As we know, two bodies undergo radiative heat exchange due to each emitting a spectrum of light according to its temperature (blackbody radiation).

When one body is hotter than the other, it emits a higher magnitude of light at each frequency. Thus the heat flow is from the hotter body to the colder body, even though light is exchanged in both directions.

My question: as the photoelectric effect showed even a large magnitude of light of the 'wrong' frequency can't eject an electron, has the experiment been done where a large magnitude (high amount of W, i.e. not according to blackbody radiation) of low-frequency light was directed to an object to observe if the large amount of low-frequency light heats the object?

Or is it not possible for other reasons?

  • $\begingroup$ physics.stackexchange.com/questions/310631/… $\endgroup$
    – Shashaank
    Nov 22, 2023 at 15:09
  • $\begingroup$ Have you used a heater , placed something near it, does it get hot? the experiment is done everyday in winter, and yes, the molecules making up solids have a lot of energy levels that can be considered almost a continuum, so photons are absorbed and their energy turned into kinetic energy/heat $\endgroup$
    – anna v
    Nov 22, 2023 at 16:00
  • $\begingroup$ Yea but the heater's temperature is larger than the object it's heating. The Q is if a lower-frequency light is used (say the light a -50C object would peak at with blackbody radiation) can it heat an object? $\endgroup$
    – Cloudyman
    Nov 22, 2023 at 16:29

1 Answer 1


Interesting question.

so ,in simple words ,what you want to know is that ,would the low freq. rays which could not cause photoelectric effect ,would at least heat the object up . and yes ,it would .

simply think of it like this ,if we were to compare net energy of :

  1. a high energy photon (high freq.) and 2. low energy photon (low freq.) of course , 1. would have higher energy ,right?

now ,taking both in 'large' quantity , of course the net energy of beam with 1. would be higher ,enough to overcome the E.M. attraction between electron and nucleus, which beam of 2. would not be able to ,since not enough net energy.

but ,of course ,it has non zero amount ,and it may not be able to cause photoelectric effect, but it would still increase net kinetic energy of molecules in the body, thus increasing it's temperature.


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