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AonSao
2009-Jan-17, 09:57 AM
Light is produced from an oscillating electromagnetic field. Does it ALWAYS happen though, or just under certain conditions?

For example, if i thrust a simple magnet back-and-forth through a coil of wire, is it producing long wave length light?

tusenfem
2009-Jan-17, 12:53 PM
You have the wrong impression here. Light itself is an oscillating EM field, with E and B always at right angles to each other and to the propagation direction.

Production of light (or EM waves) happens in various ways.

If you move the magnet like you say, you will create an oscillating current in the coil.
A moving magnet will create (in the frame in which it is moving) an electric field (through the equation v x B) however, this is not a propagating wave and hence not "light".

mugaliens
2009-Jan-17, 01:10 PM
However, as the current oscillates in the coil, it produces/radiates EM energy, which is light.

That's the basis of all antennas!

tusenfem
2009-Jan-17, 03:05 PM
However, as the current oscillates in the coil, it produces/radiates EM energy, which is light.

That's the basis of all antennas!

You are right, I should have added that, but I went on a side road.

mugaliens
2009-Jan-18, 01:41 PM
No worries, tusenfem - it's all to easy to do on BAUT!

Good explanation of the E and M orthoganal field nature of light, by the way.

sabianq
2009-Jan-21, 04:35 PM
Light is an arbitrary term,

but would not the term light encompase the whole spectrum?

is not heat light?
infrared end of the spectrum?

Heat is really really easy to make, i think i am heating up this keyboard merely by typing on it, (on the order of 100th or thousands of a degree)


i thought that heat is produced by, well... everything,

when any mechanical force cannot go anywhere else, the force itself is not destroyed, if it cant go anywhere else, then it is not simply converted to heat?


don't they have to balance?

sabianq
2009-Jan-21, 04:39 PM
i think the OP is correct
anytime you have a force that has nowhere to go, it is simply converted to heat, with a long wavelength.
hence "heat" or "light" or EM or Infrared..

http://books.google.com/books?id=pd9rm7JwShoC&pg=PA514&lpg=PA514&dq=heat+produced+form+collision&source=web&ots=kR2p4HJvxv&sig=oG0uGlJ9kNNul16xtbPs6J-JSn8&hl=en&sa=X&oi=book_result&resnum=4&ct=result

Tim Thompson
2009-Jan-21, 04:57 PM
Light is produced from an oscillating electromagnetic field. ...
As our friend tusenfem says, light is an oscillating electromagnetic field. The correct version of what you said is this: Electromagnetic radiation is produced by accelerated electrically charged particles. Now, light is electromagnetic radiation, but not all electromagnetic radiation is light. The word "light (http://en.wikipedia.org/wiki/Light)" normally refers only to electromagnetic radiation that we can see with our eyes. Astronomers often use the redundant phrase "visible light" to make the distinction clear, since we commonly observe a wide range of electromagnetic wavelengths.

korjik
2009-Jan-21, 05:07 PM
Light is an arbitrary term,

but would not the term light encompase the whole spectrum?

is not heat light?
infrared end of the spectrum?

Heat is really really easy to make, i think i am heating up this keyboard merely by typing on it, (on the order of 100th or thousands of a degree)


i thought that heat is produced by, well... everything,

when any mechanical force cannot go anywhere else, the force itself is not destroyed, if it cant go anywhere else, then it is not simply converted to heat?


don't they have to balance?

Force is not energy. Heat is energy.

Forces dont have to go anywhere, and if they dont balance you have acceleration. The force the ground exerts on you dosent cause heat, and will not go away if there are no other effects.

