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

[LogicalAcid]

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?

 

[K^2]

If you heat a human to a few thousand degrees, whatever left will emit in visible spectrum.

 

[sophiecentaur]

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.

 

[LogicalAcid]

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?

 

[sophiecentaur]

Light doesn't ionise atoms. Electrons are released from some metals by visible light photons but that isn't ionisation.

 

[ZapperZ]

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.