Why is infrared also referred to as thermal radiation?
At school, students at about Year 10 are taught that infrared is "thermal radiation". Then, at about Year 13 they are introduced to the formula E=hf; it then becomes obvious that something such as ultraviolet has more energy than infrared. And yet the dilemma with the Year 10 factoid is never expressed in either the syllabus or textbooks.
I, on the other hand, like to challenge my students :-)
So... why is infrared known as thermal radiation?
image: pixabay
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Here is a link to the experiment I make reference to in the question:
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_example.html
And here are some animations and explanations of the different ways in which molecules react with electromagnetic radiation:
http://hyperphysics.phy-astr.gsu.edu/hbase/mod3.html
http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html
This sounds like physics which I haven't done in a decade and a half lol. I dont know the answer but an interested. I could Google it but that would ruin the fun. If I were to guess I would think it has something to do with where infrared falls on the light spectrum....and light is a form of radiation...and infrared falls on a thermal part of the light spectrum.... ? I dont know obviously lol.
I am sharing this quora link which is relevant to your question. Maybe @lemouth can give a detailed answer. :)
Thanks, the "top" answer on there is wrong and it has fewer votes than the more correct answer - rather peculiar listing algorithm.
I do know the answer :-) I thought it good to create some interesting content for StemQ, especially in this case where it is confusing the way it is taught at school. The answer dips into university physics but can easily be articulated in a meaningful way for a secondary student.
I would simply answers as follows. The equality "IR radiation = thermal radiation" is wrong. Radiative heat transfers are not limited to the IR regime.
It's not?
I don't remember being taught anything else actually. :/
Exactly! Hence why I wrote "thermal radiation" in quotes. Some stuff from school just seems to stick! Weird that what gets remembered is usually wrong.
I don't know why school books shy away from even mentioning black-body radiation, yet confuse students with the absorption and reflective properties of various painted surfaces.
The original experiment is interesting, that putting sunlight through a prism and measuring the temperatures of each colour results in infrared being the hottest.
So there remains some real physics here: why does beyond-red register a higher temperature than beyond-blue? This is even more baffling for older students who then learn that ultraviolet has a higher frequency and hence higher energy than infrared.
Sometimes, it is good to start with naming things correctly. Unfortunately, this is rarely the case. By the way, a well known example of thermal radiation this is not IR is the cosmic microwave background.
Yes, and one image I'm fond of showing students is the atmosphere's absorption spectrum that shows this large open window in the microwave region.
Also interesting is that most of the Sun's thermal energy is in the infrared; this may possibly be the source of using the term thermal radiation so loosely. Perhaps the book editors just like images taken by infrared cameras!
When I posed the question in class, I ended up looking afresh at the interactions between photons and matter. Way outside the syllabus, but more interesting!
There is also the question as to why microwave ovens are used more than infrared ones. erm... you don't want to read this; the first sentence is staggering. I retire...
Just the URL is somehow preventing me from clicking :D
Might be fun and interesting to see what people remember from school physics, and science in general.
I teach in secondary and often come across student ideas they picked up in primary and just can't shake off - not the student's fault, really.
Heresy! ;-)
OK, I'll let others answer this question. ;-)
Haha, now we're gonna get all the physicists shutting up!
I bet Stackexchange didn't start this way!
Talking of which, one serious request for the StemQ site (and SteemStem!) is to implement mathjax so that we can all write proper symbols. The irony of a mathematical computational device that doesn't by default show maths symbols ;-) mathjax also works in markdown.
I know it will look like gobbledeeLaTeX on other platforms... but think of the clickthroughs to read it properly!
Ah, I wish was a physicist! :-)
Absolutely, the capability to add mathematical symbols and equations is on our list!
The problem with mathjax is that it requires javascript to run in the client.
This is an issue because, although StemQ could be updated to support this, other Steem apps wouldn't support it and wouldn't render the equations properly.
There other options such as MathML, but again most steem apps would probably get rid of the tag, though I could be wrong about that.
Picture server side rendering may be the best option, though I'm not sure yet.
A lot to take into consideration...
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