Can anybody explain why only IR radiation has the heating effect?

Answer 1

Actually that's not entirely true.

Answer 2

The others have explained it well, but let me give you something else to think about. What is temperature? It is really a measure of the average energy an object has. However the individual particles that make up that object have a wide range of energies. If you look into even deeper you find that there are different kinds of temperature. There is rotational temperature, vibrational temperature, electronic temperature...etc. At equilibrium, these temeperatures are all equal. But lets say you hit an object with UV radiation and excite an electronic quantum level. At that moment the electronic temperature is higher than the vibrational or rotational temperatures. Depending on the relaxation mechanism for the material, it may excite the vibrational and eventually the rotational levels until everything is at equilibrium, and the macroscopic effect you see would be heating.

Answer 3

As indicated by others, heating is not limited to IR photons. The energy carried by a photon is E=hv, where h is Planck's constant and v is the frequency. Berens correctly touched on the subject of equipartition of energy among the various degrees of freedom--rotational, vibrational, electronic. The energy held in each degree of freedom is 1/2k_sub_BT, where k_sub_B is the Boltzman consant and T is the temperature in Kelvins. One can easily see that the heat capacity of a material is related to the number of degrees of freedom. One missing piece that has not been mentioned previously is that the absorption cross section (a measure of the probability that the photon will be absorbed) is a function of frequency. The absorption cross section is proportional to the density of states, which is rather high in the IR region. Although IR photons carry little energy compared to photons at visible wavelengths, the probability of absorption is very high. For water, the absorption cross section is larger by a factor of about 1E7 for IR, as compared to visible wavelengths. Because IR photons have a high probability of absorption for most materials (or more precisely those with a change in the molecular dipole moment for a normal mode of vibration), IR photons transmit energy more effectively than photons with lower absorption cross sections.

Answer 4

The premise is wrong. All frequencys of light carry energy and thus potentially can "heat" a surface. How much "heat" is created in the surface depends on how much light is absorbed by the surface, and how much is reradiated which is highly dependent on the nature of the surface and the wavelength of the light. IR light is easier for many surfaces to absorb. A lot of higher frequency light is actually absorbed, converted and later reradiated as IR.

Answer 5

You are mistaken, other radiation has a heating effect. IR is just better at it than others....much better. It also depends upon your definition of heating effect. That is the nature of energy and efficiencies.

Answer 6

Actually, this is not true. ANY wavelength of electromagnetic radiation, when absorbed, can heat an object.

I.R. is normally associated with heat because objects at commonly occuring temperatures (on planet Earth, anyway) radiate mostly in I.R. wavelengths.

Answer 7

The other answers said it already, but here's an example that may help you. Consider the microwave oven, which clearly has a heating affect, but operates at a much lower frequency (~2.45GHz) than IR.

Answer 8

Ever heard of the microwave oven?

Answer 9

Not true