## EM Waves / Particles

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
JB-82-Delft
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### EM Waves / Particles

Hello everybody, I thought this the perfect place to discuss EM fenomena. I, being a student at Technical Universaty Delft, The Netherlands.<p>I would like your opinion on what Electromagnetic radiation is, on the level of particles and energy packets.
I was wondering WHY the wave nature of the magnetic field (how should one physically interpret such a wave) runs at 90 degrees of the electric field phase?<p>
Electromagnetic Radiation (EMR) is transmitted by discrete packets of energy called photons, and can be both of wave and of particle nature.
Albert Einstein was one of the first deducting that EMR consists of several quanta, (one quantum is called a photon). EMR can be created by an oscillating or accelerating charge or magnetic field. EMR consists of two perpendicular waves, an electric oscillating field at a right angle with a magnetic oscillating field. The waves have a certain frequency and the quanta have a certain density. The frequency of a quantum depicts it’s energy, the higher the frequency, the more energy it has. The density can be described as the brightness.
The visible spectrum of EMR has frequencies from about 398 to 750 THz (the visible wavelengths of EMR are from about 400 to 800 nm) and is called ‘light’.<p>All frequencies of EMR are known to have the same propagation velocity: all EMR travels at light speed (299,792458E6 m/s in vacuum).
Light in particular has the three basic properties:
- brilliance (amplitude)
- colour (frequency)
- polarization (angle of vibration)<p>EMR is in three dimensions, thus calculations with EMR involve vector equations.
In fact, the two most important formulas, which write all properties as a function of each other are:<p>These are called the Maxwell Equations, after James Clerk Maxwell who lived in the 19th century. He studied Faraday’s works, and, as Faraday did discover many things but didn’t have much knowledge of math, translated the relations Faraday found into mathematical relations.
Maxwell had a method of imagining analog systems of known behavior, i.e. he compared electromagnetic waves with a vibrating elastic medium.
He also tried to connect the electromagnetic properties with mechanical properties. He stated the following:
“All energy is the same as mechanical energy. (…) The energy in electromagnetic phenomena is mechanical energy. (…) In our theory it resides in the electromagnetic field, in the space surrounding the electrified and magnetic bodies, as well as in those bodies themselves, and is in tow different forms, which may be described without hypothesis as magnetic polarization and electric polarization.”
<p>[ January 19, 2005: Message edited by: JB-82-Delft ]<p>[ January 19, 2005: Message edited by: JB-82-Delft ]</p>

Externet
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### Re: EM Waves / Particles

Hello.
Unless someone answers your question, a suggested place for it may be:<p>http://www.scienceforums.net/forums/index.php<p>Miguel
- Abolish the deciBel ! -

Chris Smith
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### Re: EM Waves / Particles

Not every one here has done a physics class. You did forget to add in gravity, because here on earth at least, and partially in the vacuum of space, EM interacts with that other gravitational force. These equation account for why such small amounts of EM, can travel so far while under what would seem like a hindrance or load.
As to why they propagate at 90 degrees, Newton covered that with out knowing electricity. Equal and opposite reactions.

JB-82-Delft
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### Re: EM Waves / Particles

@Externet: The forum you mention shares a lot of bull with us, although I found some interesting things there. When I read several topics here they all sounded plausible to some extent <p>@Chris Smith: light has no mass therefore is not reacted upon by gravitational force (f=m.a)
On the phaseshift: I think your right. However, having read some books and more forums, I'd say at 90 degrees the electrical wave is 'steady' (top of sinus) and movement is minimal, and thus the magnetic force is minimal.

Chris Smith
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### Re: EM Waves / Particles

You got that one wrong. Gravity, EM, and light very much interact, bend, and distort. <p>So says Einstein with his curvature of space, time and light. <p>Observatories at the present moment, and for decades now look at light directly behind the Sun. <p>The sun distorts the light waves directly behind it, giving us a otherwise un-blocked view of the galaxy. <p>Light and EM also slows down in the presence of gravity.

rocket scientist
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### Re: EM Waves / Particles

I am not sure what the original question was, and I am having trouble understanding what questions the above answers are in response to. <p>If you REALLY want to nderstand E&M, you will have to get into quantum electrodynamics (QED), developed by Richard Feynman and others. <p>Short of gettinng into that, we might be able to help on some basic things if the questions were phrased better. <p>I hope people realize that the comment about Newton's law explaining the 90 deg 'thing' is wrong -- maybe that was meant to be a joke.

Chris Smith
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### Re: EM Waves / Particles

You would be wrong also. <p>For every action, there is a reaction. <p>And in this case, at 90 degrees to the original action for a given reason.

rocket scientist
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### Re: EM Waves / Particles

Smith: The accurate statement is that 'every action has an equal and OPPOSITE reaction', which I certainly won't argue with. What could this possibly have to do with the E an M fields being at 90 degrees to each other? If nothing else, at 90 deg they are not even opposite -- oppostie is 180 degrees.

