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Questions tagged [thermodynamics]

Covers the study of (primarily homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using the tag: [statistical-mechanics].

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Are calories an appropriate measurement of energy for biological systems? [closed]

According to this source, a calorie is an inappropriate unit to quantify the energy contained in food because a "calorie is heat energy" and "humans don't absorb photons" but ...
Jon Behnken's user avatar
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Friedmann fluid equation in the non-relativistic case

The Friedmann fluid equation I am referring to is: $$ a\frac{d\rho}{da} = -3(\rho+P) .$$ In the non-relativistic (low temperature) case for an ideal gas universe (representing matter), I know that the ...
Andreas Christophilopoulos's user avatar
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Do neutrons have a higher entropy than protons?

Since free neutrons want to undergo beta decay into a proton while protons are relatively stable does that mean that neutrons have higher entropy than protons?
Oreoluwa Matilukuro's user avatar
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$q$-potential in grand canonical ensemble

I was recently going through R.K. Pathria's Grand canonical ensemble chapter and found the following section confusing under physical significance of statistical quantities. The author mentions; To ...
Apoorv Mishra's user avatar
1 vote
1 answer
95 views

What is the relationship between Clausius Inequality and 2nd Law?

I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles. I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
Skaeler's user avatar
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Origin of ideal gas fluid dynamics equations including the adiabatic index

I was given a system of equations that supposedly describes the fluid dynamics of an ideal gas. The equations are: $$ \begin{align} &\frac{\rho}{m} = \frac{p}{T} &\text{(ideal gas law)} \\\\ &...
Nico G.'s user avatar
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1 answer
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$P-v$ diagrams and isotherms with two inflection points

I have a very simple naive question concerning the interpretation of the following situation. Let there be an isotherm in a $P-v$ diagram which has two inflection points (different specific volumes, ...
Stuckelberator's user avatar
1 vote
2 answers
115 views

Why clothes keep us warm?

I want to understand why clothes keep us warm. I understand that they reflect back thermal radiation and also trap air thus significantly reducing cooling due to thermal convection. My question is, do ...
Plemath's user avatar
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Generalized entropy of black holes

In the review paper 2006.06872 by Maldacena, in eq.(2.4) they wrote that the total entropy of a black hole and its environment also has a contribution from the quantum fields outside the horizon which ...
mathemania's user avatar
4 votes
2 answers
101 views

What does life (photosynthesis) change for entropy? A thought experiment

The relationship between entropy and life is complex and has even "philosophical" ramifications. The following thought experiment seems simple enough to bring a clear answer, but I'm unsure ...
YAG's user avatar
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1 answer
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Clarifying the definition of pressure in statistical physics

I am studying David Tong's lecture note on statistical physics, and I have a question regarding the precise definition of pressure. I checked other postings in this community, but was unable to get ...
Sangchul Lee's user avatar
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1 answer
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Work done by gas and it's limits

So I have read about how when pressurised gas does work, it decreases in temperature (turbo expanders, Claude liquefaction etc.). How exactly does that work? The more work a gas does, the more it ...
Aaa's user avatar
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1 answer
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Relationship between density and temperature - How to know the precise temperature at which a bell inside a Galileo Thermometer will sink?

A Galileo Thermometer consists of bells placed inside a tube that's filled with liquid. As the temperature increases, the fluid density decreases. This leads to a decrease in the buoyant force, and ...
jazzblaster's user avatar
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1 answer
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What exactly is the translational partition function for a single particle system?

I am recently reading Daniel V. Schroeder's book on thermal physics, and I am having trouble with the translational partition function for a single particle. Particularly since he defines the ...
Vivek Kalita's user avatar
6 votes
2 answers
372 views

Earthen Pots made in summers vs winters

I've heard my parents saying that the water in earthen pots that are made in winters cools more than a pots that are made in summers. Is this true according to physics? I understand the process of ...
Gajjze's user avatar
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9 votes
3 answers
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Rotating a Pot of Boiling Water on a Stove

I have just boiled a half dozen eggs and wanted to ask about a phenomenon I have witnessed for years but have bottled up inside for so long. Why, when the water is near boiling and nice and hot, does ...
Alexandre DeFreitas's user avatar
1 vote
1 answer
45 views

What's the difference between coherence evolution and thermalization?

Suppose we have a system that is coupled to a bath with non zero temperature. Through some mechanism one is able to prepare the system in its ground state (i.e. zero temperature state) and let it ...
ljc's user avatar
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1 answer
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Why would a depletion "layer" form in a PN junction?

I understand that electrons diffuse from the N to the P region due to the concentration difference. This diffusion of electrons creates an electric field opposing further diffusion. What I don't ...
Abdullah Al Jaber's user avatar
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1 answer
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Is this tuning fork forever?

