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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Model for temperature and pressure inside a heated vessel with liquid being pumped into it

I am working on a problem where a pressure vessel is pressurized by heating the vessel to a high temperature and then injecting a liquid into the vessel that boils and hence increases the pressure in ...
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21 views

Timescales for isothermal processes

My understanding is that processes in ideal gases need to take place over relatively long timescales to be idealised as "isothermal" such that the gas temperature can be assumed not to change. For ...
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42 views

Landau theory of phase transation

In his article http://www.ujp.bitp.kiev.ua/files/journals/53/si/53SI08p.pdf, Landau defines probability distribution $\rho$ which is related to symmetry of crystal. If crystal has certain symmetry ...
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117 views

How to calculate liquid pressure regardless of the gravity?

Assume we have a balloon in a tank filled with a liquid , without any gravitational forces: We just know the Temperature, V0 and V1 I want to calculate the pressure exerted from the liquid on the ...
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What would it be like “inside” a star?

This question was triggered by a discussion regarding the computer game Elite: Dangerous, where spaceships routinely operate in close proximity to stars (two or three light seconds away), at which ...
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1answer
44 views

Why is the Specific Heat of Helium 36 times greater than Xenon?

Given that these are single atoms, why should the specific heat difference be so great? And more specifically, why does it take 36 times as much energy to raise the temperature of a given mass of ...
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34 views

Which is a more effective cooling method?

Assume I have a refrigerator at 0C and I put a can of soda at the center of the refrigerator. The temperature inside the refrigerator will be increased to 5C after I put the soda in, but will go back ...
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1answer
98 views

When to use h = Cp∆T or u = Cv∆T

I'm getting myself confused on when to use h = cp∆T or u = cv∆T where cp is the specific ...
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16 views

Comparing work required at compressing gas & pumping liquid

In one of online lectures comparing Vapour compression cycles (conventional refrigerators) with Thermal compression cycles (absorption chillers) it was said that former required more 'high quality' ...
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How do I calculate temperature diffusion in a gas contained in a heatsink?

To simplify the problem, consider a sphere with a diameter of $25\mathrm{mm}$ inside an infinite heatsink at $300\mathrm{K}$. At $t=0$ I instantaneously raise the temperature of the gas in the ...
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31 views

Is the diffusion coefficient time-dependent?

It is known that in the partial differential equation: $$u_t=au_{xx} $$ within the limits $0<x<1$ and $a>0$, the diffusion coefficient, arises in the mathematical modelling of a process of ...
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46 views

Is it possible to efficiently extract phonons from a lattice?

The population inversion generated in lasers occurs in multi-level atomic systems. As an example, the Nd:YAG energy diagram is shown below. The pump pushes the Nd ions up to the upper levels, and ...
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39 views

Convection and radiation heat transfer

It's been some years since my last physics exam and I really need a refreshment in this. I'm stuck in getting a rough estimation of heat exchange between 2 objects separeted by air: let's say object 1 ...
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69 views

Entropy change in an irreversible process between 2 equilibrium state

Calculating entropy change in an irreversible process between 2 states requires computing the change in entropy for any reversible process between the 2 same states, but why? If someone could provide ...
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1answer
202 views

Do some of the laws of thermodynamics break down in quantum mechanics?

I do not know if this is a stupid question as I am not an expert in thermodynamics and certainly no expert in QM. So, we know that the laws of thermodynamics are laws based on statistics. They ...
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1answer
35 views

Spin correlation function identity

The correlation function G between two spins is usually defined as $$ G=\langle \sigma_a \sigma_b\rangle - \langle \sigma_a\rangle \langle\sigma_b\rangle $$ The $\sigma$ are the value of the spins ...
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48 views

How fast do I have to dry myself for a hot shower to heat my body?

I am not a physicist. I would like to know how fast do I have to dry myself after taking a hot shower to get more heat from the shower, than lost because the water on my skin increasing heat exchange ...
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22 views

Does the heat flow vector depend on the proximity of isotherms?

