Talk:Electromagnetic radiation

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Electromagnetic radiation

observed electromagnetic waves from the sky as evidence by marabu birds forming circular clouds oscillation west to east then back west cited: F.O.O

        Farnado Ochieng Odhiambo  — Preceding unsigned comment added by 105.161.102.41 (talk) 15:55, 17 August 2022 (UTC) 

1. The graphic of the em-wave is wrong (Onde_electromagnetique.svg/600px-Onde_electromagnetique.svg.png). A em-wave should look like this: https://www.miniphysics.com/wp-content/uploads/2015/09/linearly-polarized-electromagnetic-wave.png — Preceding unsigned comment added by 78.43.236.192 (talk) 00:30, 20 November 2023 (UTC)

Electromagnetic interference

This section improperly conflates two completely different types of interference.1.72.4.68 (talk) 23:56, 18 August 2022 (UTC)

Which section, and care to elaborate? VQuakr (talk) 00:33, 19 August 2022 (UTC)

Wiki Education assignment: Science Communication

This article was the subject of a Wiki Education Foundation-supported course assignment, between 9 January 2023 and 10 April 2023. Further details are available on the course page. Student editor(s): SaifT10 (article contribs). Peer reviewers: CurtisEmery.

— Assignment last updated by AOXQueen (talk) 14:19, 17 March 2023 (UTC)

enhancing imagery and demonstration of circularly polarized light

There is an overwhelming majority of representations of light that are polar. But it would be very beneficial to have more discussion of nonpolar or circularly polarized light that give a more whole view of the concept. I would like to request someone make a representation of the circularly polarized light figure with the magnetic field also included. Psi-Archimedes (talk) 17:55, 10 March 2023 (UTC)

Momentum

Maby I got it wrong what momentum represents in the article, if not, it is impossible for anything traveling at the speed of light to have mass (a requirement of momentum), thus no electromagnetic radiation has momentum. Please explain? 2603:6011:A004:AD0C:C930:78E0:1B1E:F07D (talk) 08:08, 7 July 2023 (UTC)

EM radiation has no mass, but nevertheless, it carries energy and momentum. Remember, E=mc², thus energy is equivalent to mass. So, if there is energy in transport, there must be momentum in transport. Constant314 (talk) 12:39, 7 July 2023 (UTC)

Thank You, for explaining a reasoning of how EM radiation has momentum, however I have never done the math before, & am more confused now: since energy is not 0 how can mass be 0? (Seems to be your answer). I always took the E and the m as convertible potentials not necessarily current states. For example: x amount of E has has the potential to produce y amount of m in relation to c². It didn't seem right to say:

X amount of energy exists at the same time as Y amount of mass in relation to speed of light squared. I could be wrong? 2603:6011:A004:AD0C:C930:78E0:1B1E:F07D (talk) 06:56, 8 July 2023 (UTC)

Think of mass as one form that energy can assume, but energy can also assume other, massless forms, such as electromagnetic radiation. Physicists also believe that EM radiation has gravity, but it is so weak that it is not possible to test that belief.

When you hit a ball with a bat, the particles in the bat never touch the particles in the ball. Instead, the bat and ball exert electromagnetic forces on each other. When momentum and energy from the bat is transferred to the ball, the momentum and energy are carried by the EM forces (light). Constant314 (talk) 23:52, 8 July 2023 (UTC)

Thank you for tolerating my confusion. Sorry, I only knew momentum p to equal the product of m mass & v velocity, which kept me in a box. I thought that some prankster got the momentum part added. While it would be interesting if a flashlight kicked back when switched on, i couldn't believe it. Then I came across these special formula gems, for massless p (momentum): p=E/c (sorry for doubting you), & if you want to take Planck at his observation p=hf/c, or p=h/λ 2603:6011:A004:AD0C:C930:78E0:1B1E:F07D (talk) 19:41, 9 July 2023 (UTC)

Yes, the flashlight does kick back, only the force is so small you cannot feel it. Photon propulsion is a possibility, but it is very inefficient in terms of power required for a given amount of thrust. Constant314 (talk) 20:15, 9 July 2023 (UTC)

If we could only get a star to follow our solar sail at the speed & direction that we want to go,,,,,then maybe? 2603:6011:A004:AD0C:C930:78E0:1B1E:F07D (talk) 06:16, 10 July 2023 (UTC)

