The potential for a thermodynamic process to be reversed in time. Alternatively, a quantification of how far an irreversible process is from being reversible, which relies on a comparison to a corresponding theoretical reversible process.

learn more… | top users | synonyms (1)

1
vote
5answers
150 views

Entropy Change in an irreversible process

I have just started learning thermodynamics and the concept of entropy confuses me. Suppose I have a gas in a cylindrical container fitted with a piston. I take it through an adiabatic irreversible ...
5
votes
4answers
251 views

Definition of Entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
3
votes
3answers
80 views

Entropy of loops in the PV plane

The change in entropy of the Carnot and reversible cycles is said to be 0. Several other loops are supposed to have a non-negative change in entropy. This presents 2 problems which I cannot ...
4
votes
2answers
107 views

Physics without time

The structure of physical law as we generally recognize it today is firmly held together by the existence of time. Although physical laws can both predict and retrodict (reversible time does not break ...
1
vote
2answers
39 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
4
votes
1answer
297 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
0
votes
1answer
46 views

Apparent Contradiction in Helmholtz Free Energy

I am looking at some mathematics of HelmHoltz free energy. Naturally, wikipedia is one of the (hopefully) more reliable sources of information. In its derivation section, the last equation states that ...
6
votes
0answers
120 views

How can dynamics be reversible if inflation-style baby universe spawning is allowed?

I just finished readying Sean Carroll's book, "From Eternity to Here", and have a question about reversibility and inflation: Assume inflation allows random quantum fluctuations to produce high ...
1
vote
0answers
24 views

Internal reversibility

The concept of reversibility always gives me a hard time.In a reversible process the change of entropy is zero. On the other hand for irreversible process it is not.But there comes another topic which ...
1
vote
0answers
11 views

What happens to magnetic $B$-field in a superconductor in the Bean model?

In the Bean model, as we start applying a magnetic field $H$ in the plane of a slab, the $B$-field inside the superconductor decreases linearly from each side, and at a sufficiently high field $H^{*}$ ...
1
vote
0answers
28 views

Necessity of infinitesimal steps for reversible processes

Is there a mathematical proof for why a reversible process is one that has many infinitesimal equilibrium steps, rather than fewer large steps? Maybe something along the lines of this?: ...
1
vote
0answers
155 views

Irreversible heat engines strictly less efficient than reversible ones

I undertand how Canot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it isless clear why they need to be less efficient, as I have seen stated in ...
1
vote
0answers
64 views

Restrained expansion of a piston/cylinder

Suppose an ideal gas in a piston cylinder has some initial pressure $p_1$, volume $V_1$, and temperature $T_1$. A pin, which holds the piston in place, is suddenly removed, and the gas quickly ...
0
votes
0answers
22 views

CP violation and arrow of time

Does CP (and thus T) violation imply a definite arrow of time? How does it relate to the thermodynamic one? Does the microscopic irreversibility reflect itself to macroscopic level? If not why?
0
votes
0answers
40 views

Are reversible and irreversible processes frame dependent?

since it is all about time. If I have a look at an irreversible process from a frame where time runs really slow. is there a possibility of considering that process reversible from that frame?