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 does human brain compare to a modern CPU in energy per bit?

Can someone compare the energy efficiency of human brain as a computer ? What is the energy in joules / flop ? may be some reasonable assumptions on the computational load of common tasks such as ...
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5answers
1k views

How is thermodynamic entropy defined? What is its relationship to information entropy?

I read that thermodynamic entropy is a measure of the number of microenergy states. What is the derivation for $S=k\log N$, where $k$ is Boltzmann constant, $N$ number of microenergy states. How is ...
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2answers
2k views

In summer are the upper storey flats more hot or the lower storey flats?

I have often heard neighbours talking things like in a multi storied apartment, the upper flats are more hot in summer then lower flats (or vice versa?) and similarly for some comparison in winter? ...
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2answers
856 views

Evaporation from a capillary tube

Consider a capillary tube (say from a liquid / capillary thermometer), that means a tube of small internal diameter which holds liquid by capillary action . The tube is fulfilled with water and closed ...
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2answers
581 views

A fan in a hot room at what point does it put in more energy that it dissipates

If a fan that is using 50 watts is moving 1 m³/min of air. Lets say the walls are the same temperature as the air so there’s no heat dissipation there. How do I know if the fan is putting in more ...
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Why did my liquid soda freeze once I pulled it out of the fridge?

Can someone explain in both layman's terms and also technically why when I pulled my glass filled with liquid soda from the freezer, the liquid soda quickly froze? Doesn't this violate the 2nd law of ...
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2answers
487 views

the form of a kettle

What is the best form for a kettle, that is, to have the water boil the fastest? I am particularly interested in the following case: for one given kettle (whose volume is constant) containing ...
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4answers
1k views

Does the Moon's core still contain significant heat?

On earth, using earth-sheltering techniques can significantly reduce the temperature fluctuations on a structure. Would the same statement be true as well on the Moon? Does the Moon's core still ...
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2answers
615 views

Limit on geothermal energy that could be extracted before the earth's magnetic field collapsed?

This is more of a theoretical thought-experiment question. Basically, how much geothermal energy can we extract before the loss of the magnetic field makes it a terribly bad idea? Will the ...
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3answers
7k views

Why does a thermometer in wind not show a lower temperature than one shielded from it?

I'm a little familiar with the physics and thermodynamics of the wind chill effect, but this question seems to come up from time to time: Why, given two temperature sensors or thermometers in the ...
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4answers
2k views

Can heat be transfered via magnetic field in a vacuum?

Say you want to store hot coffee in a container surrounded by a vacuum. To remove all sources of conductive energy loss the container is suspended in the vacuum by a magnetic field and does not have a ...
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3answers
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Is there any proof for the 2nd law of thermodynamics?

Are there any analytical proofs for the 2nd law of thermodynamics? Or is it based entirely on empirical evidence?
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249 views

Vapor pressure higher than equilibrium vapor pressure

Is there any mechanism by which the vapor pressure of a liquid substance (lets say in a vacuum) is measured to be greater than the expected saturated vapor pressure at that temperature? Specifically, ...
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2answers
3k views

LED Thermal Modeling (How to solve heat equation with constant heat source)

I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state. Knowing the LED voltage drop and current, I ...
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0answers
1k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
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1answer
151 views

thermal energy while calculating Langevin Forces

I have a quick question from thermodynamics. I remember that we take kT/2 as the kinetic energy per degree of freedom in kinetic theory of gases. But when we do langevin forces (for example in ...
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7answers
8k views

Explanation of “thermite vs ice” explosion

There are several videos of the reaction, where some amount of burning thermite explodes on a contact with ice. An "original" video: http://www.youtube.com/watch?v=IuPjlYxUWc8 A Mythbusters ...
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2answers
687 views

What happens if you connect a hot resistor to a cold resistor?

Kind of an extension to this question: If you heat up an object, and put it in contact with a colder object, in an ideal insulated box, the heat from one will transfer to the other through thermal ...
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3answers
915 views

Imaginary time in quantum and thermodynamics

The following question is about chapter 2 of Sakurai's Modern Quantum Mechanics. I wish I could link to the Google book, but it doesn't seem to have a satisfactory preview to be able to read the ...
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3answers
4k views

Pressure inside a light bulb

It is known that nowadays most light bulbs are filled with gas in order to minimise the evaporation rate of tungsten. Is e.g. argon put into the bulb with reduced pressure, so that the glass doesn't ...
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1answer
440 views

Proving that the free energy is extensive

If I have two system of an Ideal gas $A$ and $B$ each of these system has a partition function: $Z_{A,B} = \left ( \frac{V_{A,B}}{\lambda_T} \right )^{N_{A,B}}$ Where: $\lambda_T = \left ( ...
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1answer
2k views

What energy is transformed to heat when a candle is burned?

What energy is being transformed to heat when you burn a candle?
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1answer
442 views

Uses and interpretation of the 'Bowen Ratio' ($B_o=SH/LE$)

The Bowen Ratio is the ratio of sensible heat flux to latent heat flux, so presumably it gives some information about the relative importance of these processes. But it is not clear how this ...
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1answer
369 views

Violations of Dulong-Petit rule as an upper limit to heat capacity

Does any known substance have a heat capacity at constant volume ($C_V$) per mole of atoms greater than $3k_B$ ~ 24.94 J/(mol K)? In order to count, the substance must actually be made of atoms, that ...
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2answers
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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3answers
661 views

cm^3/g as a unit of adsorption

I recently saw cm^3/g as a unit for amount adsorbed. Usually, you see either kg adsorbate/kg adsorbent or mole adsorbate/kg adsorbent. Does anyone know the meaning of this unit?
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Why do power lines sag when they are heated up?

