All Questions
Tagged with thermal-radiation infrared-radiation
54 questions
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When can we expect a black-body radiation?
During the pandemic last few years, the Infrared thermometer is widely used to measure the body temperature.
However, the fundamental question or the question in the first place is, why do we expect ...
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Why is my pyrgeometer calibrated as if it has $a >1$ emissivity?
I've acquired an SL-510-SS upward-looking pyrgeometer.
In the manual it gives the formula for how to compute the downwelling infrared it picks up:
Clearly the $k_2$ coefficient is the emissivity of ...
- 1,277
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Effect of having infrared reflective paint on a room with and without a heat source
I am trying to check if my understanding is correct. This is not really a question but a request for validation. I hope this is allowed.
When painting with a heat reflective paint there are two ...
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Are there any material coatings that would currently be effective to counter the rise of directed energy weapons?
I've been reading into directed energy weapons recently, and they seem like they're going to be a gamechanger. I'm just curious as to material countermeasures. I've learnt that some dielectric mirrors ...
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Why is my aluminum foil emitting the same amount of infrared as the other objects in my room?
I got an infrared thermometer (SOVACARTE HS980E) recently and have been playing around with it.
My understanding is that it works by measuring the amount of infrared radiation coming off of the object,...
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Why does UV light feel warm on my skin? Whereas infrared light heats up space around me plus my skin?
Noticed something weird today.
I have an infrared space heater that is pretty good at heating up my desk at work (as well as my skin obviously).
I also have a UV flashlight. I noticed the UV ...
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What determines the particular frequency of infrared any given object emits?
Infrared (IR) includes EM waves between 780nm and 1mm in wavelength. (Source) As an object gets hotter, it emits a greater amplitude of infrared. What determines the particular frequency(s) of IR an ...
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What is the temperature of a greenhouse gas?
The temperature of a gas is usually the sum of the kinetic energy of its particles, right?
Whereas the temperature of a solid object is given by the Stefan-Bolzmann equation, as a function of how much ...
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How is black body radiation from sample eliminated when measuring absorption coefficient?
I wonder how absorption spectra of a sample (e.g. gas with some $CO_2$ absorbing strongly at $\approx 15\mu m$) is measured by IR spectroscopy, thereby having in mind the following arrangement, ...
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Why do dark objects absorb visible light but only emit infrared radiation?
What is it about the molecular structure of dark coloured objects that means they absorb most of the visible light that falls on them, but radiate infrared?
Naively I would think that if a molecule ...
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Effect of changing $\rm CO_2$-levels on cooling the desert at night
It is known (e.g. as mentioned in this popular article) that the reason why deserts cool down at night so much (to temperature below zero degrees celsius) is that there is much less humidity in the ...
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Is cooling by infrared absorbing rectenna possible?
We know that every hot objects emits IR radiation.
We also know that plasmonic rectenna can absorb and convert IR radiation to electricity.
Question: what will happen if we put an hot object inside a ...
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Why does cooling down thermal imaging cameras increase sensitivity?
A lot of high-sensitivity thermal cameras and sensors are (cryogenically) cooled down to low temperatures to achieve these high sensitivities. For example. the Stinger missile, and the James Webb ...
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Planck radiation law of a dielectric layer
Suppose we have a rectangular slab of thickness $h$, width $a$ and length $b$. The upper surface of the slab is put at constant temperature $T$ while all the rest is at initial temperature $T_0$. ...
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How much of the suns radiation is infrared from compression heat, not fusion?
Preface: Im a college level dropout, please dont stomp on my ignorance too hard.
As mass falls into a gravity well, it compresses and heats up. Even if fusion didnt exist/occur, in a body as large as ...
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What colors reflects the most infrared radiation?
About fifteen years ago I read in a book (Physics by James Walker 3rd edition) that dark brown color reflects IR better than any other color and consequently weather heat since our bodies get most ...
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Are window glasses transparent or opaque to infrared radiation? [duplicate]
I have been trying to understand this concept to identify on the best option to reduce temperature in my room.
I have read few article which stated that glass is transparent to IR radiation. ie Beyond ...
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Is there no way to bypass greenhouse gasses by converting excess heat to longerwave radiation?
The problem with greenhouse gases, as I understand it, is that they absorb and emit radiation within the thermal infrared range leading to increased temperatures on Earth. According to some sources, ...
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Effect of coloring on emissivity at temperatures below 150C?
I'm working on Aluminum/Copper heat sink design optimization and came across this thought.
The heat source on which the heat sink is going to be placed is approx 100C. Forced convection is absent, so ...
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If all objects emit IR radiation, would it be sufficient to place an IR mirror behind an object to propel it forward?
I'm assuming objects don't move all the time because they emit IR radiation in all directions. If we have an IR mirror behind the object to focus their direction, would this propel the object forward?
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Physics of an infrared thermometer
The thing about infrared thermometers that bugs me is how can you get the same temperature reading regardless of the distance to the object. Shouldn't there be a difference when measuring from two ...
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What variables affect an object's absorption of invisible light?
Say I have two objects (we'll call them object $1$ and object $2$) of the same material but of a different colour, placed at the same distance away from another object (we'll call object $3$) that ...
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Specular Reflection of IR Light
I have started to use thermal imaging cameras more and more and realized that I can see the reflection of my self bouncing off of a glass window through the IR camera. When viewing it on my monitor, I ...
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How do modern microbolometer cameras measure absolute temperature of an object?
I recently started working with thermal cameras and I was surprised to learn that they don't give you the temperature value of the object you are looking at for each pixel. So I did some reading. I ...
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How does a moderately hot gas emit radiation?
I have been studying black-body radiation and have a rudimentary understanding of how this works for solids (like a heated iron bar).
