Tagged Questions

Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (1)

-3
votes
0answers
27 views

why do hot food give off vapour?

Does your food melt and then boil to give off this gas ? whats going on here ?
2
votes
1answer
26 views

Thermodynamics - ideal gas [on hold]

Question: 1 mol of a monoatomic gas at 298 Kelvin acquires a volume of 3 litres. It is expanded adiabatically and reversibly to a pressure of of 1 atm. It is then compressed isothermally and ...
1
vote
1answer
30 views

Rate of Temperature Change due to Heat addition

I might be wrong but I will give a little background leading to my question. I am trying to calculate the heat generation in the advection-diffusion equation for heat generation due to friction by ...
6
votes
1answer
46 views

How does a giant walk-in fridge maintain a thin temperature gradient at the entrance?

I'm standing in a Costco store, and they have a large walled off area for chilled produce. The entrance to this section is a square opening about 10 feet on a side. When you walk in, you notice a ...
0
votes
1answer
44 views

How to convert cc to bar?

In astronomy/astrophysics, medium density is often given in cc, particles per cubic centimeter. Also, the temperature of the medium is usually given, in Kelvins. For some materials the melting point ...
0
votes
0answers
26 views

Deriving an Expression for Helmoltz free energy

Given the equations of states for an isolated system: $$E=\frac32 pV$$ $$p=aVT^4$$ I was asked to find the Helmoltz free energy per particle, $F=E-TS$, as a function of $T$ and $V$. I began with the ...
16
votes
2answers
3k views

Melting diamond and cool down as diamond

Is it possible to melt diamond? And if possible while let it cool will it became diamond again?
0
votes
1answer
15 views

Location of heat conversion in heat engines

If I put a large glass dome on a heap of coal, and burn it, I would expect the air to heat up certain amount. But if I put a coal power plant to that dome, and use it to burn the same amount of coal, ...
0
votes
0answers
31 views

How can q=mcp(deltaT) be made dimensionless?

Specifically, how can I make $m C_p$ dimensionless? I've tried using the Reynolds number and Peclet number definitions to plug into there but the closest I've gotten to was: $q=\pi D Re Pe ...
0
votes
0answers
17 views

Max thickness that can be cooled in a certain time

A frozen-food company freezes its spinach by first compressing it into large slabs and then exposing the slab of spinach to a low-temperature cooling medium. The large slab of compressed spinach is ...
16
votes
1answer
712 views

Does the heat equation violate causality?

I've ran across the idea that, besides simply writing partial differential equations in covariant form, they need to be hyperbolic with all characteristic speeds less than the speed of light. A ...
2
votes
2answers
40 views

Does the conductivity of a wire in a vacuum decrease over time?

Does the conductivity of a wire in a vacuum decrease over time, say over the period of years or decades? In other words: Does current degrade a wire, making it less conductive? If so, by how much, and ...
6
votes
3answers
621 views

How do blankets keep you warm?

I heard a famous physicist (was it Feynman?) argue that blankets do not keep you warm by trapping heat but by trapping air next to the body. Is this true?
0
votes
0answers
41 views

Non equlibrium thermodynamics: How exactly does Euler Homogenous Function Theorem allows one to go from total differentials df to f itself?

I am currently reading this book in order to learn more about entropy and nonequlibrium thermodynamics However I and stumped on how the authors do this step here as shown in the left side of the ...
1
vote
2answers
72 views

why do metals feel cold when electron moves at Fermi velocity?

This might be a very elementary question. Considering that electrons in typical metals have very high Fermi velocity, why is it that when you touch a metal you feel cold? My intuition tells me that ...
1
vote
0answers
19 views

Does degeneracy affect the adiabatic relation?

The adiabatic relation is $P=K\rho^\gamma$. For ideal monotomic gas $\gamma$ is 5/3. For nonrelativistic degenerate electron(inside white dwarf), $\gamma$ is also 5/3. Is this just an coincidence? ...
16
votes
3answers
5k views

If your hair was on fire and you entered a vacuum, could you outlast the fire?

