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Why does black a good absorber?

by Alan Tam
Tags: absorber, black
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Alan Tam
#1
Aug13-06, 06:16 PM
P: 8
Could anyone help me answering the above question? Thanks.
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nealh149
#2
Aug13-06, 06:44 PM
P: 112
Could you rephrase the question, it looks like you may have typoed.
Danger
#3
Aug13-06, 07:02 PM
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Welcome to PF, Alan. The impression that I get from your question is that you wonder why a black surface absorbs more heat from the sun than other colours do. The reason primarily is that the term 'black' refers to the fact that the surface absorbs all visual wavelengths of EM. That, of course, also means that it can give up its collected sunlight more efficiently than a less absorbtive colour can.

Mk
#4
Aug13-06, 07:22 PM
P: 2,056
Why does black a good absorber?

Black was named for an object having the quality of absorbing light in the visible range. It is inherent.
russ_watters
#5
Aug13-06, 08:06 PM
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Its a definition...
cterence_chow
#6
Aug14-06, 08:35 AM
P: 20
Hey, regarding your question, i would like to clarify that black is not a better absorber of heat, it is just a better absorber of radiation.
Danger
#7
Aug14-06, 08:52 AM
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Good catch. That was a poor choice of words on my part. I'm a little too used to conversing casually, I guess. Gotta be more careful.
cterence_chow
#8
Aug14-06, 09:02 AM
P: 20
Lol its ok.Just help answer my question on how does the boat float. Thanx!!
Danger
#9
Aug14-06, 09:32 AM
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I have to agree with Zapper on that one. Read over the previous thread, especially post #8, a couple more times. More specific questions can then be answered if necessary.
Alan Tam
#10
Aug14-06, 08:35 PM
P: 8
Sorry, I mean, why a black surface absorbs much incident radiant energy than a silvery surface?
Danger
#11
Aug15-06, 12:07 AM
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As mentioned, the term 'black' is a way of describing a totally absorbtive surface. A 'silvery' one is non-absorbtive. In astronomy, if not on Earth, the term 'albedo' is used to indicate the reflectiveness of a body. The reason that a black object absorbs more than a silver one is that it's black. Sorry that I can't be more informational, but that's pretty much the bottom line. 'Black' means 'absorbtive'.
Rach3
#12
Aug15-06, 12:28 AM
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A more precise question would be, why does a good absorber appear black. If it absorbs most incident visible light, then it reflects very little, and thus appears dark.
D_Dean
#13
Aug15-06, 01:03 AM
P: 20
Silvery surface is silvery because you can see the light with the wavelength of silver (which is a combination of wavelengths) bounce off of it and into your eye. The light that bounces off is not absorbed into the surface therefore does not transfer energy into the surface. The black surface is black because no light bounces off of it, it is all absorbed (which means the energy is absorbed). Your brain interprets lack of visual light as black.
jasc15
#14
Aug16-06, 03:40 PM
P: 156
An object is black for the same reason that it is a good absorber of electromagnetic radiation. it absorbs all wavelengths of EM radiation well (someone correct me if i am wrong). therefore it absorbs infared, ultraviolet and visible wavelengths. So in short, its not a good absorber because it is black, rather it is black because it is a good absorber.
DaveC426913
#15
Aug16-06, 04:30 PM
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Quote Quote by D_Dean
Silvery surface is silvery because you can see the light with the wavelength of silver (which is a combination of wavelengths)
No. Silver is not a colour, nor, by its essence, a combination of wavelengths.

When a surface is so smooth that it reflects the light coherently (all or most light rays are reflected at the same angle), we are able to visually distinguish individual patches of light rays that come from discrete sources.

That is to say, light rays coming from, say, a red and blue checkered light source, will be reflected off the object so faithfully that we can see the red and blue checks as if in the object itself.

A silver object reflects not only all the light incident upon it, but reflects it faithfully, rather than diffusely.

When we see this effect, we sometimes erroneously label it a "colour" which we call silver.


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