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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Heat and mass transfer modes inside rapidly rotating cylinder

My question is about simultaneous heat and mass transfer in rotating cylinder system. System can be detailed as: A rotating cylinder contains wet porous substance in a lump shape. Air stream enters ...
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0answers
28 views

Acceleration of an bubble under the sea [duplicate]

An air bubble arises from the bottom of the sea. Find its acceleration if resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ is cross section area and $v$ is velocity ...
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20 views

Acceleration of an air bubble under the sea [on hold]

An air bubble arises from the bottom of the sea. Find its acceleration if: a) There is no resistance of water b) Resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ ...
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0answers
17 views

solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.
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2answers
26 views

volume of the air bubble in the water

How does the depth affect the volume (the radius) of an air bubble in the water, if the temperature and density of the water are constant. Is there any relation combining this? Can I say that ...
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11answers
1k views

Why does hot air rise in a column instead of cold air pressing down?

Ok, this looks like a dumb question or even near trolling, but I really don't understand it. When air is heated over an oven plate, it rises. Obviously, I can check by blowing some smoke in. The ...
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1answer
20 views

What does ''population'' mean in regards to the excited and ground states of an atom?

I have a problem I'm working on. It seems simple enough, but there is a term I'm not familiar with. It asks for the ''relative populations of the first excited and the ground states for helium gas in ...
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0answers
28 views

Thermodynamics of Rubik's cube

I was wondering... Could it be possible to calculate the entropy change while rearranging a Rubik's cube from a given arbitrary arrangement? I tried with 3*3*3=27 microstates...but achieved a pretty ...
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2answers
42 views

Thermodynamics at the stoves, cooking problem

I was wondering about a daily question with respect upon heat, time and thermodynamics "made easy". Supposing I put a pot on the stove (we can say without losing so much that the pot is a cylindrical ...
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What is the correct setting for Kirchhoff's Law of Thermal Emission?

For example, is the setting free space? Is it a surface? etc. So, what is the correct setting of Kirchhoff's Law of Thermal Emission?
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2answers
39 views

Why does conservation of étendue matter when showing one cannot focus light to arbitrary temperatures?

The latest XKCD What-If post discusses how one cannot start a fire by focusing the light from the moon. The answer is no, for well-established reasons, but the explanation isn't watertight. Maybe ...
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0answers
9 views

Nose-Hoover Barostat

Much can be found about the Nose-Hoover Thermostat. However I seem to be having difficulty finding out details about the Nose-Hoover Barostat, and how it is implemented. Would anyone be able to give ...
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0answers
42 views

Physical interpretation of the chemical potential in Bose and Fermionic gas

I understand that both Fermions and bosons have the chemical potential $\nu <0$ when it is T>0, but still behave classically, the fermions would increase its chemical potential at T=0, whereas the ...
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1answer
23 views

Are isentropic closed rigid thermodynamic systems also isolated?

$\newcommand{\d}{\, \mathrm d}$Currently it seems to me that isentropic closed rigid thermodynamic systems have to be also isolated. Is this correct? The reason why it seems to me like this is the ...
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2answers
46 views

gravitational force and irreversibility

If we place a ball at a certain height it falls and the process is irreversible. Is there any entropy change associated with the falling of ball? If so why?
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1answer
23 views

Is there a difference between solid-to-fluid convection and fluid-to-fluid convection?

I found an online calculator relating to convective heat transfer, but the calculator's description says it's for heat transfer between a solid surface and a moving fluid. However, the definitions ...
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0answers
7 views

What is temperature dependence (Schottky defects)?

The problem requires us to use the following property to determine the temperature dependence: For a system in thermal equilibrium in a heat bath at temperature $T$ the Helmholtz free energy is a ...
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0answers
20 views

Mechanical equivalent of heat => transfer from work W to heat Q

Consider the following experiment to determine the mechanical equivalent of heat $\mu = \frac{\Delta W}{\Delta Q}$ Not seen in the picture is a weight with known mass hanging down the cord. When you ...
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0answers
23 views

Carnot cycle in steam processes

Our professor told us that in steam processes, such as Clausis-Rankine process, Carnot's cycle is impossible to achieve. Can someone explain why?
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0answers
33 views

Does Earth's loss of internal energy to the moon reduce local entropy?

