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

learn more… | top users | synonyms (3)

0
votes
0answers
61 views

Why does transfer of $^3$He from the rich to sparse phases in a dilution refrigerator cause cooling?

Explanations of the dilution cooling process seem to state without explanation that moving a $^3$He atom across the boundary from the $^3$He rich to the $^3$He sparse phases takes up heat from the ...
0
votes
0answers
40 views

Planck Temperature

I have heard of two different things occurring at Planck Temperature: 1. A black hole forms 2. The quantum gravity takes over and the wavelength of light emitted from the object is Planck length ...
0
votes
0answers
53 views

Heat capacity of a gas in gravitational field

How does one calculate the heat capacity of an infinitely long column (of constant cross-sectional area) of ideal gas in a uniform gravitational field? I tried using the lapse rate $dT/dH$ and putting ...
0
votes
1answer
90 views

How can i turn home gas from liquid to gas [closed]

I hope i am not too off topic, couldn't find a more suitable stack-exchange forum for this, if there is a better one, please point me to it, Well my question is the following, I am working on a ...
0
votes
2answers
550 views

Why do we feel hot because of sunlight? [closed]

sunlight , light generally , is an electromagnetic wave which turns into heat when it contacts a matter (solid,liquid,etc..) is that right ?
2
votes
2answers
71 views

Any general method of determining changes in speed of sound with pressure?

I need to correct speed of sound measurements in various gases for changes in ambient pressure, typically 700-1100 mBar. Is there any general theoretical model available for this? Especially something ...
1
vote
1answer
163 views

Boltzmann Distribution - Why maximum number of microstates?

I've recently started to learn statistical mechanics and I've run into Boltzmann Distribution. I wanted to see how it is derived and found some articles on web, but no one of them explain why the idea ...
2
votes
3answers
142 views

Does the second law of thermodynamics take into consideration of attractive interactions between particles?

If one searches Google or textbooks on 2nd Law of Thermodnamics, one usually finds a statement that is either equivalent or implies the following. The entropy of the universe always increases. But ...
1
vote
1answer
63 views

Full ionization meaning

I'm confused as to what full ionization mean? I have the mean molecular weight of electrons and ions and I have to calculate the ideal gas pressure for a star. Do I have to add them up as usual or do ...
0
votes
1answer
90 views

Series of parallel thermal resistance connection for this enclosure?

Let's say that I have an 2D enclosure in the shape of a pyramid with unequal areas for the faces and I am looking to determine in the inside air temperature. The parameters I know are the outer and ...
1
vote
1answer
226 views

Equation involving; elastic modulus, poisson ratio, radius and pressure of a sphere [closed]

I am trying to determine the expansion of a spherical pressure vessel. I am certain that an equation exist that will define the change of radius of the sphere as the pressure increases. The vessel ...
0
votes
1answer
170 views

If you heat a closed tube, does its mass change?

This is a result of a debate with friends. We were more concerned with the nano- and smaller-scale effects than the larger effects. Let's assume that we have a closed tube filled with air. We weigh ...
-1
votes
1answer
191 views

A possible way to initiate a nuclear fusion reaction without a nuclear fission trigger [closed]

A few years back I read in either Popular Science or Popular Mechanics about a new kind of high explosive that had an energy density many times higher than the most potent ones previously developed, ...
2
votes
1answer
352 views

Increasing the efficiency of solar cell systems

As far as I know, there are currently two main approaches to utilising solar radiation for maximum energy conversion to electricity. These are either direct conversion to electricity, using ...
5
votes
4answers
493 views

Causality principle and Entropy (Second Law)

I was reading about the light cone in relativity and I got to the point where in order to avoid paradoxes one can introduce the causality principle: Causality Principle: For every inertial ...
2
votes
2answers
80 views

Practical understanding of energies in LHC collisions

Is visible light emitted at the point of collision in the LHC? If so, how bright? How much water could be heated up by 10 degrees celsius (this is the energy from collision only, not the energy to ...
1
vote
1answer
53 views

What polytropic index should I use for spherical accretion onto a degenerate object?

