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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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Could light and heat reflecting off of surface ice on Earth have a noticeable impact on the sun?

If so, what could be the impact of these reflections on the sun during an ice age on Earth?
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Could micro-states not have equal probability as assumed? [on hold]

How could micro-states have uniform distribution in a 3D space unless there was 0 Gravity? Gravity violates the assumption of equal probability as it makes matter move in a predictable direction. ...
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How does flow work arises in enegy balance using Reynolds Transport theorem?

I will use the below mentioned form of Reynolds Transport theorem(usually derived in Fluid Mechanics context) to give a relation between a Control mass system(no mass in or out) and Control Volume(...
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What is the ratio $W(T_2)/W(T_1)$ for the number of micro states of a perfect gas, using the Boltzmann definition of entropy?

Consider an isobaric process for which 2 mol of a perfect gas is heated from $T_1$ = 50 ◦C to $T_2$ = 100 ◦C. Use the Boltzmann definition of entropy to determine the ratio, $W(T_2)/W(T_1)$, for the ...
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How come we can treat space as a blackbody?

I thought that the condition to be a black body was that an object had to absorb all incident radiation without reflecting any. My understanding is, electrons in atoms absorb the incoming radiation. ...
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Rayleigh-Benard convection criterion

So, every text starts with a uniform heating of the bottom plate of a horizontal fluid for Rayleigh-Benard (RB) convection. Is "uniform heating" and "horizontal plate" an essential starting point? If ...
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In the Joule-Thomson experiment, how is $T_1-T_2$ determined?

I figured out that $H = U +pV$ is constant in this adiabatic condition. I am confused about the expression "$T_1-T_2$ is determined in this condition". I don't think it's an ideal gas, so $\delta(H) \...
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39 views

Can Mars have an oxygen atmosphere?

It is my understanding that, in its gaseous state, oxygen molecules move fast enough to achieve escape velocity. On Earth, we see this more clearly with helium. Regardless of what's happening on ...
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Thermal radiations

everything having temperature above 0 k emits radiation. But those radiations depend upon temperature of the body and not on nature of the body. Why thermal radiations are not material dependent?
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Is it possible to find dry ice crystals lying around the base in Antarctica?

Dry ice sublimates at -78.5°C, while the lowest temperature registered is about -89.2°C around the Vostok station in Antarctica. Imagine a person living on that station on that day (or night, since it ...
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21 views

How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
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Assumptions and limitations for ideal gas

Assumption: In the assumption for ideal gas law, it is stated:"The time it takes to collide is negligible compared with the time between collisions." For, this assumption, can i just say there is only ...
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How to perform an isothermal reversible expansion?

Take the case of an isothermal reversible expansion of a piston to lift a weight. As the piston expands, the temperature remains constant, but the volume increases. This volume increase implies a ...
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As the universe expands, ultimately, will it continue to reach closer and closer, to absolute zero but never get there?

First law of thermodynamics, the conservation of energy, doesn't this law all but guarantee that regardless of how far the universe expands it will forever contain its original amount of energy? All ...
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How to calculate the change of heat between metal heater and air?

I have a basic system, let's say a cube of air of size $1m \times 1m \times 1m$. I place a metal heater next to it, for simplicity its size will be $0.1m \times 0.1m \times 0.1m$ (so the contact area ...
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Is anything wrong with the given statement?

If we take randomly any two bodies, the one with the higher temperature will contain more heat.
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Where do the air bubbles inside the pool come from?

Here's a pic of my legs in the pool water. There are tiny air bubbles on them. I thought this is the result of air coming out of my leg, but I learnt that this is not the case. Also, there seem to be ...
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Why does a cooking thermometer show different temperatures when touching the container of a liquid?

I have a cooking thermometer that looks like a 10-15 cm long metal rod, that can be inserted into the thing you want to measure the temperature of: When inserted into boiling water, I observed that ...
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2answers
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Contradiction in pressure exerted by compressed gas

For the pressure exerted by compressed gas, its stated in my textbook: "The result is that at high pressures the molecules of a gas are so compressed that their volume becomes a significant fraction ...
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“Microwave AB” vs “Microwave AC” on stoneware dishes [on hold]

I have two similar stoneware dishes made by the same manufacturer (seems like the only difference between them is the glaze color). At the bottom of one dish, it reads "Microwave AB", but at the ...
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1answer
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Is 1 liter always equal to 1 cubic decimeter, independently of temperature, pressure, etc?

I recently found this conversion table for the unit conversion $\rm mmol/m^3 \ \leftrightarrow\ \rm mmol/L$ (millimoles per cubic meter to millimoles per liter) My physics is very rusty, but just to ...
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1answer
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How many degrees Celsius/Fahrenheit can be reached in 1 square meter area using magnifying glasses?

The magnifying glasses are each 10 meters in diameter, their collected light is concentrated via mirrors into a 1 square meter spot. Is it possible to get a temperature higher than 2000 degrees ...
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Monte Carlo importance sampling in statistical physics finite approximation question

I am trying to understand a formula found in "Topics in Current Physics: Monte Carlo Methods in Statistical Physics Springer-Verlag" attributed to L. D. Fosdick methods comp physics 1963. I can't get ...
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What process is it when the polytropic index $n$ is equal to $- \infty$?

From $$Pv^n = \mathrm{constant}$$ When $n = - \infty$ What kind of process is it.... Eg... When $n= \infty$, It is constant volume.... Therefore when $n =- \infty$... What is constant?
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Heat transfer on Mars

SCENARIO: I have been tasked with finding the heat transfer across a composite wall on Mars. On the left of the wall there is air maintained at Earth atmospheric conditions and room temperature (101 ...
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Why does energy flow downhill/entropy increase?

