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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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Can we enhance evaporation rate with a vacuum pump?

First, consider having water at 100C and 1atm and a heat source. If more heat added to water, we have more evaporation rate according to the following formula: $$Q_{in}=m_{vapor}*h_{fg}$$ THEN ...
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1answer
20 views

Block sliding down an incline using energy methods

This is a problem on the review of my upcoming physics energy test and I was wondering how I should go about solving this problem. A 50-kg mass is released from rest and begins to slide from the top ...
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1answer
24 views

Efficiency of irreversible engine in absence of dissipative process

My book states that a heat engine based on idealised reversible processes (Carnot engine) achieves highest efficiency possible. It further states that irreversibility is associated with dissipative ...
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1answer
139 views

Why does ice freeze in feathery streaks on windows?

A twitter acquaintance asks: ...why does the ice form in feathery streaks like this?
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43 views

Speed of a particle in a gas container after 1 year [on hold]

Consider a gas of mono-atomic ideal gas which is kept at a temperature of 47 degree Celcius. Now if a dust particle of mass 0.0001 gm is introduced inside the gas what will be its speed after 1 year? ...
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3answers
59 views

Example of both energy being/not being a monotonically increasing function of entropy and vice versa?

In (https://theoreticalminimum.com/courses/statistical-mechanics/2013/spring) Dr. Susskind says we can assume that in most of the cases energy is a monotonically increasing function of entropy and ...
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4answers
116 views

Work done but no change in velocity

I’m taking an introductory course in thermodynamics right now and I have learned that in a quasi static process, one way to increase internal energy is to do work on a system or supply heat to it. But ...
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1answer
45 views

What's the value for $\lim_{T\rightarrow 0}C_V$?

$C_V=\frac{1}{kT^2}[\overline{E^2} -\overline E ^2]$ where $\overline{E}^2=-\frac{1}{Z}\frac{\partial Z}{\partial \beta}$ and $\overline{E^2}=-\frac{1}{Z}\frac{\partial^2 Z}{\partial^2 \beta}$. $Z=\...
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Point approximated scalar field with diffusion

I need help with finding an approximate model for a scalar field using randomly spaced points and only by knowing the distance between them. I have some points on the 2d plane and each Point has a ...
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2answers
48 views

Good conductor of electricity and bad conductor of heat

I wonder, how a graphite can be a good conductor of electricity but at the same time, be a bad conductor of heat.?! As we know, a body conducting electrons are bound to produce heat by resistance, ...
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1answer
81 views

My textbook sets $\ln \left\{ 1 + \left[ \frac{L}{L_0} - 1 \right] \right\}$ equal to $\frac{L}{L_0} - 1 $. What's the justification for this?

Sat to study physics. I started to study this new chapter Heat and Thermodynamics. It included these steps: $$ \int_{L_0}^L \frac{dL}{L} = \int_{\theta_0}^\theta \alpha d \theta; \text{ or } \ln \...
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Convection Currents [on hold]

In a research laboratory focused on the study of convection currents, a particular experimental arrangement consists basically of a thin tube, completely filled with a mass $m$ of water and forming a ...
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1answer
22 views

Heating effect of fast neutrons in Fast Breeder Reactors

Do fast neutrons play effective(meaningful) role in heating up the water in Fast Breeder Reactors? If so, how much do they?
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2answers
71 views

Adding heat to something without raising its temperature

I understand that you can add heat to something without raising its temperature during phase changes like from liquid to gas during boiling and solid to liquid during melting as the energy is used for ...
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1answer
28 views

Pressure inside a covered pot

If I have a pot covered with a cover and assuming that and the pressure is the atmospheric pressure outside the pot. Will I consider the pressure inside the pot also the atmospheric pressure which is ...
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3answers
39 views

Pressure inside cylinder

If I have a piston cylinder system and assuming that the position is massless and the pressure is the atmospheric pressure outside the cylinder . Will I consider the pressure inside the cylinder also ...
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2answers
1k views

A perfectly fitting pot and its lid often stick after cooking

I encountered a question that asks for the reason that a perfectly fitting pot and its lid often stick after cooking when it cools down. The answer in the solution manual was that the pressure ...
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0answers
34 views

Why am I a Bolzmann brain? [duplicate]

The Boltzmann brain hypothesis states that a big-bang-causing entropy fluctuation is larger than a brain-causing entropy fluctuation, therefore, you are much more likely to be a BB rather than a wet ...
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1answer
25 views

why high pressure systems are colder in temperate climates?

