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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Why are lasers inefficient?

Why are lasers inefficient? Is it because of the heat lost during lasing? Why couldn't there be thermocouples or turbines in parts of the cooling circuits to extract something out of that heat?
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317 views

Proof that Statistical Mechanics is a model of Themodynamics

The laws of thermodynamics are essentially four axioms of a mathematical theory. The expectation values of a statistical ensemble are supposed to satisfy the axioms of thermodynamics (under the ...
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247 views

What devices could be taken round dwellings to measure the thermal conductivities of buildings in situ?

Your lateral thinking and knowledge of lab kit could help us solve a tricky measuring problem in building-physics. One of the problems we get in modelling the heat demands of buildings, is getting an ...
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1answer
358 views

Using heat energy to increase temperature

It's been a long time since I studied thermodynamics in college years ago, but I was just wondering this: I know that a large bathtub of 10 C water has more heat energy than a small cup of 20 C ...
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513 views

Heat & thermodynamics question based on heat loss [closed]

A Sphere A is placed on a smooth table.Another sphere B is suspended as shown in the figure.Both the spheres are identical in all respects.Equal quantity of heat is supplied to both spheres.All ...
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1answer
1k views

Simple formula for liquid heat transfer

I'm trying to do a simple simulation of a solar panel coupled through some piping to a boiler, with the aid of a pump. My input constants could be something like: volume of liquid inside the panel, ...
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488 views

heater in a perfectly insulated box

Imagine a perfectly insulated box, placed inside the box is an electric heater. The heater is switched on and the box is left to reach equilibrium with its surroundings. What is the final temperature ...
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2k views

Entropy of two expanding and mixing ideal gases

I am currently stuck with the following problem: ...
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8answers
19k views

Will a hole cut into a metal disk expand or shrink when the disc is heated?

Suppose you take a metal disc and cut a small, circular hole in the center. When you heat the whole thing, will the hole's diameter increase or decrease? and why?
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254 views

Why can't Schwarzschild wormholes exist?

So, I've recently been reading up on Schwarzschild wormholes and I've learned that they cannot exist becuase they violate the 2nd Law of Thermodynamics. What I'm asking is: Why do they violate the ...
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902 views

What's the difference between different speeds of sound?

In astrophysics, I often come across the speed of sound. I understand that, broadly, it represents the speed at which perturbations travel through a medium. But there's more than one speed of sound. ...
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811 views

Why are the virial coefficients functions of temperature only?

I have read in multiple places that the virial coefficients in the virial equation of state, $Z=1+{B \over v}+{C \over v^2}...$, are functions of temperature only and are independent of pressure (or ...
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823 views

Is there a relativistic generalization of the Maxwell-Boltzmann velocity distribution?

The Maxwell-Boltzmann velocity distribution in 3D space is $$ f(v)dv = 4\pi \left(\frac{m}{2\pi k_B T}\right)^{3/2} v^2 \exp\left(-\frac{m v^2}{2k_B T}\right)dv$$ It gives the probability for a ...
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Minimal temperature achievable by vanilla Peltier element?

I wonder, are there any fundamental issues leading to reduced performance of Peltier elements at cryogenic temperatures (-100C and lower)? What is theoretical/practical minimum temperature ...
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1answer
226 views

Physicality of claims regarding AC ice energy storage units

Many of us may remember the problems from thermodynamics where we had to determine if a pretend air conditioning unit supplier's claims violated the 2nd law. I want to pose a similar question ...
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2answers
149 views

Solar chamber trapped light

Was wondering if trapping light in a reflective chamber could heat rods sufficiently enough to heat water? Trying to think of new ways in which we can utilise solar energy.
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400 views

How is information defined from a thermodynamics point of view?

How is information defined from a thermodynamics point of view ? I came across some definitions using the concept of free energy of a system. If I have information stored in a finite volume of space ...
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1answer
116 views

Is there a timeline in urban area night temperature?

Fact: We all know that during the day concrete absorbs heat and releases it during the night, making urban areas hotter than rural areas. I observed that after sunset the ambient temperature is going ...
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2answers
411 views

What are the easiest to get/make LN2 superconductors?

I am starting to build multistage Peltier cooler at the moment, and it should be able to reach -100C at least (but if I fail I can always get boring LN2). Doing some experiments with superconductors ...
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134 views

Relationship of the abundance of an isotope and the vapor pressure

Say I have a sample of some alkali metal - Rubidium for example. A sample of Rubidium consists of approximately 27% $^{87}$Rb and 73% $^{85}$Rb. Does the vapor pressure of each isotope individual ...
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747 views

What is wrong with this reasoning on chemical potential?

One definition of the chemical potential is the change of internal energy of the system with respect to a particle of the added substance with the system entropy, molar volume, and all other species ...
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2answers
362 views

Restrictions on defining microstates (Entropy)

If we have an isolated system $Sb$ with thermodynamic entropy $Eb=X$ (and growing by the 2nd law of thermodynamics), we could define an abstract system $Sa$ (containing the system $Sb$) but define ...
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4answers
360 views

Understanding Heat

Heat or thermal energy as understood is nothing but motion of molecules of the matter. If the molecules are tightly bound (in case of solids), it is to-and-fro molecular vibrations, otherwise it is ...
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2answers
77 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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1answer
6k views

How to calculate heat exchange/deltaT in a moving volume of fluid?

I am building a preheater for a maple syrup evaporator and am going to use the steam generated by the heating process to pre-heat the incoming sap from, say 5 degrees C to (hopefully) something on the ...
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967 views

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
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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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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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711 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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492 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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1answer
941 views

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
437 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
987 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
535 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
6k 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
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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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232 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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1answer
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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
943 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
147 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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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
620 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
770 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
3k 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
377 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
417 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
285 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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822 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?