Wikipedia:Reference desk/Archives/Science/2023 January 23

= January 23 =

Electricity and radio waves.
So I'm hearing electricity emits radio waves. Is that the case for both DC and AC electricity? Then can those radio waves interfere with other radio waves, or is it too low of intensity? Thanks. 67.165.185.178 (talk) 03:08, 23 January 2023 (UTC).


 * A steady direct current does not produce radio waves. Any change in current does produce electromagnetic radiation, not only for AC where the current keeps alternating, but for all changes. With an abrupt change, such as when a DC circuit is interrupted, the frequency of the wave is spread out all over the spectrum and may be noticed on any nearby receivers. This is very common for lightning. For an AC current the wave has the same frequency as the current, typically 50 or 60 Hz. The wave induces a weak current in nearby conductors. This is a known source of interference with sensitive nearby equipment, such as for taking electrocardiograms. It will interfere with other radio waves at the same frequency, but that part of the electromagnetic spectrum is not used for transmitting signals – the lowest that has been used (AFAICT), for communication with submarines, was Project Sanguine's 76 Hz. Theoretically, it has some effect on AM radio signals, but this effect will normally be not or hardly noticeable. There is no risk of interference with an FM radio signal, since these are modulated at much higher frequencies. The risk of interference with a digital signal is very low unless that signal is extremely weak. --Lambiam 12:03, 23 January 2023 (UTC)
 * Alternating current produces what is known as mains hum in audio equipment. Controlling for it has been the bane of every audio engineer since there has been electrically recorded music.  Joseph Larmor, for whom is named the Larmor principle, established that accelerating electric charges always emit electromagnetic radiation, and established the math by which it occurs.  50 or 60 Hz (one of which is the standard frequency of AC in most places) falls within the radio band, so yes, AC current produces radio waves.  Because DC doesn't have any accelerating electrons (since they don't really change directions), it doesn't emit any RF radiation.  -- Jayron 32 12:54, 23 January 2023 (UTC)
 * In the days before electronic ignition in cars the spark was obtained by breaking a steady DC current. This should have been suppressed, but older cars were known to disrupt both radio and the old VHF TVs.  On occasions you would be able to hear the car approaching and receding (by the strength of the interference) and sometimes even work out gear changes because the frequency of the interference changed. Martin of Sheffield (talk) 13:05, 23 January 2023 (UTC)
 * In that case, the "breaking" of the DC current created an RF because you're basically rapidly turning on-and-off the current, creating accelerations of the electrons; which is what generates the RF; it's basically an AC generated by rapidly switching it on-and-off. Steady DC doesn't do that.  -- Jayron 32 14:01, 23 January 2023 (UTC)


 * Deliberate radio signals started by using this phenomenon – see Spark transmitter. Because the signal included a broad band of wavelengths and could not be tuned, everyone with a transmitter/receiver within range received it, so to avoid chaos, users had to know and stick to strict rules, and (in the UK) they had to pay for a Government licence to possess the equipment. This persisted and covered pure radio receivers, and one had to have a Radio license to own one in the UK within my lifetime.
 * When invented, TV receivers also required a much more expensive TV license, and as they became more common the Radio license was merged into it and eventually dropped as a separate entity. This is why in the UK, even if one were never to tune in to Government-funded TV channel broadcasts (i.e. the BBC), one has to pay for a license (which also covers some online services) simply to possess a working TV receiver at a given address. {The poster formerly known as 87.81.230.195}2.218.227.45 (talk) 18:57, 23 January 2023 (UTC)
 * That's true for the UK. The OP geolocates to Illinois, and I don't know that such a license has ever been required in America. Of course, we have almost the same thing now, with the use of cable and its attendant taxes. ←Baseball Bugs What's up, Doc? carrots→ 19:06, 23 January 2023 (UTC)
 * I wasn't suggesting it was the case worldwide, or that it necessarily applied to wherever the OP is, which I didn't bother to snoop on. I was attempting to add some related historical information that I thought might be quite interesting to some readers. Silly me. Silly, silly me. {The poster formerly known as 87.81.230.195} 90.199.212.198 (talk) 08:22, 24 January 2023 (UTC)
 * Although I did not have a TV receiver in the sixties and seventies, I paid the licence fee to be spared further (scary) raids by agents who apparently assumed no household was without a TV set. --Lambiam 09:39, 24 January 2023 (UTC)
 * They had no legal power to enter your residence without permission or evidence. I too never had, and still don't have, a licence, because I have never myself owned a TV, or lived in a household with one for over 40 years: I simply used to tell them politely (and truthfully) that there was no TV on the premises and shut the door. {The poster formerly known as 87.81.230.195} 90.199.212.198 (talk) 17:21, 24 January 2023 (UTC)
 * I lived upstairs and could not see who was at the door nor communicate through a closed door, so when the doorbell rang I used to open the door and shout down the stairways, Who is it? So then instead of replying they'd storm up the stairs. I was told (right or wrong) that the police would only laugh at me if I tried to make a report. --Lambiam 11:05, 26 January 2023 (UTC)
 * It does emit radio waves under certain circumstances, assuming electromagnetic fields are properly aligned along the direction of electric current. Serratra (talk) 05:31, 30 January 2023 (UTC)

So the radio waves is correlated with frequency, right? 50-60 Hz. How much Hz is needed to cause it to emit the next type of radiation, micro waves? 67.165.185.178 (talk) 08:32, 26 January 2023 (UTC).


 * Look for "Microwaves" in the table at Electromagnetic spectrum and you will see they have frequencies of 300 MHz to 30 GHz. Reading the whole article is likely to answer other questions you may have about radio waves. Philvoids (talk) 09:35, 26 January 2023 (UTC)
 * I did a Ctrl F, type in ac e for AC electricity, it only showed up in the radio waves section. Similarly, typing in alternating, for alternating current, returned no results. 67.165.185.178 (talk) 13:29, 26 January 2023 (UTC).
 * High-frequency waves can be produced by a cavity resonator, such as the cavity magnetron or the klystron, as well as by any of several designs for electronic oscillators, such as the Vackář oscillator. They can also be used in combination, where the oscillator allows for fine tuning while the resonator boosts the energy output. --Lambiam 19:29, 26 January 2023 (UTC)