I have to trust, but don't understand (I'm still stuck in a Newtonian box), how light reflecting off a solar sail, doesn't loose velocity at the change in direction? A q ball hitting a side rail (in a pool hall) is supposed to have v=0 for a moment and then reflect? I'm sure that there's some special relativity for light, but I just don't know what to search? 2603:6011:A004:AD0C:614A:7F80:9A4B:7EA8 (talk) 07:21, 10 July 2023 (UTC)

It doesn't lose velocity, but it does lose momentum and energy. The reflected light has a longer wavelength hence, less energy per photon. Constant314 (talk) 08:37, 10 July 2023 (UTC)

Electromagnetic waves and energy: tautologies abound

Regarding this sentence in the page: "EM waves carry energy, momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact."

In trying to figure out a reality for myself, being 70kg of mass, and wondering how E=MC2 relates, any description or definition of energy and how it relates to electromagnetic waves constantly seems to produce tautologies, such as what I quote from the sentence above. A definition of something can't be tautological, i.e., the saying of the same thing twice over in different words.

If energy is defined as electromagnetic radiation, then how can "electromagnetic waves carry energy" without it being a tautology? Angwhit (talk) 12:37, 20 September 2023 (UTC)

Easy. Energy is not defined as electromagnetic radiation. Constant314 (talk) 12:51, 20 September 2023 (UTC)

What happened?

This article used to be fairly good. Not so much anymore. Bad grammar is just a minor failure. Here is an idea: in the sections describing the various types of emr (radio, ..., gamma), actually describe them! Radical, I know. Sources, what does the type interact with (covalent bonds, nuclear forces, etc.), what are the commercial applications, and what are the observed upper and lower bounds? It should also be mentioned that while visible emr is considered to have colors (from red to violet (although some people can see into the ultraviolet) it is not true that an object of a certain color necessarily emits photons of that frequency/wave length. (i.e photons of a certain color are one of several ways to evoke that color.) Also, it is not true that it is energy that distinguishes x-rays from gamma rays - at least by some common definitions. (It is the type of source so a higher energy photon may be considered an x-ray compared to a lower energy gamma ray.) I'm a chemist and I think it would be quite useful to describe the types of energy transitions that absorb/emit the various types of emr. (for instance, gamma rays interact with the nucleus of atoms and not (at least, the interaction is rare) with the electrons. (The article goes on and on about ionizing radiation. It's quite confused. I guess it's possible that a nuclear reaction is considered "ionizing" if the number of protons changes, but as far as I know "ionizing radiation" is radiation that knocks an electron off of an atom. Full stop. I'd have to check to see what the energy is of the 1s electrons in U or Pu, but I don't think gamma rays interact with the electron shells. (I may be wrong there.) One question that should be answered for each type of radiation is their sources. The article on Gamma Ray Astronomy claims that in 2018 the highest energy gamma ray photon ever detected was seen (1.4 peta eV) which is way off most of the charts in this article. And that's another thing that should probably be mentioned - as the subject moves from radio waves to light waves to gamma rays, their units of measure often change from wave length to wave number to frequency to electron volts. While all of these are interconvertable, it's probably notable enough to deserve mention. So, I wonder what the longest wavelength photon that's ever been observed is? Will I find it here? Why not?71.30.94.234 (talk) 10:43, 2 November 2023 (UTC)

I agree with most of these suggestions. As you say, the "Electromagnetic spectrum" section should have simpler descriptions of how each type of radiation is generated and detected, as well as the instruments used to detect it, what it is used for, and the units used to measure it. It also needs sources, most of it is unsourced.

On the other hand I disagree with you about ionizing and nonionizing radiation: the article should emphasize this difference. This is the main measure of the health risks of radiation and is widely misunderstood by the public. There is no debate that vacuum UV, x-rays, and gamma rays ionize matter. That was how they were first detected, and is the basis of most radiation detectors. As a chemist, I'm surprised you don't know that. --Chetvorno^TALK 19:09, 2 November 2023 (UTC)

Electromagnetic Radiation vs Electromagnetic Field

Somehow Wikipedia does not see a difference between Electromagnetic Field which stays with the charge and electromagnetic radiation which leaves the charge. Here we should say in the definition that there are "many non radiant EM fields causing a great many physical things like an electric motor". On line the confusion has some saying motors and wires always radiate photons. Bill field pulse (talk) 21:20, 21 January 2024 (UTC)

That is mostly incorrect. This is stuff is described with sloppy language all over the place and we are supposed to guess from context what is really meant. As a result people get misconceptions about what is meant be the electromagnetic (EM) field. For some physicists (Feynman) the EM field is nothing, but numbers attached to points in space. For others the EM field is physical, but still described completely by numbers attached to points in space. The numbers obey Maxwell's and the other equations of electromagnetic field theory. The field does not move. There is only one EM field, and it fills all of space. Since there is only one, it is always singular. It should always be the EM field and never a EM field or an EM field. Charged particles do not have EM fields. Rather, they influence the value of the EM field around them. Far away particles can also influence the local field by EM radiation.

