Fun with Nature - The Electromagnetic Spectrum
Written by Translator on May 15, 2008 – 8:50 pm -To be crossposted at Dailykos.com after midnight due to the daily limit.
I do not know if this is appropriate for this site, but since it is a slow night I will give it a try. If this sort of topic is not for here, just let me know and I will restrict my posts to those more directly related to cooking. Thanks!
Electromagnetic radiation consists of photons, particles with zero rest mass that propagate at the speed of light, “c”. In a vacuum this is 2.9979 ^8 meters/second (186,000 mph). In materials other than vacuum, the speed is reduced. The index of refraction for a material is the ratio of the speed of light in vacuo to the speed in that material. We normally think of visible light when thinking about electromagnetic radiation, but visible light is a very, very tiny part of the EM universe.
EMR can also be explained as being a wave of electric and magnetic field vectors perpendicular to each other that collapse and rise simultaneously. In fact, the wave model is much better than the particle model for explaining some phenomena, whilst the particle model is better than the wave one for others. This duality goes back a long way, with Newton supporting the “corpuscular” model and Huygens the wave model.
It was not until the 20th century that the issue was resolved with de Broglie showed that all particles have wave characteristics. He wrote his doctoral dissertation on that, all four pages so goes the story. His professors could not understand it and sent it to Einstein for evaluation. Einstein supposedly sent back a terse, “Give Dr. de Broglie his diploma” for a reply. I can not vouch for that part of the story, but the wave/particle duality is the work of de Broglie.
EMR is usually defined by the wavelength (lambda) or the frequency (nu) of the radiation. These are related to the energy by the relation E = hc/lambda where h is the Plank constant, 6.26 ^-34 Joule seconds. This is important as we will see later.
There are any number of ways to categorize EMR. A fairly common one is by increasing frequency (decreasing wavelength) into radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma. While somewhat descriptive, there are many other schemes, including the method of production of the energy rather than the wavelength. For instance, X-rays are defined in the wavelength scheme as being of wavelengths between 10 picometers and 10 nanometers, while gamma is defined as from 5 picometers to 14 nanometers, to there is overlap. However, using the mechanism of production definition, X-rays are produced when low energy electrons are forced out of an atom and higher energy ones “fall” into those empty orbitals. Gamma rays are produced by nuclear transitions and do not involve electrons. The issue is very muddy.
However, there has to be some system, so I will keep with the wavelength one and point out exceptions as they occur. The longest wavelength EMR are the radio, or Hertzian, waves. The wavelength is from essentially infinity (as a mathematical limit) to around 2 millimeters. Normally this radiation is produced in electronic oscillator circuits using vacuum tubes, transistors, wire, and other standard electronic components. Some of the higher frequency ones are produced in resonant cavities, but still electronically.
The properties of Hertzian radiation vary tremendously from one end of the spectrum to the other. At the very low end, the so called extremely low frequency (ELF) radiation, with wavelengths measured in kilometers, have good penetration in seawater, and are used to communicate with submarines. The antenna used to radiate these waves is a wire kilometers long (in radio, the antenna to be efficient has to be some multiple of the wavelength, such as one-quarter, one-half, one, two, and so forth). A huge current (thousands of amperes) from the power amplifier is fed to it after being encoded by the oscillator. Interestingly, the amount of information that can be transmitted is very small, since either the amplitude, the frequency, or the phase of the wave has to be modulated to encode the information. The longer the wavelength, the lower the bandwidth.
Nearer the middle of the Hertzian band are broadcast frequencies, such as the “AM” band with wavelengths between around 500 meters and 170 meters in the United States. AM means amplitude modulation, the method in which the information is encoded into the carrier wave. In AM, the actual “height” of the carrier wave sine function is encoded with the information.
Higher up is the “FM” band, with wavelengths from around 3.4 meters to 2.8 meters. The FM label has to do with how the information is encoded, in this case by keeping the amplitude of the carrier wave constant and varying the frequency slightly with the information. FM sounds better than AM because the shorter wavelength allows greater bandwidth, not necessarily because of the encoding method, although a frequency modulated signal is a little easier to keep clean.
The difference in range between AM and FM are solely functions of the wavelength, not the way the information is encoded. Because of the difference in properties, signals of the AM wavelength experience atmospheric “skip” off of the ionosphere, and can travel literally around the world after dark (OK, halfway, since the other half is light). Thus AM wavelength signals are called “air waves” (a term that has been broadened to include any broadcast). Wavelengths corresponding to our FM spectrum do not reflect off of the ionosphere, and are termed “ground waves”. They literally “hug” the ground. The difference is really striking when one goes through a tunnel. The air waves (AM) almost instantly are attenuated, while FM comes in just fine.
