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Is this what happens to heat physically when moving from HOT to LOW

  1. Dec 8, 2012 #1
    I was just bored during a lecture and started dozing of, then I had an idea of how heat travels. I tried searching in google if I was right, but I didn't know what to type (I tried stuff to do with second law of thermo, and IR photons travelling but couldn't find anything).

    So yeah I thought I'd ask you lot before the physicsforum because I cba to find my login/pass, when atoms vibrate/move/rotate it emits heat radiation (IR photon), what my original thought was how can these randomly emitted IR photons at random angles travel to the cooler region.

    That's when it hit me, is it because when IR photons are produced and come in contact with another atom, "all or nothing" law occurs, so either the IR photon is absorbed by the neighbouring atom or it isn't, and if it isn't or the IR photon is in the ER field of the atom, it causes the photon to be repelled by the atoms ER field thus changing the angle of the IR photon. Because the cooler region, well between the cool and hot region is a gradient of hot -> cool, thus atoms are more likely to absorb the IR photons between the gradient rather than anywhere else eventually levelling the energy of all atoms in the gradient, thus for all the deflections occurring from the IR photon to atoms, it's more likely to travel through the gradient because it will end up reaching there even if it didn't start at those atoms because other atoms NOT in the gradient are most likely at there minimum energy needs so no need to absorb any more energy.

    Sorry for the bad explanation, the image is sort of what I mean. Am I correct or ...?

  2. jcsd
  3. Dec 8, 2012 #2


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    Conduction of thermal energy through a gas is due to 'mechanical' interactions between adjacent particles. That's what the standard gas model in kinetic theory is based on. The photons that come into play with molecular 'collisions' are virtual photons (Feynman's model of force mediation between particles). This is not the same as the IR photons which are passed during radiation and absorption at a long distance (as in the greenhouse effect etc.).
    Afaik, the transfer of heat through gases is described pretty well using kinetic theory. Although your idea must have some relevance.
  4. Dec 8, 2012 #3
    I think the fact that heat travels down a temperature grade is purely statistical. Say you have region A emitting X amount of heat and region B absorbing 1/2 of it. Region B is hotter and so emits 2X, and region A absorbs 1/2 of that. So heat transfer from A to B is X/2 but heat transfer from B to A is X so the net transfer is X/2 from B to A.
  5. Dec 8, 2012 #4


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    First of all, heat is not the same thing as infrared radiation. Heat is energy that has been randomly spread out among various degrees of freedom in the system. In other words, heat is not a single form of energy, but rather energy that has been split up among all of the available forms of energy, including kinetic energy of the molecules present (further subdivided into translational, vibrational, rotational), interaction energies, and radiation (such as infrared).

    In most situations you might find on Earth, most of the heat transfer is through collisions between molecules and not through infrared emission.

    So, a high temperature gas comes in contact with a low temperature gas-- the molecules in the high temperature gas are moving faster, bouncing around like crazy. Where they come in contact with the low temperature gas, they bump into each other and the fast particles slow down, and the slow particles speed up.
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