How do we derive equations which relate the temperature and pressure anywhere in the atmosphere? (assuming earth is still so no coriolis effect and flat if that makes the problem any easier). Like ...
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1answer
25 views

Energy Equation of an ideal gas in expanding space-time

Short question: If the energy equation of an ideal plasma is written as follows: $\begin{equation} \frac{\mathrm{d}p}{\mathrm{d}t}=-\Gamma p\nabla\cdot v-\left(\Gamma-1\right)\left( \nabla\cdot q-\...
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1answer
22 views

Is molar heat capacity always greater than specific heat capacity?

Molar heat capcity for any solid is 3R which is approximately 24J/kg-K. But specific heat of aluminium is 900J/kg-K. If the molar heat capacity is M times more than specific heat capacity (M=molar ...
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0answers
111 views

Why am I a Boltzmann brain?

The Boltzmann brain hypothesis states that a big-bang-causing entropy fluctuation is larger than a brain-causing entropy fluctuation, therefore, you are much more likely to be a BB rather than a wet ...
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2answers
59 views

Does the definition of entropy rely on the Clausius equality?

I think there is a weird logical loop I keep running into with the second law of thermodynamics. One sequence is Clausius Equality: $\oint \frac{\delta Q}{T}=0$ for reversible processes. This means ...
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1answer
34 views

Joule-Thomson Expression for dT

In H. Callen's "Thermodynamics and an Introduction to Thermostatistics" in the chapter about the Joule-Thomson process, they say: "If the change in pressure in a throttling process is sufficiently ...
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0answers
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What does calorimetery have to do with potential energy, convection, conduction and radiation? [on hold]

Potential energy question was just combined in one q. Main q is how the three methods of heat transfer are used in calorimeters?
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1answer
47 views

Laplace's heat equation equilibrium functions

I simulated the Laplace's heat equation on a grid (200x200) with boundary conditions of 0 (a cold source) on the top and left and 1 (of hot source) on the bottom and right. (see gif) I stopped ...
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0answers
22 views

How do I calculate the specific heat capacity of a metal using the following information? [on hold]

We did an experiment with a calorimeter where we had to find the specific heat capacity of a metal. The metal was first placed into a beaker and then transferred to a calorimeter (with copper cup ...
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26 views

Is it possible to decompose a cooling curve into two cooling steps?

So if I have something like this, which is a cooling curve from a material we have, is it possible to decompose this into two cooling steps? What I have in mind is something like x mins in ...
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1answer
50 views

Defining work in a general, non-quasistic process involving thermal interaction

Is it possible, even in theory, to determine the work done and the heat exchanged in a general, non-quasistatic process? Example situation: Consider a tube separated into two sides A and B by a ...
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1answer
30 views

Coefficient of thermal expansion tensor

This question pertains to the general coefficient of thermal expansion (CTE) tensor, with no assumption about isotropy. The CTE tensor is $\alpha_{ij}$. Is it possible for $\alpha_{ij}$ to be non-zero ...
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2answers
58 views

Rigorous definition of Hysteresis

I have been studying thermodynamics and have come across this concept of hysteresis but am struggling to find a rigorous way to define it. Here are the types of definitions I have come across Say a ...
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1answer
41 views

Does Exothermic reactions break the law of Thermodynamics?

I was thinking about the reaction of $C$ with $O_2$ . The reaction is $C+O_2 \to CO_2+$HEAT. In this reaction the mass of carbon is $12$ and the mass of $2$ oxygens is $32$ in the reactant side total ...
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1answer
36 views

Calculating rate of heat loss through conduction and radiation

I'm trying to calculate the rate at which a hollow cylinder with a heating element inside will lose heat, specifically through both conduction and radiation. I realize that the total heat loss per ...
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How much water at $100 \ º \textrm{C}$ is needed to heat $750$g of water at $10 \ º \textrm{C}$ to $75 \ º \textrm{C}$? [closed]

