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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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When does equilibrium mean accessible microstates are represented with equal probability in an ensemble of systems?

I'm confused to when a system in equilibrium is to be found in any one of its acessible states with equal probability (accoriding to the postulate of equal a priori probabilities). Reif in his book ...
David's user avatar
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2 answers
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In summer when air temperature higher than 37 degree celsius, is it better to wear more clothes to keep cool? [duplicate]

Usually wearing more clothes will keep us warm, as we did in winter. In summer, we wear less to allow better heat dissipation to keep us cool. However, according to the Second Law of Thermodynamics, ...
Harry's user avatar
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Calculating temperature change out of a room [closed]

Currently I'm trying to find how the outside temperature affects the internal temperature of a room through its walls. I'm trying to use the convection heat transfer equation to find the exterior wall ...
invalidsyntax_'s user avatar
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Definition of heat from stat phys [duplicate]

I don't really understand how to couple the idea of entropy as info with heat. Let's say that you have an isolated system. A cube with a a series of movable partitions parallel to a face of the curve. ...
Lina Jane's user avatar
1 vote
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Energy output calculations for the very big heat exchanger [closed]

It recently emerged the concept of using deep wells as heat exchangers. It can be visualized as a long (2000 m) vertical tube with an inner diameter of 162 mm (the outer pipe diameter is 177.8 mm, ...
Dainius's user avatar
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Trouble understanding the classic approximation of a black body as a hole on a cavity

While studying the Rayleigh-Jeans attempt to explain the spectral energy distribution of black bodies I have trouble understanding the concept of a black body as a small hole on a cavity. We define a ...
Eva S's user avatar
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Why does capillary in gas thermometer have a temperature and pressure gradient?

I have been learning thermodynamics using Heat and Thermodynamics by Zemansky, in which he mentions The gas in the capillary connecting the bulb with the manometer has a temperature gradient, that is,...
Sanjay's user avatar
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2 answers
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Why there is a delay before canned fruits float to the top?

This question may appear silly compared to others asked on this site, yet, I can't get my head around it. After pouring boiling water into a canning jar with berries, berries stay at the bottom of the ...
g00dds's user avatar
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Monopoles and matter conservation [closed]

It seems i may have figured out the totality of the quantum physics challenge based on the form of magnetic and not electromagnetic dynamics. Magnetic monopoles going basically 1 0 1 0 with its spin, ...
Anthony Pulse's user avatar
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1 answer
61 views

Can particles feel hot to the touch? [closed]

The other day, I got a tiny splash of hot cooking oil on my hand. But I could barely feel it because it was so small. That made me wonder: how hot would a small collection of atoms need to be for me ...
Dennis Hackethal's user avatar
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Pressure dependence on temperature [closed]

I was doing a problem on airflow around a wing, and how water will condensate on a point on the back of the wing. After reading the solution, it said that "The relative change of the pressure of ...
Emil Sriram's user avatar
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Will a Modified Maxwellian Demon Experiment Using Charged Particles Be Able to Recycle Heat?

(If necessary this experiment can be conducted in an environment where gravity is negligible to avoid gravitational effects.) Two adjacent containers are filled with a homogenous gas composed of ...
Jacob Miller's user avatar
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How does Superconductiviy change in 3D to 2D or vice versa? [closed]

I can't really understand how these transition works, maybe someone could recommend me reading something about these tranisiontions in superconductors. How does a 3d supercon transition to 2d or vice ...
David Lagasca's user avatar
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Best Cooling method for apartment [closed]

Let's say there are two rooms in a apartment represented by this photo Room 2 has a ac unit attached to the window Room 1 does not but there is an opening between room 1 and room 2 In that opening a ...
user55665484375's user avatar
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Why does the temperature-volume diagram look the way it does?

Suppose we have a piston-cylinder system containing compressed water (water that is not about to vaporize). The pressure of water is equal to the sum of atmospheric pressure and the pressure exerted ...
Kakashi's user avatar
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How is the change in internal energy zero for the following scenario:

in the problem, they are removing partitions one by one. when they remove the first partition they've mentioned in the solution that internal energy will remain constant in the process (and after ...
khan zaid's user avatar
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2 answers
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Could you make a fire torch with electricity? [closed]

Similar to a blowtorch, is there a way to generate a flame without using gas or liquid fuel(like butane, propane, etc)? (source) For example I'm thinking about those portable air heaters, could one ...
Gabe's user avatar
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Why Does Every Member of the Ensemble Perform Work Equal to the Change in Free Energy During a Quasiequilibrium Process?

I'm studying Jarzynski's 1997 paper on the Jarzynski Equality. In the second part of the proof (from equation (9) to equation (10) in the paper), Jarzynski considers the following process: considering ...
Luessiaw's user avatar
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5 answers
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How to turn a sum into an integral?