Let's say a person's hair was on fire and suddenly we (instantaneously) pumped all the air out of the (sealed) room, then after time period X we put all the air back. Is there an X such that we will ...
0
votes
0answers
20 views

Non-steady state gas expansion

Please look at the following link for the sketch of the problem: Adiabatic Expansion with expanding control volume I have a certain amount of gas at a certain pressure and temperature at the start. ...
4
votes
4answers
450 views

Heat and work are not the state functions of the system. Why?

Heat and work, unlike temperature, pressure, and volume, are not intrinsic properties of a system. They have meaning only as they describe the transfer of energy into or out of a system. This is ...
4
votes
2answers
42 views

How does aerogel attain its enormous heat isolation properties?

In a text about properties of aerogel I read some interesting facts - clothes with aerogel proved to be impractical, being far too warm to wear. If you isolated a house with aerogel and lit a candle ...
-1
votes
1answer
35 views

How many grams of anthracite coal is needed to convert to steam? [closed]

So I have searched the internet but it would not give me the answer that will truly satisfy the question. I hope someone could answer this
0
votes
1answer
26 views

Entropy maximum postulate and reversibility

I'm studying Thermodynamics on Callen's book and he introduces entropy through the entropy maximum postulate, namely: There exists a function (called the entropy $S$) of the extensive parameters ...
1
vote
0answers
75 views

Why does graphene exist?

I started to read some articles on graphene and almost all say that graphene was discovered late because physicists thought it would be unstable. Despite this, I didn't found a clear explanation of ...
1
vote
0answers
44 views

Interpretation of partition function and thermodynamic potential

So in the microcanonical ensemble the partition function $\Omega$ counts the number of microstates for a given $(NVE)$ configuaration and $S = k_B \ln (\Omega)$ is the entropy. The most likely state ...
11
votes
5answers
1k views

Is it possible to increase temperature of sun using radiation of sun itself?

We know that we can focus radiation of sun and can burn a paper. If we think of this thought experiment, will that happen? If someone constructs a concave mirror on the sun and concentrate radiation ...
1
vote
1answer
39 views

Calculating rate of vaporization of water

Let there be a cylindrical vessel with diameter D that only has liquid water and water vapor as the picture below shows (The water vapor is the grey portion and the liquid water is the blue portion). ...
0
votes
0answers
17 views

why a engine convert all of its heat into work? [duplicate]

Why does heat is released to sink at lower temperature why all of the heat that is taken by a engine from heat reservior cannot be converted into work? I know that it has something to do with the ...
2
votes
1answer
189 views

From a particle's point of view is his temperature absolute zero [duplicate]

Since the vibration of the particles is what cause temperature and a particle from its own point of view is not moving, is its temperature 0°K from its own point of view? Is there a thing like ...
0
votes
1answer
48 views

Isothermal compressibility

How does one get from the thermodynamics definition : $$ \chi_T = -\frac{1}{V} \left(\frac{\partial V}{\partial p}\right)_T$$ to the fluid dynamics definition : $$ \chi_T = \frac{1}{\rho} ...
3
votes
2answers
475 views

Heat Temperature and my dinner

So today while revising for my QM midterm I decided to raid the cupboards for a well earned lunch, only to find nothing there but noodles and rice. So I put two metal pans of water on two pre-heated ...
0
votes
0answers
31 views

In thermodynamic identity, dU=TdS-PdV. Are dS and dV orthogonal or is (T,P) defined in a conjugated space from (dS,dV)?

In thermodynamic identity, we say dU=TdS-pdV, and only Maxwell's relation is required for U to be a proper behaved thermodynamics variable. But from multivariable calculus, that result requires dS ...
1
vote
0answers
13 views

How close to the critical point is sufficient close for measuring critical exponents?

I am learning Monte Carlo and just manage to simulate a phase transition by computing the heat capacity or the susceptibility. I wish I can also compute critical exponents.To this purpose, I have read ...
0
votes
1answer
72 views

Do physicists use agent based models?

I am hoping that this is a simple and specific question. I just wanted to know whether physicists from any branch of physics use agent based models as a tool in their research? If so, then in which ...
0
votes
4answers
70 views

Boyle's law- what's the big deal if temperature is not constant?

