# Tagged Questions

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

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### Is frictional heat just electromagnetic interactions creating infrared radiation?

Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
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### How do I compute mass flow rate for a compressible fluid?

Consider the vacuum chamber in the figure. If a hole with cross section area $A_{cs}$ is created, how can I approximate the maximum mass flow rate, $\dot{m}$, for a compressible fluid (e.g. air)?
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### Is it possible to consider PV diagrams without the equations of state?

Suppose that we have the equations of state for a particular system, or equivalently, that we have the fundamental relation $S = S(U,V,N)$. If we want to write down a PV diagram it will be quite ...
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### In enthalpy, is PV the pressure energy?

In the case of a fluid, does the $PV$ contribution to the enthalpy correspond to the pressure energy in fluid mechanics? (Related: What is Pressure Energy?)
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### Isentropic flow through nozzle

I've a question concerning the use of the Bernoulli principle. Let's say I have a pipe filled with air at atmospheric pressure, with a constricting section ala the figure below. The volume before the ...
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### Black Body Radiation of a Home

If there is a home which is far away from all other buildings, what is the heat transfer due to radiation at night? Is the governing equation this: sigma*(T_home^4 - T_space^4)? Does the home radiate ...
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### Thermodynamics: state change and process types

Why is change of state, for example: water to ice, considered an isobaric process as opposed to isothermal? I had always learnt that temperature does not change during change of state.
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### Why does cold air feel even colder when you are moving through it quickly?

My question is the following: Why does it feel colder (i.e. why does your body transfer more heat to the surroundings) when you are moving through the air at a high velocity, f.ex. when you are ...
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### What is the relation between Clausius and Kelvin-Planck statement?

What is the relation between Clausius and Kelvin-Planck statement? In second law of thermodynamics, it is said that these two statement are equivalent and inverse to each other. Violation of one ...
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### What are the limitations of velocity selective coherent population trapping?

I'm somewhat familiar with limitations of Doppler cooling, particularly with the one photon recoil limit, but what I was curious about was what is the next barrier to cooling approaching absolute zero?...
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### How to understand better this point of view on entropy?

On the book "Applied Differential Geometry" by William Burke we see a discussion about thermodynamics in which the following is said: A thermodynamic system is a homogeneous assembly that includes ...
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### Definition of emissivity?

A have come across a definition of emissivity which is along the following lines: Emissivity is the power emitted per solid angle per frequency per surface area. This definition, however seems ...
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### if copper is heated, does it become negatively charged?

i'm reading "Electronics for inventors" and there's this part where it says that free electrons never escape material due to electrostatic attraction with positive ions, but if heated, electrons are ...
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### What is an extremal horizon?

In the contest of holography and thermodynamics, what is an extremal horizon? I am going through a paper by Hartnoll, Santos - Disordered Horizons: Holography of randomly disordered fixed points. They ...
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### Is work only a change of kinetic or potential energy?

I find out on the internet that work is a transfer of energy essentially kinetic. What is the use of work if it does not consider all the types of energy applied , i mean sometimes an objects internal ...
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### Did the universe have a temperature during inflation?

I've heard it said that inflation was not an equilibrium process. But I've also heard it said that during inflation, the temperature of the universe was much cooler than before or after. If the ...
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### A question about ultimate computation capability

If we consider the physical limit of computational capability of a system with average energy $E$, then (1) According to Margolus and Levitin, a quantum system with average energy $E$ takes time at ...
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### The Ideal Gas Equation in higher dimensions

Basically I wanted to know whether or not the ideal gas equation, $PV=NkT$ would hold in higher dimensions? If so, how would you go about proving this? I can't see any reason as to why it shouldn't ...
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### solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.
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### Thermodynamics of Rubik's cube

I was wondering... Could it be possible to calculate the entropy change while rearranging a Rubik's cube from a given arbitrary arrangement? I tried with 3*3*3=27 microstates...but achieved a pretty ...
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### Carnot cycle in steam processes

Our professor told us that in steam processes, such as Clausis-Rankine process, Carnot's cycle is impossible to achieve. Can someone explain why?
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### ferromagnetic and Curie temperature. Energy question

Is energy absorb and release back when a ferromagnetic material heats and cools passing through the Curie temperature?
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### Different ways to calculate the bulk modulus

I am trying to calculate the bulk modulus of unit cells of materials with trigonal or monoclinic structure using two different methods: -The first one is by fitting the changes of volume and energy ...
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### Radiation collapse to black hole

I want to find the temperature at which radiation in AdS will collapse to form a black hole. I have even found a reference that gives the answer but I cannot understand it: http://srv2.fis.puc.cl/~...
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### why stack width is larger than the thermal and viscous penetration depth in thermoacoustic refrigerator?

The thermal and viscous penetration depth is smaller than the spacing in the stack:this assumption leads to the simplification of Rott‟s functions, where the complex hyperbolic tangents can be set ...
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### Do we know how much energy is released in internal conversion (fluorescence)?

In the Jablonski Diagram, when photons hit a surface and certain frequencies are absorbed, then internal conversion occurs to the excited portions of the surface and energy is released as heat (If I ...
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### Cooling of a surface due to fluid passing over it

I am working on a project that requires me to measure the cooling effect of a liquid flowing through a surface. In order for me to effectively calculate the cooling effect, the solution of the below ...
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### Mathematical definition of reversible processes

If I label an initial thermodynamic state as $\psi$ and the final thermodynamic state as $\xi$ then can I say that under a reversible process the two states are related to each other by a continuous ...
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### Energy contribution due to matter transfer

I have a very important question that lingers in my mind for a long time: In the fundamental relations of Gibbsian Thermodynamics, I simply don't understand how the last term appears. I have ...
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### Good thermodynamics/statistical mechanics books that treat the apparent paradoxes in the theory

I am working on a small project mainly concerning the Gibbs and mixing paradoxes arising in thermodynamics/statistical mechanics. Still cannot find good literature on the topic. Any suggestions (I ...
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### Thermodynamic derivation of condition for equilibrium of triple line

Edit:(4/1/2016) Okay, I get how the required equation arises from force balance. All forces are acting on the same length, so the length cancels out of the equation and what we've got is essentially ...
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### Why dynamic equilibrium exists?

We know that at equilibrium Gibbs energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and also we know that for a reaction to be spontaneous ...
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### Why doesn't entropy get decreased in adiabatic expansion process?

I was reading the second step of Carnot cycle in which the system undergoes adiabatic expansion doing work & thus decreasing the internal energy of itself. The entropy didn't change as no further ...
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### Dependence of the magneto-rotational instability (MRI) on thermal relaxation?

The MRI is the most efficient driver of turbulence in accretion discs (as measured by the effective scalar stress). The magnetic field, being properly coupled to the gas (weak coupling), connects the ...