Mechanical energy is a different story. It is the energy transfer that ends up as heat (to some degree). In the case of your typing on your keyboard, it is the energy lost to friction that causes the heat.

sabianq
2009-Jan-21, 05:46 PM
light is considered what we can see yes..
light is also electromagnetic radiation.
electromagnetic radiation has a spectrum.
heat is part of that electromagnetic spectrum when it is propagating through a vacuum or in between air molecules like when you can feel the heat from a fire or stove or the sun on your face.

now there is mechanical energy stored in the form of potential energy like a car driving down the road.

if the car wants to stop, breaks are applied and the break pad starts wearing away and vibrating and "heating up". as it is dissipating the potential or stored energy in the cars mass as it was traveling at 65 miles per hour. part of the fuel (or force) that accelerated the mass of the car to 65 MPH is now being used to heat up the break pads and rotors as the mass of the car is forced to come to a stop.



the potential energy turned into kinetic energy then turned into heat, the energy simply changed forms in accordance to laws of thermodynamics.


law of conservation of energy states that the total amount of energy in an isolated system remains constant. A consequence of this law is that energy cannot be created or destroyed. The only thing that can happen with energy in an isolated system is that it can change form, that is to say for instance kinetic energy can become thermal energy.

thermal radiation is electromagnetic radiation
http://en.wikipedia.org/wiki/Thermal_radiation


Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature.

anytime you do anything to something that heats it up (i.e.. add energy by force)
say walk across the earth, you the friction is causing a temp change and the surface is emitting thermal radiation, this heat is electromagnetic radiation with a 'infared' long wavelength.




Force is not energy. Heat is energy.

Forces dont have to go anywhere, and if they dont balance you have acceleration. The force the ground exerts on you dosent cause heat, and will not go away if there are no other effects.

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

In physics, a force is that which can cause an object with mass to accelerate.

like the fuel in the car or the food i ate so i can run on the beach heating up my shoes as they collide repeatedly with the ground causes them to increase in temperature and emit thermal radiation.



Mechanical energy is a different story. It is the energy transfer that ends up as heat (to some degree). In the case of your typing on your keyboard, it is the energy lost to friction that causes the heat.

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

mechanical energy describes the potential energy and kinetic energy present in the components of a mechanical system.



the lost energy is not lost, it is converted into electromagnetic radiation or "sublight" (edit: infrared)

just like the law of conservation of energy says it should be.

sabianq
2009-Jan-21, 06:46 PM
simply by heating something or part of something up to a larger temperature than the surrounding environment (regardless of how it is done by collision like banging on a keyboard or playing a game of pool or induction or conduction or whatever), the temperature increase is emitted as electromagnetic radiation in the infrared range.

http://panda.unm.edu/Courses/Finley/P262/ThermalRad/ThermalRad.html

All objects give off radiation, i.e., electromagnetic waves, because of their temperature; we refer to this as thermal radiation.

tusenfem
2009-Jan-22, 08:27 AM
simply by heating something or part of something up to a larger temperature than the surrounding environment (regardless of how it is done by collision like banging on a keyboard or playing a game of pool or induction or conduction or whatever), the temperature increase is emitted as electromagnetic radiation in the infrared range.

http://panda.unm.edu/Courses/Finley/P262/ThermalRad/ThermalRad.html

Is this going anywhere sabianq? We give an explanation to a question you ask and you keep on giving extra comments and giving the impression that you are not believing us or that we are wrong, This is rather annoying.

There are several things that are wrong in your posts above:



now there is mechanical energy stored in the form of potential energy like a car driving down the road.


No, there is no potential energy stored in the moving car, there is kinetic energy stored. Potential energy has (as the word says) the potency to be converted into other (usually kinetic) energy. The kinetic energy of the car is converted into heat by the brakes of the car. (although you seem to get the terms correctly, later in the message)



thermal radiation is electromagnetic radiation


Indeed it is, but read what Tim Thompson wrote. You talk about light, and that is defined by the VISIBLE spectrum, which means from red to violet, the other wavelengths we cannot see, so per definition they are not light.

