# Why and how exactly does the quantity of energy radiated per second increase with the temperature of the radiating object?

I read in my textbook that the quantity of energy (in the form of electromagnetic waves) radiated per second increases with the temperature of the radiating object. However, I can see two ways of interpreting this and am not sure which is correct.

Would it be true to say that an object that was a good absorber and emitter of radiation would always be absorbing and emitting as much EM radiation per second as was possible with the level of available EM radiation lying around in its environment? So, for example, in a really cold, low-energy environment, it might only be absorbing 20 joules worth of EM radiation per second, and also (of course) only emitting 20 joules of EM radiation per second. But in a much warmer, high-energy environment, it might be absorbing and emitting, say, 1000j EM radiation per second, just because there would be more EM radiation available for it to channel in the second environment. If the above is true, then is this the reason that objects with a higher temperature would radiate more EM radiation per second (since good absorbers and emitters would only have a higher temperature if they were already in a higher energy environment)?

Or, alternatively, is this phrase actually just trying to say that the higher temperature a good absorber and emitter is compared to its environment, then the more energy that object will radiate per second? If so, is this because the object would originally be emitting much more energy than it was absorbing, and then as it got closer and closer to being at thermal equilibrium with its environment (and so had a lower and lower temperature), the rate of emission would decrease until it was equal to the rate of absorption?

Which is the correct interpretation, or, if neither is correct, then what is the explanation behind this phrase, please? Thanks so much.

• The energy radiated by a body can usually be described to some extent by Black-body radiation. I would suggest you read the wikipedia article on it and hyperphysics.phy-astr.gsu.edu/hbase/mod6.html . Aug 16 at 13:11