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)

2
votes
2answers
93 views

Do the number of possible microstates increase as temperature decreases?

Entropy change, $\Delta{S}$, can be found from the $\frac{1}{T} - Q$ graph. When the temperature doesn't change during the dispersal of heat energy in the system, the area under the graph is more, ...
1
vote
2answers
32 views

resistivity and temperature scan rate

100 amperes pass through a copper bar of $5$x$5$ mm cross-section. The resistivity of copper is $1.7 $x $10^{-8}$ ohm-metres. Its volumetric heat capacity is $3.45$ joules per kelvin per cc. ...
0
votes
0answers
18 views

why do we use absolute pressure in thermodynamics

One of my university doctors asked a question and I couldn't find an answer for so If anyone can help I will appreciate that. The question is why in thermodynamics we usually work with absolute ...
0
votes
1answer
44 views

What is the density operator for an isothermal–isobaric ensemble (T,p,N)?

In the microcanonical ensemble $(E,V,N)$, the density operator is $$\hat{\rho}=\frac{\delta(\hat{H}-E\,\hat{I})}{Tr(\delta(\hat{H}-E\,\hat{I}))}$$ Where $\hat{H}$ is the Hamiltonian of the system and ...
0
votes
2answers
41 views

Residual Entropy - Third Law

I've been told that many systems possess some residual entropy at absolute zero. This would seem to disagree with the 3rd Law of Thermodynamics? How can this be explained physically speaking? I am ...
0
votes
2answers
55 views

What's wrong with this way of thinking about greenhouses?

It's a clear day, the sun is shining, warming the ground to 29°. The air is at 26°; a breeze is blowing mixing the air so the temperature is fairly uniform: Now I section a bit of this scene off ...
0
votes
0answers
47 views

Why does NASA use gold to hold heat in even though its conductive? [duplicate]

I heard that NASA uses gold to prevent heat loss even though gold is conductive. How does NASA prevent heat loss with a conductive material?
0
votes
1answer
56 views

A simple experiment and the Maxwell-Boltzmann distribution

Consider two containers separated by a removable wall, each side of which is a perfect mirror for the gas in the respective container. Also the walls of the containers are ideal mirrors. In each ...
0
votes
1answer
20 views

Van der Waals expansion?

My thermodynamics textbook says that $$pV_m = \frac{RT}{1-\frac{b}{V_m}}-\frac{a}{V_m}$$ where $b$ and $a$ are van der Waal's coefficients. Then it uses this expansions as follows: $$(1-x)^{-1}= ...
0
votes
1answer
32 views

Coefficient of volume expansion for gases

I often read that at 0 degree (Centigrade), gases expand by 1/273 of its volume at 0 degree for one degree rise in temp. So does this coefficient of expansion ( i.e. 1/273) change with temperature?
31
votes
3answers
3k views

Cooling a satellite

Satellites are isolated systems, the only way for it to transfer body heat to outer space is thermal radiation. There are solar panels, so there is continuous energy flow to inner system. No airflow ...
1
vote
0answers
6 views

In supersonic flow, why must area increase in order to have velocity increase?

Based on the area velocity relation: $\frac{dA}{A}=(M^2-1)\frac{du}{u}$ For M > 1, in order to increase u, we must increase A. I'm wondering what the explanation is physically and why it is opposite ...
0
votes
0answers
101 views

$(\frac{\partial S}{\partial P})_T=-(\frac{\partial V}{\partial T})_P$ from $(\frac{\partial S}{\partial P})_V=-(\frac{\partial V}{\partial T})_S$? [closed]

(Source: Nonequilibrium Thermodynamics, 3rd Edition | Yasar Demirel) Background: Nearly all authors just substitute the Maxwell Relation (a) into dH without ever caring about the fact that the kept ...
5
votes
1answer
48 views

How does the movement of molecules change at the edge of a liquid?

I am thinking about how the velocity of molecules measured from a small region of space might change as the region of inquiry moves closer to the edge of a container. Ultimately I am thinking about MR ...
0
votes
2answers
44 views

Entropy Change in an irreversible process

I have just started learning thermodynamics and the concept of entropy confuses me. Suppose I have a gas in a cylindrical container fitted with a piston. I take it through an adiabatic irreversible ...
1
vote
0answers
22 views

Why is not pressure as effective as temperature in changing the internal energy of solids?

The internal energy is mainly dependent on temperature in all gas, liquid and solid just because an increase in temperature makes the velocity of system's atoms greater. By the time we compress a ...
0
votes
1answer
44 views

If entropy of a closed system decreases by a certain amount, why does not the entropy of the surroundings increase by the same amount? [duplicate]

As said by the Second law of thermodynamics, Energy spontaneously disperses from being localized to being spread out if not hindered from doing so. Now, for systems other than isolated one, and ...
10
votes
6answers
629 views

Gibbs free energy intuition

What is Gibbs free energy? As my book explains: Gibbs energy is the energy of a system available for work. So, what does it want to tell? Why is it free? Energy means ability to do work. What is ...
0
votes
1answer
37 views

Can diffusion,osmosis be explained by second law of thermodynamics?

