Different regions of the electromagnetic spectrum interact differently with matter:

  • Microwave radiation can induce molecular rotation.

  • Infrared radiation can induce molecular vibration.

  • Visible and ultraviolet light can induce electron excitation.

  • X-rays and gamma rays can induce ionization.

Is there any activity specific only to radio waves? I kept on thinking how radio waves are used in NMR but I don't know what to call it.

  • 2
    $\begingroup$ Radio waves are weak; they can't do anything of the above, which leaves us with your suggestion on NMR. $\endgroup$ – Ivan Neretin Sep 4 '19 at 15:25
  • $\begingroup$ While NMR is in principle the energy range of radio waves, actual instruments do not use interaction with electromagnetic radiation, but only induce and detect near-field magnetic interactions. There are no actual photons emitted or absorbed by your sample. The advantage is of course that you can create and perfectly detect (phase sensitive!) any kind of waveform. $\endgroup$ – Karl Sep 4 '19 at 20:34
  • 1
    $\begingroup$ "actual instruments do not use interaction with electromagnetic radiation, but only induce and detect near-field magnetic interactions." Certainly NMR is not like UV-Vis, but pray what is the job of the radio-frequency transmitter then? $\endgroup$ – M. Farooq Sep 7 '19 at 14:36
  • $\begingroup$ @M.Farooq The "transmitter" powers the pulsed radio frequency $B_1$ field. It never decouples from the probe coil to become electromagnetic radiation, i.e. actual photons. Here onlinelibrary.wiley.com/doi/abs/10.1002/… is the classical text on the matter. $\endgroup$ – Karl Sep 8 '19 at 22:06
  • $\begingroup$ @Karl, the article is worthwhile and they correctly suggest that the concept of radio wave absorption and emission is rampant. However, no one can generate an isolated oscillating magnetic field without an accompanying electric field in a RF coil. This pulse is electromagnetic in nature. See RF coils - for non physicists in the same journal ncbi.nlm.nih.gov/pmc/articles/PMC6175221 $\endgroup$ – M. Farooq Sep 8 '19 at 23:47

This is a bit of a stretch, but the Zeeman and Stark effects are linked to radio frequencies, in that line splitting of a visible spectral frequency (~10^15 Hz) can give rise to a beat-frequency in the RF. Your answer of NMR, though, is more applicable. The most general term for precession in a magnetic field is Larmor precession.


Radio waves $10^4$ to $10^{11}$ Hz are not that innocent as is commonly purported. Long time ago there was an demonstration that radio waves of certain frequency can decompose salt water into hydrogen and oxygen (and ignite). There was an article in Popular Mechanics. No other type of radiation can cause this effect. See the video of burning here Burning salt water. John was trying to cure his cancer but died at young age in early 60s.

Radiofrequency is routinely used to generate argon plasma for atomic spectroscopy (which heats it up to the temperature of the Sun). One spectroscopist had jokingly mentioned that a senior advised him not to work with this equipment because it may make you sterile.

For the information of some readers who think microwaves and radiowaves are different, radio waves include microwaves. Microwaves are basically high frequency radio waves. http://wifiinschools.org.uk/15.html

Both microwaves and radiowaves can easily generate plasmas and atomic spectroscopy can be done with both.

  • 2
    $\begingroup$ This video and the now missing self-published journal report are highly suspect. Nowhere do they mention the intensity of the radiation required (while seeming to imply that they get more energy out than put in). Yes, high intensity RF can generate plasmas and possibly other effects (the 1kW or so of RF power in a microwave can generate plasma easily) but this is hardly more impressive than being burned by the IR from a domestic toaster. $\endgroup$ – matt_black Sep 6 '19 at 15:30
  • $\begingroup$ $10^{11}$ is deep in the microwave regime. A hundred Gigahertz. Your kitchen microwave oven runs at 2.45 GHz. And a plasma is electrically conductive, and you need an electrical discharge to start it. $\endgroup$ – Karl Sep 6 '19 at 19:35
  • $\begingroup$ en.wikipedia.org/wiki/Rotational_spectroscopy , done in the tens of GHz. $\endgroup$ – Karl Sep 6 '19 at 19:44
  • $\begingroup$ Radio waves do not generate plasma, you can heat and thereby keep alive a plasma with high power radio waves. Or you can generate an electric spark with radio waves, if you have a conducting antenna. Youre leaving out the central pieces of your statements. $\endgroup$ – Karl Sep 8 '19 at 22:25
  • $\begingroup$ No need to split hairs here. It might be better if you write a separate detail reply to the original query. In the ICP torch, there is an initial seeding to create ions in the argon gas, and the RF coil transmits power (inductive coupling) and creates a sustained plasma. $\endgroup$ – M. Farooq Sep 8 '19 at 23:24

Radio waves have a longer wavelength than infrared radiation and is classified between 3Hz and 300MHz frequencies. Due to its lower energy/longer wavelength, radio waves are able to penetrate deeper than higher energy radiation. For example, the skin depth is a function of frequency: $$\delta = \sqrt{\frac{2 \rho}{\omega \mu}}$$ where $\rho$ is the conductivity, $\omega$ is the angular frequency, and $\mu$ is the magnetic permeability. As the frequency increases, the skin depth decreases. This is the reason AM and FM radio (in the kHz range) is able to travel very large distances, while your standard 2.4GHz wireless router has poor connectivity through walls.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.