Questions tagged [thermodynamics]

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

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Kraus decomposition with incoherent bath state

Given a quantum channel $$ D(\rho_S):= \text{Tr}_{B}[U(\rho_S\otimes \rho_{B})U^\dagger],$$ where $\rho_S$ is diagonal (thermal state) and $\rho_B = \sum_{n,m} e^{-\beta (n+m)/2} |n\rangle\langle m|$, ...
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Endothermic Heat Pumps?

I understand roughly how a fridge works: Using energy, heat can be transferred from one room to another, and the energy required also ends up as heat on the outside: (Source) Would it be possible to ...
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Momentum-derivative of energy when mass is not constant

We know by multivariable calculus, that a scalar multivariable function such the energy function $E=E(\vec{P},\vec{L},X_{0},X_{1},...,X_{n})$, using the chain rule, can be expanded as follows: $\frac{...
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Will an egg hard boil faster at higher heat?

The water in a pot of water will boil at $100°\text{C}$ regardless of how much heat is applied to it after it begins to boil. The higher the heat, the faster the water boils off (but at $100°\text{C}$)...
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Mixture of two fluids: Is that EoS possible and how to interpret it?

In the context of cosmology, a perfect fluid is generally described by an equation of state (EoS) of the following form: $$\tag{1} p = w \rho, $$ where $p$ is the fluid's pressure and $\rho$ is its ...
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Why is the equilibrium macrostate of a system the most probable macrostate for an extremely large number of particles?

My text book is trying to explain the cause of the 2nd law of thermodynamics through statistical mechanics using the distribution of N particles free to move between 2 connected containers. The ratio ...
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De Sitter horizon area increase

Black holes increase area when any object falls past the horizon. Note: We define "when" as when the hair from the object falling in becomes undetectable for distant observers. It would also ...
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How can melting of ice be a reversible process when it produces an increase in total entropy?

The melting of ice is a reversible process according to most sources I have seen. However, the melting of ice increases the total entropy of the universe which shouldn't be possible if the process was ...
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Stephen's Law of radiation [closed]

More than one options could be correct Btw the ans to this one is A,B,C,D😅 Please provide an elaborate solution. This is not a homework question it uses multiple concepts of Physics which I am not ...
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Reversible processes do not change the entropy of the universe. What is with exergonic reactions? [closed]

I have read that in a reversible process, entropy can be transferred but not generated. Such that the entropy of the universe stays constant. On the other side, there is the Gibbs Energy, which can be ...
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Diffusion always present?

Simply asked: Is diffusion always and everywhere present? Let's reduce the question to the macroscopic world. Anytime, when two materials touch each other (air <-> wall, tea <-> cup, chair ...
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Derivation of Maxwell distribution

Short and basic/stupid question for today. I was having a second look at the derivation of the Maxwell distribution at temperature T from the definition of entropy in statistical physics. I understand ...
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Is it always true that a non-adiabatic reversible process is an isothermal process?

In a Carnot Cycle, a reversible isothermal process is a non-adiabatic reversible process. Is it always true that a non-adiabatic reversible process is an isothermal process?
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Should larger rocky planets eventually crack due to temperature differences between their inner and outer layers?

Should larger rocky planets eventually crack due to temperature difference between their layers? When a tick piece of glass is left to cool down it would eventually crack...but this is caused ...
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Why can’t you feel the collision of each air molecule?

The molecules in a gas move very fast because of its thermal motion. But why can’t we feel the hit of each of the fast gas molecules?
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How do photons reach thermal equilibrium with the walls of the blackbody cavity?

There's a lot that has been confusing to me about Planck's radiation law, and at this point I feel like I've got the hang of most of it. There is really only one last question that I can't resist ...
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How does radiation become black-body radiation?

Textbooks treat black body radiation as radiation in thermal equilibrium with its environment (more specifically - with a black body): Planck's formula is essentially derived from the partition ...
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The grand canonical potential in $d$ dimensions

For non-relativistic quantum gases the relation $J = -\frac{2}{3}E$ applies, where $J$ describes the grand canonical potential. Furthermore the equation $p = \frac{2}{3}\frac{E}{V}$ can be derived ...
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How to find the minimum of the grand canonical potential?

I have tried to solve the following problem: If I have an open system in contact with a thermostat at temperature $T$ and a reservoir of particles with chemical potential $\mu$, how can I show that ...
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Isolate object against heat [closed]

I'm trying to reduce the temperature inside of a small water tank that is standing outside. It slowly heats up over the day caused by the ambient air temperatures. Is it possible to slow down the ...
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Thermodynamics - Is this a correct explanation of the boiling point elevation of salt water?

I am writing a high school assessment on the relationship between salinity of brine and boiling point of the solution, but I am struggling with writing the background, as my teachers are not very ...
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How to calculate cooling time for copper billet after forging operation?

Presently we are heating copper billet to 740 deg. celsius and forging it in a Hydraulic press. Temperature after forging is noted at 700 deg. celsius. Room temperature is noted at 15 deg. celsius. ...
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Heat differential in irreversible process – what object is it mathematically?

In Thermodynamics, when we talk about quasi-static reversible processes, we often formalize them this way: we identify the state space with a simply connected manifold. On it we have two 1-forms, $đQ$ ...
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Coefficient of Performance and Sign Convention

I am using the sign convention: Heat absorbed by the system is positive and heat left the system is negative. Work done on the system is positive and work done by the system is negative. It was super ...
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Otto cycle reversible or not?