Suppose, there be two isotherms at varying temperatures. Heat energy will flow from higher temperature isotherm to the lower; thus we can assign vector to each point & it will tell about the rate ...
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33 views

Are there laws/equations regarding how a specific material heats up above ambient?

I'll preface this question by saying that I have limited knowledge of physics, especially in thermodynamics, so please bear with me. The goal I have an electrical resistor, like the one below (nice ...
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22 views

How is the Joule normalised?

Apologies if this question is a duplicate, I tried searching for this question both on Google and here, but was unable to find an answer. A Joule is defined in various ways, some of them being: ...
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1answer
26 views

Rough/ballpark thermodynamics and black body temperature question

This is probobly pretty basic but I got into a debate with someone and the temperature of Titan came up, and I did some quick and dirty calculations - as follows. Titan is about 9.5 times as far from ...
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1answer
51 views

Can bulk modulus ever be negative? Can somebody illustrate with an example!

I was particularly confused when my teacher proved that $C_p > C_v$ for substances other than ideal gas for which the difference between the two is R . However the proof involved assuming that the ...
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41 views

Are reversible and irreversible processes frame dependent?

since it is all about time. If I have a look at an irreversible process from a frame where time runs really slow. is there a possibility of considering that process reversible from that frame?
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230 views

Why does the system move until equal temperatures are obtained?

In my college level thermodynamics class, the teacher gave us the example of a closed system which consisted of a box thermally insulated. A piston fully divides the box in two parts, and each is ...
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41 views

Temperature in a vacuum made in the lab

Is the thermal energy of a vacuum 0? And, how close to a perfect vacuum can we make in the lab?
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1answer
44 views

Kinetic energy of different phases of water [closed]

In a closed flask at zero degrees Celsius, all three forms of water exist. Which form of water will have the maximum average kinetic energy? The answer is that all forms of water will have same ...
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54 views

What is the best thermal heatsink compound?

Re-worded This is about the Experimental Physics not PC building or how to grease a car's radiator. I have to insert a stainless steel enclosed PT100 into a block of metal to monitor its temperature ...
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How much temperature reduction can we expect when pouring water into the cup from an elevated kettle?

Turns out some people who are into green tea use the following technique to cool the water from the kettle down. They lift the kettle and pour a rather thin stream of water in the cup. Because of high ...
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17 views

Internal energy given surface tension

Could anyone offer some insight for the following problem: The internal energy and the entropy are proportional to the area. Show that the internal energy per area is given by $$u(T) = \frac{U}{A} = ...
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1answer
41 views

Work needed to pump the balloons

Let's suppose that we want to pump the balloons underwater from the initial volume $V_0$ to the volume $V_1$. The pressure there equals $p_1$ and the atmospheric pressure is $p_0$. It is claimed ...
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42 views

getting frm micro to macro entropy problem

For an ideal gas entropy forvolume change from micro to macro can be rewritten as: $S=k\ln W$ $\Delta S= S_2-S_1=k\ln W_2-k\ln W_1=k \ln\frac{W_2}{W_1} $ since we are constrained from derivation ...
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112 views

Limitations of Redlich-Kwong equation of state

I have been using the Redlich-Kwong EOS to calculate the compressibility factor for nitrogen. I am currently running an Excel VBA that performs the calculation. I have noticed that the process of ...
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12 views

Does a sonic pulse in a gas enhance thermal mixing?

I have a sonic pulse consisting of around 10 cycles that is propagated longitudinally through a gas in a tube. If there are thermal differentials in the gas (say between case and central portion of ...
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Thermal de Broglie wave length

If we refer to this wiki page thermal de Broglie wave length, we can see there are two expressions. One is derived using equipartition theorem, which makes perfect sense. The other one used $\pi kT$ ...
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232 views

Heat Transfer through a wall

If a volume of air enclosed by a physical box is kept at a constant temperature that's different from the temperature outside, will the temperature of the inner wall of the box be the same as the ...
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1answer
28 views

Will heating water vapor induce equilibrium?