The moon's orbit is increasing 3.78 cm/year due to the faster spinning Earth and tides pulling on it. The Earth slows down 15 microseconds/year. From this I've estimated (assuming the core's rotation ...
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1answer
27 views

Heat pump solution to pollution [on hold]

I have invented a process that converts an air conditioner into a heat pump. How many metric tons of carbon equivalent could be eliminated from entering the atmosphere annually if 1.every air ...
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0answers
19 views

Prove for ideal gas temperature being directly proportional to absolute temperature [on hold]

I have some difficulties proving that the ideal gas temperature is directly proportional to absolute temperature defined by the second law of thermodynamics. The ideal gas temp. is defined by the ...
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1answer
51 views

How does the fundamental assumption of statistical physics make sense?

Consider two systems A and B in thermal contact. System A has $N_A=3$ simple harmonic oscillators and the system B has $N_B=3$ simple harmonic oscillators as well. Each system has a number of energy ...
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0answers
25 views

Exhaust liquefaction in internal combustion engines

Does an internal combustion engine provide enough efficiency to still deliver mechanical power, if it is forced to liquify it's own exhaust gases by compression? If gas containers would be added to ...
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1answer
31 views

What is the correct statement of Kirchhoff's Law of Thermal Emission?

There are various quite different statements in textbooks and other science literature as to Kirchhoff's Law of Thermal Emission. So, what is the correct statement of Kirchhoff's Law of Thermal ...
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3answers
125 views

How do we define temperature?

I was watching this video What is Temperature?. It states that when we measure temperature we are measuring $dU\over dS$ at equilibrium. But at equilibrium, how the entropy and the internal energy are ...
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1answer
38 views

Reduced Pressure and Cooling

Hi Knowledgeable folks, Since boiling point of a liquid can be reduced via pressure reduction. I was wondering whether this is possible: Add some liquid (alcohol or Water) in a container, reduce the ...
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1answer
30 views

Question on the degeneracies of a thermodynamic system

I think I have a basic understanding of what degeneracies are: Two or more different states of a quantum mechanical system are said to be degenerate if they give the same value of energy upon ...
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1answer
9 views

dry adiabatic lapse rate

Adiabatic lapse rate is defined as $$ \Gamma_a \equiv -\left(\frac{dT}{dz}\right)_{\rm parcel}=-\frac{R_{\rm a} T}{c_p \,p}\left(\frac{dp}{dz}\right)_{\rm parcel} = \frac{g}{c_p} $$ $R_a$ is gas ...
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1answer
33 views

work done in reversible and irreversible process

According to maximum work theorem work done maximum work is done during reversible process . consider a reversible adiabatic and irreversible adiabatic process that occurs between two states of the ...
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1answer
17 views

How quickly does the temperature rise in a water container submerged in a hot water bath?

Let's assume I have a small bottle (neglecting any insulation from the walls of the bottle) containing e.g. 150ml water at 4°C and place it in a larger pot with sufficient water at 80°C so that the ...
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0answers
32 views

Obtain an exact expression for the heat capacity of the system

Before anyone mentions it, yes I did my research and found this question on this site. My question is his exact question, but I'd like some clarification or maybe a bit more explanation than the one ...
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1answer
29 views

Number and energy density integrals in cosmological thermodynamics

I am working through Mukhanov's book "Physical Foundations of Cosmology" and something has me puzzled in the section on evaluating integrals for number density, energy density and pressure. The ...
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0answers
20 views

specific heat capacity (temperature) [on hold]

A 60KG bushwalker is suffering from hypothermia, having an average temperature of 33.5degrees.when rescued she was wrapped in a warm blanket and given two 310ml cups of warm tea each at a temperature ...
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0answers
22 views

Latent Heat of Vaporisation [on hold]

