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11

You are likety to be directly measuring the greenhouse effect of the atmosphere. The fact that your cursory measurements seem to be correlated with the air temperature around you supports this idea: the measurement is higher in the day because the Earth itself is hotter and radiating back into space more powerfully. Greenhouse gasses are thus absorbing some ...


8

All bodies above absolute-zero emit some radiation. This is "black-body" radiation and it can be correlated to temperature using the Stefan-Boltzmann law. Your infrared thermometer uses this to calculate the temperature by measuring this radiation. The temperature you measure for the sky is the radiation of an equivalent blackbody at -2°C. This is sort of ...


4

The reason for this can be seen by examining how an infrared thermometer works. As you mentioned, it measures the infrared radiation, and uses this to determine the temperature. So, with that in mind, we consider what happens in the situations you mention. Namely, you cannot use it to measure the air temperature, because the emissivity of the air is ...


4

I would guess your meter is assuming the surface is a reasonable approximation to a black body, i.e. the emissivity is approximately one. The emissivity of polished metal can be as low as 0.1. From the fluke manual: Emissivity Of the kinds of energy—reflected, transmitted and emitted—emanating from an object, only emitted infrared energy indicates the ...


4

The mechanism of EM radiation emission in dilute gases is different from solids, liquids and dense gases. In a solid the main source of the continuous emission, i.e. black body emission, is lattice vibrations causing local oscillations in electron density. The resulting transient dipoles emit EM just like any oscillating dipole. This isn't a resonant ...


3

Kyothe was on the right track, but in fact we do radiate in the visible, just in such small amounts that it's not detectable for all practical purposes. If you look at the referenced Planck (black body) curves for objects around human body temperature, the short-wave tail is nonzero in the visible range, but it's there.


3

There are two aspects to be considered here: Does the wall reflect or absorb the radiation? If the wall reflects, is this specular or diffuse reflection? For both of these sub-questions, the answer depends on the material that the wall is made of and on the wavelength of the infrared radiation. At wavelengths close to the visible (for example, at 0.8 ...


3

All matter in bulk radiates (approximately) as a black body radiator, approximately because there are coefficients of emissivity depending on the constituents. For gases the functional form is different. The radiation has a specific spectrum and intensity that depends only on the temperature of the body As the temperature decreases, the peak of ...


3

Both Infra-red and Visible light are different. (It's BAD to call IR-radiation as IR-light either...) Visible light is everything that you see with your naked eyes. But, IR - NO, you can't see 'cause it's not light and that's why your eye won't perceive it. It's what most vipers, pythons and rattle snakes see..! This is the reason why snakes could detect ...


2

Wikipedia has a good plot of the power versus frequency spectrum, well labeled. One can integrate numerically to get the percentage at each wavelength. There exists also an article on ultraviolet. Please also tell what are the sources of infrared at night and what the power density of infrared rays at night!. Infrared at night comes from the stored ...


2

Yes it's possible. It will depend on the strength (intensity) of the infrared light being emitted and the sensitivity of the receiver or detector, but a range of 10 ft is well within the range of most TV remote controls for example. In 1917 the British develop the first infra-red search and track (IRST) in World War I and detect aircraft at a range of ...


2

In table 1 the classification of photon frequencies is given. A lamp as you describe will emit most of the energy in the infrared and some in the visible. The energy carried by the visible part will also end up in the infrared degraded by the reflections in the room. So you will get 100watts in total. The advantage of emitting mostly infrared lies in ...


2

It's all to do with the conductivity of the material, the thickness is only a secondary effect because as you reduce the thickness you reduce the conductivity. The only time that thickness has a direct effect is if you make a surface from layers of a transparent material which are a precise fraction of a wavelength in order to use interference effects to ...


2

The description infra-red covers a wide range of wavelengths from wavelengths of about 700nm out to tens of microns. Ordinary glass will transmit radiation out to at least 1 micron - the exact cutoff depends on the type of glass. In the prism experiment the geometry means that that the infra-red light detected can't have a wavelength more than (very ...