Boyle's law: At constant temperature of the gas, the volume of a given mass of a gas is inversely proportional to its pressure. So, Boyle's law is talking about isothermal condition,right? But, ...
0
votes
0answers
21 views

Adiabatic Relation in Plasma Invariant and Thermodynamics

In the problem above, I know how to do the 1D part. Basically, you just plug $V_{l\,l} = \frac{J}{L}$ into $\langle \frac{1}{2} m v^2\rangle = \frac{1}{2} k T$. After you get $T$ in terms of $L$, ...
0
votes
0answers
59 views

Is this Process Possible?

An inventor has devised a complicated non-flow process in which 1 mol of air is the working fluid. The net effects of the process are claimed to be: A change in state of air from 250$^{\circ}$C and ...
1
vote
2answers
77 views

second law of thermodynamics

I'm a high school rookie learning thermodynamics right now by myself. I got really confused that the second law of thermodynamics states that the entropy of the universe is always increasing. If the ...
0
votes
2answers
25 views

translational energy levels

My textbook says translational energy level is so closed, and it basically covers the whole EMR spectrum, so any temperature beyond absolute zero is high enough for molecules to have translational ...
0
votes
1answer
36 views

Will the heat increases with the resistance?

I have studied that the nichrome, which has high resistance, is used in heat coils to increase the heat released. But according to this equation, $$H=\frac{V^2}{R} t,$$ heat is inversely proportional ...
0
votes
1answer
30 views

Are there materials with an adiabatic compressibility higher than that of common gases?

Are there materials with an adiabatic compressibility, measured at atmospheric pressure, higher than that of common gases? Is there any fundamental upper limit to the differential compressibility of ...
0
votes
0answers
16 views

Pressure components in a film

I am performing molecular-dynamics simulations of a polymer near a crystalline substrate (polymer film). I am comparing the mechanical properties in the film with the properties in the bulk polymer. ...
2
votes
1answer
80 views

Death by entropy

An idea struck me as I was walking to class today. According to Wikipedia, entropy is defined as the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a ...
1
vote
1answer
27 views

Best airflow stategy for cooling a confined area?

I am working on a machine which has an upper side which processes a product. On the lower side of the machine there are a couple of motors with built in inverters and there is a laser unit. There are ...
0
votes
0answers
30 views

Calculating The Change in Thermodynamic Potentials for Reversible Adiabatic Expansion of Real Gas

The question asks to find which quantities have a change of zero for the reversible adiabatic expansion of a real gas: Entropy, Enthalpy, Internal Energy, Helmholtz Energy, and Gibbs Energy. Change ...
0
votes
1answer
49 views

Entropy of a system: microstates and macrostates

Currently we're deriving the Gibbs expression for the entropy during an introductory thermal physics course. We're dealing with a system with $N$ different equally likely microstates that are ...
0
votes
1answer
51 views

Why does the Nusselt Number for a Constant Surface Temperature, Thermally Fully Developed Circular Pipe Converge To a Constant of 3.66?

I have flow in a pipe with a constant surface temperature boundary condition. The velocity profile is fully developed and the temperature profile is also fully developed. In my textbook, it says that ...
-2
votes
0answers
59 views

Definition of heat and work

What is the definition of heat and work in thermodynamics? In high school textbooks, heat is defined to be the energy transfer due to a temperature difference. I think this is not a good definition. ...
1
vote
1answer
56 views

Heat Equation with In-Depth Radiation Exact Solution

I am looking to solve the heat conduction equation in a semi-infinite solid with in-depth radiation on the domain $-\infty < x < 0$. The governing equation of this problem is: $$\rho c ...
2
votes
1answer
89 views

What would a normal thermometer read at the Sun's photosphere?

I was reading about the Earth's Thermosphere, and I quote this: "The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would ...
1
vote
1answer
38 views

Speedy Cooling - Ice based Cooler - Efficient Way

Ice is used in a cooler in order to cool its contents. Which of the following will speed up the process? A) Wrap the ice in a metal foil B) Drain the water from the cooler periodically C) Put the ...