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Questions tagged [thermodynamics]

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

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Convection in standing fluid

I want to know if convection occurs, and contributes significantly to evaporation, in a puddle of water at room temperature, on a level floor. Do currents develop in the water as evaporation takes ...
Samj's user avatar
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Different Microwaves same Mug

So my old microwave (which worked fine) heated a cup of coffee in about a minute to a good temperature. I would pull it out and could hold the mug handle with no issue. That microwave recently broke, ...
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Would a hypothetical perfect reflector emit thermal radiation?

The question says it all. I believe a hypothetical perfect reflector is what's referred to as a "white body", but I might be wrong. From what I understand such a hypothetical perfect ...
Outis Nemo's user avatar
1 vote
1 answer
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Unruh Radiation from hovering?

I know that masses on their own don't produce Unruh radiation outside of black holes which produce a similar effect known as Hawking radiation. However, what if some observer hovers above the Earth ...
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About simple thermalization simulation: why the final distribution is not $E^{2}\exp[-E/T]$ but $E\exp[-E/T]$?

I made a simulation that studies the thermalization of massless particles, assuming isotropic and homogeneous spatial distribution, in 3 dimensions. Namely, I started with $N$ particles having random ...
Name YYY's user avatar
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Radiation through optical windows

Edit: I have tried answering this a different way since posting this, see my newer answer below. Problem I'm interested in solving: How much radiative heat load is entering the system through optical ...
Dominic Brennan's user avatar
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What would happen if you add ice to an isolated system of water that is already at 0°C?

So here’s my question: Say there is some ice at -2°C. And water at 0°C. The ice is added to the water. Now this is a completely isolated system. There is no heat exchange whatsoever with the ...
Shakthi Weerawansa's user avatar
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Effects of measurement on the entropy in quantum mechanics

How does measurement in quantum mechanics (QM) impact the system's entropy? The measurement process in QM is considered time-irreversible. Are there principles akin to the second law of thermodynamics ...
Omid's user avatar
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Thermal expansion at atomic level [duplicate]

In my textbook they tried to explain thermal expansion at atomic level with the potential energy curve but it was very complicated.I wish someone could explain it to me:) A high school level ...
Kushagra Mishra's user avatar
1 vote
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Coefficient of thermal expansion on cooling and heating [duplicate]

Apologies if this is a very basic question, but I cannot seem to find anyone else asking or answering it. Is the coefficient of thermal expansion (CTE) the same when cooling and heating a material? ...
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Long-range fluctuations induced forced (or the classical Casimir effect)

According to literature, the Casimir effect refers to attraction of two parallel neutral metal plates due to the wavelength cutoff of quantum fluctuations between the two plates. I come from condensed ...
YoussefMabrouk's user avatar
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Black Body Radiation similarity to Hawking Radiation

Do black body radiation of a 40-Earth mass osmium planet with radius of Earth which was just formed and has a temperature of 10000 degrees Celcius emit photons not just near it but even at infinity ...
Roghan Arun's user avatar
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Understanding $\mathrm dP_x$ in the derivation of Maxwell-Boltzmann distribution

In my physical chemistry book, it says: In the study of molecular speeds, we must consider a range of speeds. If we don’t, the probability would be zero. This probability is proportional to the range ...
Kintoke 's user avatar
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Okay, I know the risks. ( Amateur Rocket.) [closed]

I am currently attending a school for electrical science. A small group of students and our instructor are attempting group project to build a liquid fuel rocket. (I know it is a bit out of the scope ...
TylerTheSparky's user avatar
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1 answer
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Clarification on the Use of $\frac{dS}{dE} = \frac{1}{T}$ vs. $\frac{dS}{dQ} = \frac{1}{T}$ in Thermodynamics

I'm currently studying thermodynamics and have encountered two expressions relating changes in entropy to temperature, but applied in seemingly different contexts: $\frac{dS}{dE} = \frac{1}{T}$, ...
Hakan Akgün's user avatar
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Why do some nuclear tests feature what seems to be an additional fireball on top?

Have a look at this frame from footage recorded during Operation Hardtack I - Test POPLAR Clearly the bit on top is extra hot, and it seems to be above the main fireball, or at least not part of the ...
user3371024's user avatar
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What is the equation for the speed of a molecule at a specific temperature?