Now, thermal energy does not equal thermal radiation, because you are forgetting two very important ways of heat transport: conduction and convection. If you put a spoon in a cup of coffee the spoon gets hot, not because of thermal radiation (infra-red, not visible) but because of heat conduction, the hot "coffee molecules" (yes I know there is no such thing) hitting the "metal molecules" of the spoon, and transferring momentum, i.e. the coffee gets colder as the spoon gets hotter.

And how does the heat from the CV radiator get distributed through the room? Close by the air gets heated through conduction and then the hot air is convected through the room.





In physics, a force is that which can cause an object with mass to accelerate.

like the fuel in the car or the food i ate so i can run on the beach heating up my shoes as they collide repeatedly with the ground causes them to increase in temperature and emit thermal radiation.


What do you mean "like the fuel or the food" those things are NOT forces, they are energy carriers that may be freed under the right circumstances. Forces create acceleration, through F = m a (or to be more correct F = dp/dt, where p is the momentum). Now there are other processes that convert the deceleration into heat, yes, but there are a few more steps in between, the force itself does not create the heat directly. (the shoes are heated, but first because the rubbing force between the shoe and the street will deform the rubber on the bottom of your shoes, there this force is doing work, storing energy into the deformation of the sole, and then the potential energy that is in the deformed shoe gets released into kinetic energy of the "shoe molecules" which then give the impression of heat).

And yes, ANY object with a temperature unequal to 0 Kelvin will emit EM radiation, most easily described by a black body spectrum.



the lost energy is not lost, it is converted into electromagnetic radiation or "sublight" (edit: infrared)


No, there is no lost energy, in a closed system there is conservation of energy, but it is not all converted into electromagnetic radiation, I hope I was able to explain that to you in this message.

Just wondering how we got here from the OP though. Ah okay, I see, the OP was another member.

Jeff Root
2009-Jan-22, 09:55 AM
The term "light" often refers to any or all parts of the electromagnetic
spectrum. That is why it is sometimes necessary to say "visible light"
when one is talking only about the visible part of the spectrum. I use
the term that way myself.

Thermal radiation is not the same as infrared radiation.

We can feel infrared radiation as heat when it is absorbed by the skin,
but the same is true of visible light and ultraviolet light. I just recently
had X-ray photos taken of my teeth, and I'm fairly sure that I was able
to feel a slight sensation of heat in my jaw after each photo.

Infrared is more closely associated with heat for two reasons:

- In the range of temperatures that our bodies can tolerate, the peak
intensity of the spectral distribution of energies is in the infrared. At
higher temperatures, such as the temperature of the Sun's surface,
the peak can be outside the infrared.

- The infrared band is considerably wider than the visible band, so it
may contain more energy than the visible band even though each photon
of visible light carries more energy than a photon of infrared.

There may be other reasons that IR is associated with heat that aren't
coming to my mind right now.

If something is hot enough, most of the thermal radiation it gives off
will be in the ultraviolet and visible bands. There will still be enough in
the infrared band to roast you, but it will be less than that of the higher
energy bands.

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-22, 10:06 AM
Also, thermal radiation is not heat. Heat is essentially the random motion
of small particles such as ions, atoms, and molecules. It includes linear
motion, rotation, flexing, and springlike motions. Not all motions of small
particles are necessarily heat, though.

Heat can be converted into electromagnetic radiation, and vice-versa.
The thermal motion of molecules in my body emit infrared radiation, and
light from the monitor in front of me is converted into heat when it is
absorbed by my skin.

-- Jeff, in Minneapolis

sabianq
2009-Jan-22, 01:17 PM
However, as the current oscillates in the coil, it produces/radiates EM energy, which is light.

That's the basis of all antennas!

he said EM radiation is light.

