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Science > Physics |
| User: |
"" |
| Date: |
01 Apr 2005 05:00:31 AM |
| Object: |
Do photons have temperature? |
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
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| User: "Supertech" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 11:23:05 AM |
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<tianshuo@gmail.com> wrote in message
news:1112353231.712293.200060@o13g2000cwo.googlegroups.com...
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
Temperature is a macroscopic concept derived from what humans feel from the
skin.
Photon is a substance that causes the temperature of an object to rise.
In the world of photons, I don't think there is a concept of tempertature.
Does the heat have temperature?
Now you realize it sounds stupid.
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| User: "Creighton Hogg" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 11:28:08 AM |
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On Fri, 1 Apr 2005, Supertech wrote:
<tianshuo@gmail.com> wrote in message
news:1112353231.712293.200060@o13g2000cwo.googlegroups.com...
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
Temperature is a macroscopic concept derived from what humans feel from the
skin.
It is macroscopic, but it has nothing to do with what you
feel on your skin. What you feel is heat flow, not
temperature.
Photon is a substance that causes the temperature of an object to rise.
Well, it can cause this, but that isn't the definition of
photon.
In the world of photons, I don't think there is a concept of tempertature.
Sure there is. A photon gas can be treated as a thermal
system with a temperature.
Does the heat have temperature?
That wasn't the question.
Now you realize it sounds stupid.
It wasn't a stupid question at all.
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| User: "Andy Resnick" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 08:12:27 AM |
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wrote:
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
It is true, but recall that thermodynamic properties can only be
assigned for colelctions of objects. It does not make sense to speak of
the temperature of a single photon (although one can be assigned based
on energy).
Blackbody radiation is what you get for an electromagnetic field at a
certain temprature, or equivalently, in equilibrium with a thermal
reserviour at temperature T.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
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| User: "RP" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 10:47:51 PM |
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wrote:
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...\
Did you ever wonder "wtf is a photon, anyway?"
You see how subtle shades of a concept can change the entire meaning
of a statement? :)
Light is just a bad habit; photons are the hallucinations that follow.
Richard Perry
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| User: "Gregory L. Hansen" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 11:12:36 AM |
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In article <1112353231.712293.200060@o13g2000cwo.googlegroups.com>,
<tianshuo@gmail.com> wrote:
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
Temperature is a thermodynamic concept, a property averaged over many
particles. A photon gas has a temperature. Probably the most famous one
is the cosmic background radiation. The temperature is the average photon
energy, and you can use Boltzmann's constant to convert from energy to
degree kelvin, if you like.
--
"The average person, during a single day, deposits in his or her underwear
an amount of fecal bacteria equal to the weight of a quarter of a peanut."
-- Dr. Robert Buckman, Human Wildlife, p119.
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| User: "" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 10:12:02 PM |
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I'm not quite sure how a photon gas behaves. (Yes, I am talking about a
collection of photons, not just one)
By common sense, I think that photons in a a laser should have a higher
temperature--but is that true??
How about temperature of fields (not temperatures in fields)?
I'm not too sure if you can say there are so. Since fields are usually
behavior from wavelike interactions. Can I just calculate a temperature
of a field from the temperature of a photon and the Maxwell equations?
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| User: "Bjoern Feuerbacher" |
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| Title: Re: Do photons have temperature? |
02 Apr 2005 03:03:41 AM |
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wrote:
I'm not quite sure how a photon gas behaves. (Yes, I am talking about a
collection of photons, not just one)
That is described in detail in most textbooks discussing statistical
mechanics.
By common sense, I think that photons in a a laser should have a higher
temperature--but is that true??
You can only talk about the temperature of a photon gas when that
gas is in thermal equilibrium. The photons in a laser aren't.
How about temperature of fields (not temperatures in fields)?
See a book on Quantum Field Theory at finite temperature. ;-)
I'm not too sure if you can say there are so. Since fields are usually
behavior from wavelike interactions.
And what is this supposed to mean???
Can I just calculate a temperature
of a field from the temperature of a photon and the Maxwell equations?
As already several people explained, a single photon has no temperature.
Just as a single atom or molecule has no temperature. A quote from the
post you replied to here, but which you apparently did not read or not
understand:
"Temperature is a thermodynamic concept, a property averaged over many
particles."
Bye,
Bjoern
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| User: "Josef Matz" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 05:51:44 AM |
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Yes they have. All you assume is fully right
<tianshuo@gmail.com> schrieb im Newsbeitrag
news:1112353231.712293.200060@o13g2000cwo.googlegroups.com...
They have mass they have energy, momentum... but do they have classical
thermodynamic properties?(For example, temperature, entropy,
enthalpy,etc)
If true, doesn't that mean a electromagnetic field has a temperature??
I don't remember hearing about that anywhere before...
.
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| User: "" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 06:18:58 AM |
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Are there any equations for it or something...
it's funny that we don't often here about the temperature of photons or
magnetic fields...
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| User: "bz" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 08:15:26 AM |
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wrote in news:1112357938.160556.254970
@g14g2000cwa.googlegroups.com:
Are there any equations for it or something...
it's funny that we don't often here about the temperature of photons or
magnetic fields...
heat radiation from a black body can be calculated:
http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html
You can take the wavelength at the 'peak' of radiation for a particular
temperature of a black body.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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| User: "Bjoern Feuerbacher" |
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| Title: Re: Do photons have temperature? |
02 Apr 2005 03:04:48 AM |
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wrote:
Are there any equations for it or something...
E.g. Planck's radiation law for black bodies. That gives the spectral
energy density of a photon gas at a fixed temperature.
[snip]
Bye,
Bjoern
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| User: "tj Frazir" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 07:21:05 PM |
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its a rize and fall in the conductor .
wave top to wave top can be a mile .
light changes direction to remain at C .
its wavical both partical and wave.
Its the sum of all it's qualities.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 06:28:14 PM |
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tian Heat does not pass through a vacuum,yet the Earth gets its heat
from the Sun. Best you read up how this takes place Bert
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| User: "Sam Wormley" |
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| Title: Re: Do photons have temperature? |
01 Apr 2005 08:07:04 PM |
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G=EMC^2 Glazier wrote:
tian Heat does not pass through a vacuum,yet the Earth gets its heat
from the Sun. Best you read up how this takes place Bert
Photon "gas" has heat... 2.7 K or so and passes through a vacuum, otherwise
I enjoyed your point, Herb.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Do photons have temperature? |
02 Apr 2005 07:22:02 AM |
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Hi Sam Glad you enjoyed my point. But did you really get it? All
energies end up as heat. Even ocean waves transfer their final
energy(a ripple against the shore) as heat. Photons vibrate,and makes
no difference if they hit our Earth from coming from the sun,or those
created from the big bang. These vibrations are energy,and can,and do
create heat. Do you get it Sam??? Bert
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