An isentropic process is an idealised process which is adiabatic and reversible (in thermodynamics). there is no transfer of heat or matter and the work transfers of the system are frictionless. can you explain to me which of the 4 processes in the carnot cycle are isentropic and why - so that i can understand it. i have read two articles about it, but dont understand.

Explanation:

An isentropic process is one that does not change the entropy of the system. A reversible of the universe, and it is reversible because of that. Real processes increase the entropy of the universe, so trying to reverse them would decrease the entropy of the universe, which is impossible, so they are irreversible.

The Carnot cycle has 4 phases:

-Isotermal expansion of gas. In this process it takes heat from a hot source. It is a reversible process, but not isentropic.

-Adiabatic expansion. This one is isentropic, the entropy of the gas remains constant and it doesn't interact with the surroundings. The gas expands not by its own, but the machine makes it expand (it pulls on the gas). The gas cools down.

-Isotermal compression. Reversible but not adiabatic. The gas exchanges heat with the cold source, reducing its volume.

-Adiabatic compression. Adiabatic and isentropic. The machine compresses the gas, causing it to heat up.

they should be similar or the same

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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