questions about light & radiation

Hi all

wanted to ask following questions, just out of curiosity:

About visible light being electromagnetic radiation:

  1. since visible light is essentially electromagnetic radiation, has any experiments been made to take, let's say radiowaves, and increase the frequency to make visible light?

  1. since visible light has a magnetic component to it, has any experiments been made to see if this can be used to direct the light with the help of an external magnetic field (for e.g. creating holograms or invisibility without metamaterials)?

About using the magnetic component of an electromagnetic field to transfer power:

  1. I remember reading somewhere that the magnetic component does not propagate through the space between the sending and the receiving units. In other words that there is no wave between the sender and the receiver as there would be with the electric component does (such as in case of a radio wave). The question I have about this is whether this means that the transfer of the magnetic component can be considered "superluminal"?

thanks in advance,

JJ

Reply to
jjoensuu
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Light is not "essentially electromagnetic radiation".

Light is electromagnetic radiation.

How do you increase the frequency of "radiowaves"?

See above.

I would highly suggest reading up on electromagnetic radiation before asking any more questions as you current questions show zero understanding.

--
Jim Pennino

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Reply to
jimp

Infrared can be multiplied (through nonlinear crystals and such) into visible or UV, but I've never heard of a way to multiply RF the millions of times necessary to become visible light.

Magnetic fields do not deflect electromagnetic radiation.

An electromagnetic wave does indeed have real electric and magnetic components. They reinforce one another and travel together at the speed of light. Both components can be measured.

Light waves and radio waves are the same thing, just with different frequency/wavelength. Both are quantized.

John

Reply to
John Larkin

That would be very difficult. But some of the higher-frequency microwaves in the cosmic microwave background were visible red light at the time they were emitted.

When two electromagnetic fields are in the same place, they just add together. They don't affect each other in any other way. So you couldn't bend light with magnets.

There are certain materials in which the above does not hold. Of course, in those cases, it's really the magnetic field affecting the material, in turn affecting the light, rather than a direct effect.

I doubt it. Probably they meant that the magnetic field is either a standing wave or a static field, but it's hard to tell what they meant by that description.

--
Jim E. Black
Reply to
Jim Black

Reminiscent of a radium post.

Graham

Reply to
Eeyore

Yes, nonlinear processes allow for second, third, fourth.... harmonic generation. For example, it's fairly common for the 1064 nm output for a Nd:YAG laser to be doubled to green (532nm), or quadrupled to 266 nm. I think the record is 33rd harmonic generation.

Radio has wavelengths in the cm range (IIRC), so you would be talking multiple harmonic generation to reach the visible, and I don't know if there are obvious materials that respond appropriately in the radio range.

For linear media, there is no interaction between an external electrostatic, magnetostatic, or electromagnetic field with a given electromagnetic field. You require nonlinear materials (which exist) and large magnetostatic fields.

Can you provide a reference? This does not make sense. Some of the new wireless power transfer ideas involve evanescent fields, which are quite different prom propogating fields.

--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
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Reply to
Andy Resnick

Circa Thu, 09 Aug 2007 04:34:59 GMT recorded as looks like snipped-for-privacy@specsol.spam.sux.com sounds like:

Hi there. I try not to be the preachy type, but I hope you would have noticed that you crossposted this reply to sci.electronics.basics. That group is rather specialized in that it is devoted to answering questions posed by those with little knowledge of the field, hence "basics."

At any level, however, I fail to see any gain in a response that, paraphrasing, says, "You don't know the answer, so don't ask the question." Telling is the fact that while others considered the posted question and gave good answers, you only criticized the poster. What's the point of that, unless to mask ignorance on your own part?

Reply to
Charlie Siegrist

Didn't notice that, but that just means none of the groups posted to is really relevant.

sci.phyics.electromag would be the place to post something about electromagnetics.

The questions as posed show not only a lack of understanding but also total mis-understanding of what light and electromagnetic radiation is.

Had the poster bothered to spend a few minutes with Google, none of those questions would have been asked.

And yes, there is such a thing as a bad question.

--
Jim Pennino

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Reply to
jimp

If you remove the "essentially", you have it right.

No real use for such an experiment. Simply for the fact that radio waves travel at c just like light is sufficient to confirm identity in nature.