In, An Introduction to Thermal Physics, page 235, Schroder wants to evaluate the partition function $$Z_{tot}=\sum_0^\infty (2j+1)e^{-j(j+1)\epsilon/kT}$$ in the limit that $kT\gg\epsilon$, thus he ...
GedankenExperimentalist's user avatar
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2 answers
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Regarding the absorption property of a blackbody

Consider a blackbody of surface area $S_b$ and at temperature $T_b$. It is placed inside an evacuated chamber (to neglect all the effects of convection), with walls of chamber at temperature $T_c$ and ...
CP of Physics 's user avatar
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Energy range when deriving heat capacity in Sommerfeld model

In my textbook, they assume a scenario in which the thermal energy of electrons is $k_BT << E_F$ , then only electrons which are near the Fermi level could be excited due to external thermal ...
Thành Nguyễn's user avatar
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What would the temperature of the tropics be if the atmosphere did not try to balance out heat the latitudinal surplus and deficit

The atmosphere acts to even out the heat imbalnce between the surplus at the tropics and the deficit at the poles. Assuming that the composition and density of the atmosphere stay the same, what ...
Geoff Parsons's user avatar
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1 answer
37 views

Argument for relationship between density of states and degrees of freedom and energy

From Reif's Fundamentals of Statistical and Thermal Physics chapter 2.5 Behaviour of the density of states: Can anyone give a clear explanation for why the density of varies rapidly as Energy ($E$) ...
David's user avatar
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1 vote
2 answers
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Which kinds of systems are described by a heat equation?

Every extensive thermodynamic variable has a continuity equation associated to it: $$\frac{\partial \rho}{\partial t}+\vec \nabla \cdot \vec J=0$$ where $\rho$ is the density of said variable and $\...
Lagrangiano's user avatar
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Paul trap for dipolar BEC [closed]

Can i use a Paul trap to help to create Bose-Einstein-Condensate of dipolar molecules? I think a Paul trap is only for ions, for bipolar molecules the dipole moment is affected, right?
F.Rauch's user avatar
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Thermodynamics exercise on transformations

An exercise in my book states the following: n = 0.42 moles of an ideal biatomic gas are stored in an adiabatic cylinder with volume $V = 10^{-2} \text{ m}^3$, with an initial pressure equal to one ...
NICOLA TROMBINI's user avatar
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3 answers
60 views

Should the air specific heat ratio be included in the ideal gas law or not?

As you can see, both equations use the ideal gas low with the universal gas constant in J/kg.k Both equations are used in published articles as follows: "Application of dynamic programming to the ...
Ameen Mohamed Bassam's user avatar
1 vote
2 answers
44 views

Cooling properties of trees and thermal radiation

A question about trees, shading and thermal radiation: Will the shaded area under trees have lower average air temperature than adjacent non-shaded areas? On the one hand, I've read that the real air ...
user131627's user avatar
1 vote
0 answers
41 views

Does the isotropy definition of a perfect fluid imply no heat conduction?

Weinberg defines a perfect fluid (Chapter 2, Section 10) as one where each fluid element appears isotropic in a reference frame moving with that element. From the definition of the stress-energy ...
Khun Chang's user avatar
2 votes
1 answer
49 views

Two interacting blackbodies (one inside another) - when will thermal equilibrium be attained? [closed]

As I understand it, an ideal blackbody absorbs (and subsequently starts emitting) all incoming radiation. In typical setups like determining a planet's temperature given its albedo and distance from a ...
Faiyaz's user avatar
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A 1m diameter sphere contains a Avagadro Number (mass 2.015g) of ideal gas particles of mean velocity 550m/s, what is the pressure in the sphere? [closed]

I get an answer of 1.552 kPa using surprisingly simple mathematics and wonder if my method is valid. I used P(sphere) = M(gas) * v(particles)^2 / r(adius sphere)^3 / 4 / Pi() Can it be that simple.
Bryan Major's user avatar
2 votes
1 answer
71 views

Helmholtz decomposition of flow at non-equilibrium steady state

I'm trying to work through Karl Friston's mathematical derivation of the Free Energy Principle from Langevin Dynamics (see this paper). I'm confused about the part at the end of page 8 where he uses ...
Ariel's user avatar
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2 votes
0 answers
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How can we calculate entropy produced by plastic deformation in this example?

Suppose we have a massless spring of spring constant $k$ attached to a mass $m$ at equilibrium position $x_{0}$ at temperature $T$. The mass may oscillate in one dimension only for simplicity. We ...
Maximal Ideal's user avatar
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1 answer
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Precise relation between temperature change and physical quantities [duplicate]

I've learnt that many physical quantities like length or volume etc depend on the change in temperature and some proportionality constant as: $\Delta{L}=l\alpha\Delta{\theta}$. In our physics class, ...
ekl1pse's user avatar
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3 votes
3 answers
178 views

How does the temperature of the condenser impact an air conditioner's energy usage?

