Tagged Questions
1
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1answer
47 views
Entropy of Black Hole
What is the relation between the entropy of rotating and non rotating Black hole?
Which one's entropy is greater?
1
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1answer
44 views
Sackur-Tetrode equation - clarification required - problem with units
I'm a 2nd year physics undergraduate and recently I've volunteered to give a short presentation on the Sackur-Tetrode equation derivation and its use at removing the Gibbs paradox. I've looked on the ...
4
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3answers
180 views
Definition of entropy
In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is ...
1
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1answer
101 views
Mathematical proof of non-negative change of entropy $\Delta S\geq0$
I understand that we can prove that for any process that occurs in an isolated and closed system it must hold that
$$\Delta S\geq0$$
via Clausius' theorem. My question is, how can I prove this in a ...
1
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0answers
32 views
Calculating the change in entropy in a melting process
I have a homework question that I'm completely stumped on and need help solving it.
I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
1
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3answers
132 views
Integrating factor $1/T$ in 2nd Law of Thermodynamics
How would you prove that $1/T$ is the most suitable integrating factor to transform $\delta Q$ to an exact differential in the second law of thermodynamics:
$$dS = \frac{\delta Q}{T}$$
Where $dS$ is ...
5
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1answer
69 views
What happens at the interface between two universes with opposite thermodynamic arrows of time?
I was trying to think but cannot figure it out. For instance, if the interaction is small, for instance limited to a windows, the observers in each universe will see that the other goes in reverse. ...
0
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1answer
76 views
Uncertainty and Thermodynamics
Dilemma
The uncertainty principle of energy and the 2nd law of thermodynamics don't add up : the uncertainty principle of energy says that
$\Delta \tau \cdot \Delta E \ge \frac{h}{4\pi} = ...
4
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3answers
320 views
Is there a mechanism for time symmetry breaking?
Excluding Thermodynamic's arrow of time, all mathematical descriptions of time are symmetric. We know the arrow of time is real and we know the equations describing physics are real so is there any ...
1
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0answers
100 views
Difficulties with understanding total entropy change and unavailabillty
Of course, I know the fact that the entropy of an isolated system never decreases. Neverthless what makes me confused about the entropy(or change of entropy) of an isolated system is the explanation ...
0
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1answer
59 views
Why is the equation for Entropy of an ideal gas that undergoes reversible change in T at constant Pressure like this?
Why is the equation for change in Entropy for a reversible change in $T$ at constant $P$ described as
$$\Delta S = n C_p \ln\frac{T_f}{T_i}$$
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1answer
75 views
Is there a relation between supersymmetry and entropy?
Considering that entropy denotes the level of order/disorder in a system, would it be possible for entropy and supersymmetry to exist at the same time? Or, are they entirely unrelated?
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3answers
236 views
Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?
Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
1
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0answers
43 views
How to solve state parameters using these givens for an ideal gas?
In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
2
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1answer
63 views
How can dQ/T be interpreted as a system's level of disorder?
Long before statistical mechanics, entropy was introduced as:
$dS = \frac{dQ}{T}$
At the time when entropy was introduced in this manner, was it known that entropy represents how "disordered" a ...
0
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1answer
120 views
relation between first law of thermodynamics and statistical mechanics definition of entropy
From the definition of entropy as $S= - Tr (\rho\, ln \rho)$ one obtains that
$S = \frac{\langle E \rangle}{T} + \log Z.$
The first law of thermodynamics has
$dS = {dE \over T}$.
Why is there no ...
3
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1answer
160 views
Why is (von Neumann) entropy maximized for an ensemble in thermal equilibrium?
Consider a quantum system in thermal equilibrium with a heat bath. In determining the density operator of the system, the usual procedure is to maximize the von Neumann entropy subject to the ...
2
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2answers
162 views
Entropy exchange of a free fall
I have a problem in which the tell me that you drop a bag of 50 kg of sand from 10 meters high, and you have to caltulate the entropy difference of the sand, asuming that the speific heat of the sand ...
