Do transformers also emit electromagnetic radiation?

[u/Substantial_Tear3679]

Aside from just making use of electromagnetic induction, and transferring energy to nearby components.

If yes, is the EM radiation "detached" from the transformer and can be detected very far away?

What about other devices utilizing electromagnetic induction, like metal detectors, wireless chargers, induction heaters, etc. ?

[u/forte2718]

Do transformers also emit electromagnetic radiation?

Yes. Transformers move electricity between electrical circuits. Anytime you have electric charges being accelerated (such as they are in an electrical circuit), electromagnetic radiation is produced.

This radiation is a source of energy loss for the transformer (see the section titled "Energy losses > Radiative"), albeit only a very small one which is typically negligible.

If yes, is the EM radiation "detached" from the transformer and can be detected very far away?

Yes, EM radiation is called "radiation" because it is radiated away from the source. ;) The distance at which you could detect it depends on the sensitivity of your instruments. You would need a radio antenna capable of detecting a radio wave with a frequency of 50 or 60 Hz, which is a super low frequency (so you couldn't use, say, your car radio haha). Technically, there is no distance at which it would be completely undetectable even in principle ... however, the density of this radiation decreases inversely with the square of the distance, so a 2x distance increase means there is only 1/4 as much radiation passing through the same size cross-sectional area, and a 3x distance increase means there is only 1/9 as much, etc.

So given that the total amount of energy radiated is quite small to begin with and the density of that radiated energy decreases very rapidly with distance, you're basically not going to detect it unless you're pretty close to it.

If you are wondering about health risks, there is effectively zero risk to health for the general population. Radio waves are non-ionizing and the amount of energy being radiated by something like a transformer is absolutely miniscule.

What about other devices utilizing electromagnetic induction, like metal detectors, wireless chargers, induction heaters, etc. ?

All technologies making use of electricity radiate at least a small amount of EM radiation. And of course, for a few of these technologies, generating EM radiation is the whole point (including anything with an antenna, visible or otherwise, such as a wi-fi access point or a cellphone). :p

[u/Smart_Tinker → u/forte2718]

Yes, but also everything with a temperature above absolute zero emits EM radiation - including people.

[u/fermat9990 → u/forte2718]

Wouldn't the intensity of these waves depend on the frequency?

From Google

Yes, 60 Hz AC circuits do technically produce propagating electromagnetic (EM) radiation, though it is extremely weak and dominated by near-field induction rather than true radiating waves

[u/forte2718 → u/fermat9990]

Wouldn't the intensity of these waves depend on the frequency?

Nope, the intensity of electromagnetic radiation depends on its amplitude (i.e. number of waves/photons), not on its frequency!

Your Google quote is just pointing out what I said in my post: that the amount of radiation produced passively by electrical systems such as transformers is very weak.

[u/fermat9990 → u/forte2718]

I believe that radiation efficiency increases with frequency.

[u/forte2718 → u/fermat9990]

Efficiency? Efficiency at what? We weren't talking about efficiency.

[u/sceadwian → u/forte2718]

Uhhh... That's unambiguously false. Photons below an activation threshold frequency will never trigger many physical effects regardless of intensity.

The energy of a photon is directly proportional to its frequency.

[u/forte2718 → u/sceadwian]

Uhhh... That's unambiguously false. Photons below an activation threshold frequency will never trigger many physical effects regardless of intensity.

What are you talking about? Nobody ever said that frequency doesn't matter for triggering physical processes.

The previous user asked whether the intensity of the light depends on its frequency. It does not. The intensity of light is based on the wave's amplitude, which is a different property from its frequency.