What happens to the vapor content if a mixture of gases saturated with water vapor is heated isobarically? Will the amount of liquid water present decrease, yielding up more vapor so as to ...
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3answers
68 views

Heat loss from water surface heated in a room

I have one question regarding total heat losses from water surface. Water is heated with immersion heater in open condition in a room. Heat losses from the top of the pan to air is to be calculated. ...
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1answer
41 views

What is the gas entropy as a functional of a one-particle distribution function?

There are some discrepancies on how to introduce entropy in classical kinetic theory. In what follows $f(r,p,t)$ is the usual one-particle distribution function of a monatomic gas, normalised to the ...
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Effective Area of Isotropic Antenna: Explanation?

I'm reading some introduction to antenna theory and I've often puzzled on the equation: $$ A_{eff} = \frac{\lambda^2}{4\pi} $$ which relates the effective area by which an antenna captures radiation ...
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4answers
453 views

I don't understand why a cavity with a hole is a black body [duplicate]

It makes no sense to me that a cavity with a hole is identical to a black body. Sure, the cavity will probably be a near perfect absorber, but I don’t see how it will be a perfect emitter as well. ...
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Number of particles in a box at thermal equalibrium

Consider a cube box of volume $V$ in thermal equilibrium at temperature $T$. We have 3 pieces of information: The probability of finding a particle of mass $m$ in the box having momentum in ...
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1answer
30 views

High pitched noise as hot object hits water?

https://www.youtube.com/watch?v=9qSEfcIfYbw Just wondering what this phenomenon was called, and its cause? Would have googled, but I don't even know what it's called.
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1answer
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rocket propulsion [closed]

As I understand it, in rocket propulsion a converging/diverging nozzle is used to convert the random velocity vectors of the combustion chamber gases into a mostly unidirectional velocity field at the ...
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4answers
116 views

Why doesn't fire flow back INTO the cylinder?

Let us take into a consideration a (pressurized) kerosene stove. The pressure drives fuel out of the nozzle, like or in a much simpler arrangement as in Question- Why doesn't fire flow back ...
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1answer
45 views

Gibbs free energy for an ideal gas (problem)

so I'm trying to find the gibbs free energy for an ideal gas $$g = u -Ts + pv $$ Hence, $$dg = du -Tds -sdT +pdv +vdp = -sdt + vdp$$ The entropy is $$s = c_{p} \ln T -R \ln P + s_{o}$$ Which ...
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Landau's derivation of the law of entropy increase - clarification

In Landau&Lifshitz V: Statistical Physics the following derivation of the law of increase of entropy is given. I need help understanding several crucial steps; I'll briefly summarize the notations ...
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2answers
49 views

What is the theoretical instantaneous temperature of a gas?

When we measure the temperature of a gas we typically integrate the molecular collisions and wind up with an 'average' temperature due to the sensor comprising a relatively large thermal mass. And ...
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1answer
30 views

There is some attempt to build a magnetic flywheel (reservoir of motion)

We know how flywheel works! There is some attempt to substitute the flywheel-friction mechanism for some magnetic torque ? Exist some mechanism that uses thermal cycle of gases for generate magnetic ...
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74 views

Partition function: Number of states? Doesn't add up for ising

While trying to really understanding the partition function in statistical mechanics, I tried looking at it for a 2D ising model, as that's been helpful for me for all kinds of thermodynamic values. ...
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3answers
108 views

Why is the change in entropy for a given energy input dependent on the temperature?

In my thermodinamics class, we saw that $$dS=\frac{dQ}{T}$$ and $$\Delta S=\int_{a}^{b}\frac{dQ}{T}$$ My question is: why for the same energy input $dQ$ the entropy increases more in lower ...