2

A human body feels heat while in contact with the air, so it is desirable to heat the air. This is what convectional heaters do - they have a developed surface and relatively low temperature to transmit the heat to the air. The radiation power is proportional to the following temperature difference: $Q \propto (T_{heater} ^4 - T_{air} ^4)$, so it can be ...


2

At or around room temperature objects emit light in the far infrared. Cameras that detect this radiation generally give the false colour images that you describe. Because the camera sees radiation emitted by the objects no external source of light is required. However a second type of camera operates in the near infrared and requires an external infrared ...


2

I'm no specialist on this, so, take this answer as thoughts from someone that also wants to know the answer to your problem. This is a very interesting problem, and one that I have interested myself. If you try modelling this process using some kind of kinectic theory (e.g. Boltzmann Equation) approach, naturally apears several time scales from the diferent ...


2

As a general rule there are three mechanisms by which molecules absorb light: Electronic transitions - visible/uv wavelengths Vibrational transitions - infra-red wavelengths Rotational transitions - microwave wavelengths In solids you don't often get rotational spectra because the molecules usually aren't free to move without interacting with the ...


1

The kinetic equation for the distribution function $f(x,v,t)$ is $\partial_t f + v \partial_x f + F \partial_v f = S$ This equation is basically the conservation law for the density in the phase space (x,v); F is the force acting on particles; the term on the right-hand side is the so-called collision integral, it is what drives the distribution function ...


1

This is the Stefan Boltzmann law. The quantity $dE/dt$ is (I quote from the link) total energy radiated per unit surface area of a black body across all wavelengths per unit time, so $E$ is indeed energy, and specifically total energy per unit area.


1

From http://pixsylated.com/blog/canon-speedlite-optical-wireless-fundamentals/ : With optical wireless, the master sends instructions to the slave(s) via a series of pre-flashes that come just before the main flash. These instructions tell the slave what mode to use (ETTL, Manual, or Multi), what power to fire at, and what sync speed to use. ...


1

From what I read here: http://scantips.com/lights/awl.html, the master flash uses IRlight to control the other flashes (just like a TV remote control), not visible light. (The red thing is the IR sensor) Anyway, light can transmit information just as any electromagnetic wave. Otherwise, you wouldn't be able to see the objects around you! There would be ...


1

We radiate infrared rather than UV or visible light because we aren't hot enough. See http://en.wikipedia.org/wiki/Planck%27s_law for more details.


1

Monochromator rail setup If you have access to a white light source, a pair of lens (to columnate the light source and focus it into the monochromator), a monochromator and a photodetector, then the experiment is fairy easy. Measure the spectrum of the white light source, $I_0$ Place the filter in between the source and the monochromator, $I_f$ The ...


1

The electromagnetic processes between atoms and molecules in all phases, solid, liquid, gas, depend on what is generically called "Van der Waals" fields and subsequent forces. It is well known that the atoms/molecules are neutral, nevertheless there exist for all matter dipole and quadrupole and higher order fields which are mainly attractive and form the ...


1

Convective heaters do indeed radiate, but they radiate much less than an infrared heater because they are at a lower temperature. The amount of energy radiated by an object (strictly speaking a black body) is determined by Stefan's Law and varies as $T^4$ so a small increase in temperature makes a big difference. Air is transparent to infrared radiation, so ...


1

Silicone polymers are transparent. They do absorb some IR light: there is an infrared spectrum here, or Google for more examples, but they are only opaque if some filler has been added. So whether or not any particular silicone polymers will transmit IR depends on what filler has been used in it. I think fillers tend to be aluminosilicates or metal oxides. ...


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The most obvious targets are protostar disks (T Tauri, Serpens FIRS 1), the Milky Way's central black hole Sgr A*, and nearby large stars (Betelgeuse). The MPIfR interferometry group web page has an impressive sample


1

Probably your instrument is calibrated against something with an emission spectra more similar to the coolant and thus reporting a different temperature while reading the emission spectra of steel at 90° C.



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