Date: Thu Feb 8 09:32:43 2007

Author: Wolfgang Rueckner

Subject: Re: CO2 demo

Post:
First, I would like to apologize to the list for posting information
that I had remembered incorrectly. Paul is absolutely right in that
"there is enough IR coming through the band of wavelengths in the IR
between the two absorption bands of CO2" to mask any difference
between seeing through air-filled versus CO2-filled balloons. The
experiment that I had remembered incorrectly was done by Daniel
Rosenberg in which he demonstrated the following:

A fine mesh was put in front of the lens of the IR camera to act as a
diffraction grating. The camera was focused on a hot soldering iron
about 10 meters away. When a CO2-filled balloon was placed in front
of the soldering iron, a bit of the first-order spectrum was cut
out. The mesh was too coarse to resolve any absorption lines, but
the effect was there. It would be nice to secure a wire grating with
an appropriate number of slits per centimeter to really spread out
the IR spectrum.

The camera we have is a used Sierra Pacific Corp "ThermalEye." They
have many kinds of used demo models at reduced prices.

Again, sorry for posting something too quickly without thinking it
through. -- Wolfgang




On Feb 6, 2007, at 4:19 PM, Paul Doherty wrote:

> Hi Wolfgang
>
> What camera are you using?
>
> And for the rest of you tappers.
>
> We use a FLIR type camera at the Exploratorium.
> I don't see any difference with an air filled versus a CO2 filled
> balloon.
> I even took a 15 cm diameter 1 meter long PVC pipe, covered the
> ends with saran wrap and filled it with CO2 to get more path length
> and still saw no visible absorption.
> I wonder if there is enough IR coming through the band of
> wavelengths in the infrared between the two absorption bands of CO2
> and if IR FLIR cameras are designed to see through CO2?
>
> We do see a difference with balloons full of cold air which are
> opaque and balloons full or warm air (breath inflated) which are
> transparent.
>
> If you have a FLIR camera note that clear acrylic is black opaque.
> Brown plastic trashbags are opaque in the visible and somewhat
> transparent in the IR.
> a second surface mirror is black with the IR yet the copper bottom
> of a Revereware frypan is a great IR mirror (or just a sheet of
> copper)
>
> And you must take a beaker of hot water which glows white
> and a beaker of cold water which is black
> and then pour the white liquid into the black while watching on the
> IR camera
>
> Here is our You Tube Video as part of our global climate change
> webcast which shows several of these activities.
> (Note behind Stephanie's head there are three mirrors, the two
> black ones are actually mirrors in real life while the one that
> looks like a mirror in IR is actually a sheet of copper.)
>
> http://youtube.com/watch?v=6fASzACILH4
>
> Paul Doherty
>
>
> On Feb 6, 2007, at 9:44 AM, Wolfgang Rueckner wrote:
>
>> We do something similar, except with balloons. An air-filled
>> balloon is completely transparent whereas a CO2-filled balloon is
>> opaque. -- Wolfgang
>>
>>
>> On Feb 6, 2007, at 12:04 PM, Rick Tarara wrote:
>>
>>> There is a demo used in the PBS film 'What's up with the weather'
>>> that looks effective but requires some specialized equipment.
>>> They use a chamber with clear end plates through which an
>>> infrared TV camera can view. They put a person on the far side
>>> of the chamber and get a head shot through the infrared camera
>>> with the chamber filled with normal air. Then they flood the
>>> chamber with CO2 and the image quickly starts to fade, ultimately
>>> to disappear. This clearly indicates that the CO2 is absorbing
>>> the IR.
>>>
>>> I have no idea about the cost of such a setup.
>>>
>>> Rick
>>>
>>> ***************************
>>> Richard W. Tarara
>>> Professor of Physics
>>> Saint Mary's College
>>> Notre Dame, IN
>>> rtarara@saintmarys.edu
>>> ******************************
>>> Free Physics Software
>>> PC & Mac
>>> www.saintmarys.edu/~rtarara/software.html
>>> *******************************
>>>
>>>
>>>
>>> ----- Original Message ----- From: "Urs Lauterburg"
>>>
>>> To:
>>> Sent: Tuesday, February 06, 2007 11:42 AM
>>> Subject: Re: [tap-l] List conversations. Please Read.
>>>
>>>
>>>> Michael,