When you hold your hand out in bright sunshine, you can feel EM radiation. EM radiation is a real physical phenomenon. The EM field is a tool invented by humans. Of course, the EM field and EM radiation are not the same. However, the concept of the EM field readily accommodates both EM radiation and static EM forces. There is no great wrong here that needs to be righted. Constant314 (talk) 02:38, 23 January 2024 (UTC)

I think maybe Bill field pulse is referring to the difference between the near fields and far fields of a source of electromagnetic radiation. Bill, the article does mention this issue: the introduction says "Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them . . ." although maybe this could be stated more clearly.

Electromagnetic waves are defined as the part of the field of accelerating charges that can carry energy arbitrarily far away from the charges. Unless they are reflected back to the source charges, they cause the source to lose (radiate) energy. Close to moving charges there are other components of the oscillating electric and magnetic field which just store energy in the space around the charges. If there is a conductor near the moving charges, the alternating electric field can induce a charge in it by electrostatic induction, and the alternating magnetic field can induce current in it by electromagnetic induction. The latter is how motors and generators work. But if there are no nearby conductors, the energy just stays close to the charges, stored alternately in the electric and magnetic field. These are usually called the induction fields or near fields. --Chetvorno^TALK 11:41, 23 January 2024 (UTC)

Chetvorno, I appreciate your effort to see intelligence in my comments. Classically experimenters thought a field existed around any charge and the field obeyed coulomb law getting weaker with distance. When hairs repel due to static electricity it is said that the surplus electrons on each hair are repelling. The elections stay as far apart as possible. When current travels on a wire the free electrons are said to be on the outside of the wire. This is all considered evidence that electrons have fields on them which reach distances far beyond simple atomic distances. If a charge moves quickly the rather large field around it would need to be super rigid not to lag behind. I believe it is not infinitely rigid and that it arrives a very tiny instant later (at the speed of light is very very rigid but not infinitely rigid.) This slight non infinite rigidity is necessary for a field around a fast charge to differ from a field around a slow charge. The slightly compressed field causes magnetism. Bill field pulse (talk) 21:27, 23 January 2024 (UTC)

John J Barton mentioned the near and far field again and I had a second look at your answer, and the article. You seem to be right the far field and near field seem to capture the difference I am talking about without needing to get into particle effects. That the near field effect diminishes with 1/r x 1/r makes perfect sense since it is governed by Coulombs law. That the far field which is the essentially the EM radiation requiring photons diminishes with 1/r also is possible because the photons don't loose strength they only become further apart.

I think the EM Field article only refers to far field effects and even has a drawing of this. I would like to see near and far field effect and link holding a higher place in the EM Field article. Having only the picture of the far field effect misses the near field reality. What do you think?

Thanks for something I did not give nearly adequate thought the first time I read your reply. Sorry for that . Bill field pulse (talk) 21:18, 27 January 2024 (UTC)

Thank you for taking a little time to discuss this it is much appreciated. When you have an electron surplus on two metal coated balloons separated a small distance and no radiation. How do you see them repelling each other what goes between the balloons. I am curious to understand the mechanism you see. Perhaps I am only using different terms and need to learn yours? Bill field pulse (talk) 21:10, 23 January 2024 (UTC)

If Constant314's distinction is accepted (between EM radiation as real physical phenomenon vs. EM field as tool/human invention), then "consists of" in the lead sentence is misleading (because it suggests that radiation is composed of waves). The second source citation seems to try to express that distinction (to some extent), but it could be emphasized more explicitly, while the first cited source (Purcell) only refers to the properties of electromagnetic waves, but does not connect that discussion to the meaning of radiation. Same point for the second sentence. There are other sources (e.g., Zangwill, Griffiths) that give more precise ways to indicate the meaning of electromagnetic radiation. Sdc870 (talk) 14:50, 12 November 2024 (UTC)

I am not clear on why you think Wikipedia "does not see a difference"; we do have a separate article at Electromagnetic field. VQuakr (talk) 22:24, 23 January 2024 (UTC)

The electromagnetic field is something which is around a charge and drops of with distance squared. The primary cause of quantization of the electromagnetic field is that charges are quantized. The net steady EM field we measure is the result of "billions" of tiny EM Field caused by "billions" of moving charges. Electromagnetic radiation is very different. An electron continuously produces an EM field in all directions and in rare instances it sheds or absorbs a whole photon as radiation.