Is there a diagram which shows the effect of reducing pressure on Latent Heat of Vaporisation of water. Thank You.
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0answers
24 views

Specific Heat capacity [on hold]

The total heat capacity of a caloriemeter, heater, stirrer is 107 joules per kelvin. Mass of the liquid in caloriemeter is 0.241 kg. The power supplied by heater is 41.48 watts. The initial rate of ...
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1answer
74 views

Gibbs entropy, Clausius' entropy and irreversibility

I have a bunch of doubts and confusions on the concept of entropy which have been bothering me for a while now. The most important ones are of a more technical nature, arisen from the reading of this ...
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3answers
59 views

Is the internal energy of an ideal gas always $\frac{3}{2}nRT$?

Is the internal energy of an ideal gas always $\frac{3}{2}nRT\,?$ I saw in Wikipedia that it is $\alpha nRT\;.$ Is $\alpha$ always equal to $\frac{3}{2}$ for an ideal gas?
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2answers
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Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false, and if not why not? [on hold]

In his book ‘The Theory of Heat Radiation’, Max Planck adduced his theoretical proof of Kirchhoff’s Law of Thermal Emission. In a recent paper, I argued that Planck's proof is wrong. I'm looking for ...
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0answers
18 views

Understanding the concept of temperature vs. mean energy/heat capacity of a system

I need help understanding a concept in thermodynamics. What is the relationship between temperature and mean energy? What is the relationship between temperature and heat capacity? What I know: ...
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1answer
54 views

Why the 3D heat equation is $\frac{\partial u}{\partial t}=\alpha\nabla^2u$ [on hold]

Why the 3D heat equation is $$\frac{\partial u}{\partial t}=\alpha\nabla^2u=\alpha\left(\frac{\partial^2 u}{\partial x^2}+\frac{\partial^2 u}{\partial y^2}+\frac{\partial^2 u}{\partial z^2}\right)?$$ ...
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1answer
66 views

Light from Absolute 0 [on hold]

Would matter that is cooled closest to instant to a near 0 temperature emit light?
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0answers
28 views

What constitutes an answer to a physics question on this forum? [migrated]

On this page Dr. Pierre-Marie Robitaille: On the Validity of Kirchhoff's Law there are the following comments this might enlighten you rationalwiki.org/wiki/Pierre-Marie_Robitaille . There was ...
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2answers
55 views

How to show state functions are perfect differentials, or vice-versa?

Suppose a variable $z$ is a function of two independent variables $x$ and $y$. Now, if z can be expressed in its total differential form as $$dz=Mdx+Ndy$$ Then show that $z$ is a state function iff ...
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0answers
24 views

ferromagnetic and Curie temperature. Energy question

Is energy absorb and release back when a ferromagnetic material heats and cools passing through the Curie temperature?
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3answers
46 views

How do free electrons conduct heat in a metal?

In a metal, how do free electrons conduct heat? Does the specific heat of a metal should be then related to the electrons and not the atom of the metal?
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1answer
44 views

Differential derivation based upon time and space confusion

I have been doing a lot of derivations recently involving heat transfer. I was attempting to derive heat accumulation in a differential element based upon inflow and outflow as well as thermodynamic ...
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1answer
27 views

Methods to solve a vapor pressure equilibrium question with water on the moon? [on hold]

"Imagine a tall column of water on the Moon, maintained at a temperature of 50°C and left to the open vacuum at the top. Up to what depth will the water continue to boil? The Moon's radius is 0.273 ...
2
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0answers
20 views

COP and input work in a refrigerator [duplicate]

Where can i find a COP and input work requierd in a standard modern refrigerator? I need a sample refrigerator, so that I can calculate the heat disposed to the surrounding and use that to design an ...
3
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1answer
45 views

Partial derivatives vs total derivatives in thermodynamics

The specific heat of a system is defined as $$C_z = T \left( \frac{\partial S}{\partial T} \right)_{z=\text{const}}$$ Sometimes however, I find the same definition, but with total derivatives ...