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In a cyclic process, ΔU = 0 and so Q = We. But for the engine, Q = QH - QC. This means that if we define the efficiency as ε = We/QH we find that ε is just 1 - (QC/QH).
A heat pump takes heat from a low temperature region and dumps it into a higher temperature region.
The refrigerator/air conditioner scheme involves vaporizing a liquid in the low temperature region and condensing it in the external world.
Entropy is a measure of probability. If we make an opening in a container of gas, very quickly there will be the same gas pressure, and the same number of gas molecules, in both new and old regions.
Statistical definition of entropy: S = kBln[Nms].
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Increase in the
entropy of the entire universe? As the average density
of the universe has dropped tremendously over the last
13.8 billion years, the rate of star formation has
declined equally tremendously, dropping to 1 % of
its value when the universe was only 2 billion
years old. |