What is the equation for the speed of a molecule at a specific temperature? I saw two equations $v = \sqrt{\frac{3 k T}{m}}$ and $v =\sqrt{\frac{3RT}{m}}$. What is the difference?
Arjun Raj's user avatar
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How to measure actual conductive & convective losses inside an enclosed container?

I've been studying convection and come across empirically-derived formulas for calculating the Nusselt number for various geometries. For my particular use case, I'd like to measure the actual ...
Cloudyman's user avatar
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The expectation value of intersecting particles

If I have a light beam (a straight line) it goes through a box of dust, which has travelling length $l$, dust molecule cross section $\sigma$, dust number density $n$. how to calculate the expectation ...
Firestar-Reimu's user avatar
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How is number of collisions per unit distance related to mean free path?

Recently I have been studying Kinetic Theory Of Gases, with one of the topics as collision frequency. I know that collision frequency is inverse of relaxation time which is also the measure of number ...
Ankita Bharati's user avatar
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How mass change can be converted to energy? [closed]

Some gas with initial mass $m_{1}$ was put in a container under high pressure and temperature. After some time its mass became a bit smaller ($m_2$). Additionally, some energy was released and it was ...
renathy's user avatar
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Why $∆U=Q_v$ only at isochoric condition for real gas?

U is a state function.So, ∆U should be same if we carry out an isochoric process from state A to State B or through any other process for real gas. And as ∆U=Qv for real gas in isochoric process, so,∆...
Parth Sahayata's user avatar
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Second law of thermodynamics does not seem to hold under radiation

The Second law of Thermodynamics can be stated as heat always flows from hot to cold. Consider the following system described in the image, where we have two parts A and B, at some time $t = 0$ we ...
Joseph K.'s user avatar
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Why Onsager's formulation of thermoelectricity is better than Bridgman's?

General comment: despite the longish historical introduction this question is not about the history of physics but rather about a specific conceptual problem in physics. Following Bridgman in the ...
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Hydrogen under pressure and high temperatere released energy: what is this process? [closed]

I am given hydrogen that is put into some pressure and high temperature conditions. After this it was found out that mass has decreased. It was also found that energy was released. Can someone, please,...
renathy's user avatar
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A quantum machine that works unitarily and doesn't produce heat

For decades since my physics master's I daydreamed about machines that work on a quantum level unitarily. The reason I found it interesting was because I knew that unitaries map pure states to pure ...
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2 votes
1 answer
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Is the blackbody intensity from a hot object always higher than from a cold object?

This is a conceptual question I can't quite wrap my head around. Take two blackbodies with temperatures $T_{hot} > T_{cold}$. Both should have a spectral intensity described by Planck's law $$I(\...
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Why is the work done by an expanding ideal gas $\textbf{P}_{ext}\Delta V$?

Consider an ideal gas in a cubical container as our system (only the gas is the system, not the walls of the container). If I understand correctly, if the gas expands at constant pressure $P_{int}$ ...
cloud's user avatar
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What is meant by a "critical system"?

I see "critical system" being used all the time. For example: Excellent candidates for this approach are systems exhibiting phase transitions. At the critical point of a phase transition, ...
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Electrical energy is $I^2Rt$, and heat dissipated is also $I^2Rt$?

My book says: Let a current $I$ be flowing through a conductor of resistance $R$ for a time $t$, when a source of potential difference $V$ is connected across its ends. Then, it proceeds to prove ...
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8 answers
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Can I get burned with warm air?

If temperature is the "average" result of measuring a mix of hot and cold air particles, then I can be in a room of some warm temperature but being hit with both extremely hot particles and ...
user1589188's user avatar
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Neutron Star formation Entropy

When a neutron star forms, is its entropy lower than when it was in the form of the star core. In the case of a black hole the entropy becomes the surface area, so what happens in a neutron star ...
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Why should the heating coil of a heater have high resistance?

In my book, it is given: The resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are ...
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Isn't the derivative of internal energy with respect to volume with constant temperature in the isobaric heat capacity zero?

