# Emission of Infrared radiation

## Main Question or Discussion Point

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?

## Answers and Replies

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russ_watters
Mentor
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.

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?