2
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1answer
122 views
The definition of entropy
As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
3
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1answer
59 views
Amount of energy to separate Gases - relationship to concentration
I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the wikipedia page for entropy of mixing, I find the ...
1
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1answer
179 views
Isentropic Processes
I'm having trouble understanding why reversible adiabatic processes are isentropic.
I understand that in a reversible adiabatic process there is no heat exchange and so $dQ = TdS = 0$. However, if ...
2
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2answers
447 views
Entropy Change During Reversible Processes
I'm confused about the Second Law of Thermodynamics. The Second Law of Thermodynamics prohibits a decrease in the entropy of a closed system and states that the entropy is unchanged during a ...
0
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0answers
196 views
Entalpy and entropy role in freezing-point depression phenomena
There's this "atomic" explanation of the freezing-point phenomena on Wikipedia that leaves me really intrigued.
Consider the problem in which the solvent freezes to a very nearly pure
crystal, ...
0
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0answers
43 views
Entropy of binding two rigid bodies together in a closed system (e.g. forming a diatomic out of two monatomic gas particles)
When I bind two molecular complexes together, or in the simplest case, form a diatomic out of two atoms in a monatomic gas, the entropy of my (closed) system will decrease. We can perhaps understand ...
2
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1answer
113 views
free energy and entropy of 2D soap froth
This is a (exploratory) computational project. The soap froth was created by injecting bubbles into a chamber formed by two rectangular plates which are 0.16cm. From the moment the soap froth was ...
3
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2answers
448 views
Can entropy be equal to zero?
I've searched for it but I only found contradicting answers from "scientists":
Mr. David Balson, Ph.D. states: "entropy in a system can never be equal to zero".
Mr. Sam Bowen does not refutes the ...
0
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0answers
93 views
Is it possible to add heat to a monoatomic ideal gas without increasing entropy? [closed]
The Sackur-Tetrode equation expresses the entropy of a monoatomic ideal gas:
[Equation from HyperPhysics]
11
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5answers
680 views
Why does the nature always prefer low energy and maximum entropy?
Why does the nature always prefer low energy and maximum entropy?
I've just learned electrostatics and I still have no idea why like charges repel each other.
...
0
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1answer
217 views
How much energy Maxwell's demon will earn?
Suppose we have one mole of one-atom ideal gas at temperature $T$.
Suppose Maxwell's daemon has separated molecules into two sections, one with speed below mean and another with speed above mean.
...
2
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1answer
282 views
Physics-based derivation of the formula for entropy [duplicate]
Possible Duplicate:
Proof of $S=-\sum p\ln p$?
I am looking for a derivation of the formula
$$S~=~-\Sigma_ip_i \log (p_i).$$
for entropy, from first principles. I only wish to assume the ...
1
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0answers
116 views
An explanation for the Landauer's principle
Has anyone understood the Landauer's principle? What is the current status?
In specific, is there a theoretical derivation of the Landauer's Principle?(not the heuristic one based on Salizard's ...
2
votes
1answer
116 views
Minimal Maxwell's Demon
I would like to understand where the waste heat is generated in the Maxwell's demon problem. To this end I've come up with the simplest scenario I can think of. If my scenario is workable I am hoping ...
2
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3answers
421 views
Does high entropy means low symmetry?
According to Bogolubov postulate (various texts name it differently) in Non-equilibrium thermodynamics, the number of needed parameters to describe our system is decreasing with time, and finally at ...
2
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1answer
296 views
Why does the law of increasing entropy, a law arising from statistics of many particles, underpin modern physics?
As far as I interpret it, the law of ever increasing entropy states that "a system will always move towards the most disordered state, never in the other direction".
Now, I understand why it would ...
3
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4answers
241 views
Does entropy decrease through measurement?