I will prepare another installment if there is enough interest. I do not want this post to get too long. As always, comments, criticism, suggestions, and other feedback are welcome. In particular, if I got something technical wrong, please let me know. I do not desire to mislead anyone. Warmest regards, Doc.
Tags: Electromagnetic, EM, EMR, Light, Radio, Teaching
Posted in Diaries |
There is a lot in your diary that has to do with Political Cookery - like microwaves, radiation of food, bandwidth, and FM radio!
I remember driving across Texas one winter with my brother, on the way to California, and picking up all kinds of interesting AM stations from far away. And then there were the “pirate” stations in Northern Mexico and offshore that played wicked rock-and-roll.
Microwaves are next on the agenda and would have been included in this one but it was getting too long. I will also discuss food irradiation in some detail if these kinds of posts are approved. The Mexican stations pumped (I guess they still do) huge amounts of power into their signals.
In the US, only a few AM stations are authorized to broadcast at full power and omnidirectionally after sunset. Those allowed to keep at the limit of 50 kW include WLS in Chicago, WHB in Iowa, WOAI in San Antonio, and several others. The are termed “clear channel” stations, a name co-opted by a corrupt and evil corporation. Thanks for the encouragement! Warmest regards, Doc.
I just remembered another useless fact. In the US, all stations, by international agreement, had the letter “W” as the first. Later, when it was discovered that there were not enough, “K” was added to the list. The convention became that east of the Mississippi river, “W” would be used, and west would be “K”. WOAI is a very old station and was allowed to keep its original designation. Warmest regards, Doc.
You can win a bet in any bar in any state BUT Texas with this fact and that WRR in Dallas, Texas is a very old station too!
You know, are there any stations west of the Mississippi that start with W?
I mentioned WOAI in San Antonio, and I am sure that there are other, now including WRR. Of course there is WWV in Denver, but it does not really count since the government owns it and uses it to synchronize clocks around the planet. I am not sure what side of the river that WSB in New Orleans is located. Warmest regards, Doc.
I’d like to hear your opinion on food irradiation, definitively interesting.
Wow, this site is dying due to lack of participation. I really regret that. I should have 15 folks egging me on, and 5 telling me to go to hell. But there are five comments, and three of them are mine. What can we do to help? Warmest regards, Doc.
This may be because we’re some six hours ahead of you here in Europe.
We’re not dying. We’re a relatively new site in a blogdom where there are hundreds of thousands of new blogs showing up every - what - month? something like that.
And it’s the week, not the weekend. I know I’m buried in work, wake up every morning at 5, have to do laundry etc. then, get home at 5:30 or 6, have to mow and do other chores then — and we all have other obligations. Like me making an offer on a house today, obligations like that that take us out of the world of the blogs.
But I’d rather have it this way - I’d rather have a blog populated by people who have lots of life things and life issues to deal with - than have us crowded with 19 year olds who have little to no experience and nothing better to do than start a fight on a blog. Not that there’s anything wrong with being 19. I was 19 once, and running away to California in a car with no floorboards.
Great diary, btw. I know nothing of electromagnetic spectrums, but I love reading science!
I used a very poor choice of words, and I apologize for that. I just hope that more folks come to visit, and will what I can do to help, like poke tomorrow. I will be sure to mention the crosspost. I am having trouble attaching pictures here, though. Perhaps you might be able to assist me. Warmest regards, Doc.
Let me know when you want to post a pic and I’ll take you through it. M
Damn! The box absconded for a second! Make sure you upload the pics you want to post, on your desktop (no need to upload directly to Photobucket as our site can upload straight from your desktop onto our writing page)
Well, there are about eight or nine. I would like to get the post here ready early tomorrow afternoon, but understand that we live in radically different time zones. Can you take my Kos post and import it? That would be a whole lot less work for everyone, and I know how to publish pictures there. Would that work? Warmest regards, Doc.
I’m not sure it can work but I’ll give it a try, one never knows!
The site did not allow me to reply directly to you. Let us try for just import the whole thing, and if that does not work we can go to plan B. Warmest regards, Doc.
Well, it’s very hard to comment on this diary since I for one don’t know much about the subject. Maybe my wattage is a little low since it somewhat went over my head (sorry). Please keep enlightening us though, since I love the stuff you write. BTW, could you write about the impending reversal of the Earth’s magnetic fields - and what it will do to life as we know it..it worries me.
I am not sure that even the “experts” know what is going on with that. If it happens, we will have some very confused migratory birds.
However, the most important thing that the magnetic field of the Earth does for us is to intercept the solar ,wind, and that will continue regardless of the polarity of it.
If it were to go away, it would be serious for us. But because of the nature of our core and electrohydrodymanics, going away is not likely at all, at least for any extended period of time. Warmest regards, Doc.
You must be logged in to post a comment.
Meta
Categories
Blogroll
Our Ex-Blogs