The temperature-dependant emission of electromagnetic waves. Combine this tag with [tag:thermodynamics] for a macroscopic view or [tag:quantum-mechanics] for a microscopic explanation.

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148 views

Commercial Infrared lights

I purchased an infrared light. It's a 100 W Philips infrared lightbulb. Says it's infrared, but I haven't done any spectrum analysis so I don't know for sure if it's just red or really infrared. As I ...
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2answers
423 views

Do gases reflect some IR radiation?

The usual definition given for a greenhouse gas is that it absorbs infrared radiation. Of course, then the gas emits its own thermal radiation, and it does so without preference for direction ...
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1answer
167 views

Equations for the two-plane model of the greenhouse effect

I'm trying to understand this "toy model" of the greenhouse effect. http://www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model The model predicts the surface temperature of ...
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2answers
711 views

Radiated power and energy density for a black-body

I am having an hard time trying to understand why the radiated power per unit area $P$ of a black body is given by $$P=\frac{c}{4} u$$ in terms of the energy density $u$ and the velocity of light. I ...
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3answers
887 views

What's the physical difference between a convective heater and an infrared heater?

Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air? ...
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2k views

Calculate temperature of the earth through blackbody radiation

I don't understand the solutions to a problem about blackbody radiation and was wondering if anybody could help me out. Here is the question: The sun can be considered as a blackbody radiation ...
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1answer
335 views

Energy loss in pipe/hose with hot water (how its affected by pipe/hose size, temperature)?

I'm working on low budget small solar power project. I want to transport heat (peak heat power about 1kW) over ~10 meter (~30ft) long pipe or hose. I was thinking about thin hose (6-8mm / about 1/4 ...
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2answers
618 views

At the atomic level, is heat conduction simply radiation?

Radiation and conduction are two ways that heat is transferred. Convection isn't really a mode of transfer as the actual heat transfer really occurs through radiation/conduction and not by some other ...
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2answers
435 views

What are thermal energy distributions?

I am trying to understand the photoelectric-effect deeply. My teacher used the Planck's law and integrated it to deduce the Stefan-Boltzmann law. He somehow showed some quantum-physical ...
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1answer
323 views

What is the relation between surface area and radiation, if any?

Basically I wonder what happens to emitted radiation by douubling a light e.g. twice the surface area of the sun will emit how much more radiation? 4 times more? Is there a formula?
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0answers
72 views

Photon pumping in Laser

Let's consider a ring laser where the laser must pass through the gain material before it is sent toward a partially reflective surface $\ R=1-T $. The other mirrors are perfect reflectors with $\ ...
3
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2answers
516 views

How to interpret Stefan-Boltzmann's law?

The Stefan-Boltzmann equation states $e=\sigma T^4$, but how do we interpret this? Is this completely wrong: A body of size $s^2$ generates the radiation/temperature $T^4$ for a given size and a ...
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3answers
163 views

Why is the planck function continuous and not discrete?

If we imagine a object made up of Hydrogen gas that is optically thick to all radiation, and is in thermal equilibrium, then, microscopically, photons will be emitted and absorbed as ...
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1answer
333 views

Quantum uncertainty of particle falling in black hole

A stationary observer at infinity sees a particle of mass m falling in a supermassive Schwarzschild black hole. He observes an increasing redshift and sees the particle ceasing to progress when it ...
2
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1answer
654 views

What really is Planck's constant and what are its origins?

In the physics texts I have read and other info online, they says Planck's constant is the quantum of action or that it is a constant of the ratio of the energy of a particle to its frequency. Im ...
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2answers
1k views

Possible colors of fire?

I have learnt that depending on the various gases those are involved in the reaction that produces fire, different colors (yellow, red or blue) of flames become visible. I have a question .. what are ...
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4answers
283 views

what is the basic form of the 'fire'? [duplicate]

Possible Duplicate: Is fire matter or energy? What is the basic form of fire? physics defines every entity by a basic form either solid or liquid or as a gas, example: water is liquid, ice ...
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1answer
282 views

Is the Unruh radiation isotropic?

The Unruh effect is the prediction that what appears to be a Minkowski vacuum to an inertial observer, would appear to be a thermal bath of particles to an observer accelerating uniformly in the same ...
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1answer
77 views

Is synchrotron radiation considered incandescent?

Synchrotron radiation is produced via the acceleration of charged particles, much like incandescence. However, all information I've seen state that incandescent light is produced exclusively from the ...
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2answers
298 views

Temperature of a black-body in LEO on the dark side of the Earth

Questions about the temperature of something in space are often very hard to pin down (example), since there is radiative transfer to/from many different regions in the field of view at dramatically ...
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1answer
101 views

What would the spectral distribution of a greenbody look like?

Suppose you had a body that behaved like a blackbody for all wavelengths except some range that we would call "green". For those wavelengths it reflects all radiation incident upon it. Am I just ...
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1answer
6k views

How do you change Planck's law from frequency to wavelength? [duplicate]

I have to derive Wien's displacement law by using Planck's law. I've tried but I come to a unsolvable equation (well I can't solve it) anywhere I look online it comes to the same conclusion, you need ...
5
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1answer
261 views

How do I measure the temperature of a tiny water droplet?

How do I accurately (+/- 0.1 degrees Celsius or better) measure the temperature of a small (5 to 50 microliter) water droplet without noticeably affecting its temperature? The mass of a thermistor or ...
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1answer
248 views

Mathematical derivation of $N(\lambda)d\lambda$

We all know that in Rayleigh-Jeans law, $$N(f)df ~=~ 8\pi f^2 df/c^3.$$ How do you derive $N(\lambda)d\lambda$? I am sort of confused...
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1answer
162 views

What is the diameter of the sun as a function of wavelength/frequency (around 10GHz)?

