Why does black color asorb light?

[ChmDudeCB]

I think you are looking at it the "wrong way around". There is nothing about "being black" that causes something to absorb light. Rather there is some chemical property (outer electron shell, etc.- often it is that the material is made of many different elements that have different "energy levels") that causes the material to absorb all wavelengths of light- and since little or no light is reflected, we call it "black".

Uhhhh

What about the blackness of space? Even in areas with no known matter it absorbs AND emits radiation. Oh and the sun is a pretty good black body.

As far as the original questions goes, something which is black to our eyes is one which is emitting no colored light. That means, as said above, the properties of the molecular orbitals absorb a wide range of colored light. I'd bet you the funds to kickstart me a privet lab that in the microwave and IR regions it does not absorb or transmit all light. UV rays will cause excitations that will lead to gradual degradation. Xrays will be diffracted and you will get cool patterns.
https://wiki.brown.edu/confluence/download/attachments/5896/diffraction.jpg?version=1

High energy Xrays and gamma rays will excite the nuclei. So nothing is ever truly black.

 

[jetwaterluffy]

I suppose a black hole is a "true" black object. And the reason why they are black is that the escape velocity is faster than the speed of light.

 

[Johnahh]

If there is no known matter how can radiation be absorbed? Electrons are needed for absorbtion/emission. Colours reflect light of the same colour I.e a plants leaf reflects green light and absorbs blue and red. If "black" is colourless surely it will not reflect any colour of light.

 

[Drakkith]

If there is no known matter how can radiation be absorbed? Electrons are needed for absorbtion/emission. Colours reflect light of the same colour I.e a plants leaf reflects green light and absorbs blue and red. If "black" is colourless surely it will not reflect any colour of light.

There is no such thing as a perfect black body. Everything will reflect light at least a little bit. However in our day to day lives something that reflects a very low amount of visible light will look black to us.

 

[ChmDudeCB]

If there is no known matter how can radiation be absorbed? Electrons are needed for absorbtion/emission. Colours reflect light of the same colour I.e a plants leaf reflects green light and absorbs blue and red. If "black" is colourless surely it will not reflect any colour of light.

Photons have a practically infinite number of potential wavelengths. There is a wide range of what is called black. Black to our visual stimulation is limited to a total absorbtion of light in the visual spectrum. Color refers to relative wavelength in regards to physics. Generally used as a relative term. This photon is more red (longer wavelength) or blue (shorter wavelength) than this other photon. A true black body only emits radiation based on its temperature. As has been stated, a black hole is a real black body, matter free space is a real black body. However, both have a temperature (albeit rather cold) so they do emit very very long wavelengths of light. However, even when something appears black to us, it is because MOST of the visual light has been absorbed, not all. Our eyes are not equally sensitive to all wavelengths of light, as absorbtion comes in bands based on the molecular orbitals of the molecules. This is how you get different shades of "black". I mentioned the absorbtions of other named wavelength bands because, as stated above, no real matter is a true black body. Black pigments may absorb most light in the visual spectrum but most pigments are organic and all organic molecules have very specific vibrational excitations in the IR region. Most molecules absorb part of the UV spectrum but few absorb all. All molecules absorb in the microwave and radio wave regions, but not wide band. This is because those frequencies excite rotational and translational energy levels and ALL molecules exhibit these absorbtions at some point in the spectrum. Just imagine my first post about "black" being said by someone with a **** eating grin.

 

[ehild]

As we know that energy can neither be created nor destroyed then the light absorbed by a blackbody has to leave the body in some form or the other.. If u say a black body just keeps on absorbing light then that means that the temperature of the blackbody will keep on increasing with time...There would be something happening with the light falling on it..What is that after absorption of light happens with EM rays..

You are right, the body will not warm up infinitely: it also loses energy.
The loss of energy can happen

by induced emission, when the body emits photons of the same wavelength and direction as the absorbed ones, but the probability of induced emission is very low in ordinary bodies.

by by spontaneous emission: the wavelength is the same, but the direction of the emitted photon is random

the absorbed radiation energy is converted to the random motion of the atoms and electrons, increasing the internal energy of the object, that is, increasing temperature. The body radiates according to its temperature and its material. The temperature increases till equilibrium is reached: the rate of absorption balances the rate of radiation.


ehild

 

[Claude Bile]

@Claude Bile: Do u mean to indirectly say that black is also emitting a wavelength which is outside Visible range and occupies some other EM spectrum. If you are saying so, i feel that you are denying the real definition of Black. "Black is something that absorbs all color",..so if something absorbs all color how can it reflect anything..And as per the experiments done since time in memorial "Black doesn't reflect any thing..It does emit different rays as per its temperature"..

Well, it depends what you define as being "black". In everyday life "black" means "none of my color receptors are being stimulated". Even the night sky has a long wavelength glow to it. Occasionally in physics we might define black as encompassing all wavelengths, such as in black body radiation. Whatever the case, the moral of the story here is to be explicit by what is meant when you describe something as "black".

@sophiecentaur: I hadn't realized this, good to know!

Claude.