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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How much energy does lowering an object into a black hole generate?

An object of mass m is slowly lowered into a black hole of mass 1000 m. Is the amount of braking energy larger than $0.6 mc^2$? Now what if, after lowering the mass close to the event horizon, we ...
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1answer
1k views

Understanding the Seebeck effect

Thermoelectricity is, as I understand it, the difference in voltage between the hot and cold ends of two dissimilar materials. If two materials are connected at two different junctions, the hot ...
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2answers
375 views

why egg cooks slowly in mountains?

A quick Google tells me "Because water boils at a lower temperature at high altitudes". But I am not being able to understand this answer and fill-in the gap. Like, how does an egg cook in the first ...
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1k views

Heat exchange depending on coolant flow direction

Consider a simplest case of a heat exchanger - two parallel pipes of flowing liquids (say, hot and cold) that have physical contact along some part of their length. Hot water of a certain temperature ...
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80 views

In a gas of particles, how is the displacement vector related to the number density?

Suppose I have a gas of particles that is initially uniformly distributed so that the number density is $n_0$ (number of particles per unit volume), and then I displace the particles by the vector ...
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1k views

Solids with very large specific heats

I've noticed that for many solids, specific heat is around 1 Kj/Kg*K is there a theoretical explanation for this? What common solids have the highest heat capacity per mass and per volume?
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1answer
1k views

time dependence of temperature equalization

Suppose you have two thermodynamical systems $X_1$ and $X_2$ (for example water and air) with different temperatures ($T_1 > T_2$). Now put them into thermal contact. Is there a formula which ...
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3answers
68 views

Is heat a property of Something?

There are some unique properties of things in our world. For example, charge is a property of mass. Is heat a unique property of something? Can a vacuum/void have a finite amount of heat in it? What ...
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57 views

Why does air feel cooler when blown through a small hole and warm through a big one? (for example from a mouth) [duplicate]

I hope the question is clear enough and I'm sure that you can try this thing quite easily yourself. When I blow air from my mouth to my palm through a small opening, I feel cool in my palm, but its ...
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34 views

Energy Flux due to Diffusion

Per the Fundamental Thermodynamic Relation, I know that the chemical potential of $i$ represents the energy which would added to a system if a particle of $i$ were added with all other system ...
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1answer
50 views

Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. ...
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1answer
54 views

Why do windows fog quickly?

I'm from Bogotá, Colombia. In my city the temperature is all the year between 12ºC and 25ºC (bus mostly under 19ºC) and when I drive and it's raining, there is accumulation of fog on the windows, but ...
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61 views

Expectation value of $a_i^\dagger a_i$ for thermal density matrix

Suppose we have some heat bath with Hamiltonian, $$H=\sum_n \left(a^{\dagger}_na_n+\frac{1}{2}\right)\hbar\omega_n$$ and a density matrix $\rho=Z\exp(-\beta H)$ for some normalisation $Z$. ...
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139 views

Heat generated by collision

Suppose there are two objects: A = m1 and B = m2 . A is travelling at a constant velocity v toward B and collides inelastically: is there a way in which I could determine the energy which is ...
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47 views

Thermal emission cathode electron velocity distribution

I can't find any experimental data (or theoretical expression) on what is the velocity (or energy) distribution of thermal emission cathode electrons emmited from the cathode at approximately 2000 K ...
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6answers
109 views

Thermodynamics only deals with homogenous systems?

In Thermodynamics quantities like pressure, temperature and entropy are associated with overall states of a macroscopic system. In that case, we do not talk about "the quantity $Q$ at the point $p$ of ...
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69 views

What's the point with equilibrium in Thermodynamics?

All the Thermodynamics books I saw until now state that in Thermodynamics we are mainly concearned with equilibrium states (I know there's "non-equilibrium Thermodynamics", but I'm interested on the ...
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1answer
85 views

The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

Consider an Einstein solid with quantized energy values $U=q\epsilon$ and $N$ oscillators. I calculated some values of an Einstein solid numerically through a function in R (at the bottom of the ...
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165 views

Is the second law of Thermodynamics an immense tautology?

Let's imagine for a second a system that is changing constantly from one microstate to another one. It could be a given volume of a gas with its atoms moving and bouncing around, or a deck of cards ...
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46 views

Thermometer reading

I quickly plunged a room-temperature thermometer into very hot water, the mercury level went down briefly before going up to a final reading. Why?
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1answer
55 views

P-N junction voltage under polarization

All the books that deal with the p-n junction under applied bias assume that the same equations used for the equilibrium case (no bias) can be used for the biased case provided that the junction ...
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1answer
53 views

A gas close to zero Kelvin

Consider an adiabatic expansion of an ideal gas that work is done against friction or a piston. Since no heat exchange can occur the gas keep on losing energy and its temperature decreases and the gas ...
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1answer
50 views

How much electricity could be generated by cloths made of thermocouples?

Lets say that we made a glove, shirt, pants and a hat out of the most effective thermocouple material available today. How much electricity would be generated by each, by a healthy person, on a cool ...
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596 views

How much energy in form of heat does a human body emit?

How much energy in form of heat does a human body emit at rest level?
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154 views

role of entropy in gibbs free energy intuition

I have looked at various derivations of the Gibbs free energy equation and the underlying definition of the gibbs free energy. However I have been unable to attain direct insight/intuition over the ...
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2answers
82 views

Can 'Backradiation' warm its own source? [duplicate]

Ok, although this question arises out of the global warming debate, this is a question purely for physicists and not intended to branch into that particular debate. We are told that LWIR from the ...
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102 views

Container divided in two parts with ideal gas

I wanted to ask your help with the following problem: Consider a closed container, that is, with insulated walls impervious, and rigid. The container is divided into two parts by a wall having the ...
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1answer
77 views

Details in the derivation of the second law starting from the phase space volume

I had a question on one of the details of the derivation of the second law of thermodynamics starting from the phase space volume. I'll type out what I understand so far: Letting the Hamiltonian ...
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310 views

Would sea water moderate a nuclear submarine meltdown?

