Whenever they show a graphic illustration of the EM spectrum, the graphic typically depicts the region between Gamma rays and shortwave radio (or thereabouts). But obviously, at both ends, the spectrum continues on for infinity as any frequency can be produced. Okay - that’s my first question - is there a fundamentally lowest possible frequency and highest possible frequency that can exist?
Are ALL frequency ranges observed in nature? Or man-made?
Similar to #1, we never seem to hear about EM radiation beyond Gamma, and lower than, say VLF (? I’m probably wrong here). Why? Is above-gamma radiation completely useless? Is super-low freq. radiation completely useless? How do we know? Has it ever been looked into?
Prisms can split apart white light into its component visible light frequencies, and some frequencies to the “left and right” of visible light (IR & UV). But how far left and right does the splitting extend?
In terms of prism operation within the visible light spectrum, it just splits apart all the different frequencies that have been combined together to form white light, correct? Well, what if you combined together, say, X-Rays and microwaves…could a standard glass prism break them apart?
Related to the above, do different frequncy ranges require differently designed prisms? Do “standard” glass prisms only work in the visible spectrum?
Mirrors: Does the standard mirror work only in the visible spectrum, or can it reflect the entire range of EM radiation?
Where would 60hz AC fall in the EM spectrum?
Okay, I hope this isn’t asking too much of you guys…just wait 'till I post all my pulsar questions
Highest possible frequency would be a single photon carrying all the energy in the cosmos… Of course, this would be unstable, and would break down immediately. (In fact, very high-energy gamma-ray photons are unstable and break down into other junk in very short order.
Lowest possible frequency would be a photon with a wavelength the diameter of the known cosmos…
(These answers from Isaac Asimov…)
Just about all possible photon energies have been observed in nature.
As noted, above gamma-rays, photons tend to spontaneously decay. I’m not sure why… Really low energy photons are all over the place, but hard to detect. I mean, how would you detect a photon with a wavelength of, say, two light-years? You’d need an antenna that big!
Dunno… It would depend on the properties of glass… I know that they can use diamonds to “diffract” x-rays…
Dunno…
I think that glass prisms only work in visible light, plus a little way into the IR (you can actually observe this with an ordinary thermometer!)
Dunno…
A photon with a frequency of 60Hz has a wavelength of 5000km… Really low energy…
In theory, no. There’s no fundamental reason why the EM spectrum can continue at both ends to infinity. There may, hoever, be practical limitations. For example, frequency is related to energy; the higher the frequency, the greater the intrinsic energy. Eventually, you’ll reach a point where all the energy in the universe would be required to create a photon of a given frequency, and then you’re kind of stuck.
The current limits of the EM spectrum are based on observations. The shortest wave gamma radiation thus far observed is in the order of 10[sup]-15[/sup] meters, so we use that for the high end, normally. On the low end, equipment limitations keep us from observing RF much below a few hertz, though we can’t say it doesn’t exist lower. This covers #3 too, I think.
It depends on the glass, or whatever the prism is made from. Most glasses are opaque to shortwave UV, and x-rays and gamma rays pass through virtually unimpeded. I’m not sure about a cutoff for the low end, but microwaves are barely refracted by glass, if at all.
No.
Yes and mostly yes (with the exception of near IR and near UV)
Yes. Radio waves mostly pass right through an ordinary mirror, thought some are reflected by the metal. The exact properties depends on the band in question. Microwaves might be reflected more than VHF frequencies. Meanwhile, x- and gamma-rays also mostly pass right through. Almost none is reflected, though some might be absorbed.
Pretty much at the bottom. Where you’d expect it. or is this a trick question?
The lowest possible frequency is 0. This would produce a wavelength infinitely long. It’s theoretically possible, but probably not in real life.
Wavelengths can keep getting shorter, but when they get really short, the energy contained in the photon gets really big. Such a photon is not stable; if it interacts with just about anything it will form matter (usually an electron and positron pair with lots of energy). So there is no theoretical upper limit to the frequency of a photon, but there is more or less a practical limit.
In a broad sense, yes. We see objects in space that emit at extremely low frequencies (cold gas, for example) as well as high (active galaxies, supernovae, accretion disks near black holes).
But we have limits to our technology; we cannot detect a wave that has a wavelength that is a light year long, for example. And most super-high-energy gamma rays don’t get far before turning into matter/antimatter pairs as I said above.
They are just hard to detect on the low end, and not stable enough to see on the high end.
That depends on the prism. Glass lets through some UV, but not far into that part of the spectrum. Some is opaque to IR, which is why your car and greenhouses get hot. Another material would let through more or less UV and IR. It depends on the physical properties of the material of which the prism is made.
Some X-rays can go right through glass, as would (I think) microwaves. A prism has limited usefulness to split out different types of light. It works best near the optical.
You got it. I worked on a camera that had a prism that worked from near UV out to near IR, and there are other kinds that work farther in the IR. A grating works better for higher energies; it’s a piece of metal with finely grooved lines in it. This can be used to break up EM energy into different frequencies. This is how X-ray spectrometers work, for example.
Glass is transparent to, say, gamma rays. So it won’t work there, or in X-rays either. Oddly, a relatively rough piece of copper (even slightly oxidized) will reflect thermal infrared pretty well. It acts like a mirror there, even though in optical light you can’t see a reflection at all. It depends, again, on the material you are using for a given frequency of light.
AC electricity is not EM radiation. You are moving electrons back and forth, which can create EM radiation, but is not the radiation itself.
For tons of info on like this, try http://imagine.gsfc.nasa.gov, the Imagine the Universe website. It’s designed for kids, but has some very clear explanations of things I glossed over here.
Actually, The Bad Astronomer, I was looking at that website. That was sort of what spawned this onslaught of questions.
I realize AC electricity is not EM radiation, and no, it wasn’t a trick question. But would it not produce (very weak) EM radiation with a frequency of 60 hz?
Adding to #3, I’m still curious as to whether or not ultra-low frequency wavelengths are believed to hide any possible information. Is it a case of “we’d like to look, but we don’t have the technology” or “we know they aren’t important”?
Adding to #7, does there exist a “perfect mirror” for any given wavelength?
Probably not as it would require a lossless material. EM waves penetrate conductors a short distance and when they do some of the energy is dissipated in the conductor.
Super conductivity at low temperatures might do it but that specialty is outside my area of knowledge.