You are right, I should have added that, but I went on a side road.
17-January-2009 01:10 PM

you seem to agree


i thought that it would also be agreed that infrared radiation would also be considered light too.
because as the current oscillates in the coil, it produces/radiates heat energy, which is also light. in the IR spectrum.



all i am saying is that it is really really easy to produce light in the infrared range.
either by rubbing your hands together,
moving a magnet through a coil
or pounding on a keyboard.

the mere friction or resistance of doing anything will cause heat which radiates outward from the object is electromagnetic radiation in the infrared range.

if i smash a lead ball with a sledge hammer and pick up the smashed ingot, it will be warm to the touch, if i image it with a thermal camera, the camera will indeed be showing that it is radiating electromagnetic radiation in the IR spectrum.

if you agree as mugaliens suggested that

mugaliens EM energy,[in the radio end of the spectrum] which is light.
is light
then why is there such a debate that IR is not light?

that is all



Thermal radiation is not the same as infrared radiation.



-- Jeff, in Minneapolis

no.
this statement is dead wrong.

Thermal radiation is indeed electromagnetic radiation in the infrared spectrum
here is a source that backs up my statement.

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

Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature.


Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb.

is this source wrong?

tusenfem
2009-Jan-22, 03:00 PM
If it is warm to the touch, then you feel that through conduction and not through ratiation.

Next to that, I don't see the point to this pointless discussion we are having. What exactly are you trying to tell us or to ask us?



is this source wrong?


no it is not wrong, from such a electric heater there is also EM emitted, however, a lot of the heat is also transported through convection in the room.

Concerning "light" please forget that we ever said that light means visible. To the common folks, if you ask "what is light" they will not say infrared or X-ray radiation. Light is EM radiation, and it depends on your definition of the L-word whether you can say that EM radiation is light.



i thought that it would also be agreed that infrared radiation would also be considered light too.
because as the current oscillates in the coil, it produces/radiates heat energy, which is also light. in the IR spectrum.


yes and no, naturally if there is a current flowing there will be heat generated, but the main emission of this coil will be in radio waves, the heat production and thus the IR emission will be negligible.

sabianq
2009-Jan-22, 03:13 PM
i am exactly trying to say:
[edit:]
that it is very very easy to generate EM radiation and it does happen all of the time.
if heat is being generated, then IR radiation must also be generated,

also
that if something is warm, it is radiating electromagnetic radiation in the form of IR (infrared) radiation.
Even if the IR emission is negligible, it is still an emission of electromagnetic radiation.


also you seemed to agree that radio waves were also light

http://www.bautforum.com/space-astronomy-questions-answers/83644-electromagnetic-radiation.html#post1412625




Quote:
Originally Posted by mugaliens View Post
However, as the current oscillates in the coil, it produces/radiates EM energy, which is light.

That's the basis of all antennas!
You are right, I should have added that, but I went on a side road.

is this correct?


if radio waves were considered light in post 4
then

IR should also be considered light too.

korjik
2009-Jan-22, 04:10 PM
i am exactly trying to say:
[edit:]
that it is very very easy to generate EM radiation and it does happen all of the time.
if heat is being generated, then IR radiation must also be generated,

also
that if something is warm, it is radiating electromagnetic radiation in the form of IR (infrared) radiation.
Even if the IR emission is negligible, it is still an emission of electromagnetic radiation.


also you seemed to agree that radio waves were also light

http://www.bautforum.com/space-astronomy-questions-answers/83644-electromagnetic-radiation.html#post1412625



is this correct?


if radio waves were considered light in post 4
then

IR should also be considered light too.

1) You can have heat generated without IR radiation. Take a heating coil in water. The coil, heated by ohmic heating will get warmer, but the heat will be transferred into the water by conduction, with no IR radiation.

1a) IR is the cost common radiation, at the temperatures humans live at. If the temperature is alot higher, there will be more heat radiation at different frequencies. In a really big blue giant, the heat generated is mostly UV.

2) if something is warm, it will emit EM radiation, if it can. In air there will be some radiation, but in water there wont be.

3)The strict definition of light is that it is the visible portion of the EM spectrum. The sloppy definition is any EM radiation. You have to be careful about your useage.

Gigabyte
2009-Jan-22, 04:54 PM
All EM radiation generates heat.