My son asked me: If nuclear submarines get sunk or blown up, what is to stop them going into nuclear meltdown? I thought about it and came to the conclusion that because they're in the sea the ...
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325 views

Work done by isothermal expansion from two different viewpoints

Consider an adiabatic system as follows. It consists of a gas in a container and a piston. Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ ...
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245 views

How do I calculate the curve of a parabolic mirror to melt the ice from my street gutter?

I want to make a concave parabolic mirror that will have a focal point six inches below where I place it (on the edge of the sidewalk) so that it will melt the ice collecting in the gutter below and ...
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1answer
124 views

What happens when a black hole dies?

It just vanishes into space leaving nothing behind or does it expel some material? Also, talking more about black holes, as far as i understand the term "temperature", it is defined by the amount of ...
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1answer
80 views

Change of heat capacity fluid when you add solvent

I am considering a liquid for which I know $C_p$ or $C_v$. I am wondering how this changes when you add a (minor) amount of solvent to the liquid. Is there a general theory around describing how a ...
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439 views

Probability of Different States - Canonical Ensemble - Partition Function

Consider a canonical ensemble of $N$ ideal gas atoms, which could have spin up or spin down. Why is it that the probability of finding the particle in a spin up state generally only involves the ...
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3answers
279 views

How does that Boltzmann distribution interact with entropy?

In an ideal gas, the Boltzmann distribution predicts a distribution of particle energies $E_i$ proportional to $ge^{-E_i/k_bT}$. But, doesn't entropy dictate that the system will always progress ...
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1answer
248 views

Volume quotient in Carnot-cycle

Problem: One kilomole of an ideal, monatomic gas undergoes a reversible Carnot-processes between temperatures 300 °C and 20 °C. The work done during one cycle is 1500 kJ. a) Find the ...
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1answer
156 views

Why is $0 \,\mathrm{K}$ so special?

I know that $0 \,\mathrm{K}$ cannot be reached, this is discussed here and here. But, why is it such an important statement? I mean, there are many properties which will never be zero, like: ...
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2k views

Would a Cup of Tea Be Hotter If you Add the Milk Before or After Boiling Water?

This is a bit of dispute between work colleagues. An answer would be greatly appreciated. My argument is as follows: If you add X amount of milk at a temperature of M to a mug at room temperature R ...
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1answer
347 views

Understanding heat pump efficiency

I have read that heat pumps are more efficient than generating heat directly for heating homes, until the temperature gets down to a critical value. I just asked how to calculate temperature of ...
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1answer
137 views

Deriving the condtion for spontaneity using gibbs free energy

While deriving the condition for spontaneity, $\Delta$G$\leqslant$0, we start by saying that $\Delta S_{tot}$ $\ge$0 $\Rightarrow$ $\Delta S_{sys}$ + $\Delta S_{surr}$ $\ge0$ If $Q$ is the heat ...
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1answer
664 views

Pressure derivatives of the bulk modulus of materials? (Solved) [closed]

Isotherm bulk modulus is defined by $$K=\rho\left(\frac{\partial p}{\partial\rho}\right)_T=-v\left(\frac{\partial p}{\partial v}\right)_T$$ wherein $v=\tfrac{1}{\rho}$ is the specific volume. Studying ...
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1answer
132 views

Clarification on the Seebeck Effect

Alright, I've been interested in the Seebeck effect lately, so I've been trying to learn it. From what I understand, this is measured with the Seebeck Coefficient, which gives you the $\mu\textrm{V}$ ...
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1answer
1k views

Thermodynamic cycles, when is the work negative/positive?

ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is ...
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1answer
94 views

How to homegrow large, momocrystalline water ice crystals

This is a follow up to this question:Can one get clear ice crystals from a dirty suspension?. How could one grow a large - meaning visible with the naked eye - water ice crstal with common household ...
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227 views

Why increase pressure to go from liquid to steam?

Assume the following phase diagram $T-H$ of water At a nuclear engineering course, I was told that in order to increase the performance of a pressurized water reactor, one has to increase the ...
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1answer
350 views

Does increasing the pressure of the gas in a container by pumping gas into it increase temperature?

Basis is the ideal gas law: http://en.wikipedia.org/wiki/Ideal_gas_law This law only states a mathematical relationship between many variables. It does not state what happens if one of the variables ...
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2answers
52 views

Gas Circulation Using Pressure Difference

Dear all, see attached picture Please, is it possible to have the gas recirculated from the gas phase to the liquid as described in the diagram assuming the gas is not soluble in the water. These ...
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1answer
122 views

Is the crystallization of a heat pack the same as the crystallization of freezing water?

Is the crystallization of a heat pack the same as the crystallization of freezing water? If so, why does one generate heat where the other does not?
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1answer
162 views

How can dQ/T be interpreted as a system's level of disorder?

Long before statistical mechanics, entropy was introduced as: $dS = \frac{dQ}{T}$ At the time when entropy was introduced in this manner, was it known that entropy represents how "disordered" a ...
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258 views

Phase volume contraction in dissipative systems

I am confused about phase-volume contraction in dissipative systems. Please help me catch the flaw in my understanding. From a macroscopic point of view I understand that a dynamic system tends to go ...