What is Quasi-static: Definition and 24 Discussions

In thermodynamics, a quasi-static process (also known as a quasi-equilibrium process. From the Latin quasi, meaning ‘as if’), is a thermodynamic process that happens slowly enough for the system to remain in internal thermodynamic equilibrium. An example of this is quasi-static expansion, where the volume of a system changes so slowly that the pressure remains uniform throughout the system at each instant of time during the process. Such an idealized process is a succession of equilibrium states, characterized by infinite slowness.Only in a quasi-static process can we exactly define intensive quantities (such as pressure, temperature, specific volume, specific entropy) of the system at every instant during the whole process; otherwise, since no internal equilibrium is established, different parts of the system would have different values of these quantities.
The theoretical term 'reversible process' is sometimes used. It refers to a theoretically convenient idealization that can in practice be realized only approximately, for exactly reversible processes are ruled out by the second law of thermodynamics. For example, slow compression of a system by a piston subject to friction is irreversible; although the system is always in internal thermal equilibrium, the friction ensures the generation of dissipative entropy, which goes against the definition of reversible. Any engineer would remember to include friction when calculating the dissipative entropy generation. An example of a slow process that is not even idealizable as reversible is slow heat transfer between two bodies on two finitely different temperatures, where the heat transfer rate is controlled by a poorly conductive partition between the two bodies— in this case, no matter how slowly the process takes place, the states of the composite system consisting of the two bodies is far from equilibrium, since thermal equilibrium for this composite system requires that the two bodies be at the same temperature.

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  1. H

    I Exploring Work Done in Quasi-Static & Non Quasi-Static Expansion

    I'm wondering what's the difference between work done on quasi-static and non quasi-static expansion. In a quasi-static process, the gas inside the system must do a work to "extend". However, in a non quasi-static process, where the gas inside the system doesn't move fast enough to "push" the...
  2. ergospherical

    I Quasi-Static Change of Event Horizon Area

    Let ##\mathscr{H}## be a constant-##v## cross-section of the event horizon (area ##A##). The expansion is the fractional rate of change of the surface element, ##\theta = \frac{1}{\delta S} \frac{d(\delta S)}{dv}##. The problem asks to prove the formula ##\frac{dA}{dv} = \frac{8\pi}{\kappa}...
  3. Rahulx084

    Irreversible quasi-static processes?

    I read an example where if I go from initial to final state extremely fast (gas inside a piston cylinder assembly) , the gas inside it will be very unhappy, its not going to stay in equilibrium, parts of the system are going to be at different pressure and parts of it at something other...
  4. PetesMcSkeets

    Quasi-Static Magnetization of a Magnetic Substance

    Homework Statement Homework Equations energy=-u_0(B)[/B] The Attempt at a Solution According to the back of the book, a. energy level separation increaess b. mean energy decreases which makes sense since B is increasing then E must be increasing negatively. c. negative (not too sure why...
  5. M

    I Quasi-Static Processes: Does dQ = 0?

    We know that dQ = dE + dW for any system. However, in quasi-static processes, dW = -dE. Does this mean that dQ = 0 and no heat (Q) is absorbed or given off? If so, why is that?
  6. mayank pathak

    Is the Work Done in Charging an Inductor Different in Non-Quasistatic Scenarios?

    As we know, work done by an outside agency in creating some current ''I" in an inductor 'L' is 1/2LI2. Now this result is derived by quasistatic approximation if I am not wrong. Now, I am assuming that in non quasistatic (real) scenarios, the work done by outside agency would be different(If you...
  7. T

    Is the PV diagram in this quasi-static cycle correct?

    Homework Statement Hi guys can someone tell me if I am wrong, or missing reading this question. For part a I need to draw a PV diagram now it states that is is being expand isothermally yet when I look at the pressure it dose not change, which is confusing me beacuse it dose in a isothermal...
  8. G

    I Is a quasi-static but irreversible process possible?

    Hello. I read the textbook of the thermodynamic and it said the definition of the reversible process as "thermodynamic process which is slow enough so the system state is always infinitesimally close to the thermodynamic equilibrium (quasi-static) during the process. Such a process can always...
  9. B

    Prove irreversibility in this quasi-static process.