Take a degenerate object, such as a white dwarf, embedded in a gas cloud. The cloud is small enough such that the size of the object is non-negligible in comparison - that is, the white dwarf takes up ...
2
votes
1answer
229 views

Rate of evaporation of water with mass loss at set temperature and pressure

I have a cylindrical tank with an 'm' amount of water in it. The tank is sealed except through an exhaust with a fan that keeps a lower than atmospheric pressure (but not vacuum) inside the tank. The ...
2
votes
2answers
831 views

Susceptibilities and response functions

It is often confusing whether a susceptibility is the same as a response function, specially that often they are used interchangeably, in the context of statistical mechanics and thermodynamics. Very ...
0
votes
1answer
370 views

Thermodynamics Work Done At constant pressure and charles law

If we fix a piston in the mouth of a cylindrical container in such a way that the piston settles when the pressure from outside the piston is equal to that of the gas within the container, and ...
1
vote
2answers
336 views

How do we know that the Law of Cooling is true?

According to James Stewart's Calculus book (exercise 14, page 609), Newton’s Law of Cooling states that the rate of cooling of an object is proportional to the temperature difference between the ...
0
votes
2answers
25 views

Maximal work from cooling a portion of water

Let's consider a portion of water of mass $m$. We want to find out how much work (electric energy) we can acquire by cooling it from temperature $T_1$ to temperature $T_0$. The most efficient way is ...
12
votes
7answers
4k views

Drying clothes with the sun's heat, without any air

Will my wet clothes dry if I hang them under the sun, and if there is no air around the clothes? In other words, do I need both air and heat to dry wet clothes, or is heat alone (in the imagined ...
0
votes
1answer
68 views

Apparent Contradiction in Helmholtz Free Energy

I am looking at some mathematics of HelmHoltz free energy. Naturally, wikipedia is one of the (hopefully) more reliable sources of information. In its derivation section, the last equation states that ...
2
votes
2answers
541 views

Blackbody radiation and emissive power

According to blackbody radiation theory, and thanks to Planck, we now know that there is a energy density, $u(\lambda,T)$ [$J/m^3$], associated with a certain wavelength at a particular temperature. ...
6
votes
3answers
202 views

Is the Boltzmann brain problem really clearly established as a problem?

Starting from the assumption of a cosmology in which Boltzmann brains dominate over evolved ones, it is not immediately obvious to me that there is a real problem, since only Boltzmann brains ...
10
votes
2answers
1k views

Why is pale coloured skin said to absorb more UV?

Many resources state that light skin/pale skin absorbs more UV than dark-colour skin. Doesn't black absorb maximum radiation? For an example, see this article: Natural selection therefore ...
0
votes
2answers
111 views

Is liquid helium expensive because of its rarity or because of its low liquidification temperature?

I once argued with my roommate about this problem. Of course it is rare. But presumably the low liquidification temperature makes the cost high too. So which is the primary reason?
0
votes
1answer
397 views

Change in entropy of the Universe for charging/discharging a capacitor

I just need to know what exactly happens when charging/discharging a capacitor. Is there any heat transfer between the capacitor and the surroundings? Is there a heat transfer between other parts of ...
24
votes
4answers
2k views

The unreasonable effectiveness of the partition function

In a first course on statistical mechanics the partition function is normally introduced as the normalisation for the probability of a particle being in a particular energy level. ...
0
votes
1answer
88 views

Is thinner glass more heat resistant?

I heard that vessels made of thin glass are more heat resistant (less likely to crack) than those made of thick glass. Is that true, if so, and why? On one hand, heat propagates more quickly through ...
6
votes
1answer
267 views

Do magnetic fields cause ionisation of gases?