Imagine a tuning fork struck in the Boötes Void. At first, the phonons convert to friction \ heat and radiate off into blackbody photons. This happens for a long time, and then at some point, we reach ...
Travis R's user avatar
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11 votes
2 answers
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When we pour cold water on a closed jar containing only hot water and water vapour, why does the hot water in jar start boiling?

Here is a video link for the experiment. In the experiment, cold water is being poured on a closed jar containing hot water and water vapour and we observe that the hot water inside jar starts boiling....
Navneet's user avatar
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2 answers
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Maximum work (free energy) from the fundamental thermodynamic relation

I want to derive the maximum (free) work function $M$: $$M=U_1-U_2 +p_s(V_1-V_2) -T_{s}(S_1-S_2)$$ where the variables with the index $1$ represent the initial state of the system and the variables ...
User198's user avatar
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2 votes
2 answers
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What is the difference between a reversible process and an equilibrium? [closed]

I am confused about the differences between a reversible process and an equilibrium when considering their energy aspect. Here is what I know so far. (1) Equilibrium and Reversibility Equilibrium ...
Skaeler's user avatar
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0 answers
21 views

Is the force due to effusion simply the product of the pressure and area?

Consider the simple setup of an ideal gas in a container with pressure $P$ effusing out of a small hole of area $A$ into vacuum. In this case, the container experiences a force which can be explained ...
Ram Narayanan's user avatar
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How is free energy in thermodynamics related to free energy in information theory/neuroscience?

Background In thermodynamics, free energy refers to either Helmoltz ($U - TS$) or Gibbs ($H - TS$) free energy, the quantity that is minimised at equilibrium in a closed system maintained at constant [...
Jake Levi's user avatar
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2 answers
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What happens if you factor in the energy required to switch between the reservoirs and insulating stand of the Carnot engine?

I'm reading about the Carnot cycle (as a non-physicist!) and much of the focus is on the idealisation around the infinite time needed due to the requirement of only infinitesimal differences in ...
Kathryn Nave's user avatar
1 vote
2 answers
57 views

Why does a heated body emit a continuous spectrum of waves, while a burning body emits one color?

Why does a heated body emit a continuous spectrum of waves (as I understand it, that's why they burn red/white/blue), and a burning body is one color? as I understood it, for example, the green flame ...
buujek's user avatar
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1 vote
0 answers
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Solving a system of equations involving Gaussian Integrals numerically [closed]

I wish to solve the following system of equations numerically in any software, I tried in Mathematica using the expectation functions, but I have a difficulty in understanding how to go about solving ...
rhombicosicodecahedron's user avatar
13 votes
5 answers
7k views

How do photons have temperature?

On the internet, I found "Temperature is a measure of the average kinetic energy of the particles in an object." (source) So, this temperature should be a result of friction. Light is also ...
Shristeerupa's user avatar
3 votes
4 answers
395 views

Average energy in Boltzmann statistics

Currently, I am learning the Planck's radiation law and I got stuck in the average energy calculation as done in this video as below: $$\bar{E}=\frac{\int_0^\infty Ee^{-E/kT}\mathrm{d}E}{\int_0^\infty ...
CP of Physics 's user avatar
1 vote
1 answer
21 views

Thermal Smearing in Josephson Junction

I'm basically trying to simulate a josephson junction at a particular temperature. As per some of the plots I could find, the rise in temperature leads to a rounding of the I - V curve. I was ...
L lawliet's user avatar
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Is there a practical distinction between functions of state and functionals in thermodynamics?

In thermodynamics, and more precisely when talking about continuous systems, some sources [1, 2] introduce functionals of state: $$F[s(x), \dots]:=\int_VdV(x)f(s(x),\dots,x)$$ In order to derive ...
GvPStack's user avatar
1 vote
0 answers
91 views

How fast does a gas expand in vacuum?

A gas is initially confined to a small portion of an empty container. At time $t=0$ gas is allowed to expand to homogeneously occupy the container after some time $t$. What is the time $t$? This ...
YoussefMabrouk's user avatar
1 vote
3 answers
85 views

What is the actual meaning of $dx$ in $W=-F.dx $, in work in thermodynamics?

what I want to ask is that the $dx$ in that formula is the displacement of piston or the displacement of the center of mass of the gas. also is there any situation where this clarity is useful.
Ujjwal's user avatar
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2 answers
54 views

Heat exchange speed of two liquids separately vs their mixture

I'm quite oblivious about basic high school physics, so pardon my misuse of terms and inability to google the answer. I want to solve a puzzle that I face in my daily routine. Suppose I want to make a ...
Alexey S. Larionov's user avatar
1 vote
1 answer
47 views