In my course it states that the Otto cycle is an irreversible process. I'm not really sure why. I have also found by a quick google search that a lot of people say the cycle is reversible. To my ...
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Heat Transfer Kirchhoff's Law [closed]

Pls Explain with the help of Kirchhoff's Law the second paragraph of the image attached here. A remarkable thing is worth noting here. The total radiation emanating out of a non black body placed in a ...
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Why don't we turn on the air conditioner instead of the heater during the winters? [closed]

During winters the temperature at my area drops to around $5° \text C$. I feel comfortable around $25° \text C$. To stay warm, we usually turn on the heater instead of air conditioner even tough I ...
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James Thomson's hypothetical ice engine

I do not have a background in Thermodynamics. Imagine a piston/cylinder arrangement (like the one in a steam engine) in which the space below the piston is filled with water. This is cooled to 0°C. ...
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Does ferromagnetic sheets still act as magnetic shield above the Currie temperature?

Well... Everything is in the title... Does ferromagnetic sheets still act as magnetic shield above the Currie temperature ?
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Can adiabatic processes decrease entropy (the Second Law as defined in Reif)?

In Chapter 3.11 of the book "Fundamentals of Statistical and Thermal Physics" by F. Reif, the following is given as a definition of the Second Law of Thermodynamics: In any process in which ...
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Does bitcoin mining take work?

I'm neither a professional in cryptocurrency nor physics, but an interesting idea occurred to me. Bitcoin involves mining, which generates a lot of heat as waste. Is the amount of heat produced by a ...
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What is the problem of the emergence of the macroscopic world?

In the concluding section of the paper (Ref 1) I'm reading, it says "we must return to Maxwell’s original concern about the second law and try to address the basic problems of statistical ...
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Why does a hollow and solid sphere expand the same volume when heated to the same temperature? Explain it quantitatively, not via a formula

Why does a solid and hollow sphere go through the same expansion in volume when raised to the same temperature? Please explain it at the molecular level with an example and not via a formula.
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Degenerate perturbation with the projection operators

I'm studying degenerate perturbation theory in graphene superlattice. The problem is \begin{align} H=H_{0}+\lambda V \end{align} with \begin{align} \mathcal{H}_{0}=&D\begin{pmatrix} 0 &a &...
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Non-invertible function in the context of Legendre transformations

I'm in my 4th semester of physics and currently visit a course about Thermodynamics. We currently deal with Legendre Transformations and my textbook gave the following example: Given the function $$U(...
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Heat Capacity at absolute zero

As Heat Capacity of solids has two contribution: One arising from lattice, called lattice heat capacity and another from electrons, called electronic heat capacity. At absolute zero, we say that heat ...
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Are charged particles cold?

Are charged particles colder than neutral ones? If a charged particle is vibrating due to temperature, it will release some of its energy as electromagnetic waves. So that means it's losing energy, ...
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Conductivity of an Ideal Gas

I'm currently going through the derivation of heat flow equation of an ideal gas in the An Introduction to Thermal Physics book by Schroeder and had some trouble understanding it. It uses the setup ...
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Pressure after cooling of the closed vessel

I have stuck with the engineering calculation for my work Suppose that we have a underground pipeline with constant flow of liquid, which connected with closed underground vessel through the valve (...
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The basic ontology of Statistical Mechanics [closed]

Motivated by the question ("Ontology of QFT", the accepted answer is the perfect example of how ontology questions can be answered and I strongly encourage to read that answer if one is ...
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A question on melting ice

I have a question on melting ice using solar energy. Assuming solar energy transfer in ice obeys Beer's law, i.e. $$R(z)=R_0e^{-z/d}$$ then the intensity could be expressed by $$I(z)=\frac{dR}{dz}$$ ...
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Entropy creation during a simple chemical reaction (Electrolysis of water)

Consider the Electrolysis of water reaction $$H_2O \rightarrow H_2+\frac{1}{2}O_2$$ At room temperature and atmospheric pressure, the change in enthalpy of this reaction is $\Delta H=+286kJ/mol$. Now ...
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How can the heat absorbed by an engine be measured by “measuring the fall in a weight”?

In Atkin's Introduction to the thermodynamics, he speaks about the definition of the absolute thermodynamic temperature scale and in his discussion he states that the work done by any engine can in ...
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Does the amount of water vapor air can “hold” depend on the temperature of the 'water' or the temperature of the 'air'?

The amount of water vapor that the air in a large region (say a suburb) can hold should be dependent on the average temperature of the liquid water within that region. Not the air temperature of that ...
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Does specific heat capacity of an ideal gas depend on static or total temperature?

The specific heat capacity $c_p = c_p(T)$ (J/kg/K) of an ideal gas depends on its temperature. However, the gas has a static temperature ($T_s$) and a total temperature ($T_i$). As we have for the &...
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Steam flow direction through valves - Watt Engine

I don't have a background in Thermodynamics. I am trying to understand a paragraph from the book - Einstein's Fridge. The author says that when the piston is near the bottom of the cylinder, and the ...
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Why are thermodynamic processes slow?

Back when I sat through my thermodynamic classes, I remember my physics professor attempting a joke during one of his lecture demonstrations. While waiting for some beaker of water to boil, he warned ...
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Is there a fundamental reason for the exponential dependence of the evolution of the temperature in an electronic deviced that is powered on?

I used an electronic device during a certain time. Due to the powering of this device, the temperature, measured with an NTC, increased. After a certain time, I switched off the power of the device ...
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Legendre transforms validity

Someone asked me recently about Legendre transforms and I realized there is something I didn't understand. The basic idea of a Legendre transform is to treat a function instead of a mapping from its ...

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