Look at the article electromagnetic field there is a picture of an entity which moves in one direction without loosing strength; it is a classic diagram of electromagnetic radiation. Look at the electromagnetic radiation article, it is the same diagram!!! Why not say "see electromagnetic radiation in the electromagnetic field article".

It is very easy for beginners to mix up the em field moving out in all radial directions around a charge at the speed of light and em radiation moving out at the speed of light in a single direction; both must move at the speed of light and I can explain why in detail if you are interested. Bill field pulse (talk) 21:39, 24 January 2024 (UTC)

I think you have some things confused. The drawing Onde electromagnetique.svg on both pages is showing the same thing: an electromagnetic wave, as it says in the caption of both. This drawing is in the Electromagnetic field article because electromagnetic radiation is one phenomenon or aspect of electromagnetic fields. I don't see anything misleading or confusing in these two articles. What specific changes or edits would you like to make? --Chetvorno^TALK 01:49, 25 January 2024 (UTC)

I would like to see the Electromagnetic radiation article focus primarily on electromagnetic radiation. I would like to see the electromagnetic field article focus primarily upon non radiant fields with a note linking to the electromagnetic radiation article. Lastly, I would like to see quantization of the electromagnetic field focus on the quantization of charges whereby all the small fields around charges sum together to produce a net EM field. Ideally, the quantization of electromagnetic radiation would be in a section with a heading "The quantization of Electromagnetic Radiation. Bill field pulse (talk) 18:22, 25 January 2024 (UTC)

Convenience links: Quantization of the electromagnetic field, Electromagnetic field. @Bill field pulse: I don't feel your comments so far are specific enough to be actionable. Can you present what you are proposing (or a part of it) in a clear "change x to y" format with the exact text and sources you would like to add/change? VQuakr (talk) 19:14, 25 January 2024 (UTC)

I made a very small change to start with..... I added "if any" to radiation out of a wire and removed "propagated at" since radiation has a frequency or is propagated with a frequency.

You can delete or reword. Note the magnetic field around a wire is not radiation. Radiation occurs when it is intended or when the design is poor. Bill field pulse (talk) 20:04, 25 January 2024 (UTC)

Reverted. Radiation occurs but can be minimized by the nature of the design. VQuakr (talk) 20:24, 25 January 2024 (UTC)

Yes there are very few photons produced inside household wires. It is 99.999% the EM Field that things like current meters measure Bill field pulse (talk) 18:35, 26 January 2024 (UTC)

Any time there is any change in the electromagnetic field, it is communicated to the rest of the universe as radiation. Constant314 (talk) 18:44, 26 January 2024 (UTC)

I think that only changes due to electrons changing energy levels are communicated via photons. The continuous changes in ac current are communicated by the field itself which drops quite fast with distance squared. Bill field pulse (talk) 18:54, 26 January 2024 (UTC)

It is still radiation, regardless of the mechanism. Constant314 (talk) 19:39, 26 January 2024 (UTC)

I think I visualize a mechanism and you don't see the point. but my silly mechanism lets me look at how quarks might move and how gravity and strong force might arise perhaps leading to experiments Maxwell used mechanisms Einstein used an elevator and stuff to visualize things. Bill field pulse (talk) 20:09, 26 January 2024 (UTC)

Even Newton said he does not know the mechanism for gravity but if he knew of quarks you can bet he would have come up with a mechanism Bill field pulse (talk) 20:11, 26 January 2024 (UTC)

@Bill field pulse: I think I visualize a mechanism... is this your theory? This is an encyclopedia, not a journal: we don't publish original work. VQuakr (talk) 20:44, 26 January 2024 (UTC)

I shall try not to do any thinking which is original Bill field pulse (talk) 19:38, 27 January 2024 (UTC)