    Consider a piston-cylinder arrangement with an ideal gas inside the cylinder. The region outside this arrangement or thermodynamic system is absolute vacuum. The piston has some mass and initially everything is in equilibrium. The inner surface of the cylinder is rough hence friction force comes...
  10. M

    Quasi-static and reversible processes in thermodynamics

    Too much confusion in my head about these concepts... Is every reversible process quasi static? If not, what are some examples? If process is irreversible then it doesn't need to be non quasi-static, I understand that. (eg. free expansion of the gas) Can irreversible process be quasi static...
  11. B

    Tensile Test Specimen Point of Failure

    I am a part C Mechanical Engineering student and have been undertaking a project investigating the strain sensitivity of a particular glass filled composite. From my quasi-static results, the stress-strain curves seem to be reasonable and match that of the mechanical material properties...
  12. Useful nucleus

    Is every reversible process coincident with a quasi-static process?

    For a closed system: If we define a quasi-static locus (process) as an ordered and dense succession of equilibrium states in the thermodynamic configuration space. Then we define a reversible process as one in which no entropy is generated. Then it is clear that there are some quasi-static loci...
  13. S

    Quasi-static Approximation for coaxial wires

    Homework Statement A coaxial cable with inner radius a and outer radius b lies on the z-axis (such that the cable's axis merges with the z-axis). its length (along z-axis) is L. at z=-L there are voltage sources that are distributed uniformly connecting the inner wire to the outer one. at...
  14. M

    Quasi-static, adiabatic problem

    Two moles of a monatomic ideal gas are at a temperature of 0°C and a (dQ = 0) and quasi-static volume of 45 liters. The gas is expanded adiabatically until its temperature falls to - 50°C. What are its initial and final pressures and its final volume? I've been beating my head against a wall...
  15. P

    Reversibility, adiabatic-ness, quasi-static

    I am taking a course in statistical physics where we keep using the terms in the title. I think I understand them as stand alone terms, but I do not understand any relationships. For example, does quasi-static and reversible imply adiabatic? Does one of them imply some of the others? What...
  16. J

    Proof of work done by an ideal gas in a quasi-static adiabatic expansion

    Homework Statement Prove that the work done by an ideal gas with constant heat capacities during a quasi-static adiabatic expansion is equal to W= (PfVf)/(Y-1)[1 - (Pi/Pf)^((Y-1)/Y)] where Y = gamma, which is heat capacity at constant pressure over heat capacity at constant volume...
  17. J

    First law of thermodynamics and quasi-static processes

    why is du = δq - δw valid for all processes while du = δq - p dv valid only for quasi-static processes ?
  18. S

    Understanding Quasi-Static Process: Work and Temperature Changes

    Consider a quasi-static expansion of a gas. If you change the external force by dFext, then the system will do work on the surroundings until the internal pressure equals the external pressure, right? Now, how does the temperature of the system and the surroundings chnage in the process...
  19. K

    Is There Any Reversible Quasi-Static Process?

    Just out of curiosity, is there any quasi-static process that is completely reversible? I think the answer is an obvious no because any quasi-static process experiences a net energy loss but I'd like to know if there are any, possibly something abstract rather then mechanical.
  20. J

    Trying to understand quasi-static processes

    In my thermo course, we made a distinction between quasi-static and reversible transitions (which apparently some don't make). Reversible means both system and surroundings need to be able to return to their initial state. Quasi-static only means that the system transitions to a new state by...
  21. N

    Schroeder on thermodynamical reversibility, entropy and quasi-static equilibrium

    Hello, In "An Introduction to Thermal Physics" Schroeder goes to deduce that for any quasi-static process: W = -PdV (p.21), and then on page 112, with the help of dE = Q + W (= first law of Td.) and dE = TdS - PdV (= the Td. identity), he deduces that Q = TdS for ALL quasi-static processes...
  22. J

    Finding the work done by a gas under quasi-static, isothermal expansion

    1. So, an ideal gas is initially at 293K and 200kPa, and has a volume of .004m3 It undergoes a quasi-static, isotheral expansion until its pressure is reduced to 100kPa What is the Work done by the gas 2.I know that for isothermal conditions W=nRTln(Pf/Pi) 3. my first attempt was...
  23. K

    Reversible, equilibrium and quasi-static

    Hi there, I found it is too much concepts in my head after reading more and more about thermodynamics. In the very beginning of the text, it emphize that in many cases (at lease in beginning level), we only deal with the equilibrium state in thermodynamic system. To make sure every stage of...
  24. O

    Understanding Quasi-Static Processes and Reversibility in Thermodynamics

    Hi I have difficuly understqanding this: If a gas undergoes changes in its thermodynamic states, then the process is irrversible unless it is conducted at such an infinitely slow pace that at every instant of the process, the system is in thermodynamic equilibrium.Ok, so the text gives the...