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Thread: entropy

  1. #1 entropy 
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    can anyone elaborate the concept of entropy in this example?<br>if we have hot pan and with the passage of time its heat release and meanwhile its temperature also decrease.so if we see the relation of entropy which is (S=Q/T)<br>in this relation if heat decrease then entropy also decrease and if temperature decrease then entropy increase.so is it not contradictory ?


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    Forum Ph.D. stander-j's Avatar
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    Quote Originally Posted by abdulrehman134 View Post
    can anyone elaborate the concept of entropy in this example?<br>if we have hot pan and with the passage of time its heat release and meanwhile its temperature also decrease.so if we see the relation of entropy which is (S=Q/T)<br>in this relation if heat decrease then entropy also decrease and if temperature decrease then entropy increase.so is it not contradictory ?
    Entropy cannot decrease, entropy is a constant. In the greater scheme of things, looking beyond 'heat death', entropy is just the decline of energy (and therefore temperature) into nothingness.


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    Quote Originally Posted by abdulrehman134 View Post
    can anyone elaborate the concept of entropy in this example?<br>if we have hot pan and with the passage of time its heat release and meanwhile its temperature also decrease.so if we see the relation of entropy which is (S=Q/T)<br>in this relation if heat decrease then entropy also decrease and if temperature decrease then entropy increase.so is it not contradictory ?
    Be careful, this is not a closed, isolated system. If it were, then Q and T do not change independently, the two are connected. In a closed system the total entropy either increases or stays constant.
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    Forum Ph.D. stander-j's Avatar
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by abdulrehman134 View Post
    can anyone elaborate the concept of entropy in this example?<br>if we have hot pan and with the passage of time its heat release and meanwhile its temperature also decrease.so if we see the relation of entropy which is (S=Q/T)<br>in this relation if heat decrease then entropy also decrease and if temperature decrease then entropy increase.so is it not contradictory ?
    Be careful, this is not a closed, isolated system. If it were, then Q and T do not change independently, the two are connected. In a closed system the total entropy either increases or stays constant.
    Because Absolute Zero is the ultimate outcome, doesn't it just remain a constant? I don't understand why it would increase. The ultimate outcome is absolute zero is it not? Why would it increase?
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    Quote Originally Posted by stander-j View Post

    Because Absolute Zero is the ultimate outcome, doesn't it just remain a constant? I don't understand why it would increase. The ultimate outcome is absolute zero is it not? Why would it increase?
    Don't confuse entropy with temperature. Entropy has nothing to do with absolute zero per se.
    According to the second law of thermodynamics the entropy of a closed system will either stay constant or increase. The point is that it will never decrease.
    I didn't say it will increase, the specifics depend on the setup of the system. At the very least - as you correctly say - it will remain the same.
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    Quote Originally Posted by Markus Hanke View Post
    I didn't say it will increase.
    Oh yeah, I know that - I just meant I don't understand why it would increase under certain circumstances. I'm thinking I have a bad habit of only looking at entropy in regards to the possible fate of the universe.

    Then again if I've said it once, I've said it at least one more than no times: Real Sciences (as opposed to Social Sciences) aren't an area where I excel.
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    Quote Originally Posted by stander-j View Post
    Quote Originally Posted by Markus Hanke View Post
    I didn't say it will increase.
    Oh yeah, I know that - I just meant I don't understand why it would increase under certain circumstances. I'm thinking I have a bad habit of only looking at entropy in regards to the possible fate of the universe.

    Then again if I've said it once, I've said it at least one more than no times: Real Sciences (as opposed to Social Sciences) aren't an area where I excel.
    Yup, that's the second law of thermodynamics - the entropy of a closed system always increases or remains unchanged.
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    you are saying dont confuse entropy with temperature but relation(S=Q/T)is confusing me bcz S is inversely proportional to T.then what is the meaning of this relation?
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    can we not decrease the entropy of one system by increasing the entropy of another system?
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    3rd law of thermodynamics says that entropy of a perfect crystal at absolute zero is exactly equal to zero.right?
    can we achieve absolute zero temperature ?if yes then how and if not then what is the meaning of this law?
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    Quote Originally Posted by abdulrehman134 View Post
    you are saying dont confuse entropy with temperature but relation(S=Q/T)is confusing me bcz S is inversely proportional to T.then what is the meaning of this relation?
    What I meant to say by that is that temperature and entropy are not the same thing.
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    Quote Originally Posted by abdulrehman134 View Post
    can we not decrease the entropy of one system by increasing the entropy of another system?
    Yes of course, but then the system is no longer a closed one.
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  14. #13  
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    Quote Originally Posted by abdulrehman134 View Post
    3rd law of thermodynamics says that entropy of a perfect crystal at absolute zero is exactly equal to zero.right?
    can we achieve absolute zero temperature ?if yes then how and if not then what is the meaning of this law?
    Yes, that is correct.
    It is not possible to achieve absolute zero, because of quantum effects in vacuum. For the same reason it would also not be possible to create such a thing as a perfect crystal. The third law is there merely to establish a gauge for how entropy is measured, much like when we say that the boiling point of water at sea level corresponds to 100 degrees Celsius. It is a necessary convention.
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  15. #14  
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    if you dont mind sir then can you please elaborate the concept of quantum effects?
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    Entropy is the process whereby information needed to describe the universe increases over a time period.
    Science cannot solve the ultimate mystery of nature. And that is because, in the last analysis, we ourselves are a part of the mystery that we are trying to solve.
    Max Planck
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  17. #16  
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    Quote Originally Posted by abdulrehman134 View Post
    if you dont mind sir then can you please elaborate the concept of quantum effects?
    Basically a vacuum is never truly empty - it is filled with virtual particles as well as non-zero vacuum energy; thus absolute zero can never truly be achieved, since the presence of energy (particles) implies a non-vanishing temperature.
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