A couple of questions about light.

Holmes
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Topic 192302

I have a couple of questions regarding light that I'm surprised nobody I've asked so far can answer. lol 1) Does light change it's frequency the more times it's refelcted? and 2) Are there any known frequencies of light are have magentic properties?

Odysseus
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A couple of questions about light.

Quote:
I have a couple of questions regarding light that I'm surprised nobody I've asked so far can answer. lol 1) Does light change it's frequency the more times it's refelcted? and 2) Are there any known frequencies of light are have magentic properties?


1. Reflection has no effect on frequency; imperfect mirrors reduce the number of photons in a beam of light, and hence its energy, but don’t reduce the energy of individual photons.

2. I don’t know what you’re asking here: light is just one kind of “electromagnetic radiation�, and all frequencies of light are a partly magnetic phenomenon. But if you mean “can light be bent by a magnet?� I’d say no.

Mike Hewson
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RE: 1) Does light change

Quote:
1) Does light change it's frequency the more times it's refelcted?


Hmmmmm .. yes, no and maybe!! Take your pick. It depends on circumstance and your definition of reflection.

In the simplest sense, no is the answer.

But if you model reflection as being absorption plus re-radiation - due to electrons being accelerated by photons thus inducing photon emission - then it depends on the detail of the electron's circumstances.

Suppose you have light as a general spectrum of frequencies, a large bunch of various photon energies/frequencies. Most mirror surfaces will react differently depending on frequency - a shiny metal surface to our eyes will be quite transparent to X-rays. They will absorb some light ( perhaps re-radiating as heat, say ), and then repeated reflections will steadily remove photons of certain 'colors' with respect to others and thus will be percieved as an alteration ( a reddening for instance ) of the overall hue.

In a given frame relative motion of surfaces will shift frequencies, you can think of this as momentum/energy transfer to/from the photon.

Quote:
2) Are there any known frequencies of light are have magentic properties?

Light is electromagnetism. I think there is a subtle effect on light in very high electric and magnetic fields, but I can't remember the details - got something to do with virtual photons becoming actual or somesuch - but I could be talking rubbish here.... :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Odysseus
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RE: RE: 2) Are there any

Message 59217 in response to message 59216

Quote:
Quote:
2) Are there any known frequencies of light are have magentic properties?

Light is electromagnetism. I think there is a subtle effect on light in very high electric and magnetic fields, but I can't remember the details - got something to do with virtual photons becoming actual or somesuch - but I could be talking rubbish here.... :-)


If you stretch the meaning of “light� to include other frequencies, there are more prosaic phenomena that might be considered to involve “magnetic properties�, indirectly at least. In particular I’m thinking of the microwaves (& EHF radio?) in NMR spectroscopy, and in its (mainly) medical cousin MRI.

BTW, the Web server seems to be rather intermittent today.

Mike Hewson
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RE: If you stretch the

Message 59218 in response to message 59217

Quote:
If you stretch the meaning of “light� to include other frequencies, there are more prosaic phenomena that might be considered to involve “magnetic properties�, indirectly at least. In particular I’m thinking of the microwaves (& EHF radio?) in NMR spectroscopy, and in its (mainly) medical cousin MRI.


It's tricky, as there is language/definition dependence. Magnetism can be viewed/morphed from electrostatics + movement + special relativity ie. magnetism is the 'force' that arises when you account for propagation delays. So it's no longer purely radial as you are responding now to where the charge was in an 'above frame sense'. We'd really be viewed as boring old f**ts ( if not already ) if we always answered according to gold standard quantum electrodynamics or whatever.... :-)

Quote:
BTW, the Web server seems to be rather intermittent today.


Absolutely! Popping, whistling and banging...... but holding up, eh Scotty? :-)

Cheers, Mike.

( edit ) In fact you could think of gravity waves as a sort-of 'magnetic' effect laid upon static gravity fields when movement applies with propagation delays. It's not dipolar, but the effect occurs on axes perpendicular to the source's direction..

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Holmes
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Let me re-word my question

Let me re-word my question then. Understanding that light is elctromagnetic, is there one frequency that might be more magnetic than the rest? I know this question might open itself up to endless answers, but I can't seem to find any research on this particlular topic to give myself a lead into my project.

gravitysmith
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RE: I have a couple of

Quote:
I have a couple of questions regarding light that I'm surprised nobody I've asked so far can answer. lol 1) Does light change it's frequency the more times it's refelcted? and 2) Are there any known frequencies of light are have magentic properties?

1)
Not quite the original question, and perhaps someone more knowledgeable can correct me, but I thought a moving mirror would actually change the frequency of the reflected light. If the mirror is moving toward the light source wouldn't the reflected light would be shifted toward higher frequency? I don't think this plays a part in LIGO though, given the incredibly small mirror movements (they are looking for a motion on the order of something like the size of an atomic nucleus).

2)
My view of light is sort of similar to what Mike says. As I learned it, light is a propagating electro-magnetic wave. A time changing electric field creates a time changing magnetic field which in turn creates a time changing electric field, and so on. In that sense all frequencies of light have magnetic properties.

So why don't we see the magnetic properties more frequently? For most interactions, the electric field portion of the light dominates because it is significantly stronger than the magnetic field portion. In fact, if memory serves me correct, it is stronger by a factor of the speed of light which means the electric interaction is about 300 million times stronger than the magnetic interaction!

At the same time, I know the magnetic portion can play an important role in some interactions. For instance, in some materials, quantum mechanics forbids the electric field portion from diving a particular transition between two energy levels. In those cases the magnetic portion of the light is the strongest effect and it often can drive the transition. A particular example I know of is the transition in the element caesium which currently defines the second as a unit of time. Quantum mechanics forbids (to first approximation) the electric field from driving the clock transition and so the magnetic portion becomes the strongest. The frequency of the radiation to drive the transition is in the microwave region of the spectrum, but I don't know of any significance of that fact to the question at hand.

To answer your question Holmes, I think the ratio of electric to magnetic is always the same with the electric being much stronger than the magnetic. There are however some special cases where the electric field portion of the light will have no effect, in which case the magnetic effects dominate.

smith

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