Air conditioners have a condenser after the compressor, in the high pressure side of the system. I've found graphs that show the compressor takes less energy if the condenser is colder. That makes ...
scosman's user avatar
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3 votes
1 answer
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Proportionality of Pressure and Temperature in defining Absolute Temperature scale

I am studying thermodynamics and came across this kind of loop: First, an absolute temperature scale is attempted to be defined as follows Assume that temperature is proportional to the pressure of ...
CP of Physics 's user avatar
7 votes
2 answers
3k views

Do thermodynamic cycles occur only in human-made machines?

Intuitively, it seems like heat engines and refrigerators require a good bit of technology to make a working substance pass through different thermodynamic states and then finally return to the ...
ether's user avatar
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1 answer
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Confusion regarding the equation $dS=\frac{\delta Q_{rev}}{T}$

In Reif's Fundamentals of Statistical and Thermal Physics he outlines a "proof" (sections 3.8 and 3.9) of the equation $dS=\frac{\delta Q}{T}$ for any quasi-static, infinitesimal process (i....
user62783's user avatar
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1 answer
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Why the Sun has a higher temperature than humans?

Why the Sun has a higher temperature than humans if the energy/gramme of matter ratio of humans is greater than that of the Sun?
Aarnihauta's user avatar
6 votes
6 answers
3k views

Why is pressure in the outermost layer of a star lower than at its center?

I have done the math and I have obtained the hydrostatic pressure in a star is lower at the outermost layer of a star than in its center, where the pressure is actually maximum. Although the equations ...
Lagrangiano's user avatar
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1 vote
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How to calculate enthalpy in this case? [closed]

I have an evaporating side ($T_1$) and a condensing side ($T_2$). Vapor mass is transferred due to partial pressure gradient. The heat transfer in the middle section is $J\Delta H_v$ plus conduction ...
Lost Bubblegum's user avatar
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1 answer
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Can ideal gas equation $PV = nRT$ be used in the intermediate stages of a irreversible and reversible process?

Suppose we have two processes, one is reversible and the other is irreversible. The ideal gas undergoes from state A to state B in both processes. I want to know that can I apply the formula $PV = nRT$...
Divyanshu Dwivedi's user avatar
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1 answer
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What is the distribution of speeds in an ideal liquid?

By ideal, I mean similar conditions to the ideal gas-in-a-box with perfect spherical perfectly elastic homogenous atoms, so no inter-atomic forces, evaporation, gravity, rotations or phase changes. ...
monosodiumg's user avatar
4 votes
3 answers
497 views

Why potential energy is not considered in the internal energy of diatomic molecules?

In thermodynamics, I am taught that there are 5 degrees of freedom in diatomic molecules since there are 3 for translational and 2 for rotational. I interpret degrees of freedom as "ways you can ...
bluesky's user avatar
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1 vote
1 answer
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Gibbs Free Energy and Definitions of Entropy [duplicate]

When we speak about entropy, it's classically defined as $\delta S = \frac {\delta Q}{T}$ Where, I emphasize that it's the definition for only a change in entropy and not entropy itself (That's how I ...
BlackKnight23's user avatar
3 votes
1 answer
95 views

Different Bekenstein bound equations – what’s the difference?

Can someone help me understand the difference between the Beckenstein bound equations that I’ve come across? They all appear to have different dimensions. I’ve been told that if you include the ...
Nate S's user avatar
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1 answer
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Why does entropy obey the superposition principle?

I was deriving the Boltzmann's entropy formula $${\displaystyle S=k_{\mathrm {B} }\ln \Omega}$$ We start with two prepositions: Let's consider two systems and we know the entropy of the first is $S_1$...
User198's user avatar
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3 votes
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Definition of entropy and microstates (Huang)

The definition of Boltzmann entropy given in Ref. 1 appears to be different from most sources I've seen up to this moment. Let me start from the latter: typically textbooks assume that in a given ...
Mr. Feynman's user avatar
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2 votes
1 answer
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Precise relation between theromdynamic beta and coupling constant in Euclidean QFT

In statistical mechanics, the thermodynamic is inverse of the temperature: $\beta \propto T^{-1}$. In Euclidean QFT, I have often run into the expression like $\beta \propto g^{-2}$ where $g$ is the ...
Keith's user avatar
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1 vote
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Bubble behaviour during water / vapour coexistence in the most idealised scenario without boundaries

Consider the following statement: during a 1st order phase transition, the temperature of the system stays constant and any extra heat goes into turning a larger portion of the system into the new ...
Rudyard's user avatar
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