Gigabyte
2009-Jan-22, 04:55 PM
But not all heat transfer is by EM.

And I think you mean "most" rather than cost.

Jeff Root
2009-Jan-22, 05:13 PM
Thermal radiation is not the same as infrared radiation.
no.
this statement is dead wrong.
No, I got it exactly right.



Thermal radiation is indeed electromagnetic radiation in the
infrared spectrum
No, thermal radiation can be in any part of the spectrum.
Which part of the spectrum depends on the temperature.



here is a source that backs up my statement.

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


Thermal radiation is electromagnetic radiation emitted from the
surface of an object which is due to the object's temperature.


Infrared radiation from a common household radiator or electric
heater is an example of thermal radiation, as is the light emitted
by a glowing incandescent light bulb.
is this source wrong?
Both of those quotes are exactly and entirely correct.

Read the second quote again and understand what it says.

Thermal radiation is not the same as infrared radiation.

Examine the Planck curves for different temperatures.

-- Jeff, in Minneapolis

sabianq
2009-Jan-22, 05:33 PM
if anything is warmer that the surrounding environment even by a billionth of a degree, it is generating more infrared radiation than the background.
if something is cooler than the surrounding environment then it is absorbing heat energy but is still emitting EM radiation just in lower levels than the back ground

Take a heating coil in water. heats up by conduction, then transfers the energy to the water by convection, the temperature increase of the water radiates outward from the system as radiant thermal radiation in the form of Infrared electromagnetic radiation.

now, the the warmer than room temperature cup of water is emitting more electromagnetic radiation than the background.


The strict definition of light is that it is the visible portion of the EM spectrum. The sloppy definition is any EM radiation. You have to be careful about your useage.

The term "light" was defined in post 3 & 4, not by me.
also the title of this thread is "Electromagnetic Radiation" and not "light"



However, as the current oscillates in the coil, it produces/radiates EM energy, which is light.

in post 10
labeled Semantics

light is considered what we can see yes..
light is also electromagnetic radiation.

"Electromagnetic radiation" is the title of this post, and the question was directly about generating "long wave light" which is infrared electromagnetic radiation.


For example, if i thrust a simple magnet back-and-forth through a coil of wire, is it producing long wave length light?

the answer is yes, if the system is heating up, "long wave light" is being produced.
and this happens all of the time.
even merely rubbing your fingers together will produce "long wave light" in the form of infrared radiation.


question:
why is there is such a resistance to the idea that electromagnetic radiation is really easy to make?




when in fact thermodynamics which is the study of energy transfer. states that energy is always conserved and if it cannot go anywhere, it is not destroyed rather it just changes form.

moving a magnet through a coil will cause a resistance which will heat up the system, this temperature change manifests itself as heat, the system now warmer from the force of moving the magnet through the coil shows a temperature difference, the warmer system is generating more electromagnetic radiation in the infrared spectrum than the background.

Hornblower
2009-Jan-22, 05:44 PM
No, I got it exactly right.


No, thermal radiation can be in any part of the spectrum.
Which part of the spectrum depends on the temperature.


Both of those quotes are exactly and entirely correct.

Read the second quote again and understand what it says.

Thermal radiation is not the same as infrared radiation.

Examine the Planck curves for different temperatures.

-- Jeff, in Minneapolis
My bold for reference. My preferred choice of words would be "Thermal radiation is not necessarily infrared radiation". As has been noted, thermal radiation can include visible light, ultraviolet, even X-rays in the case of an extremely hot object such as a newly formed neutron star.

When any of these emanate from a hot macroscopic body, they are considered thermal radiation. If they are from quantum jumps in separated atoms in a rarified gas, they are considered nonthermal in nature.

sabianq
2009-Jan-22, 05:44 PM
hey jeff
you are correct.

