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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At what size of matter does the second law of thermodynamics breakdown?
I'm in high school and I was studying some topics related to heat transfer. While studying, I was curious about why heat strictly flowed from a higher temperature (more energy) to a lower temperature (...
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Is the increase in the internal energy of an ideal gas equivalent to an increase in thermal energy?
ΔU = Q - W
Q: Heat received by the gas from the surroundings (positive if received, negative if given to the surroundings)
W: Work done by the gas on the surroundings (positive if done on the ...
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Where do we get $\Delta U = nC_vT$ from? [duplicate]
The change in internal energy at constant volume is $Q=nC_v\Delta T$
Why does the same equation apply for constant pressure?
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Thermodynamic work and potential functions
I was reading about the maximum thermodynamic work of a system (Z) that is going to equilibrium.
\begin{equation}
dZ = dU + p_0 + T_0dS
\end{equation}
I then came across the thermodynamic potential ...
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Is the 2nd law a reason for the irreversibility of natural processes or a consequence of it?
I have been introduced to chemical engineering thermodynamics due to my academic background. I had learnt about internal energy, entropy etc and applied the equations to various scenarios of practical ...
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Entropy change of an isolated system consisting of two thermally conductive blocks of equal isochoric heat capacity at different temperatures
A classic example considered in most introductory treatments of elementary thermodynamics consists of two thermally conductive (e.g., metal) blocks placed in thermal contact. In particular, I find ...
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Relating specific heat capacity with the rate of cooling
By Newton’s law of cooling, the rate of heat loss (cooling) is directly proportional to the difference in the temperatures between the body and its environment.
On the other hand, Specific heat ...
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Measurability of the energy difference of two states with different mole numbers
In H.B. Callen's thermodynamics (2nd ed. p. 18), after expaining why "the methods of mechanics permit us to measure the energy difference of any two states with equal mole
numbers", the ...
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If I'm inside water, is the amount of heat energy I can receive capped because water can't go above 100°C?
I just learned about double-boiling, where instead of putting a pot directly on the flame stove (where it can get too hot), you put a big tub of water on the flame, and put the pot in the tub of water....
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What do we mean when we say the CMB has a temperature and how do we measure it?
I have read this:
An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
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Does the expansion of the universe cause the universe reach maximum entropy faster than a non expanding universe?
I've seen Does an expanding universe cool down?
So I understand an expanding universe cools down, my question is, does an expanding universe reach maximum entropy faster than a non-expanding universe?
...
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Thermodynamic diagrams in Hamiltonian mechanics
If we compare the fundamental thermodynamic relation $(1)$ and the Hamilton's principal function $(2)$, than we have two practically identical equations:
$$dU=TdS-pdV \tag1$$
$$dS=pdq-Hdt\tag 2$$
In ...
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Should I hold a baby formula bottle to cool it down faster?
This is an interesting and somewhat surprising physics problem - holding a hot object in your hand will cool it down faster, even if the air around is colder. I guess that 90% of people would be ...
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What are good introductory books for contact geometry in non-equilibrium thermo?
As far as I can understand, Mrugala's paper on the geometry of thermodynamic processes covers introductory prerequisites for the contact formalism applied to thermodynamics, however, I know there's a ...
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Landau and Lifshitz Principles of Statistical Mechanics
I've been reading Landau and Lifshitz book on Statistical Mechanicals and some aspects about how they lay out the principles has me a little confused.
Let us now consider a macroscopic body or system ...
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Unitary Evolution and the Second Law of Thermodynamics [duplicate]
Apologies for the long question. This problem has been mentioned multiple times on this platform, with no real resolution, in my opinion. So I'd like to gather all my thoughts below with hopes of ...
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Estimating Heat transfering by measuring [closed]
Consider the setup with closed chamber with two flat metal objects with know dimensions.
The first object can be heated or cooled by peltier module and the second one is placed on top of the first one....
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Contribution of rotational mode in ideal gas law
The ideal gas law is very accurate for an $N_2$ gas when the temperature is around 300K and the pressure is around 1atm. At these conditions, $N_2$'s compressibility factor is 0.997, which means that ...
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Why can photon be treated like gas?
In Cosmology, especially when studying Cosmic Dynamic, sometime we will treat photons as gas to calculate its pressure, but according to my understanding, photon and gas are nothing alike. Why can ...
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Net particle number density for relativistic particles at finite chemical potential (tricky integral)
Question: How does one show that the chemical potential of relativistic fermions is negligible at high energies? In particular, I would like to show that the difference between the particle density $n$...
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Why is the First Law of Thermodynamic related to Fluid Equation?
In Cosmology, there is a equation called Fluid Equation:
$$\dot{{\varepsilon}}+3\frac{\dot{a}}{a}(\varepsilon+P)=0.$$
It is derived by taking time derivative of the First Law of Thermodynamic:
$\dot{E}...
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What book should I read to learn about the magnetocaloric effect
I am trying to study the magnetocaloric effect for a project but I can't find any good resources that deeply talk about it.
Could you make any good recommandation to learn the basics about this effect ...
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In a universe with no photons, will everything necessarily be at absolute zero temperature?
