Why do different objects absorb and reflect different wavelengths of radiation?

In summary: Please start by reading an entry in the FAQ thread in the General Physics forum. Pay attention to the entry on light transport in matter, and the point made regarding phonons.
  • #1
LogicalAcid
137
0
For example, humans emit primarily in the Infrared part of the spectrum, so then why is it that when visible light falls upon us, it is not converted to heat immediately?
 
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  • #2
If you heat a human to a few thousand degrees, whatever left will emit in visible spectrum.
 
  • #3
LogicalAcid said:
For example, humans emit primarily in the Infrared part of the spectrum, so then why is it that when visible light falls upon us, it is not converted to heat immediately?

The peak in the spectrum of radiated em energy depends upon the temperature of the surface of the object. For humans, at normal body temperature, the peak is in the IR region. If visible light falls on a human then his / her temperature may rise a tiny bit due to the absorbed energy. That will alter the peak in the radiated spectrum but, of course, humans regulate their (core) temperature so there will be compensating mechanisms to keep the surface temperature from getting too high. For an inanimate object, the temperature that it will finally reach will be higher, according to just how much energy falls on it and also on the temperature of the source of the radiation.
 
  • #4
sophiecentaur said:
The peak in the spectrum of radiated em energy depends upon the temperature of the surface of the object. For humans, at normal body temperature, the peak is in the IR region. If visible light falls on a human then his / her temperature may rise a tiny bit due to the absorbed energy. That will alter the peak in the radiated spectrum but, of course, humans regulate their (core) temperature so there will be compensating mechanisms to keep the surface temperature from getting too high. For an inanimate object, the temperature that it will finally reach will be higher, according to just how much energy falls on it and also on the temperature of the source of the radiation.

This is wiens law, but I still don't understand, if the visible radiation around us can ionise atoms, why aren't we glowing masses of plasma?
 
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  • #5
Light doesn't ionise atoms. Electrons are released from some metals by visible light photons but that isn't ionisation.
 
  • #6
LogicalAcid said:
This is wiens law, but I still don't understand, if the visible radiation around us can ionise atoms, why aren't we glowing masses of plasma?

Please start by reading an entry in the FAQ thread in the General Physics forum. Pay attention to the entry on light transport in matter, and the point made regarding phonons.

Zz.
 

1. Why do different objects absorb and reflect different wavelengths of radiation?

Different objects absorb and reflect different wavelengths of radiation because of their unique molecular and atomic structures. The electrons in these structures can only absorb and emit specific wavelengths of energy, causing some objects to absorb certain wavelengths and reflect others.

2. How does the color of an object affect its absorption and reflection of radiation?

The color of an object is determined by which wavelengths of light it reflects and absorbs. For example, a red object appears red because it reflects red wavelengths of light and absorbs other wavelengths. Therefore, the color of an object can greatly affect its absorption and reflection of radiation.

3. Are there any factors that influence an object's absorption and reflection of radiation?

Yes, there are several factors that can influence an object's absorption and reflection of radiation. These include the object's material, temperature, and surface properties such as texture and smoothness.

4. Can two objects of the same color have different absorption and reflection properties?

Yes, two objects of the same color can have different absorption and reflection properties. This is because their material composition and surface properties may differ, causing them to absorb and reflect different wavelengths of radiation.

5. How does the absorption and reflection of radiation affect an object's temperature?

The absorption and reflection of radiation can greatly affect an object's temperature. Objects that absorb more radiation will become warmer, while objects that reflect more radiation will remain cooler. This is why dark-colored objects tend to be warmer than light-colored objects when exposed to sunlight.

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