I was reading some information about the 2003 power blackout in the Northeastern US. Beginning early in the afternoon of August 14, 2003 big transmission lines began to fail in First Energy's ...
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1answer
404 views

Coffee cooling in a cup

Will coffee in two differant size styrofoam cups in the same room conditions cool at the same rate? One cup is 8 oz. and the other would be 12 oz.
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1answer
535 views

free adiabatic expansion

My question is mainly an engineering question. Assume I have a turbine in which I adiabatically expand compressed air. The air cools down and does work to its surroundings, which is captured by the ...
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2answers
775 views

Energy of unmixing

Mixing of two different fluids is associated with an increase of entropy. Conversely, separation of two gases must be associated with a decrease of the entropy of the two fluids. Is there a minimum ...
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3answers
6k views

Derivation of polytropic process equation

I know that a polytropic process equation is often the result of an empirical fit of a P-V curve that allows one to derive some nice analytical equations for the process. Is there actually a ...
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3answers
892 views

Does opening or closing the window in a non-AC car in the summer affect how much heat is felt inside?

This will perhaps look like a very basic and trivial question. But I find it confusing. As an experience, when you are travelling in non-AC car in summer, have people felt if putting on or putting off ...
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1answer
518 views

Reversible Stirling Engine

So it has been asserted that a Stirling engine with proper regeneration can be made reversible. It will consist of two isothermal quasi-static processes connected by two constant-volume processes. The ...
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2answers
2k views

Heat equation on ball - one-dimensional description

I want to solve the transient heat equation on a ball. The boundary condition is the same over the hole outer surface. So this should reduce to a one-dimensional problem in radial direction. However I ...
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1answer
1k views

Work for constant volume compression by adding moles of gas

I often see the expression $W = V \Delta P$ for the work of a constant volume compression where there are a fixed number of moles and the compression is caused by heating. Is this the work equation ...
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4answers
373 views

Discontinuities and nondifferentiability in thermodynamics

In physics and engineering sources, calculus-based formalisms - whether differential forms on a manifold, or "differentials" of functions of several variables - are presented as a way of modeling and ...
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3answers
359 views

How to think physically about basic “fields”

"Field" is a name for associating a value with each point in space. This value can be a scalar, vector or tensor etc. I read the wikipedia article and got that much, but then it goes it into more ...
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1answer
277 views

Heat reflection on distant planets

I was watching a documentary last night on the first planet discovered outside our solar system. The first one apparently is a giant gas planet that orbits very close to its sun over a very fast ...
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1answer
324 views

Is it possible that Atomic Electron Probability Density is a result of Heat?

The Schrödinger Equation provides a Probability Density map of the atom. In light of that, are either of the following possible: The orbital/electron cloud converges to a 2d surface without heat ...
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1answer
428 views

What is a quasicontinuum?

I'm currently going through statistical physics, especially on Fermi energy when I came across a term called "quasi-continuum", what exactly is it?
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0answers
653 views

How do I derive the critical temperature for bose condensation in two dimensions?

In class we derived the 3D case, but there's a step I don't understand: $$ N = g \cdot {V \over (2 \pi \hbar)^3} \cdot \int\limits_{0}^{\infty}{1 \over{e^{\left( E_p \over{K_B T}\right)}-1}} d^3 p = ...
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1answer
283 views

Does the Grand Canonical Ensemble allow for exchange of particles or not?

I was doing some reading on wikipedia and found it interesting that one page says the Grand Canonical Ensemble does not allow for exchange of particles, however another page says it does. So I went on ...
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0answers
93 views

How to compute the heat flow for a specific material for some given boundary temperature?

Assume I have a bounded material with heat sources inside. The material is known (i.e. I know heat capacity and all relevant data) and the temperature of the boundary is fixed. I solved the (steady ...
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1answer
584 views

Temperature vs AC energy consumption

I'm need to understand the following: to keep the room at confortable temperature (70 degree, for example), how does the amount of energy consumed by the AC grow as the outside air temperature rises ...
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0answers
732 views

Why is it when you microwave cold coffee and then add milk it creates a foam head? [closed]

As compared to when the coffee is just hot from brewing. I suspect it has something to do with the way the microwaves are affecting the molecules of the coffee.
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6answers
2k views

What exactly is heat?

Is it energy? Is it energy per unit volume? Is it energy per unit time i.e power? What is it?
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3answers
8k views

Why does microwaved food get cold faster

My evidence is entirely anectodal and non-scientific, but I've noticed food gets cold faster when it's been heated in a microwave instead of a stove. Is this true? And if it is, why does it happen?
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4answers
11k views

How does a maple syrup evaporator work?

Some background info on what an evaporator is: It is a system of metal pans set over a heat source. Sap constantly enters the first pan controlled by a float valve to keep a constant depth. The pans ...
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5answers
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Does the foam on top of boiling maple sap affect the rate of evaporation?

This is a serious question from someone engaged in evaporating large quantities of water to turn sap into syrup at this time of year. Probably some background will help. When sap boils vigorously it ...
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2answers
327 views

How might a resonant antenna and black body radiation interact?

How does an antenna behave when it is cooled so that its black-body radiation is emitting energy at its resonant frequency? Edit: To clarify, its not how they're related in general, but how might ...