For an electron in its rest frame, we have an entropy
$$
S = \log 2,
$$
which comes from the 2 possible spin directions along z-axis.
If the measurement $S_z$ changes its state to $\left| + ...
5
votes
2answers
959 views
Why do reversible processes not increase the entropy of the universe infinitesimally?
The book Commonly Asked Questions in Thermodynamics states:
When we refer to the passage of the system through a sequence of internal equilibrium states without the establishment of equilibrium ...
2
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1answer
85 views
Zero entropy change
If you put a object in contact with a heat reservoir that is infinitesimally higher in temperature than the object and allow equilibrium to be reached the entropy change is zero right?
2
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2answers
553 views
Was the Universe's entropy equal to zero at the Big Bang? Is zero-entropy state unique?
It is postulated by many cosmologists that at the Big Bang time the universe was in an unusual low entropy state.
Does this claim specifically mean that the entropy of the initial universe was zero?
...
0
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0answers
37 views
Relation between maximum entropy thermodynamics and entropy bounds
Here is a question which I've been thinking about, I'm sorry if it's little too vague, maybe you could point me to some source to read, if there's no clear direct answer.
The whole concept of ...
3
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2answers
192 views
Entropy: two explanations for the same quantity?
I studied thermodynamics and I saw the following definition for entropy:
$$
\Delta S = \int_1^2 \frac{\text{d}Q}{T}
$$
that we use to calculate $\Delta S$ for different types of transformations.
In ...
15
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7answers
610 views
How is $\frac{dQ}{T}$ measure of randomness of system?
I am studying entropy and its hard for me to catch up what exactly is entropy.
Many articles and books write that entropy is the measure of randomness or disorder of the system. They say when a gas ...
6
votes
4answers
353 views
Second Law of Thermodynamics and the Arrow of Time: Why isn't time considered fundamental?
I've come across this explanation that the "arrow of time" is a consequence of the second law of thermodynamics, which says that the entropy of an isolated system is always increasing. The argument is ...
1
vote
1answer
86 views
Where is the critical moment where the microcanonical ensemble enters the justification for the equilibium state?
As explained in many books, for the microscopic justification of the second law of thermodynamics (lets formulate it as the total entropy takes maximum among all possible exchanges of two systems), ...
1
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2answers
159 views
Question about entropy and “smart materials” (that remember shape)
We all know that entropy is the measure of chaos in the system, and it's always increasing in the system.
Now comes my question - how does entropy work in smart materials? Here is a youtube video ...
4
votes
1answer
727 views
What is the relationship between Energy, Entropy, and Information?
What is the relationship between Energy, Entropy, and Information?
I read this - What Is Energy? Where did it come from? - and the top answer says that 'energy' is an abstract number that is a ...
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1answer
237 views
Loschmidt's paradox - really a paradox? [duplicate]
Is Loschmidt's paradox a paradox even today?
In other words, is the paradox resolved or not?
3
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1answer
223 views
Wasn't the Hawking Paradox solved by Einstein?
I just watched a BBC Horizon episode where they talked about the Hawking Paradox. They mentioned a controversy about information being lost but I couldn't get my head around this.
Black hole ...
8
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0answers
147 views
How is the logarithmic correction to the entropy of a non extremal black hole derived?
I`ve just read, that for non extremal black holes, there exists a logarithmic (and other) correction(s) to the well known term proportional to the area of the horizon such that
$S = \frac{A}{4G} + K ...
5
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3answers
299 views
Confusion regarding entropy, reference papers request
1.a In paragraph at Wikipedia/Entropy it is stated:
This is because energy supplied at a high temperature (i.e. with low entropy)
tends to be more useful than the same amount of energy
...
3
votes
1answer
236 views
Relation between external magnetic field intensity H, magnetisation M and the entropy?
How are the external magnetic field intensity H, magnetisation M and the entropy related to each other? i.e. if I change the magnetic field intensity by dH what will be the change in entropy dS in ...
