Emission of Infrared radiation

[BBRadiation]

Question regarding the emission of infrared radiation, for personal knowledge.

Why do humans emit infrared radiation? Is it because it just so happens that the energy humans absorb (from sunlight)/ the energy humans produce just so happens to correlate to the frequency of infrared, as according to E = hf? Or am I wrong in my assumptions of where the source of the energy comes from?

Additionally, I read that many everyday objects, such as an ice cube or a textbook emit infrared. How can objects such as these, which have a much lower temperature than humans (which I assume correlate to lower energy) emit in the same frequency. Can this only be the case if infrared has a large spectrum, and thus can correlate to different amounts of energy?

 

[russ_watters]

Welcome to PF.

Why do humans emit infrared radiation? Is it because it just so happens that the energy humans absorb (from sunlight)/ the energy humans produce just so happens to correlate to the frequency of infrared, as according to E = hf? Or am I wrong in my assumptions of where the source of the energy comes from?

All objects emit electromagnetic radiation in relation to their temperature via the mechanism of black body radiation: http://en.wikipedia.org/wiki/Blackbody

So the source of that energy is our internal body heat, which we generate using food as fuel.

Additionally, I read that many everyday objects, such as an ice cube or a textbook emit infrared. How can objects such as these, which have a much lower temperature than humans (which I assume correlate to lower energy) emit in the same frequency. Can this only be the case if infrared has a large spectrum, and thus can correlate to different amounts of energy?

Yes, "infrared" is a range of frequencies, not a specific frequency.

 

[BBRadiation]

Thanks a lot. Is the energy we generate from food the sole source of energy? Or does other factors play a role, such as friction from movement or absorption of energy from the sun?

If all these factors are prevalent, how does one determine the energy of an object? For example, if I wanted to know what electromagnetic energy a fish emits, how would I calculate its energy?