Imagine a universe governed by the same physical laws as ours, i.e., the same fundamental forces, with the only caveat that there are no photons, hence no electromagnetic radiation in this universe. ...
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Is it physically possible for an ordered system to endure forever? [duplicate]
I am seeking to understand whether my theological views align with the current understanding of the second law of thermodynamics. As a physicalist, I believe that all ontological existents consist of ...
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Modified Joule-Thomson expansion
I was trying to solve a thermodynamics problem about the Joule-Thomson (Joule-Kelvin) expansion and I can't reach the answer. The book has the solution, but there's a term which I don't get where it ...
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Why different references express mass densities as $\mathrm{MeV}/\mathrm{fm}^3$ or $1/\mathrm{fm}^3$?
I was reading some papers about equations of state and have found that some of them express the mass density in terms of $\mathrm{MeV}/\mathrm{fm}^3$ and others in terms of $1/\mathrm{fm}^3$. Why is ...
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Is there an analogous Unruh effect for observers on a rigidly rotating ring?
I read up on the Unruh effect recently and what I got from it is that its basically a result of transforming to Rindler coordinates and using a Bogoliubov transformation to change the creation and ...
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Can we derive friction from collisions with environment?
I would like to know if friction, that is, the term $-\alpha \dot{x}$ in the equation of a conservative system $\ddot{x} = -\nabla U(x) -\alpha \dot{x}$ can be derived in some way, by assuming elastic ...
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Gibbs phase rule argument about battery voltage dependency on the state of charge
I'm studying battery physics, particularly the dynamics of full discharge, and I am having trouble understanding an argument that is based on the Gibbs phase rule
$$F=C-P+2.$$
I understand the phase ...
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Meixner and the Impossibility of Non-equilibirum Entropy [closed]
Meixner in a series of publications, see a short list below, starting from 1959 criticized and ultimately denied the possibility of defining the entropy concept in an irreversible process. His ...
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Entropy in irreversible adiabtic process
We know that,
$$dS=\dfrac{\delta Q_{rev}}{T}$$
If you have an irreversible adiabatic process between two thermodynamic equilibrium end states of a system, there exists no possible reversible adiabatic ...
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Use of Clausius theorem to prove entropy inequality in Fermi's Thermodynamics
At the beginning of Section 13 (at the bottom half of page 54 through the top half of page 55) of Enrico Fermi's classic Thermodynamics, he sets out to prove the relation (using his notation)
$$S(B) - ...
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Why is warming food in the microwave work and not heat? [duplicate]
In Schroeder's An Introduction to Thermal Physics, heat is defined as the "spontaneous flow of energy from one object to another" and work is defined thermodynamically as any other transfer ...
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Microscopic derivation of Newtons law of viscosity?
Newtons viscosity law says that viscous stress is proportional to spatial velocity gradient. When used in hydrodynamic problems it results in the Laplacian of the velocity field appearing in the ...
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Experiment to determine friction coefficient
I've come up with an experiment to determine the dynamic friction coefficient of two bodies made up of arbitrary materials, and I'd like to know whether it is good enough or if it needs polishing (...
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Definition of convection heat transfer not unambiguous? [duplicate]
What is actually the definition of convection in the context of heat transfer, if there is one?
Wikipedia states:
Convection (or convective heat transfer) is the transfer of heat from one place to ...
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Heat equation two stage process - Additivity? some other approach?
I'm struggling a bit how to apply a standard solution to the heat equation to my own practical problem. I have some intuition, but do not know whether this intuition is justified. I don't understand ...
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Meaning of $n$-critical point
My lecture notes about field theory refer to a tricritical point as a point in which a continuous phase transition line meets a discontinuous phase transition line.
In the following it refers to a ...
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How to obtain the first law of BH mechanics from the Smarr formula
In general relativity coupled to electromagnetism in $d$ dimensions, the Smarr formula relates the thermodynamical variables present in a rotating, electrically charged black hole. More specifically, ...
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How can red LEDs still give a faint glow at a voltage of only 1.4V? [duplicate]
How can a red LED work at a voltage of only $1.4{\rm V}$? Red photons have an energy of $1.77{\rm V}$ if we use $\lambda = 0.7\mu\text{m}$ in the relation:
$$ E = \hbar \omega = \frac{2\pi\hbar c}{\...
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What causes the latent heat of solidification?
Every explanation that I read says:
"When a crystal (solid state) forms from a liquid, heat is being produced."
This seems rather weird, why would the production of something as ordered as ...
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Is it possible to arrange two or more lenses and mirrors so that I can focus both sun’s rays at a single point
I know similar questions have been asked but I’m still not convinced. I understand it would violate 2nd law of thermodynamics to generate a temperature hotter than the sun using one lens. I’m asking ...
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How does doppler cooling work?
I have trouble understanding how doppler cooling works. I understand that an atom moving towards laser sees the laser light blue-shifted and if the laser frequency is slightly below the atom's ...
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Why does fat get stuck to ice after solidification?
Suppose we put ice cubes into soup, which consists of saturated fat in liquid form and water in liquid form. When we put ice cube inside of it, fat gets solidified and when we remove ice cube, fat is ...
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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)} \\\\
&...
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