All Questions
Tagged with thermal-radiation visible-light
139 questions
0
votes
3
answers
471
views
Why do black bodies in thermal equilibrium with their surroundings only emit in non-visible regions of the electromagnetic spectrum?
This question is a follow on from my previous question; Under what conditions can a body be approximated as a black body?.
This question is also about one specific part of an answer given to this ...
- 2,520
1
vote
2
answers
351
views
What effect does color on the upper and lower side of umbrella have?
This question isn't referring to the general use of umbrella to provide protection from rain rather it concerns the optical effects of the color on lower and upper portion of umbrella.
Umbrella are ...
user238497
3
votes
2
answers
6k
views
Why do dark colors absorb light more than light colors?
Black color absorbs light better than any other. The thermodynamics explains the propagation of heat but never really answers why exactly specific spectrum of color has different absorption ...
0
votes
0
answers
128
views
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 ...
- 127
2
votes
1
answer
5k
views
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 ...
- 21
0
votes
4
answers
3k
views
Why do we see black objects if they absorb all frequencies?
Black object absorb all frequencies, yet maybe some light is reflected anyway, but why do we see pitch black?
- 691
2
votes
2
answers
480
views
Does all thermal energy eventually turn into light?
Any object with a nonzero temperature emits energy as light, right? This means that the kinetic energy of its particles (thermal energy) is being converted to light. As it loses thermal energy, its ...
- 21
0
votes
1
answer
553
views
What is the average energy of visible light photons, of what we perceive to be white light? (i.e. visible spectrum of 5500K radiation)
Visible light is anything between 1.65eV and 3.10eV, so the answer is somewhere between these values. Naively we could average this to 2.375 eV, but that would not be actual average of full spectrum ...
- 439
0
votes
1
answer
93
views
If the Sun had a larger surface temperature how would that affect its appearance to us in the sky?
I thought about this when I came across wiens displacement law which says the higher the temperature, the lower the peak wavelength. If the sun was a lot hotter, and its peak wavelength wasn't in the ...
- 1,545
1
vote
0
answers
430
views
Difference between color and effective temperature
What is the difference between color temperature and effective temperature of a star?
I have gone through the pages at wikipedia, but I still do not understand that. Can anyone please help?
- 1,888
19
votes
5
answers
5k
views
If perfect blackness violates the Uncertainty Principle, how isn't dark matter a violation?
In a recent tweet, Dr. Michio Kaku stated that perfect blackness would violate the Heisenberg Uncertainty Principle, i.e. every object must emit some radiation. I have two questions regarding this ...
- 353
1
vote
1
answer
114
views
Missing link re: how does kelvin relate to temperature when talking about color temperature?
I am an electrician at a commercial electrical company. There is an in-house training program that posits the datum that when talking about the designations of color temperature for lights (for ...
0
votes
0
answers
20
views
How does brightness affect color? [duplicate]
How does brightness affect the color of light? For instance, the sun might be yellow because of the blue scattering when the light travels through the atmosphere - but if you look at it, it seems ...
- 201
0
votes
2
answers
147
views
Why does the sun always have some whiteness? [duplicate]
So the atmosphere scatters light on its way to earth, making the color of our sky. For example, when the sky is blue on a clear, sunny day, the sunlight appears somewhat yellow because the blue light ...
- 201
2
votes
3
answers
741
views
Black Body radiation curve - Does it depend only on temperature.? [duplicate]
Couple of questions on Black body radiations
1. Blackbody emits a continuous spectrum. But blackbody is an idealized body. Do normal objects like a bulb or a table emit a continuous spectrum too.?
2. ...
- 1,471
3
votes
2
answers
521
views
Black body radiation and spectra lines
My understanding was that all objects emit light of continuous spectrum when hot ( black body radiation) but then you see discreet wavelengths in spectra lines and I am confused. I know I am making a ...
- 1,471
0
votes
2
answers
128
views
Planck's Constant, factor of 2
I'm just starting to look into the birth of Quantum mechanics, but I'm already a little confused by something.
I've seen 2 different equations involving the Planck's constant so far:
$hf = \mathrm{...
- 3,125
2
votes
0
answers
183
views
Why do black bodies or black colored bodies cool down faster than white ones? [duplicate]
Recently, I found an exercise in which a graph was shown with the variation of temperature of two painted cans as they received sunlight.
