A couple of basic questions about electromagnetic waves

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Hi, I'm new.

From what I understand, radio waves are generated these days using alternating currents or mechanically moving charges. The highest frequencies that modern technology reaches is somewhere in the bottom of infrared.

Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?


Also, are all possible frequencies "charted"? That is, there's radio, micro, infrared, visible light, ultraviolet, gamma...
But this can go on to infinity; so do we know what happens to extremely high frequencies of electromagnetic waves?


Thanks.
 

Answers and Replies

  • #2
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Originally posted by Atlas
Hi, I'm new.

From what I understand, radio waves are generated these days using alternating currents or mechanically moving charges. The highest frequencies that modern technology reaches is somewhere in the bottom of infrared.

Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?

To go higher in freq. you use molecules and atoms as "antennae" and use masers and lasers

Also, are all possible frequencies "charted"? That is, there's radio, micro, infrared, visible light, ultraviolet, gamma...
But this can go on to infinity; so do we know what happens to extremely high frequencies of electromagnetic waves?

Pretty much yes to those questions.

Thanks.
 
  • #3
I suspect that as one rises up through the infrared level of frequencies from below, overheating becomes a completely disruptive factor for a classic oscillator. Also, if the light range is entered from below, the behavior becomes more and more hard quantum-like rather than wavelike. Red light is still pretty wavelike, but getting on up into the ultraviolet range gets very quantum-like. By the time one gets to the range of xrays and gamma rays, quantum behavior totally dominates. For several years after gamma rays were distinguished from alpha and beta rays in radioactivity they were thought to be neutral mass particles, until someone managed to diffract them (with great difficulty). Cosmic rays hitting the earth atmosphere are sometimes said to produce ultragamma rays, but these should be very hard quanta and scarcely wavelike at all.
 
  • #4
russ_watters
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Originally posted by Atlas
Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?
Hi. Welcome. Uh... We call these things "light bulbs." Or maybe I'm missing your question...

EM radiation is created simply by exciting electrons. And there are lots of ways to do it, most of which can be achieved with electricity (since electricity moves around electrons, obviously). Incadescent lights work on the principle of hot objects give off heat. The electricity excites the electrons in the filament by heating up the filament. Flourescent lights work by the electricity exciting gas in the tube which gives off uv light, which is then converted to visible.
 
  • #5
Integral
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Also, if the light range is entered from below, the behavior becomes more and more hard quantum-like rather than wavelike. Red light is still pretty wavelike, but getting on up into the ultraviolet range gets very quantum-like. By the time one gets to the range of xrays and gamma rays, quantum behavior totally dominates.
ElectroMagnetic radiation of ALL energies has quantum and wavelike characteristics.
 
  • #6
Originally posted by Integral
ElectroMagnetic radiation of ALL energies has quantum and wavelike characteristics
, but manifests these through a widely variable range, from very-much so down to hardly-at-all so.
 
  • #7
Yeah, you don't hear people talking about 'photons of radio signals' because at (comparatively) low levels of energy like those used by radio, the wave-like properties of the spectrum are the dominant properties.
 
  • #8
Electrons can surf in long radio waves, but NOT in short gamma waves. There it is pretty much BAM or miss.

I am not at all in disagreement with Integral's statement. I should remember xray diffraction and the work of Max von Laue and the Braggs; so should you. ----->

http://www.phy.cam.ac.uk/camphy/xraydiffraction/xraydiffraction5_1.htm [Broken]

Bragg's Law
William Henry Bragg & William Lawrence Bragg

The experiment that showed gamma rays to be EM waves was by Rutherford and Andrade, and it was written up in 1914. I can't find much stuff about it online.
 
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  • #9
I am not in disagreement with either of you, I was just supporting your argument that certain wavelengths of electromagnetic radiation have tendencies to manifest themselves in different ways.
 
  • #10
I said: "so should you".

I should have used 2nd person plural:

"so should y'all".

Sorry! :)
 
  • #11
So that wasn't really directed at me then? Just sorta... everyone?
 
  • #12
Yes-- just any reader--
it balances the first clause.
 
  • #13
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Originally posted by Atlas
Also, are all possible frequencies "charted"? That is, there's radio, micro, infrared, visible light, ultraviolet, gamma...
But this can go on to infinity; so do we know what happens to extremely high frequencies of electromagnetic waves?
"...These two terms, x-rays and
gamma rays, are used almost synonymously. Usually electromag-
netic rays coming from nuclei are
called gamma rays, while those of high energy from atoms are called x-rays, but at the same frequency
they are indistinguishable physi-
cally, no matter what their source. If we go to still higher
frequenies, say to 10 (to the)24
cycles per second, we find that we
can make those waves artificially,
for example with the synchrotron
here at Caltech. We can find ele-
ctromagnetic waves with stupendously high frequencies-with
even a thousand times more rapid
oscillation-in the waves found in
cosmc rays. These waves
cannot be controlled by us."

