How fast does the air in an oven warm up

The air inside an oven begins to get warm as soon as we switch it on. We can regard the interior of the oven as a fixed system, so the internal energy U of the 

On a macroscopic level, the rate at which the quantal states are filled as a body absorbs energy is reflected by its heat capacity C. We can tell how quickly the quantum states are occupied because the temperature of a body is in direct proportion to the proportion of states filled. A body having a large number of quantum states requires a large number of energy quanta for the temperature to increase, whereas a body having fewer quantum states fills more quickly, and becomes hot faster. 

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