Talk:Electromagnetic radiation

Merger or crosslinking with spectrum?

I understand fully these are quite similar topics, but are closely related. May I ask that you look at electromagnetic spectrum, especially the graphic, and think about at least more crosslinking among the articles?

Here's my problem, in an article such as radar: I often need to talk both about radiation, and its being emitted by the transmitter. "The transmitter sends out radiation" is a reasonably intuitive thing to say. When I start talking about its antenna, however, I start needing to discuss the wavelength and the effect on antenna geometry. Maybe there need to be more, not less, articles, to encourage wikilinking, such as something on wavelength and frequency that points to both. Intuitively, I think of the energy being more of a radiation than spectrum issue, but there are arguments either way. Howard C. Berkowitz 15:03, 12 October 2008 (UTC)

I am all in for crosslinking, merging, whatever it takes to make CZ better organized and easier to consult. I saw your graphic, but I must confess that I don't find it very clear, it is too small for my old eyes.

I don't quite understand what you mean by "energy is more of a radiation than spectrum issue". The energy of a photon is inversely proportional to its wavelength and for me spectrum and wavelength are practically the same, so that energy and spectrum are one-to-one. There is also the issue of intensity (number of photons per volume). Maybe when you say energy you refer to energy density, which is intensity (number of photons per volume) times wavelength (energy per photon)? --Paul Wormer 15:45, 12 October 2008 (UTC)

A better graphic can be found or redrawn; that shouldn't hold us back.

My concern is that this is an absolutely accurate definition from physics, but isn't necessarily going to help people from other disciplines. In some, the terminology is painful (see acute radiation syndrome, where protons and neutrons clearly are not EM waves).

In medical imaging, it sometimes truly is energy per particle, not per volume, at least in principle, for techniques such as single proton emission computed tomography; the volumes are low enough that sometimes part of the image construction does depend on single events. In other imaging systems, of course, you need a volume for anything.

For engineering and military, perhaps there's more of a table than a spectrum drawing needed. Within the RF spectra, you have the various EU-NATO-US, IEEE, and ITU Frequency Bands, now in separate articles with the same table in each. There are wide engineering examples on knowing the boundaries of near, intermediate, and far IR.

Paul, please understand I'm fumbling for a solution to what I see in problems; this isn't meant as criticism but to help elucidate what will eventually be one of the most cross-linked articles in CZ. Howard C. Berkowitz 16:05, 12 October 2008 (UTC)

I looked at acute radiation syndrome, and basically that articles is clear to me. Paul Wormer 16:47, 12 October 2008 (UTC)

Since I wrote the article, I'm happy to hear that!Howard C. Berkowitz 17:27, 12 October 2008 (UTC)

In the first place you need ionizing radiation, which by definition consists of individual photons with sufficient energy to shoot electrons off molecules in the cell (short UV, X-ray, and gamma). Second you need many photons (high intensity) to damage enough cells to get sick. My guess is that the unit "Rad" measures the absolute number of ionizing photons received by the body. (But it could also be defined per unit time and/or per unit body weight, I don't know that). Paul Wormer 16:47, 12 October 2008 (UTC)

The units have been evolving; Rad, which replaced rem, which replaced roentgen (in a biological context) has been replace with Gray. Essentially, they try to express not only radiation energy over time, but the effect of that radiation on tissue. The same energy delivered by neutrons is more harmful than by gamma rays. I'd have to go back to some literature to give you exact definitions. Howard C. Berkowitz 17:25, 12 October 2008 (UTC)

It is not clear to me what exactly you're proposing, but go ahead and do it, if I don't like it I tell you in my Dutch uncle way.--Paul Wormer 16:47, 12 October 2008 (UTC)

I've only been to Amsterdam, but I received a great deal of good advice there. I hope to be back and see more of the country, but, in quite a few different forums, I like Dutch advice (and chocolate). Mind you, I made the mistake of walking into an Amsterdam coffeehouse in search of a cup of coffee. Howard C. Berkowitz 17:25, 12 October 2008 (UTC)

PS Electron and helium nucleus (positive particle) beams are often referred to as beta and alpha radiation, resp. --Paul Wormer 16:52, 12 October 2008 (UTC)

Right. But isn't the definition of EMR is that it is composed of photons? Howard C. Berkowitz 17:25, 12 October 2008 (UTC)

We call it in good Dutch coffee shops (D. equivalent: koffiewinkels), not coffeehouses, and they do serve ordinary coffee. Don't eat their cakes, though, they make you feel giggly. Before 1905 EMR consisted solely of waves, and since 1927 you may pick your choice: either particles or waves. --Paul Wormer 06:52, 13 October 2008 (UTC)

I may just have learned something. Neutrons and protocols can be considered part of the EM spectrum? Howard C. Berkowitz 16:45, 13 October 2008 (UTC)

What are you talking about? Did you read too much homeopathy?--Paul Wormer 16:55, 13 October 2008 (UTC)

Don't frighten me like that. so when you referred to particles and weaves, the particles are restricted to photons? That was my understanding, but I thought you were suggesting something else.Howard C. Berkowitz 17:10, 13 October 2008 (UTC)

I take it that when you write protocols you mean protons and weaves are waves? Yes: EM radiation can be seen as consisting either of waves or of particles (photons), this is the famous particle-wave duality of quantum mechanics. Photons are funny in that they have no mass. Alpha and beta radiation consists of helium nuclei and electrons, respectively, and here the particle-wave duality strikes again, you may choose to see α- β-radiation as waves or particles. --Paul Wormer 07:10, 14 October 2008 (UTC)

(sorry, was still stuck in computer science) protons and neutrons is what i meant. Is there a fixed or variable wavelength associated with these other particles? (making notes as all these things should go into the article, to educate non-physicists such as myself).Howard C. Berkowitz 13:12, 14 October 2008 (UTC)

Yes: massless particles (such as photons) can only travel with the velocity of light c (in the vacuum) and massive, free (no force acting), particles can have any speed v < c. Their wavelength λ was first derived by Prince (really) Louis de Broglie (1923), it is

$\lambda ={\frac {h}{mv}}$

with h Planck's constant and m the particle mass. --Paul Wormer 14:11, 14 October 2008 (UTC)