I have this vague recollection of being told that the diameter of the apparent surface of the sun is a function of what band you observe it in. I'm looking for a model of this that works for bands in ...
0
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1answer
285 views

Implementing a black-body using Planck's Law in a 3D ray tracer

1_ In one of my software projects, I need to implement Planck's Law in terms of wavelength. I can't be sure if it's right because I've seen different variations of it, and all the implementations ...
2
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1answer
217 views

total noise power of a resistor (all frequencies)

Let's calculate the power generated by Johnson-Nyquist noise (and then immediately dissipated as heat) in a short-circuited resistor. I mean the total power at all frequencies, zero to infinity... ...
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67 views

A problem concerning the change of temperature and spectrum of a filament

The spectrum of a filament has been given before, the left one having the lowest temperature, the middle with a medium temperature and the right one with the highest. My question is this: Why does ...
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5answers
7k views

Will adding heat to a material increase or decrease entropy?

Does adding heat to a material, thereby increasing electrical resistance in the material increase or decrease entropy? Follow up questions: Is there a situation were Heat flux ie. thermal flux, ...
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3answers
1k views

Does radiation change entropy?

Are there entropy changes associated with the transmission of energy from the sun to the earth? Does radiation differ from other modes of heat transfer with respect to the entropy changes? Are the ...
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1answer
1k views

Do materials cool down in the vacuum of space?

Do materials cool down in the vacuum of space? If yes, how does it really work?
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3answers
409 views

black body and cosmic microwave background radiation

Why is the sprectum of the cosmic microwave background radiation (or seems to be) that of a black body?
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2answers
2k views

Why do we use Planck's constant?

I have been trying to reason why energy packets (i.e. photons) are assumed to be quantized. I know this originated from Max Planck, but may someone explain why energy couldn't be emitted continuously ...
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5answers
8k views

Is fire plasma?

Is Fire a Plasma? If not, what is it then? If yes why, don't we teach kids this basic example? UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify ...
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2answers
399 views

Greenhouse gases

A post (below) on the Bishop Hill blog relating to climate change asserts that no warming effect can be attributed to $\mathrm{CO_2}$. I don't know whether the author is really a physicist but it ...
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1answer
249 views

Black body balloon in vacuum [closed]

The problem statement, all variables and given/known data There is a perfectly spherical balloon with surface painted black. It is placed in a perfect vacuum. It is gently inflated with an ideal ...
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1answer
216 views

2d or 1d conduction in this scenario?

There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
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2answers
705 views

Deriving Planck's radiation law from microscopic considerations?

In the usual derivation of Planck's radiation law, the energies or frequencies $\omega$ of the oscillators depend on the measurements $L$ of the black body. The model is such that the only ...
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4answers
3k views

Which is more efficient, heating water in microwave or electric stove?

So our propane tank in the kitchen ran out again today. Which is more energy efficient, boiling water in a microwave on an electric stove? All things being equal i.e. starting temperature and mass ...
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1answer
1k views

How do we see different colours?

Why do different wave lengths cause electrons to behave(?) differently, causing us to see different colors? What is happening at the quantum level which causes the colour black to absorb all of the ...
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1answer
3k views

Why are umbrellas black?

Why are umbrellas specifically in black? Of course we do have colored ones, but black is the majority. Is there any scientific reason behind it?
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5answers
180 views

Will a warm body naturally slowdown?

Suppose a warm body moving in an empty space with high speed. The body emits radiation based on its temperature. The protons emitted forwards of the body will have higher energy due to Doppler shift ...
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3answers
750 views

How is Planck's law defined?

Now, I found three different definitions of Planck's law: $$ P_1(\nu,T) = \frac{8 \pi}{c}\frac{h \nu^{3}}{c^2} \frac{1}{e^{h\nu/kT}-1} $$ $$ P_2(\nu,T) = 2\frac{h \nu^{3}}{c^2} ...
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2answers
222 views

Global warming and planetary thermodynamics

To a first approximation, the earth currently radiates out as low frequency thermal radiation the same amount of energy as it absorbs as high frequency solar radiation. (This ignores energy generated ...
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2answers
249 views

Polarisation directions in standing waves in cubical cavity

I was studying Rayleigh-Jean's formula. The author has assumed a cubical cavity of each side $L$ with perfectly reflecting surfaces. According to author, there are two perpendicular directions of ...
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2answers
166 views

Optical element is heated by laser: is it possible to get oscillating heat distribution?

Imagine that we have thin optical element, which is irradiated by laser. Laser heats element, so there is some heat distribution in element. There is a heat sink through upper and lower element faces ...
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5answers
2k views

Entropy of radiation emitted into space

In several papers I see something equivalent to the following expression for the entropy of radiation given by an astronomical object such as the Sun (assuming the object can be approximated as a ...
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1answer
4k views

Planck's Law in terms of wavelength

I am drawing a blank when it comes to equation transformation. Wikipedia gives two equations for the spectral radiance of black body: First as a function of frequency $\nu$: $$I(\nu, T) = \frac{2 h ...
3
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1answer
259 views

Will this poor-man's single band pyrometer work?

One of the unsolved problems I still have is measuring temperature in furnace at 700-1100C range (I need some +-0.1% repeatability and +-1% precision). Obviously, contact thermometers are quite rare ...
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2answers
1k views

How thermal imaging cameras work

As far as I see from wiki, 'consumer'-grade(non-cryogenic) thermal imaging cameras use microbolometer sensors to get integrated IR intensity over some 5-12um range. But I had an impression, that ...