I am doing my final year engineering project on Magnetic Field Assisted Combustion and was curious to see what people thought about it. Companies sell rare earth magnetic arrangements to be attached ...
-1
votes
1answer
58 views

Specific heat ratio range [closed]

I know that the specific heat ratio, $\gamma$, exists in the range $1 <\gamma< 2$, and I am required to demonstrate a proof of this. I have come across the following proof (but I don't really ...
5
votes
1answer
749 views

Speed of sound of a gas mixture

Is there a general mixing rule for estimating the speed of sound of a gas mixture, given the speed of sound in the components? From the ideal gas relation: $$c = (kRT/M)^{1/2}$$ (where k is the ...
0
votes
0answers
48 views

Pressure change in throttling & flow rate reduction in a water circulation

If the pressure in a water pipe line is reduced from 7kgf/cm2 to 4 kgf/cm2, what is the % reduction in flow rate?
6
votes
5answers
2k views

What exactly is fire? [duplicate]

What is fire? Is it a wave or is it matter? Where does fire come from? Does everything burn with fire? (for example: water and some metals don't burn).
2
votes
1answer
104 views

Steady State For An Air Conditioner

Here's the problem I'm trying to solve (from Blundell's Concepts In Thermal Physics): I just don't understand what "steady state" exactly means here. Does it mean that the temperature of the house ...
2
votes
1answer
600 views

Significance of Reversible and Irreversible Process

I would like to ask the following questions: What is the significance of reversible and irreversible nature of thermodynamic process? (I understand that reversible processes are quasi-static, ...
0
votes
1answer
67 views

Does the rate of heat dissipation slow as the temperature differential between the heated object and the surrounding environment decreases?

Does the rate of heat dissipation slow as the temperature differential between the heated object and the surrounding environment decreases, or is it constant? To put this into context, picture the ...
0
votes
1answer
125 views

General relation between power density of any engine and dissiapation rate and temperature

Many years ago ( before my university studies ) I read that renewable resources are fundamentally limited by laws of thermodynamics to produce energy very slowly (low specific power or power density) ...
2
votes
2answers
165 views

Violently shaking object

Would violently shaking something cause a temperature change? For example, if a container of water was shook violently enough; would it be possible to make it boil?
7
votes
2answers
1k views

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

With regards to Thermal Radiation, given a stable body initially at 300 Kelvin placed in isolation, after continuous Thermal Radiation will it's temperature gradually reduce to 0 kelvin ...
0
votes
0answers
61 views

What will be the final temperature of water when heating at a a rate 10J/s?

If I supply heat of rate 10W to water of mass 250g and initial temperature of water is 29 degC then what will be the final temperature of water when steady state is reached. **Water is heating in open ...
1
vote
1answer
101 views

COP of Stirling engine

If we consider the theoretical maximum of COP for a heat pump, we will see that it is possible to make it infinite by approaching the temperatures of each source to each other. Yet, in a real engine ...
0
votes
2answers
89 views

Using Maxwell's demon alongside quantum mechanics to contradict 2nd law of thermodynamics

Suppose we have a steady state universe with a gas chamber resembling that of Maxwell's demon that is used to power this hypothetical heat engine as molecules transfer to their respectable sides based ...
0
votes
0answers
37 views

Water as heat source in a heat pump

Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information ...
1
vote
1answer
36 views

The potential profile of two batteries in series

I would like to know the potential profile in two batteries in series, like the battery in the attached image.
2
votes
1answer
127 views

Can sound frequency create more ideal conditions for fire?

You may have seen the recent story of a device that engineers claim can extinguish flames using sound frequency. An older article loosely explains the theory behind how this works: Sound travels ...
0
votes
1answer
98 views

Why is $\int_{s} \mathbf{h}\cdot \mathbf{n} da = - \dfrac{dQ}{dt}$ & not $\int_{s} \mathbf{h} \cdot\mathbf{n} da = - \dfrac{dQ}{dt} .{dt}$?

I was reading the Lectures of Feynman about surface integral where a situation in which heat is conserved has been dealt. Let there be $Q$ heat energy present inside a body. Now, if there is net heat ...
1
vote
1answer
248 views

Why temperature of liquid drops after spraying thru a nozzle?

We have tested in our lab as mentioned in the picture. We connected hot water at 130degree F at 40Psig to a nozzle(bottle sprayer).we measured the temperature differences inside tank and after ...