-Richard Feynman
Six Easy Pieces
P.33, Basic Physics

So, Cosmic Rays seem to be the
highest frequency waves anyone
has discovered.
 
  • #14
Feynman was a hell of a guy.
 
  • #15
I wonder what Feynman meant by "... If we go to ... 10 (to the)24 cycles per second ... we can make those waves artificially, for example with the synchrotron here at Caltech." If he meant they are made by the synchrotron itself and not from nuclear reactions inside it, then this would counter what I said and answer Atlas's last question.
 
  • #16
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1,277
quart,

Here's a site about the synchrotron. What Feynman is
talking about is obviously
the radiation coming from
the accelerated electrons
as they pass by the magnets:

Introduction to the SRS
Address:http://www.srs.dl.ac.uk/TOP/intro.htm [Broken] Changed:12:10 AM on Wednesday, August 9, 2000

-zoob
 
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  • #17
Thanks, Zoob! So the particle accelerating fields themselves are still in the RF (Radio Frequency) range?
 
  • #18
I don't see why there should be any extremes to the spectrum. I would assume that it would be infinite, or close to, with waves ranging from near zero energy to near infinite energy.
 
  • #19
I meant "particle accelerating fields of actual synchrotrons".
http://public.web.cern.ch/public/about/how/howaccework/howaccework.html [Broken]

It's RF cavities that accelerate the particle beams.

The problem of the upper limit of accelerating frequencies in an operating synchrotron is probably a complex one, involving the bending and focusing fields also. That and matters of timing and synchronization come into play. Then comes my issue of overheating that I suggested earlier.
 
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  • #20
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Originally posted by Atlas:

Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?



In order to try this we need to
be able to alternate the current
at a frequency anywhere in the
range of visible light, and also
to put this through a conductor
that we can prevent from over-
heating.

I know that people who want very
strong magnetic fields, such as
in induction heating of metal for
heat treatment, actually use cop-
per tubing as the coil, and it is
kept cool by pumping water through
it to carry away the heat.

For our experiment we wouldn't
need a strong magnetic field, so
I think the main obstacle would
be generating the frequency we
need with conventional electronic
oscillators.

Here, my knowledge ends. I don't
know what the limitations are or
what problems to expect.

Theoretically, though, all that
needs to be done is to get current
to alternate back and forth along
a length of conductor somewhere in
the frequency of visible light.

For the conductor think along the
lines of an inch long wire no
thicker than a hair. Hardly any
current but lots of voltage.

-zoob
 
  • #21
1,525
10
Einstein believed there was a difference between electromagnetically generated waves and photons - a photon is created by an abrupt transition from one energy state to another (instantaneous?) and therefore the spectrum is not continuous since each photon is associated with a discrete increment of energy E=hf ( - radio waves (or any wave generated electromagnetically by acceleration of electrons) on the other hand, appear to have a continuous spectrum - that is, we can vary the electrical values of C and L to produce any desired frequency. Moreover, An individual photon exhibits a finite incremental size - electromagnetic waves appear to have a spatial extension - e.g., if a vertical antenna generates isotropic signal strength in the plane perpendicular thereo - how would a particular accelerated electron know in what direction to emit a photon? These were Einstein's concerns - maybe some of you have the answers.
 
  • #22
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1,277
Yogi,

If Einstein's belief was correct
then there is something incorrect
in the way we have arranged "The
Electromagnetic Spectrum" isn't
there?

Can you direct me to where he spoke about this?

Many Thanks

-Zoobyshoe
 
  • #23
Einstein said that E = h[nu] exactly defines the size of a quantum of EM energy. If it is in fact quanta (photons) instead of waves, then what is the frequency [nu] for? That is evidently the normal EM spectrum variable.
 
  • #24
FZ+
1,561
3
appear to have a continuous spectrum - that is, we can vary the electrical values of C and L to produce any desired frequency.
uh.. no we can't. For example, the value of C is restricted to discrete electrons etc. Planck thought that descrete quanta were products of restrictions in the oscillation of electrons(as he was studying black body radiation, or the emmission of photons), but Einstein realised by virtue of the photo-electric effect(studying the absorption of light) that this was in fact fundamental to the nature of light, in doing so practically creating wave-particle duality - the theory that waves and particles represent different sides of the same thing, and that in different measurements, different sides show up.
 
  • #25
1,525
10
The value of a capacitor "C" will depend upon the spacing of the plates (and other factors) which do not depend upon a discrete number of electrons. Same as to inductance L - the length or shape of a wire for example.

Some of Einstein's thinking on the subject was revealed in a personal interview with the author of a book called "Before the Big Bang" Don't remember his name - and I do not have access to the book now. While Einstein was instrumental in developing the notion of light as quanta - it nonetheless remained a puzzle for him - near the end of his life he wrote his friend Besso saying: "All these years of conscious brooding about the photon have brought me no closer to the truth. Nowdays every Tom, Dick and Harry thinks he knows the answer, but he is wrong."

Best I can do with regard to the questions - anyway its an interesting subject
 

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