One of the questions was "Which of these two bodies will ...
0
votes
3
answers
466
views
What color are stars?
I know that the sun looks white to us because it emits a large variety of color, making it appear white to our eyes but does this mean that all stars emit a variety of light? If so, then how can we ...
2
votes
0
answers
74
views
Does the black-body radiation formula (Stefan-Boltzmann) change if the photon turns out to be massive?
The black-body radiation formula, the Stefan–Boltzmann law, is derived treating photons as massless.
Questions:
What would the Stefan–Boltzmann law look like if derived assuming that photons have ...
- 324
5
votes
4
answers
1k
views
Why doesn't the moon appear yellow?
The sky is blue (I'm told) because nitrogen in the atmosphere scatters short blue wave lengths of light from the sunlight, which is also why the sun appears somewhat yellowish rather than white, as it ...
- 154
1
vote
2
answers
343
views
Why are people dark skinned in hotter areas despite dark colour absorbing the most heat? [closed]
I’m not sure if the reason is in the field of biology or more towards physics but as my reasoning is based on the physics part being that perfectly black bodies are perfect absorbers of heat and light ...
- 119
15
votes
5
answers
9k
views
Why is a black body visible?
A black body absorbs all energy. It doesn't reflect or transmit energy. It also absorbs all light and doesn't reflect any light. Why, then, can we see it? For instance, burnt platinum is 98-99% black ...
1
vote
3
answers
7k
views
Why isn't the Sun blue?
If I believe right, blue flames are hotter than red ones and if I recall correctly it's because blue tend to ultraviolet. Then why is the sun, which's capable of warming whole planets, red instead of ...
- 49
0
votes
5
answers
2k
views
Is a purely white light made up of an equal amount of all wavelengths of light in the visible spectrum? [duplicate]
I've heard that a blackbody radiator at 6500 K, for instance, emits pure white light, but does that mean it's made up of all wavelengths in the visible spectrum in equal proportions? Or is the ...
- 11
0
votes
1
answer
191
views
Blackbody radiation, de Broglie equation, and lightwaves to be shifted left
I'm having a hard time figuring this out.
Say we heated a lead ball to 1,000 Kelvin. Not all of the particles
are at the exact same temperature--some parts are a little hotter,
some are a little ...
- 1
6
votes
2
answers
3k
views
Why is the sky blue and the sun yellow?
The blue color of light of the sky is due to Rayleigh scattering.
But the sun itself appears yellow in color whereas the scattered sunlight itself appears blue.
Why does this happen?
Should the sun ...
- 454
0
votes
2
answers
323
views
Changing the Color Temperature of Light [closed]
Suppose I have a lamp that produces light at 5,5000 k. I need to play around with the color temperature and change it up and down (4,000 k, 6,000 k etc) at will. Based on my research, I believe there ...
- 101
4
votes
2
answers
442
views
Why are the colors of metal different than the blackbody spectrum?
The blackbody color spectrum up to about 11,000 degrees Farenheit looks like this:
However, when iron or steel is heated it produces light in the following colors:
So it starts to luminesce at about ...
- 4,504
1
vote
2
answers
4k
views
Why does the sun appear yellow? [duplicate]
I read an article by NASA in which the following assertion was made:
The sun, in fact, emits light in all colors, but since yellow is the
brightest wavelength from the sun, that is the color we ...
- 4,504
6
votes
1
answer
8k
views
Why is black a better emitter of heat than white? [duplicate]
I know that black absorbs light and converts it into heat which makes it a good emitter of radiant heat while white reflects it. Let's say if I place 2 cups, 1 black and 1 white, same material, in a ...
- 63
2
votes
2
answers
3k
views
What does the spikes and curves in the spectral graph for compact fluorescent lights represent?
I have read from sources that the curves are generated by the phosphors in the bulb, and the spikes are caused by the mercury vapor.
However, if the mercury vapor's release of uv particles combine ...
- 159
2
votes
1
answer
8k
views
Why does the LED light colour spectrum spike in the blue and green wavelengths but CFL lights have lots of smaller spikes across a few wavelengths?
What is the theory behind this? Incandescents produce smooth curves as they are similar to black bodies, but for these non-blackbody bulbs, what creates their unique spectral curves?
