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Carnot Cycle - Doubt

  1. Jul 2, 2017 #1
    In Carnot cycle during the process - "Reversible isothermal heat addition"

    Q (supplied) = ∫pdV

    This means that the supplied heat is utilized for pdV work.

    My doubt is if the Q supplied is converted to work in this process then how Carnot cycle can reject heat during the upcoming isothermal heat rejection process ?

    Please help to clear the miss concepts.

    Thank You
  2. jcsd
  3. Jul 2, 2017 #2


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    In the compression process, the system is in thermal contact with a cold reservoir just as it is in thermal contact with a hot reservoir during the expansion. You do work on the system, which is kept at a fixed temperature set by the cold reservoir.
  4. Jul 2, 2017 #3
    Thanks for the reply..But still confused..

    Carnot Cycle have 4 process
    Two reversible isothermal and two reversible adiabatic process
    adiabatic process starts after isotherm. Now if heat added in isotherm is transferred to pdV work and there is no change in internal energy then how work is done in the next adiabatic process ?
  5. Jul 2, 2017 #4
    Work(significant work) is done at two stages i.e. at the higher temperature isotherm (isothermal expansion) and at the lower temperature (isothermal compression). In between these processes we have adiabatic expansion of the gas where the gas cools to the lower temperature. The key here is that work is done BY the system when it expands isothermally at the higher temperature whereas, work is done ON the system when it is compressed at the lower temperature.
  6. Jul 3, 2017 #5
    Thanks for the reply..Who supplies the energy to do work on the system ? Is it supplied externally ? I mean the only energy source available for the system is the heat supplied during isotherm process.
  7. Jul 3, 2017 #6


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    This is not true, the work the system does must be on an external system just as the work done on the system must be supplied from an external system. What it is depends on your actual system.
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