I'm not sure if this is asked anywhere else before, but so far my search isn't fruitful. I'm in my second bachelor of physics and mathematics, and currently taking a thermodynamics course. We just ...
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When we burn a wood it burns with flame although it do not contain any gaseous substance [duplicate]

In books it is given that flame is only produced when gaseous substance burn but when dry wood is burnt it also burn with flame.why.
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Confusion about microstate probabilities

So I know we have the Gibbs Entropy Formula $$S=k\sum_i p_i \ln p_i$$ And I've seen the probabilities for the microstates be said to be the Boltzmann probabilities $$p_i\propto e^{-\frac{E_i}{kT}}$$ ...
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Equivalence of thermodynamic ensembles

It is often argued that thermodynamic ensembles are equivalent in the sense that no matter what ensemble one uses for the calculations, one should end up in the same macroscopic equations of state. ...
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Diffusion between unequally spaced points?

I believe what I have is a rather simple issue at heart: assume I have a number of $M$ scattered points in an $N$-dimensional space $\mathbb{R}^N$. Each of these points has coordinates $x \in \mathbb{...
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Black hole absorbing photons?

If a black hole has a radius that is not that much smaller than the wavelength of light emitted by the sun, and is at the same temperature, shouldn't it be able to absorb photons as well as emit them? ...
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1answer
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Are quasistatic processes in thermodynamics achievable or an approximation?

According to Wikipedia: "In thermodynamics, a quasistatic process is a thermodynamic process that happens slowly enough for the system to remain in internal equilibrium." But if we look things more ...
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Query about working out the Specific heat ratio of a gas

The specific heat ratio for $\rm CO_2$ at room temperature is $1.28$ according to my tables. Since $C_V= \left.\frac{\partial U}{\partial T}\right|_V$ and $C_P=\left.\frac{\partial U}{\partial T}\...
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Is reversing the arrow of time that same as going backward into the past?

I read an article today that somwhat confused me. Is this the same as time travel...which I have always thought was a contradiction. Are they talking about reversing law of thermodynamics? In which ...
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Have researchers managed to “reverse time”? If so, what does that mean for physics?

According to press releases, researchers have reversed time in a quantum computer and violated the second law of thermodynamics. What does that mean for physics? Will it allow time travel? Further ...
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Why does the temperature have to change when there's no heat loss in an adiabatic expansion?

Adiabatic expansion is known to cool gases to a substantial temperature and it's caused by pressure drop. Now if I have a tank full of an ideal gas (nitrogen) at high pressure and temperature, and I ...
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The influence of a temperature gradient on the growth of dendrites in a solid liquid interface

Not sure if this is the correct place to ask... My book states that, for a Solid Liquid interface in which the liquid has an increasing positive temperature gradient (increasing temperatures in ...
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1answer
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Why are wet bulb temperatures so warm compared to a naive calculation?

Wikipedia defines wet bulb temperature as: the temperature of a parcel of air cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat supplied by ...
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Is the Ideal gas approximation still valid if I have sizeable dynamic pressure

Say, if I have a hose blowing or sucking air into/outo a bigger compartment, can I still regard the static preassure as obeying ideal gas law?
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Thermodynamics Gas-Piston Problem [closed]

![:/A gas in a piston cylinder assembly is compressed (through a combination of external force on the piston and cooling) in such a manner that the pressure and volume are related by PVn=constant ...
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Derivative of the Euler equation for internal energy with respect to entropy

I have run into an issue while messing around with the fundamental equation for internal energy. $$dU=TdS-PdV + \sum_{i=1}^N{\mu_idn_i}$$ Using Euler's theorem for homogenous we get. $$U=TS-PV + \...
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How to calculate the specific weight of air?

First of all sorry for my bad English ... I have to calculate the specific weight of air knowing that in the air there is actually a small percentage of water vapor. Therefore the specific weight of ...
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1answer
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Do Maxwell relations hold during a phase transition?

Maxwell relations are found by taking mixed derivatives of a thermodynamic potential. Does this mean that they do not hold at a first-order phase transition, where the thermodynamic potential is ...
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1answer
43 views

How many $\text{watt}$ are required to obtain $500°$$\text{C}$? [closed]

I am using two $1000$ $\text{watt}$ heating elements in a cylindrical chamber of volume $7500$ $\text{cm}^3$ with a limited opening at two sides. The cylinder has a radius of $6$ $\text{inch}$. How ...
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4answers
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Why does the negative sign arise in this thermodynamic relation?

I can't understand why $\left(\frac{\partial P}{\partial V} \right)_T=-\left(\frac{\partial P}{\partial T} \right)_V\left(\frac{\partial T}{\partial V}\right)_P$. Why does the negative sign arise? I ...
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2answers
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Is it work or heat?

One student of mine has found one question in a book of thermodynamics (1st year university level). Work or Heat? You grab a bottle of juice and shake it thoroughly. Is this an example of a work ...
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From Boltzmann transport equation to fouriers law - infinite speed of propagation of information

The macroscopic Fourier's law can be derived from the Boltzmann transport equation using the relaxation time approximation for the collision integral. This is demonstrated for an ideal gas in this ...
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2answers
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Piston Cylinder with stops - I don't understand why is it constant pressure?

My question is why if I heat the cylinder why is it constant pressure? I will tell you what I understand, from state 1 to 2 - it is clear why is it constant volume (because we required 300KPA and in ...
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1answer
64 views

Reversible vs. Irreversible Expansion

Suppose I have a gas in a piston expanding adiabatically against atmospheric pressure. If I do this reversibly, the final state is uniquely specified by the final volume $V_F$ of the gas. What ...
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1answer
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Emissivity and absorptivity relation question

This question is related to another discussion here about emissivity of bodies. What interested me is to verify what extend the wavelength between emissivity and absorption is conserved at thermal ...