Re: [Phys-l] Greenhouse gases

[Bernard Cleyet <bernardcleyet@redshift.com>]

This is another case of bad test questions.

D is correct, but NOT what makes gasses green house gasses.  It's an  
artifact of their character.**  What makes a gas green house is its  
absorption in the mid and far IR and its transmission in the near and  
visible.   This is because, not the mechanism, which was your  
principal question, most of the sun's energy is in the vis. and near  
IR; not the UV.

Regarding your mechanism question, its dealt with in most optics  
texts, e.g. Jenkins and White.

Again not the basic mechanism you desire, but that of simple global  
warming (greenhouse) is found in wiki's Greenhouse effect page.

http://en.wikipedia.org/wiki/Greenhouse_effect

Especially note:

http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png


**Note O3/2 are anti-greenhouse gasses as they absorbs UV and  
transmits vis. and IR.   The absorption above 190 nm is due to O3, as  
O2 completely absorbs below 190, and is transparent above thru the vis.

bc


On 2009, Jun 11, , at 04:32, Brian Whatcott wrote:

> Casting around for context, I recall that greenhouse gases attract  
> that
> name by
> acting like a blanket while passing light, and I recall the warnings
> that it is too easy to become sunburned on an overcast day.
>  On the basis of these possibly irrelevant, even doubtful data,
>  I need to vote for D
>
> Brian W
>
> Ken Fox wrote:
> > I am not at all sure what the mechanism for the process in this  
> > question is.
> > This comes from a recent IB Physics exam, aimed at a Honors HS or  
> > early
> > college level student. I'd like to be able to explain it on that  
> > level.
> >
> > Greenhouse gases
> > A reflect IR radiation but absorb UV radiation.
> > B reflect UV radiation but absorb IR radiation
> > C transmit IR radiation but absorb UV radiation
> > D transmit UV radiation but absorb IR radiation
> >
> > I apparently don't know what happens to photons when they interact  
> > with any
> > kind of material, (metals, dielectrics or gases) to ultimately  
> > just be
> > absorbed, transmitted or reflected. Is there a brief answer?
> >
> > Thank you
> >
> > Ken Fox
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>
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