# Infrared waves and heat

## Main Question or Discussion Point

I know there is an equation somewhere that tells the wavelength of light given off by an object at a certain heat. So does this work backwards as well? do you get maximum heating of an object if you heat it with that wavelength light? if so, then you could vary the wavelength as the heat in the object increases to continue maximum heating?

1 more:
is it just a coincidence that infrared electromagnetic waves are considered "heat" waves, the coicidence being that most objects at normal heat give off infrared wavelengths?

do any objects give off things like radio waves when excited or cooled?

Related Other Physics Topics News on Phys.org
I think you're referring to blackbody radiation, whereby a body that has temperature will radiate heat energy, and the frequency/wavelength of that radiation is only dependent on the body's absolute temperature.

I don't think it works the other way round. The amount of radiation absorbed by a body depends on the type of surface, which has no relation to the absolute temperature (that is to say, the type of surface doesn't vary with temperature).

In general, heat in the form of radiation is infrared waves, so I don't think it's coincidence... they are the same thing.

russ_watters
Mentor
For a perfect "black body" the radiation and absorption work exactly the same way and depend on the temperature of both the black body and the incident radiation.

"In general, heat in the form of radiation is infrared waves"
yea that's what everybody tells me, but i'd like alittle better explaination insated of 'this is the way it is, go figure'
\
thanks for any replys so far tho. =]

jimmy p
Gold Member
Dont radiating sources give off waves from all of the electromagnetic spectrum??

Dont radiating sources give off waves from all of the electromagnetic spectrum??

Yes, and the equation works for the wavelength of maximum emission.

russ_watters
Mentor
Originally posted by jimmy p
Dont radiating sources give off waves from all of the electromagnetic spectrum??
Yes, but in the energy levels generally associated with sensible heat, its centered around ir.

Njorl
If you're talking about a true blackbody, then all incident radiation is absorbed and converted to heat. There is no most efficient wavelength. Of course, there are no true blackbodies, just approximations.

To heat true materials, you do best by applying radiation at the electron transition levels. Which transitions to use is temperature dependent, as some levels become depopulated at different temperatures.

Generating light in narrow bands is inefficient though. This is why we don't cook things with lasers. The efficiency you gain by applying the correct wavelengths is not enough to make up for the efficiency you lose generating the light.

Njorl

I think you're referring to blackbody radiation, whereby a body that has temperature will radiate heat energy, and the frequency/wavelength of that radiation is only dependent on the body's absolute temperature.

I don't think it works the other way round. The amount of radiation absorbed by a body depends on the type of surface, which has no relation to the absolute temperature (that is to say, the type of surface doesn't vary with temperature).

In general, heat in the form of radiation is infrared waves, so I don't think it's coincidence... they are the same thing.

I think that infrared just defines a temperature range of heat and is not heat in an exclusive way. When temperature rises to a point that green and yellow light are emitted(as in the solar light spectrum) heat is being produced by almost just as much from these bands than from the infrared band. This is my understanding. In general, I think the confusion arises for many people because they don't understand the difference between heat and radiation. Electroradiation of all kinds can be transformed into heat.

"In general, heat in the form of radiation is infrared waves"
yea that's what everybody tells me, but i'd like alittle better explaination insated of 'this is the way it is, go figure'
\
thanks for any replys so far tho. =]

Hope this will help: Radio-waves can be transformed into heat, but it is usually a low form of energy(frequencies are low) so low emissions of heat are associated with these waves and can't be felt unless you ramp up the intensities. Micro-waves generate heat: as they are absorbed, the absorbing substance uses some of the energy in the form of kinetic movement of its particles and the rest gets transformed into heat(which we take advantage of to "heat our food"). Infra-red also get absorbed into things, transforming some of it(in varying degrees according to the substance) into heat. Most of the heat we feel in normal ranges is associated with the conversion of infrared energy waves into heat energy. But even optical light being absorbed gets to varying degrees transformed into heat. Some light gets absorbed and used to do work(ie photosynthesis) and other parts of that light can get converted to heat. Infrared is not in itself heat. Electromagnetic radiation is a method for transferring energy; heat is another method. Electromagnetic energy can and often is transformed into heat energy.