The formula for the isobaric heat capacity is $$C_p = \left(\frac{\partial U}{\partial T}\right)_V + \left[\left(\frac{\partial U}{\partial V}\right)_T+p\right]\left(\frac{\partial V}{\partial T}\...
Henry05's user avatar
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3 votes
1 answer
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Entropy change due to a growing plant

Sunlight hitting a patch of the earth's surface causes the sun to lose entropy and the earth to gain entropy and there is a net gain in entropy (Delta S). But if that sunlight causes a plant to grow ...
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Bethe approximation for two-dimensional Ising model

The logarithm of the canonical partition function in two dimensions when the interaction energy is zero and in the absence of the external magnetic field is expected to be log 2 in the thermodynamic ...
sangara's user avatar
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Sublattice model for ternary system

Much like in an earlier post of mine, I'm now calculating the phase diagram of a ternary system (Ag-Al-Cu, to be specific), which has some phases modelled as sublattices (using this publication for ...
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What is the difference between the cosmological and the black hole horizons in thermodynamics?

I want to know the different thermal behaviors between cosmological and black hole horizons, such as temperature, entropy and so on.
Dongba's user avatar
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Energy exchanges between a Brownian fluid and particles

In the context of the dynamics of polymeric models, and specifically the dumbbell model, one of the forces acting on a dumbbell spring is said to result from "a time smoothed Brownian force" ...
Joce's user avatar
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What happens to the molecules during Latent heat phase?

From my current current understanding of evaporation and boiling - when we put a beaker filled with water under the sun we observe evaporation. Evaporation is a surface phenomenon. Surface molecules ...
Blank's user avatar
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1 answer
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Why can't Rayleigh Flow admit total temperature ratios higher than 1?

In a constant area duct inviscid flow where heat is added, there are some well established results in the literature known as Rayleigh flow (https://en.wikipedia.org/wiki/Rayleigh_flow). In this ...
aetherflo's user avatar
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Shape of an isochoric curve in T-s and h-s diagrams during phase changes

In the pV diagram an isochoric curve is, of course, a vertical line whereas in the T-s diagram it has the form: $$T(s)=T_0 \space e^{\frac{s-s_0}{c_V}}\tag1$$ so it is an exponential function (steeper ...
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3 answers
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Can I modify the heat transfer equation by including the volumetric heat capacity in the partial time derivative? [closed]

Consider a porous material in which the pores can be drained or filled with water gradually in time. Thus, the volumetric heat capacity changes with time. Can I write the heat transfer equation ($\dot{...
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Can the specific heat capacity be time dependent, but not temperature dependent? [closed]

Can the specific heat capacity be time dependent, but not temperature dependent in a close system that does not have a heat source/sink term?
RTT65's user avatar
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Electromagnetic entropy maximum in Planck's black-body radiation law

I am reading Planck's work on black-body radiation. In the paper on the page 19 it is said that the expression $$R_\nu=\frac{\nu^2}{c^2}U\tag1$$ where $R_\nu$ is the intensity of a linearly polarised ...
User198's user avatar
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1 answer
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Applicabilty of the definition of thermodynamic temperature

I have a question about the definition temperature, given by $\frac{\partial S}{\partial E}(E,V,N) = \frac{1}{T}$ Is this valid only for isolated systems (and not applicable, for instance, to a (...
Varidhi Shayana's user avatar
6 votes
4 answers
2k views

Can people feel the low heat radiation from very cold surfaces?

Here's a thought experiment about the way that heat is transferred through radiation. Humans can physically feel when a hot object radiates heat on them, such as a campfire or an infrared-based space ...
Ram Rachum's user avatar
1 vote
2 answers
108 views

Thermal radiation in hollow sphere

I have been asked to calculate the time taken for a highly conducting hollow sphere to cool down from a certain temperature say $\theta_1$ to a temperature $\theta_2$ ($\theta_1, \theta_2 > \...
QuantumQuipster's user avatar
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Does work done by gravity (alone) heat things up?

If we take the first law of thermodynamics: $$ΔQ = ΔU+ΔW$$ And we consider a system of a ball falling from height $h$ in an Earth-like gravitational field(no air drag and $h$<<$Rₑ$) $$ΔU = mgh$$ ...
TheTheoMess's user avatar
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4 answers
201 views

Is there a force related to temperature? [closed]

From my understanding, when an object is heated, there is an increase in the average kinetic energy of the molecules of the object. So if the temperature increases the average kinetic energy increases....
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