My work: the (positive) heat gained by the water at $10$ degrees is $0.75 \cdot 4190\cdot(75-10)$, the (negative) heat gained by the boiling water is $m \cdot1.996 \cdot10^3 \cdot (75-100)$ and at ...
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1answer
32 views

Questions on derivation of the Rayleigh-Jeans law

I'm following this derivation of the Rayleigh-Jeans law: https://thecuriousastronomer.wordpress.com/2013/10/28/derivation-of-the-rayleigh-jeans-law-part1/ There are a few points that I don't quite ...
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2answers
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Why don't all gasses have infinite entropy? [duplicate]

Entropy of an ideal gas is defined as the logarithm of the number of possible states the gas can have multiplied by Boltzmann's constant: $${\displaystyle S=k_{\mathrm {B} }\log \Omega .}$$ In ...
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1answer
107 views

Question about Isentropic flow

I'm reading a book "A Mathematical Introduction to Fluid Mechanics" by Alexandre J. Chorin that says that the flow is isentropic if $$ \nabla w = \frac{1}{\rho}\nabla p $$ where $w$ is an enthalpy, ...
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43 views

What is the source of discontinuity of heat capacity?

Here's something that's been bothering me. Given the density matrix of a system: $$ \rho = \sum_{ij} p_{ij} |\psi_i \rangle \langle \psi_j |$$ Now, we can define it's entropy given by: $$ S= \text{...
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5answers
106 views

Explain the second principle of thermodynamics without the notion of entropy

I will teach some basic physics concepts to a group of university students not having to do with maths, physics, engineering and the like (mainly students of law, of political sciences and of similar ...
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1answer
34 views

Time rate of change (the time derivative) of the internal energy.

I am reading in an article that according to the first law of thermodynamics, the time rate of change of the internal energy obeys the following relation, $\dot{E}+\int_A \mathbf{q} \cdot \mathbf{n} \...
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1answer
41 views

Entropy of an expanding early universe. Why is it constant?

When one models the early universe it is most often assumed to be in thermal equilibrium i.e. the entropy is maximized and therefore constant $$dS=0$$ As far as I understand this can be explained as ...
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3answers
60 views

Change in heat in Isothermal process

I have trouble to understand that if $$\frac{\mathrm{d}q}{\mathrm{d}t} = n\cdot C $$ then during an isothermal process change in heat must also be zero , but why do we say only change in internal ...
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0answers
41 views

What is the entropy of the oscillating air column?

Standing waves in woodwind instruments vibrate with a fundamental mode and its harmonics . Those vibrations involve a large number of particles, /in a range of Avogadro number/, which vibrate in a ...
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1answer
44 views

Carnot cycle with isometric processes

Consider the following slightly modified Carnot cycle with two extra isochoric processes for an ideal gas of adiabatic constant $\gamma$ working between temperatures $T_H>T_C$. A pV diagram is ...
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2answers
64 views

Can shining a laser pointer on an Ice Cube melt it?

I heard in videos that if you use a laser pointer (Green if I recall) and point it on a ice cube, that it would cause it to start melting, is that true?
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How much natural decay heat does thorium produce? [closed]

How much natural decay heat is produced by thorium 230? I was not able to find a clear answer anywhere else. Thanks
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1answer
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If energy can't order itself, how did energy get ordered or made? [duplicate]

In the universe we see that hydrogen (bound up energy) is found in a highly concentrated ordered state in some places and it's highly dispersed in most other places. There is a natural progression ...
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23 views

Volumetric heat source in the 3D Heat Equation

The heat equation on Wikipedia is listed as $\rho c$ $\partial T/\partial t -\nabla\cdot(k\nabla T)=\dot{q}$ where $\dot{q}$ is a volumetric heat source. If this is the case, would $\dot{q}$ be ...
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0answers
30 views

Specific heat capacity is a function of temperature for ideal gases?

So far, I have the impression that temperature is the unit energy per unit entropy of a system. And entropy is some (logarithmically increasing) function of the average number of significantly ...
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1answer
32 views

Fractional change of density

I'm asked to prove that the fractional change of density of a fluid ($\frac{\Delta\rho}{\rho_0}$) is so that $$\frac{\Delta\rho}{\rho_0}=-\beta\,\Delta{T},$$ where $\beta$ is the volumetric ...