There are problems with verifying such a thing. The first is that despite Maxwell's perfect description of electromagnetic energy at the general level, some many still think in the community that electromagnetic energy can have no electric nor magnetic component. Interesting no ?

Second, we know since Planck/ Einstein that light is in fact made up of myriads of localized photons traveling at c, each one coming into being as electrons move to lower energy states in atoms. This means their individual electric and magnetic components of such small quanta will be close to infinitesimal in intensity.

The speed is the major hindrance for observing possible light deflection with magnets since the technological level to reach the intensities required to deflect the trajectory of anything moving at c that has no mass in a manner that can be measured has not been reached yet.

We know however since Faraday that magnetic fields can affect the polarity of light subjected to magnetic fields. This observation by Faraday is in fact what started Maxwell thinking in the mid 1800's and caused him 26 years later to come up with his final theory.

Yes. All magnetic fields seem to act only locally.

Not likely.

You would gain much understanding by reading some intro undergrad reference, such as Halliday & Resnick, Sears Zemansky and Young, or any other intro undergrad ref.

Andr=E9 Michaud

Reply to
srp

This "quantized" stuff really bothered me when I was first into ham radio - I just couldn't visualize an individual photon 40 meters long! ;-)

Thanks! Rich

Reply to
Rich Grise

I agree with the poster you quoted. Posting to a newsboard should not be a first effort. The first effort should be some personal effort by way of reading, Google searches, etc.

Your post is, in part, a flame based on your *assumption* that his point was anything other than to redirect the OP with some good advice. You are ignorant of his knowledge in the subject area.

Reply to
Don Bowey

I figure that a 1-watt, 1 MHz transmitter sprays out about 1.5e27 photons per second, and they are each (fuzzily) about 300 meters long.

John

Reply to
John Larkin

On Thu, 09 Aug 2007 13:45:06 -0700, in message , Don Bowey scribed:

And I will continue to disagree with both points of view presented to me in reply. Had the OP not posed the question, the several excellent replies would never had been made. Those answers immediately remove the question from the "stupid question" category, and have improved the reading of the newsgroup. Sorry, this is a "basics" newsgroup, and any on-topic and sincere question should be welcome without undue criticism.

Reply to
Charlie Siegrist

I drive through a tunnel on my commute. Early on, I noticed that I could get an FM station all the way through the tunnel, but I couldn't pick up any AM stations. I told myself it was because the photons couldn't fit into the tunnel.

--
Al in St. Lou
Reply to
Al in Dallas

Exactly.

John

Reply to
John Larkin

Yeah - right after I posted this, I realized - it shouldn't be too hard to capture these photons, since there are so many.

But where do you get 1.5e27? I'd think a 1-MHz transmitter would only send out 1,000,000 photons per second. Aren't "photon" and "wave" almost interchangeable at the quantum level?

Thanks, Rich

Reply to
Rich Grise

I once had a pick-up at a little industrial/office/warehouse complex, that had a broadcast transmitter and antenna array on top of it. It was kind of weird - drive into the complex, just like going into any little industrial park, but there was a grid of wires from rooftop to rooftop, which clearly shielded the underneath from the RF, because my car radio didn't get disrupted at all.

Cheers! Rich

Reply to
Rich Grise

Think about it - this is where the "1 watt" specification comes in. A single quantum of light - which is what a photon is - carries a specific amount of energy, depending on the frequency of the light in question.\\

Or another way to look at it - suppose I have a light on a dimmer. I start with the light dim and then turn it up. What changed, in terms of "photons"?

Bob M.

Reply to
Bob Myers

Each radio "wave" is a heap of quanta piled on top one another. The higher the transmitter power, the more quanta in each wave.

Each quantum carries a tiny amount of energy.

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A 1 MHz quantum carries about 1e6 * h joules, or about 6.6 e-28 joules.

John

Reply to
John Larkin

Hmmm, that leaves me imagining the photons as huge invisible spheres. Is there really severe attenuation when the slits in a double-slit experiment get smaller than a wavelength? If not, the "not fitting" wouild seem to be a poor heuristic.

--
Al in St. Lou
Reply to
Al in Dallas

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