave have cross-section area !! |
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Ok One last time:
As I see it EM wave DOES NOT have a cross section of its own.
ahmed osama asked (in a twisted way) if geometrical (ray) optics can handel the source of EM wave
the answer for this is definately NO!
bibo1978 actually mixed the EM Theory with the Photon picture and I guess left the question unanswerd
So djalli and wlcsp thought of the optical rays which ahmed osama asked about as only EM wave and persued to the sink and source
but I will close this talk from my side with that:
Ray Optics: Light is rays and rays are only lines with zero cross section
EM Theory: Light is wave and wave is spread in space (i.e infinite cross section)
Quantum Theory: Light is photons and photons are quasi-particles with zero restmass and no face no volume just an amout of (localised) energy interacting with matter to give (or take) more intensity to the interaction wave that goes on propagating in space
That's all falks
I'm out of here
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bibo1978
Joined: 01 May 2004
Posts: 229
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17 Sep 2004 22:32 Re: Does the ElectroMagnetic Wave have cross-section area ! |
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sifeddin, sorry I hadn't been clear in my description I meant that Maxwell's equation is just a realization of the Quantum wave of the photon, which is not actaully what light is and according to the Quantum theory the EM wave "which is the matter wave of the photon" can be realized as having a wave packet "when we are considering several photons together thats why in fact the light travels with various speed when travelling in different permeability spaces". However, one photon can't have a cross sectional area because it can't have a wave packet simply. hope this was clear.
thats all folks
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