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Consider the following processes: I. Energy flows as heat...

  1. Nov 4, 2016 #1
    1. The problem statement, all variables and given/known data

    Consider the following processes: I. Energy flows as heat from a hot object to a colder object II. Work is done on a system and an equivalent amount of energy is rejected as heat by the system III. Energy is absorbed as heat by a system and an equivalent amount of work is done by the system .Which are never found to occur?
    A. Only I
    B. Only II
    C. Only III
    D. Only II and III
    E. I, II, and III
    ans: C
    2. Relevant equations


    3. The attempt at a solution
    Why its C??
     
  2. jcsd
  3. Nov 4, 2016 #2
    It is wrong. That's why.
     
  4. Nov 4, 2016 #3
    I mean why it is wrong?
     
  5. Nov 4, 2016 #4
    This is the same thing as an isothermal expansion, which you can always do. What they erroneously neglected to consider is this can never be done for a system operating in a cycle using a single (isothermal) reservoir.
     
  6. Nov 4, 2016 #5

    vela

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    It looks like whoever wrote the question is using the word system to mean heat engine. Try calculating the efficiency of the described engine.
     
  7. Nov 4, 2016 #6
    Another requirement is that there be only one reservoir to supply heat (and no reservoir to remove heat). This is basically the Kelvin statement of the 2nd law.
     
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