>>>>
>>>> Your judgement is correct. I tried the original setup with Argon
>>>> and got the same behavior as with CO2. Convection was inhibited
>>>> which caused most of the heating. Lower convection of course
>>>> influences thermal conditions a lot.
>>>>
>>>> I am however working on a demo which will show how CO2 absorbs a
>>>> certain range of infrared radiation. However, the real challenge
>>>> is to make it simple and straight forward. Not the effect I mean
>>>> but how it's best brought to the minds of our pupils.
>>>>
>>>> Thank you for pitching in your estimate and regards
>>>>
>>>> Urs
>>>>
>>>> Urs Lauterburg
>>>> Physics demonstrator
>>>> Physikalisches Institut
>>>> University of Bern
>>>> Switzerland
>>>>
>>>>> Urs,
>>>>>
>>>>> I'm guessing convection was inhibited by minimal mixing between
>>>>> the pure CO2
>>>>> layer and the air above it. You created a greenhouse without
>>>>> any glass on
>>>>> top?
>>>>>
>>>>> Michael Thomason
>>>>> Director of Physics Learning Laboratories
>>>>> University of Colorado Boulder Department of Physics
>>>>> 303-492-7117
>>>>> thomason@colorado.edu
>>>>> http://physicslearning.colorado.edu
>>>>> -----Original Message-----
>>>>> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-
>>>>> owner@lists.ncsu.edu] On
>>>>> Behalf Of Urs Lauterburg
>>>>> Sent: Monday, February 05, 2007 2:10 PM
>>>>> To: tap-l@lists.ncsu.edu
>>>>> Subject: Re: [tap-l] List conversations. Please Read.
>>>>>
>>>>> Dear Tap-lers,
>>>>>
>>>>> I very much second what Jerry said. After all, there always
>>>>> have been
>>>>> relations between physics, the world, religion and politics and
>>>>> it's
>>>>> the broader content of things which make certain aspects more
>>>>> relevant than others.
>>>>>
>>>>> Of course the list is primarily targeted at creating and
>>>>> maintaining
>>>>> educational hardware for physics education but since we often deal
>>>>> with young people, who are for good reasons concerned about the
>>>>> ways
>>>>> our planet is treated by mankind it's also important to exchange
>>>>> ideas about hot topics through the list. Global warming is hot and
>>>>> involves a lot of physics too.
>>>>>
>>>>> A few months back I posted a contribution to tap-l about a
>>>>> demonstration experiment that showed the greenhouse effect
>>>>> produced by CO2. The setup was strikingly simple. I had an
>>>>> infrared
>>>>> light bulb shine into a glass, rectangular aquarium shaped
>>>>> container
>>>>> which was open on the top. At the bottom on piece of plywood I
>>>>> hade a
>>>>> thermal sensor to measure the temperature at equilibrium. Now
>>>>> after
>>>>> filing the container with CO2 it soon led to a considerable
>>>>> temperature increase of about 2 to 3 degrees Celsius.
>>>>>
>>>>> Now just recently when wanting to show this rather impressive demo
>>>>> again I discovered that we measured another effect. The largest
>>>>> part
>>>>> of the temperature raise was not caused by the absorption of
>>>>> infrared
>>>>> by the CO2 as is the case with the REAL greenhouse effect. I
>>>>> leave it
>>>>> up to you physics professionals to make a guess. Maybe some others
>>>>> have already discovered the true reason for the heating in my
>>>>> case in
>>>>> the first place but have politely retained from letting me know
>>>>> back
>>>>> then. This of course would have been a wrong form of politeness.
>>>>>
>>>>> Now, I am still thinking about a nice and simple demo to show the
>>>>> energy absorption of greenhouse gasses and I'm right now tampering
>>>>> with some other more promising setup. However this time I will
>>>>> only
>>>>> make public comments when I am dead (well almost dead) sure
>>>>> that it
>>>>> shows the correct physics.
>>>>>
>>>>> Anyway, have fun guessing what it is that caused the greenhouse
>>>>> effect in my aquarium !
>>>>>
>>>>> Thank you for the lively and polite discussion and for caring
>>>>> about
>>>>> the subject by looking at the actual facts caused by the
>>>>> present, to
>>>>> some extent man-made and altered composition of the earth's
>>>>> atmosphere.
>>>>>
>>>>> Urs
>>>>>
>>>>> Urs Lauterburg
>>>>> Physics demonstrator
>>>>> Physikalisches Institut
>>>>> University of Bern
>>>>> Switzerland
>>>>>
>>



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