Chris Smith
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### Re: EM Waves / Particles

For every action,.... this includes the electron and photon.<p> If you take a wire, say tungsten for example, and you inject along its axis a current, then what happens at 90 degrees to this current? <p>Light is produced. <p>Physics is far more along than you have achieved so far, its simple, complex, and mysterious to most. <p>But it is almost 100% predictable and simple as well, if you know the “laws of physics”.<p>I only mention them partially so that you can investigate them on your own, like I have.

dyarker
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### Re: EM Waves / Particles

If you accept e = m * c^2, then ElectroMagnetic Radiation (energy) has mass of:
m = e / c^2. A VERY small number, but not zero.<p>EMR has direction. Direction and speed define a velocity. A change in velocity is defined as acceleration. So f = m * a applies, solved for a it becomes a = f / m. The acceleration can be a change in speed, or a change in direction, or both.<p>In a vacuum c is constant, therefore the tiny force of EMR's mass interacting with other masses can ONLY result in a change in direction. Any possible changes in speed approaching and receding would be equal and opposite, and would cancel in the RESULT. Thus the gavitational lens affect predicted by Einstein and confirmed by observation.<p>(to ignite a separate debate - The speed of light does not change in our 4 dimensions when approaching or receding from a mass because the curvature of space changes the distance traveled in a 5th dimension? repeat is a question)<p>In optics it is "c" that changes when EMR (light) passes from one medium to another, while unbalanced forces due to mass remain near zero. The change in c is so huge compared to the force of gravity that eye glasses don't have to be the size of the sun to work.<p>Back to why M is 90° from E. It is not a phase shift. It is an orientation. Of three dimensions, the direction of propagation is one, the E field is in another, that only leaves one other dimension for M to exist in. Time as a fourth dimension is directly linked to the position along direction of propagation dimension.<p>((I'll bet THAT stirs up the do-do pile )
Dale Y

JB-82-Delft
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### Re: EM Waves / Particles

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Dale Y:

(to ignite a separate debate - The speed of light does not change in our 4 dimensions when approaching or receding from a mass because the curvature of space changes the distance traveled in a 5th dimension? repeat is a question)
<hr></blockquote><p>Integrate the eq. E = m . c^2 with respect to the fifth dimension; just because we can't understand higher dimensions doesn't mean the rules differ. E and M will then depend on some speed in 5 dimensions. Still one can't really imagine a 5th dimension even the equotions hold.<p>@ Rocket Scientist: My intentions were not to really ask a question, but to ask opinions. I find old JC Maxwell's methods very convenient (rationalize fenomena with common models, such as imagining some elastic medium in which a wave propagates). <p>@ Dale Y: I don't understand the 'orientation'-explanation. Could you elaborate some more on that?<p>@ Chris Smith: Indeed light bends around a corner, that is, such a minimal amount we can't see it. And: photon = not light; light = photon.

dyarker
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### Re: EM Waves / Particles

Imagine an EMR packet is going straight away from you and the E field is vertical, then the M field is horizontal. 3 dimensions all 90° from each other.
Dale Y

Bernius1
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### Re: EM Waves / Particles

I think the real reson why is way deeper than this forum. There are 6 quantum poles, not just the two electrical ( Google 'leptons' , 'bosons'), and although the Standard Model DESCRIBES them , it doesn't give all the 'why's. Think, light travelling through air is absorbed and re-emitted by electrons AT RANDOM, yet travels in a reasonably straight line ( Feynman says shortest TIME , not shortest distance). It then hits a lens, and it bends according to its change in probability amplitude. SO, is it really slowing ? Yes, but what if the bend is caused by the TIME at which the electron re-emits? But it doesn't scatter (much), its planar vector continues ( although reflective and dispersive vectors are now present ). It's interesting to me that the magnetic energy decreases with frequency, but photon energy is proportional (a mag. field exists @ DC, but low freq. photons have lower energy). Ever make an electro-magnet from a fiber-optic cable ?
Can't we end all posts with a comical quip?

Chris Smith
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### Re: EM Waves / Particles

Photons through glass are thought to be absorbed and re emitted from each atom of glass as it passes through the glass. No actual original photon is thought to pass through the glass, but rather the energy of the photon cascades through the glass like billiard balls.

JB-82-Delft
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### Re: EM Waves / Particles

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Chris Smith:
Photons through glass are thought to be absorbed and re emitted from each atom of glass as it passes through the glass. No actual original photon is thought to pass through the glass, but rather the energy of the photon cascades through the glass like billiard balls.<hr></blockquote><p>Yep. That's the Compton scattering effect. Though 'delta lambda' is extremely small.

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