I am having trouble grasping how a "warm" gas emits a ...
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Why can visible light go through green-house gases? [duplicate]
I understand that visible light can (largely) go through greenhouse gases, but infrared radiation can get reflected back... why can visible light go through green-house gases?
Does it have to do ...
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How does sunlight feel hot through glass?
My confusion is this. I can shine a flashlight through a window at someone, and they don't feel any heat. Yet, sunlight shines through a window, we feel the heat. I want the scientific explanation of ...
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Thermal emission from a metal surface
We know from Kirchhoffs law that at thermal equilibrium the absorbance is equal to the emissivity. Let's consider some opaque layers of Al, Ag, Au for which I found reflectances at google:
When I ...
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Can radiators cool down using only back body radiation?
If you could produce a very thin tube, say less than the thickness of a human hair, designed to carry a hot liquid inside, the diameter is small so that the liquid would have a high surface area to ...
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What processes permit (presumed) emission by, but prohibit absorption of, IR photons by non-greenhouse gas molecules?
It is said that because of bond-structures / possible vibrational states, non-greenhouse-gases / homonuclear diatomics cannot absorb IR.
Presumably there is no question that all gases, being matter, ...
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Painting a vehicle black to avoid radar detection: a bad idea?
A lot of people on the Radar Detector & Laser Jammer Forum are trying to paint their cars in the deepest black to avoid getting a speed ticket by making their vehicle stealthier for incoming radar ...
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How many degrees Celsius/Fahrenheit can be reached in 1 square meter area using magnifying glasses?
The magnifying glasses are each 10 meters in diameter, their collected light is concentrated via mirrors into a 1 square meter spot. Is it possible to get a temperature higher than 2000 degrees ...
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Infrared pass material thermal camera
I have a situation in which I need to use a thermal camera in a rain enviroment, the camera is mounted on a gymbal and can rotate 360 degrees, so I tought it may be an option to build a dome in order ...
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Why a metallic mirror temperature cannot be read by a thermal camera?
When I look at a first surface mirror with a thermal camera I don't see the temperature of the mirror but the temperature of the reflected objects. It is like if a polished metallic surface don't lose ...
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Why don't we use infrared light to heat food?
Why don't we use infrared (IR) or even the far IR just to heat food in a microwave oven instead of, of course, the conventional 2.45 GHz microwaves? Don't people call IR heat waves?
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How does an IR camera determine the temperature?
The IR cameras detect light in the IR where low temperature bodies (-20 - 40 deg) have their peaks of the black body radiance.
How the detectors associate temperature to intensity measurement on a ...
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How does a microbolometer array resolve temperature?
I'm told that handheld thermal sensors measure black body radiation with a bolometer array.
I don't understand how ones goes from IR photon counts to temperature. Is the camera somehow spectrally ...
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Different methods for measuring intensity of IR wavelengths
I am proposing a teaching experiment at my university for undergraduates to learn about black body radiation and part of it will involve measuring intensities of different near - mid IR wavelengths. ...
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Why can a regular infrared camera not show temperature (thermography)?
There are a lot of questions here dealing with infrared cameras and thermographic cameras. I think I understand the reason why a thermographic camera is able to retrieve the temperature values from ...
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Can our emitted infrared light turn on the TV?
We know that TV can be turned on with infrared light and we know that our body emits infrared to. Does the frequency of our emitted infrared corresponds to the frequency of the device that turns on ...
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Why do we feel heat from infrared light but not from shorter wavelengths?
My guess would be that light with a higher energy such as visible or UV would feel hotter, but this is not the case!
Is this something to do with human senses or is there a physics explanation?
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How can IR cameras see things colder than the camera?
I’ve read that only cold-blooded animals develop IR vision to spot warm prey because a mammal would blind himself with his own heat and not be able to see anything.
But I’ve seen a FLIR camera, ...
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How / why do infrared thermometers work?
How can reading the intensity of infrared radiation coming from an object let you calculate its temperature? Could any wavelength be used to measure temperature - why infrared, and not, for instance,...
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Radiation-Glossy Black vs Matte White
Well, studying the chapter Heat I know that a matte black body radiates heat more than a glossy white one but can anyone give me an answer about what happens when its a glossy black body and a dull ...
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Why 8–15 µm is considered "thermal infrared" if typical room temperature kT is 48 µm?
According to Wikipedia:
Long-wavelength infrared (8–15 µm, 20–37 THz, 83–155 meV): The
"thermal imaging" region, in which sensors can obtain a completely
passive image of objects only slightly ...
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When thermal IR gets reflected from an object, does it change its wavelength (frequency)
I'm working with thermal infrared (IR) cameras to detect human thermal radiation.
I notice I can easily distinguish non-human objects throughout the camera's field of view, though all are at same room ...
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How does an infrared thermometer actually calculate temperature?
I am slightly confused about infrared radiation and the equations related to it.
$P = A \epsilon \sigma T^4$ (1)
and
$B_{\lambda}(\lambda,T) = \frac{2hc^2}{\lambda^5} \frac{1}{e^{\frac{hc}{\lambda ...
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Why do metal surfaces reflect thermal signature?
I recently borrowed a thermal camera from a friend and I tried to observe my palm print over a reflective metallic plate. When I looked at it through the camera, it reflected my thermal signature too. ...
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How damaging is light?
On Surely You're Joking Mr Feynman, when talking about the Trinity test, the author states:
the only thing that could really hurt your eyes (bright light can never hurt your eyes) is ultraviolet ...
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Why does my infrared thermometer say the sky is at -2 °C?
I just got myself an infrared thermometer. I wouldn't have been able to predict what temperature it would give me when pointing at the sky, but it turned out to be -2 °C the first time I measured, and ...
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