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

Thermal radiation covers the entire EM spectrum from <0 hz to gamma
and infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (3-300 Ám) and microwaves (~30,000 um). Infrared radiation spans roughly three orders of magnitude (750 nm and 1000 Ám).
http://en.wikipedia.org/wiki/Infrared_light
Thermal radiation is electromagnetic radiation.
however infrared radiation is not the same as thermal radiation because IR does not cover the entire spectrum.

I agree.

however, that is not my argument,
i am merely stating that any object that is heated up by any force (regardless of the force applied) acting on it will emit electromagnetic radiation in the form of infrared.

and i am also saying that electromagnetic radiation in the infrared range is really easy to produce.

tusenfem
2009-Jan-22, 05:50 PM
also you seemed to agree that radio waves were also light


Yes I wrote that, but basically I meant the emission of radio waves.
In normal life I would never call anything in the non-visible spectrum light.

Can we now stop this pointless discussion?

tusenfem
2009-Jan-22, 06:16 PM
i am merely stating that any object that is heated up by any force (regardless of the force applied) acting on it will emit electromagnetic radiation in the form of infrared.

and i am also saying that electromagnetic radiation in the infrared range is really easy to produce.

And that is where you go partly wrong.

First of all a force does not heat, we went over that in the previous message.

A body at any temperature will emit EM radiation into space, and not just one frequency (e.g. infrared) but a whole spectrum of EM radiation, the so called black body radiation. This radiation peaks at a certain frequency, depending on the temperature.

Take a metal rod and stick it in fire:


first it will be warm and not "shining" in visible spectrum
then it gets red-warm, the temperature increased, and the metal is red
then it gets "white"-hot (actually yellow), temperature increased more and the metal is yellow
one could get further and in the end it will be X-ray extrahot

The thing is that most of the radiation will be emitted at the color that you see, so one is quickly away from infrared. Just try and look up black body spectrum.

If the only thing you wanted to say is that IR emission is easy to make, I fail to see the point of this comment, as it has absolutely nothing to do with the OP.

mugaliens
2009-Jan-22, 06:16 PM
i think the OP is correct
anytime you have a force that has nowhere to go, it is simply converted to heat, with a long wavelength.
hence "heat" or "light" or EM or Infrared..

"Force?" or "power?"

My potted plant exerts a force on the floor. It has nowhere to go, but there's no heat involved.

sabianq
2009-Jan-22, 07:04 PM
"Force?" or "power?"

My potted plant exerts a force on the floor. It has nowhere to go, but there's no heat involved.

your potted plant is in static equilibrium
http://www.rwc.uc.edu/koehler/biophys/2h.html

The simplest case of static equilibrium occurs when two forces are equal in magnitude but opposite in direction. For example, an object on a level surface is pulled (attracted) downward toward the center of the Earth by the force of gravity. At the same time, surface forces resist the downward force with equal upward force (called the normal force). The situation is one of zero net force and no acceleration.
University Physics, Sears, Young & Zemansky, pp18–38


i am talking about an external force applied, not a system in static equilibrium like your potted plant.


a force is that which can cause an object with mass to accelerate.
Earth Observatory. NASA. Retrieved on 2008-04-09. "Force: Any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body."

like pushing a magnet through a coil.

sabianq
2009-Jan-22, 07:36 PM
And that is where you go partly wrong.

First of all a force does not heat, we went over that in the previous message.

A body at any temperature will emit EM radiation into space, and not just one frequency (e.g. infrared) but a whole spectrum of EM radiation, the so called black body radiation. This radiation peaks at a certain frequency, depending on the temperature.

Take a metal rod and stick it in fire:


first it will be warm and not "shining" in visible spectrum
then it gets red-warm, the temperature increased, and the metal is red
then it gets "white"-hot (actually yellow), temperature increased more and the metal is yellow
one could get further and in the end it will be X-ray extrahot

The thing is that most of the radiation will be emitted at the color that you see, so one is quickly away from infrared. Just try and look up black body spectrum.