- 159
5
votes
2
answers
12k
views
Why are light bulbs black body radiation emitters?
If the definition of a black body is:
"A blackbody is an object that absorbs all of the radiation that it receives (that is, it does not reflect any light, nor does it allow any light to pass through ...
- 159
1
vote
3
answers
12k
views
How could I measure the colour spectrum of a light bulb and investigate how closely it matches a black body radiation curve?
Here is my research question:
What is the colour/spectrum produced by each globe type? What is the temperature equivalence? How closely does a globe match a black body radiation curve?
I will be ...
- 159
3
votes
1
answer
2k
views
Can you use sun light to heat an objects surface to hotter than the surface of the Sun? [closed]
I was reading this question: Concentrating Sunlight to initiate fusion reaction and some of the comments, as well as an answer, suggest that thermodynamics second law prevents what I ask in the title. ...
- 2,623
0
votes
3
answers
5k
views
How much of the electromagnetic spectrum does Sun emits?
I'm wondering how much of the electromagnetic spectrum does the sun emits! It obviously emits visible light, but what about the other?
Does the sun emits radio waves? If that's the case why them do ...
8
votes
1
answer
5k
views
Black Bodies and appearing black
I know a black body is an object that absorbs all wavelengths of light, and also emits all wavelength of light too back out, but if it emits all wavelengths of light, why does it appear black, as all ...
- 283
5
votes
2
answers
1k
views
Incandescence vs. black-body radiation
So in a discussion today I wanted to show someone the relationship between a star's color and their surface temperature.
Expecting to find a chart such as this one, I first found this one instead. ...
- 151
2
votes
2
answers
619
views
Why do holes appear black during the day?
Why is it that when an object has a small hole, the hole appears dark during the day? Why doesn't sunlight fill the enclosed space and make the hole appear to be the color of the interior walls?
- 259
92
votes
7
answers
28k
views
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
Why don't metals glow from red to yellow to green to blue etc.? Why only red, then yellow and then white? Shouldn't all wavelengths be emitted one by one as the temperature of the metal increases?
...
- 1,657
1
vote
0
answers
1k
views
Why does the intensity of radiation decrease as the frequency increases?
Image Source
I am well aware of that what I am going to ask may sound really stupid and easy to answer so forgive my ignorance on the matter. Basically, why does the intensity of radiation decrease ...
- 123
3
votes
4
answers
4k
views
What are the differences between light from the Sun and light from a laser?
The sun and the laser both give off photons, but there is clearly going to be a difference(s) in the light I receive from both sources. What are those differences (energy, intensity, orientation of ...
- 455
0
votes
2
answers
2k
views
Energy and colours of the stars
We know that stars have different colours because they have different energy. So blue stars have a lot of energy because the blues's frequency is very high $E = h\nu$. The colour of the star is its ...
- 209
0
votes
1
answer
211
views
Is thermal EMR just another form of Fluorescence / Phosphorescence?
Normally when thinking about Fluorescence one only deals with visible light, but is it fair to say that the thermal EMR (heat) that's generated from a light source is also a fluorescent effect? For ...
- 1
8
votes
3
answers
6k
views
Is it better to wear black clothes in the summer?
Okay I saw all these people saying that new studies show black is better to wear in the heat. They say it's cause "black clothes absorb the heat emitted by the body while white clothes reflect it back ...
- 85
58
votes
6
answers
45k
views
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?
- 2,030
1
vote
1
answer
3k
views
How is it possible some substances burn with an invisible flame
I know some substances such as Methanol fuel burn invisibly, but according to the following picture, every black-body emitter still emits light at the blue part of the spectrum, even when it's ...
- 123
21
votes
7
answers
5k
views
What can we deduce by the fact that mirrors cannot get a ray hotter than Sun's surface?
I think it is quite counter-intuitive that some lenses or mirrors focusing sunlight to a single spot cannot produce a temperature higher than Sun's Surface.
What could a scientist deduce from that ...
- 737
3
votes
2
answers
5k
views
Is it possible that fire produces only invisible light?
I was just wondering that is it ever possible that some object produces only invisible light when it catches fire? Something like invisible flames.
If this is possible, can you please give one ...
- 127