Radiation power emmited by a material with two different temperatures [closed]

Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
aaa6's user avatar
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0 votes
0 answers
45 views

Why vacuum does not have absolute zero temperature? [duplicate]

Extrapolation of P vs. T graph gives absolute zero or 0K. Does that mean that if we achieve perfect vacuum, we can have absolute zero? If not why? Let us assume a perfect vacuumn space where there are ...
Vinay5101's user avatar
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0 answers
22 views

What is the value of the ideal gas constant in J/(mol*°C)? [duplicate]

I've seen in some sites that it is the same as in J/(mol*K), is that true? $8.314 \frac{J}{mol×K}=8.314 \frac{J}{mol×°C}$
Malcolm's user avatar
1 vote
1 answer
34 views

Determining Critical Temperature of Oxygen from Six $p$-$V$ Diagrams [closed]

So the question is to plot six $p$-$V$ curves for oxygen at various temperatures ranging from 80 K to 170 K, using the Van der Waals equation. Having done that, the next part asks to estimate the ...
Nero's user avatar
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0 votes
4 answers
73 views

Would a Particle being attracted to a particle that is repulsed by it break the laws of thermodynamics? [closed]

Working on an idea for a magic system in my writing but I want to know what would actually happen if this was a thing. Let's say we have particle A and particle B. Particle A is attracted to particle ...
Dromeoraptor pennato's user avatar
0 votes
0 answers
48 views

Fermi-Dirac integrals of different orders

Which physical quantities are related to the Fermi-Dirac integrals of different orders? If fermi-dirac integral, write like this: $$F_\xi(\eta_c) = \frac{1}{\Gamma(\xi+1)} \int_{0}^{\infty} \frac{x^{\...
xing zheng's user avatar
1 vote
2 answers
52 views

Does diffusion current "consume" thermal energy?

My (possibly erroneous) understanding of solid state physic has led me to the belief that diffusion current may "consume" thermal energy. Here is my (possibly erroneous) understanding. When ...
Math Keeps Me Busy's user avatar
0 votes
2 answers
133 views

Does information always gravitate?

I'm trying to wrap my head around Bekenstein's loose argument that a bit of information added to the black hole corresponds to an added Planck surface area to its horizon. In it, he argues that one ...
Lourenco Entrudo's user avatar
1 vote
2 answers
67 views

How do differently colored objects reach the same temperature if they are completely isolated together?

Imagine a perfectly reflective container, filled with vacuum and two bodies with different colors, i.e. they have different emissive and absorptive properties. The bodies don't touch each other or the ...
Sándor's user avatar
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0 votes
1 answer
48 views

Strength of a phase-transition

I'm currently studying neutron stars for a summer research project, and it uses the terms 'weak' and 'strong' transition for nuclear matter in its literature. Can someone explain (in terms that a ...
physicsnoob's user avatar
1 vote
3 answers
94 views

Why can you integrate with different bounds in thermal expansion differential equations?

I am just an independent student and was learning thermal expansion with differential equations and i saw someone on the internet solving the differential equation for the law like below: $$\frac{1}{L}...
Alexandre Carneiro da Silva's user avatar
0 votes
0 answers
18 views

Penning trap laser cooling

In the penning trap, I know that there is a quadrupole electric field and a magnetic field. This results in three eigen motions with three eigen frequencies: magnetron freq, modified cyclotron freq, ...
lalala's user avatar
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7 votes
3 answers
2k views

Will a piece of coal burn at the atomic level at room temperature?

If there is a piece of coal in the open air at room temperature, some of the molecules in the surrounding air will have sufficient velocity to oxidize the carbon in the coal. Will the surface of the ...
Belu boy's user avatar
2 votes
1 answer
51 views

What if acceleration changes in the Unruh effect?

Based on the Unruh effect, when a observer accelerates then he will see a thermal bath. mathematically the vacuum state for a non-inertial observer is $$|0\rangle=\text{cos}^{-1}(r)\sum_{n=0}^{\infty}\...
reza's user avatar
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0 answers
15 views

Thermodynamics of flow boiling in expanding cross section

Say you have some water flowing through a heat exchanger where sufficient heat is added to heat the water until it begins boiling. In a usual boiler the temperature and pressure is practically ...
Tyler Lee's user avatar
2 votes
1 answer
95 views

Deriving partition function for various ensembles

I'm wondering the derivation of following partition functions corresponding to various ensembles: $$ \begin{aligned} \Xi(V, T, \mu) & =\sum_N Q(N, V, T) e^{\beta \mu N} \\ \Delta(p, T, N) & =\...
Arete's user avatar
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