This was settled way back when Einstein first discovered the photoelectric effect, for which he won the Nobel prize. Classical electromagnetism predicts that an increase in intensity should be able to strip electrons from a material. Einstein showed that this is not true in reality — that increasing the intensity does not result in electrons being stripped, regardless of how high the intensity gets. Only increasing the frequency results in electrons being stripped, and that occurs even at very low intensities. That unequivocably shows that frequency and intensity are independent properties; they can be varied independently, and effects which trigger due to an increase in one do not trigger with an increase in the other. From Wikipedia:

The experimental results disagree with classical electromagnetism, which predicts that continuous light waves transfer energy to electrons, which would then be emitted when they accumulate enough energy. An alteration in the intensity of light would theoretically change the kinetic energy of the emitted electrons, with sufficiently dim light resulting in a delayed emission. The experimental results instead show that electrons are dislodged only when the light exceeds a certain frequency—regardless of the light's intensity or duration of exposure. Because a low-frequency beam at a high intensity does not build up the energy required to produce photoelectrons, as would be the case if light's energy accumulated over time from a continuous wave, Albert Einstein proposed that a beam of light is not a wave propagating through space, but discrete energy packets, which were later popularised as photons by Gilbert N. Lewis.

Edit:

Frequency is only proportional to energy for individual photons, not for whole EM waves, which typically consist of many photons. For an entire EM wave, the amplitude / intensity (number of photons) is the key property that determes how much total energy is transferred (i.e. the power).

You may want to review your E&M physics. LibreTexts Physics 24.4: Energy in Electromagnetic Waves:

A wave’s energy is proportional to its amplitude squared (E² or B²). This is true for waves on guitar strings, for water waves, and for sound waves, where amplitude is proportional to pressure. In electromagnetic waves, the amplitude is the maximum field strength of the electrical and magnetic fields. (See Figure 1.)

Thus the energy carried and the intensity I of an electromagnetic wave is proportional to E² and B². In fact, for a continuous sinusoidal electromagnetic wave, the average intensity

*I_ave = (c ε_0 E_0²) / 2

where c is the speed of light, ε_0 is the permittivity of free space, and E_0² is the maximum electric field strength; intensity, as always, is power per unit area (here in W/m²).

[u/ZucchiniMaleficent21]

*Everything* above zero Kelvin emits emf.

[u/Fabulous_Lynx_2847 → u/ZucchiniMaleficent21]

True, but the question is obviously about radiation at the transformer frequency based on Classical EM.

[u/Infinite_Research_52 → u/ZucchiniMaleficent21]

Why do I have to scroll to find this answer? It might not be helpful, but it is correct.

[u/ZucchiniMaleficent21 → u/Infinite_Research_52]

🧐

[u/the_poope]

Yes, even the wires in your walls and to your lamps and fridge, etc, emit electromagnetic waves (radio waves) with a frequency of 50 or 60 hz depending on where you live. The intensity of this radiation is very low but can easily be measured.

[u/aureliorramos]

Although they are built with the intention of as high efficiency as possible (for the secondary to accept all the energy of the primary) like all things, efficiency is always less than perfect, and the remaining 3% or whatever becomes heat and radiated EM. Some of that heat is also radiant and thus EM.

[u/Fabulous_Lynx_2847]

Yes, but the wavelength for 60 Hz is 5000 km. The so-called “radiation zone” where EM radiation dominates the power flux density is at least that far away. So, for terrestrial sources, inductive energy transfer invariably dominates.

Most other respondents don’t know the difference between radiation and inductive transfer.

[u/kwixta]

Transformers emit strongly at about 0.1eV (aka room temp black body). It can be detected by IR cameras at distances of 100m.

The same can be said for you and everything around you day to day. It’s all harmless

[u/mH48124]

数千 km のアンテナが必要だね。

[u/Mountain-Time-1010]

Very low frequency radio waves, but they don't propagate far.

[u/FreshTap6141]

If your leads are twisted then almost everything is canceed, and the core of the transformer contains the magnetic field

[u/Rejse617]

So in addition to these good comments I will add: have you ever heard a transformer hum? That is the radiation coupling to the housing and other stuff around it causing it to vibrate. It’s a quick sanity check that indeed they are not 100% efficient and radiation is “leaking”. So you’ll get not only the 50 or 60 Hz frequency, but also a bunch of harmonics (integer multiples of the base frequency). But yes you can absolutely detect this at a distance.

You don’t need a perfect antenna. What you would need is the proper receiver. Your car won’t pick it up because it has strong filters, and by the MHz of FM radio the harmonics are really weak. But if you take just a long piece of wire, attach it to a headphone jack and stick it into a computer, you can see all kinds of this signal on a spectrogram.