# Questions tagged [thermodynamics]

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

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### Can we calculate the average time a photon is "held" by a black hole?

I have a thought experiment. Imagine the Universe is made only of photons. We know we can add one "bit" of information to a black hole if it absorbs a photon whose wavelength is the same as ...
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### Since water can evaporate at any temperature above absolute 0, would the water cycle still be possible even without the Sun?

Since water can evaporate at any temperature (or even sublimate at less than 0°C, although at a very low rate: Why does water not evaporate in below 0 degrees?), could there be a water cycle if there ...
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### Relation between entropy and information

Lack of information is entropy. But entropy has dimension and information has no dimension. Then how do we relate these two terms..
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### Poincaré Recurrence Theorem and the 2º Law of Thermodynamics [duplicate]

I am currently working on a 15 pages project about ergodicity and I wanted to include some discussion about the Poincaré Recurrence Theorem (PRT) and, as far as I know, it contradicts the 2° Law of ...
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### Maximum information transmission rate using an electrical wire

Suppose that we're trying to transmit information at a distance $L$ using an electrical wire made out of a material with known properties. The circuit setup is as follows: there's a wire that's ...
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### What is the temperature at the center of a square plate subjected to 4 different temperature at each edge? [closed]

Dear all, assuming temperatures have all reached steady-state, is the center temperature will be exactly (T1+T2+T3+T4)/4 assuming this is a square plate with 4 different temperature at each edge?
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### Clarifying volume symbol notation with a slash through it

I am reading Munson's book on Fluid Dynamics. One thing I found confusing was this notation in the image below, where the Volume has a slash or strikethrough through it. I am not clear about the ...
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### Optical Isolator Violation of Second Law of Thermodynamics

Okay, so I feel like I'm probably missing something obvious, but I will ask my question anyway (pardon my ignorance). I've been reading recently about optical isolators, and have read articles ...
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### Gravity train in other planets?

A Gravity train (https://en.wikipedia.org/wiki/Gravity_train) goes through a tunnel inside a planet that connects point A with point B. On Earth, the train would not gain enough impulse to reach the ...
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### Thermal Expansion of Two substrates/layers/materials [closed]

The Part Displacement Equation for Thermal Expansion Study is Now, if we apply this equation to a random example, we get: ΔL = (1.8 * 10 -5 K -1)(100°C - 25°C)(50.8mm) = 0.068 m However, what do you ...
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### What does volume parameter for a real gas equation mean for a fluid flowing in a pipe?

I want to understand what the volume means in a $(p,v,T)=0 \$, for a system of real gases flowing in a pipe. Will it be that since the fluid is flowing, $V$, will be the local volume in a given ...
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### Book recommendation for blackhole thermodynamics?

So I was reading this wonderful article about blackhole thermodynamics. https://hapax.github.io/physics/teaching/bh-thermo/ Can someone recommend a book which covers all 4 laws of blackhole ...
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### How can the internal energy of a system at fixed entropy and volume change? [duplicate]

I'm reading Blundell's Thermal concepts in physics and on page 169 he explains that the different thermodynamic potentials are actually the same quantity, the change in which will take on different ...
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### What is the coefficient of thermal expansion of real gases in terms of temperature and pressure

Is there an equation for the coefficient of thermal expansion of real gases. If there is, what is it then? because I tried to use Peng Robinson equation of state, by substituting it's equation in ...
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### Why does a photon with wavelength equal to the radius of the blackhole it's falling into have 1 bit of information?

In this lecture: https://www.youtube.com/watch?v=yMRYZMv0jRE&t=1260s Susskind derives the entropy of a black hole by assuming a bit of information could be added by a photon with wavelength equal ...
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### Relation between time it take to diffuse and temperature

I was reading Reif's Statistical physics. In problem 7 in chapter 2, It says "Consider a thin copper wire stretched out along the $x$-axis. A few of the copper atoms, located near $x=0$, are ...
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### What are Applications of Thermodynamics in Real Life? [closed]

I am looking for some interesting applications of thermodynamics, in real life, that involves not only some text and formulae, but some interesting calculations.
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### Would superconductors made from heavy radio-isotopes transition at higher temperatures?

I read somewhere that heavier variants of water (using deuterium or hydrogen) melt at higher temperatures compared to normal water. A simple argument for why this is could be the following: heavier ...
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### How does the density of the air affect our perception of temperature?

The classic experiment where you have someone put one hand in a bowl of hot water and the other in a bowl of cold for a while then move their hands to a warm bowl is a classic demonstration that our ...
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### Can trains use permanent magnets to be propelled?

Can a train (e.g. like a maglev train) use a set of permanent magnets (not electromagnets) that somehow can be propelled and maintain at least a constant speed with them? Is this an example of such ...
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### Why isn't the free expansion of a gas in an adiabatic container isentropic?

If you expand a gas adiabatically using a piston, the process is isentropic. However, if you simply remove the piston and let the gas expand freely, the process is now not isentropic. What makes these ...
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### How do I calculate the albedo of planets at different energy wavelengths? [closed]

So, I was given this question for a task: Find the surface albedo of each planet (Venus, Earth, Mars) where the reflected energy and emitted energy from the planet's surface are equal at λ = 5μ𝑚 and ...
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### Why does sound travel faster while light travels slower in hotter mediums?

Sound travels at its slowest speed in a vacuum. Once it enters hotter mediums, it travels faster. On the other hand, light travels the fastest in a vacuum. Once it enters other mediums, it travels ...
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### How do units work? [closed]

If an ice sheet at 0 degrees Celsius is being exposed to a heat source from the Earth, which is x watts/m^2 for 1 year, then the thickness, d, of the ice sheet melted would be $$x = pdL$$ where $p$ ...
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### Does pressure decay exponentially for a mixture of gases?

According to this answer, the partial pressure of a gas decreases exponentially in height, when placed in gravity. For a mixture of gases, the partial pressures of each component follows this law ...