If the only thing you wanted to say is that IR emission is easy to make, I fail to see the point of this comment, as it has absolutely nothing to do with the OP.

you are right, this whole thing is getting silly.
but i really feel like i must clarify.
[edit: about a force,
from here:
a force is that which can cause an object with mass to accelerate. "Force: Any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body."
absolutely a force can cause an object to heat up, hitting a ball with a bat imparts a temperature change, hitting a slug of lead with a sledge hammer imparts a temperature change...]

the OP asked

if i thrust a simple magnet back-and-forth through a coil of wire, is it producing long wave length light?

friction produces heat, this heat is produced from induction.
http://en.wikipedia.org/wiki/Electromagnetic_induction
http://en.wikipedia.org/wiki/Induction_heating
if it is a closed loop thrusting a simple magnet back and fourth through a coil produces a "resistance" known as induction. this induction causes the system to heat up.
the warm system is emitting EM radiation or black body radiation.

http://en.wikipedia.org/wiki/Black_body_spectrum
the term black-body just refers an object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. A star is regarded as a black-body.

black-body radiation on the other hand depends on the temperature of the black body.
in the case of the iron rod, as you heat it up, even as it is just warm to the touch, it is emitting EM, as the temperature increases and it begins to glow, the glow is just the temperature at which the radiation is the strongest, that does not mean that the wavelengths of a lower temperature are all of a sudden not there. While yes, the temperature increase moves the electromagnetic spectrum emission toward the blue end, the IR part of the spectrum is still there. even if you can get the rod to X-ray hotness, the rod will still be visible in the blue spectrum.

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

The wavelength at which the radiation is strongest is given by Wien's displacement law, and the overall power emitted per unit area is given by the Stefan-Boltzmann law. So, as temperature increases, the glow color changes from red to yellow to white to blue. Even as the peak wavelength moves into the ultra-violet, enough radiation continues to be emitted in the blue wavelengths that the body will continue to appear blue. It will never become invisible — indeed, the radiation of visible light increases monotonically with temperature.
Landau, L. D.; E. M. Lif****z (1996). Statistical Physics (3rd Edition Part 1 ed.). Oxford: Butterworth-Heinemann.

tusenfem
2009-Jan-23, 09:02 AM
friction produces heat, this heat is produced from induction.
http://en.wikipedia.org/wiki/Electromagnetic_induction
http://en.wikipedia.org/wiki/Induction_heating
if it is a closed loop thrusting a simple magnet back and fourth through a coil produces a "resistance" known as induction. this induction causes the system to heat up.
the warm system is emitting EM radiation or black body radiation.


I thinks this will be my last post here (going on vacation tomorrow, sliding down the slopes, without any heat, only lots of cold).

Friction produces heat, yes.
Induction is NOT a resistance, induction is the reaction of a circuit to the change in a magnetic field, creating a response in such a way to negate the change in the circuit.
Yes, there is such a thing as "induction heating" which is short for a rather complex number of processes happening. There is a coil with a current, creating a magnetic field, induction sets up currents to negate this magnetic field. As the inside is not super conducting there will be a resistance, which will create Ohmic heating in the inside. So, it should have been called: magnetic field induced currents Ohmic heating, but they thought that induction heating would be a bit more user friendly.
The heat created by this process can either be radiated away in EM radiation or can be (more likely) conducted into the water that needs to be heated. (it is rather difficult to heat water with just radiation).

And I never said that the other wavelengths at black body radiation are not present, I specifically said that BB is a spectrum. If I simplified it too much for you, I am sorry, but as I described it, I thought it would be the way you would understand.

sabianq
2009-Jan-23, 12:54 PM
(going on vacation tomorrow, sliding down the slopes, without any heat, only lots of cold).



Lucky you!
Have a blast.
I sure do miss the snow.
Have a wonderful time!
Cheers!

captain swoop
2009-Jan-24, 12:23 PM
sliding down the slopes, without any heat
but there will be heat. friction melts the snow and you slide along on the water.