Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: AdiDex on August 17, 2015, 04:01:31 AM
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Usually when anybody refers infrared radiation he says that we experience it as heat , why it is so ? why we don't perceive UV or visible radiation as heat ?? What biological process is behind of this ??
I think it is something about providing energy to our organic molecules which lead to some excitation which results some electrical impulse so we perceive it as heat .
As excitation can only occur by some of the particular range of radiation so that why it is so.
Can anybody help me ?
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I think you're on the right lines. Remember, our bodies are mostly water, which (along with many organic molecules) strongly absorbs infrared, while it is transparent in the visible and UV. Visible or UV radiation will also cause heating if absorbed, e.g. a black car gets hotter on a sunny day than a white one.
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I think you're on the right lines. Remember, our bodies are mostly water, which (along with many organic molecules) strongly absorbs infrared, while it is transparent in the visible and UV. Visible or UV radiation will also cause heating if absorbed, e.g. a black car gets hotter on a sunny day than a white one.
may be i got something more precise -:
In General ,
infrared radiation causes transition between molecular vibrational states wheres visible and UV cause transition between molecular electronic energy levels .
(Reference to Chemistry3 Burrows, Oxford Publications , Pg. No. 81 .)
So this should be the reason .
you mentioned earlier that our body mainly consist water , and i have read that water vapor is the reason of Global Warming because of its high heat capacity
Can you give me more precise answer ?
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[...] why don't we perceive UV or visible radiation as heat ? [...]
Yes we do!
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I don't really understand the question....
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The blackbody radiation spectrum for objects at temperatures of around 300K is predominantly in the IR range:
http://hyperphysics.phy-astr.gsu.edu/hbase/bbrc.html#c4
If the world were 20x hotter, heat would be radiated primarily as visible light, which is what occurs on the sun.
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I don't really understand the question....
How may i help you to understand the question ?
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The blackbody radiation spectrum for objects at temperatures of around 300K is predominantly in the IR range:
http://hyperphysics.phy-astr.gsu.edu/hbase/bbrc.html#c4
If the world were 20x hotter, heat would be radiated primarily as visible light, which is what occurs on the sun.
that's sound nice but mine question is different .
Why we perceive IR as heat ? why don't UV or Visible radiation as heat ?
Technically speaking IR, UV and visible all are form of energy (Heat from another perspective ) . but usually when we are standing beside a bulb we feel heat , what we feel is because of IR only not because of visible light .
My question is that why we can't feel Visible light from our skin ??
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Why we perceive IR as heat ? why don't UV or Visible radiation as heat ?
Technically speaking IR, UV and visible all are form of energy (Heat from another perspective ) . but usually when we are standing beside a bulb we feel heat , what we feel is because of IR only not because of visible light .
My question is that why we can't feel Visible light from our skin ??
You can perceive both IR and visible light as heat. Some wavelenghts may be absorbed more than others, but any light that gets absorbed by your skin will heat up your body (otherwise, visible light lasers could not cause burns).
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Which is because, excited state relaxation after electronic excitation is, in the overwhelming majority of cases, driven by internal conversion of the absorbed energy to molecular kinetic energy (vibrations, rotations, etc.). Literally, absorption of UV and visible radiation heats the absorbing sample with high efficiency.