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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186 views

What causes a heat generating source to stabilize at a certain temperature? (Answered by myself, I think)

For example, we out a heat sink on a microprocessor to keep it cooler. I understand that if we run 100 watts of electricity through the microprocessor, it will generate 100 watts of heat, or 100 ...
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9answers
36k views
+50

Does hot air really rise?

"Heat rises" or "warm air rises" is a widely used phrase (and widely accepted phenomenon). Does hot air really rise? Or is it simply displaced by colder (denser) air pulled down by gravity?
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0answers
10 views

Hagedorn temperature as a control parameter of saddle - node bifurcation

Can we interpret the Hagedorn temperature as a control bifurcation of equilibrium parameter of the saddle - node type?
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3answers
52 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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0answers
16 views

Number of impacts nitrogen molecules make with the palm of a hand

What is the number of impacts one mole air makes with the palm of your hand assuming air is entirely made up of nitrogen?
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3answers
63 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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11answers
3k 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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0answers
23 views

Sun Spots and Black Holes

Are sun spots possibly the same material that black holes are made of? Why do they float or is it like the tip of an ice burg?
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1answer
70 views

Light from Absolute 0 [on hold]

Would matter that is cooled closest to instant to a near 0 temperature emit light? the question is whether light is emitted during the cooling process, not whether light is emitted at absolute zero. ...
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2answers
39 views

Can two different objects or system of molecules have different temperatures, but having same internal kinetic energy?

If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and ...
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0answers
30 views

The Ideal Gas Equation in higher dimensions

Basically I wanted to know whether or not the ideal gas equation, $PV=NkT$ would hold in higher dimensions? If so, how would you go about proving this? I can't see any reason as to why it shouldn't ...
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0answers
19 views

What is collimated/paralell beam of atoms? [on hold]

This question is related to following exercise: "The intensity of the collimated, paralell beam of atoms of potassium was reduced by 3% by a layer of argon at 1 mm thickness and pressure $6,0\cdot ...
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2answers
110 views

Is Planck’s proof of Kirchhoff’s Law of Thermal Emission false; and if it is not false why is it not false? [on hold]

In his book ‘The Theory of Heat Radiation’, Max Planck adduced his theoretical proof of Kirchhoff’s Law of Thermal Emission. However, there are some problems with that approach, some of which we ...
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1answer
12 views

Example of a system where we cant measure the total possible microstates of a system but can measure the microstates of most probable state?

I have been reading about entropy and I read that entropy is basically a measure of total possible microstates but there was an approximation that when no. of particles become very large we take ...
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0answers
44 views

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

[ edit: Since posting this I had 3 very contrary thoughts: 1) If the moon had been orbiting faster than the Earth, to the same degree, it seems like everything would be the same except that ...
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1answer
26 views

Deriving Boyle's law from only the Gay-Lussac laws

My physics professor during a lecture presumably mathematically derived Boyle's law from the two Gay-Lussac laws for ideal gasses. What he said is also printed in his own textbook. He states that, ...
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4answers
15k views
-1
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1answer
21 views

Calculate the pressure in a container given moles and volume [on hold]

Say there are two containers with the same volume. The first has a temperature T and pressure P and contains 1 mole of $O_2$. The second has a temperature 2T and contains 1 mole of $He_2$. I'd like to ...
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3answers
173 views

Why do some substances undergo sublimation while others do not?

This question is indeed lengthy...but please go through the question at least. From the study of kinetic theory I know that for intuitive answers we can associate the states (liquid, solid,gas) with ...
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0answers
13 views

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 ...
5
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4answers
2k views

Understanding mathematically the free expansion process of an ideal gas

I'm trying to understand mathematically that for the free expansion of an ideal gas the internal energy $E$ just depends on temperature $T$ and not volume $V$. In the free expansion process the ...
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2answers
231 views

Second law of thermodynamics (in terms of entropy)

Is the second law of thermodynamics (in terms of entropy) for closed systems or isolated systems? I thought it must be valid for isolated systems, such as the Universe. But the book Fundamentals of ...
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1answer
122 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
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2answers
32 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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0answers
30 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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0answers
28 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
20 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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1answer
24 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
10 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
29 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
306 views

Book with solved problems on thermodynamics

I am working on honing my engineering thermodynamics problem solving skills at the undergraduate and graduate level. It would be much help if you could suggest me some good books with solved ...
26
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8answers
3k views

What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
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0answers
33 views

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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4answers
2k views
+100

Specific heat capacity

Which of two objects at the same tempreature can cause more intense burns when you touch it: the one with the greater specific heat capacity or the one with the smaller specific heat capacity and why? ...
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0answers
13 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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2answers
50 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
27 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 ...
3
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0answers
46 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
26 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 ...
4
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3answers
130 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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0answers
24 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
24 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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8answers
13k views

Why does maximal entropy imply equilibrium?

From a purely thermodynamical point of view, why does that entropy have to be a maximum at equilibrium? Say there is equilibrium, i.e. no net heat flow, why can the entropy not be sitting at a ...
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2answers
629 views

If an object falls - regarding air resistance - does the Potential or Kinetic energy get converted into thermal energy as it is falling?

I read a paragraph on the transfer of potential energy to kinetic energy and heat from this website: Even if air resistance slows down the ball, the potential energy is the same (Mb x g x H). ...
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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
28 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
52 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 ...
7
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2answers
126 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = ...
3
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0answers
26 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 ...