Second law of thermodynamics states: Energy tends to disperse from localized to more spread out form, if not hindered from doing so. So, can the two processes diffusion,osmosis be explained by ...
1
vote
3answers
56 views

Would using a fan cause an air conditioning system to think it's cold?

Recently my office manager said this, after I requested a desk fan: ...using a fan causes a draught, which then leads the air conditioning to believe it’s cooler than it is and it then blows out ...
0
votes
0answers
26 views

Johnson Noise: Source of thermal fluctuations

I've read a lot online about Johnson noise being caused by thermal fluctuations, and the Wikipedia page of thermal fluctuations attributes this to the fact that particles don't all have the same ...
1
vote
4answers
37 views

Best way to heat something in aluminum foil? [closed]

Let's say we have a wet piece of paper, wrapped in aluminum foil, that we need to heat up in the fastest and most energy efficient way possible (no flamethrower). What would that be? Details ...
1
vote
0answers
70 views

Calculate Helmholtz Free Energy with Entropy, Work given [closed]

it's my first time here and I hope the post complies with the general rules. My problem originates here: I'm doing a statistical physics task which unfortunately leaves me clueless atm. I keep my ...
2
votes
1answer
50 views

Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. ...
2
votes
2answers
60 views

What would a graph of temperature increase of a cup of water in a microwave look like?

My lunch had been in the microwave for a minute or so, and I was wondering if I took it out 10 seconds early, would the amount of temperature it increased in that 10 seconds be more significant, less ...
0
votes
2answers
35 views

Entropy change in irreversible heat flow

For an irreversible heat flow from an object $A$ at temperature $T_A$ and another object $B$ at temperature $T_B < T_A$ , I'd like to know how to evaluate the change in entropy using the following ...
0
votes
1answer
20 views

Difference between solid and gases thermal expansion

The coefficient of linear expansion is $$\Delta L = L \,\alpha \Delta T,$$ where $\Delta t$ can be the difference of any two temperatures. However, in volume expansion of gases, $$\Delta V = V ...
2
votes
1answer
41 views

Water behaviour under theoretical near-infinite pressure conditions

I've asked a similar question here but the answer given shows the behaviour of water under general conditions. I'd like to know what the behaviour of water is like as pressures increase towards ...
0
votes
2answers
45 views

What unit would the answer be in?

So I have used this formula: $$W= PV_1 \times \ln\frac{V_2}{V_1}$$ and I have converted my values to cubic meters and pascals. So Work Done, $W$, what would be the unit for that answer? I already ...
1
vote
1answer
46 views

Physical Meaning Of $ dQ/T $ Regarding Clausius Inequality: Is it related to Energy Loss in form of heat or Something Else?

What is the physical meaning of term $ dQ/T $ in Clausius Inequality $ dQ/T \le dS $ ? Physically we can relate entropy to number of microstates of a system, which relates to number of possible ...
3
votes
2answers
102 views

Why does a cooling car engine crackle?

Why does a cooling car engine crackle? What determines the frequency of the crackles?
2
votes
3answers
146 views

Interpretation of systems in different state of matters BUT almost identical configuration

For a start, let me clarify that by "almost identical configuration" I mean same volume, temperature and number of molecules (but different pressure). One could for instance take two identical systems ...
2
votes
1answer
60 views

How does the second law of thermodynamics follow from low entropy of early universe?

One of the explanations of the second law of thermodynamics is that it goes back to the low entropy in the early universe (How do you prove the second law of thermodynamics from statistical ...
1
vote
1answer
130 views

Total and partial derivatives in thermodynamics and Maxwell relations

Consider the expression $$dS=\left(\frac{\partial S}{\partial T}\right)_VdT+\left(\frac{\partial S}{\partial V}\right)_TdV$$ I'm trying to understand how to derive an expression for $\left( ...
1
vote
3answers
74 views

Why does the blackbody radiate even at thermal equilibrium?

Everytime, I read about blackbody, I always get confused at the point where it is written Under thermal equilibrium conditions , the blackbody radiation depends only on temperature. ..... . At ...
1
vote
0answers
70 views

Why doesn't the 1 dimensional ising model have a transition temperature?

Consider a 1 dimensional chain of spins that are able to either have the value $\sigma =$ $+1$, $-1$, from now on referred to as up and down. For the Hamiltonian $H = J \sum_{i,j} \sigma_i \sigma_j$ ...
1
vote
1answer
41 views

Heat Transfer and Thermal Energy

Some hot water radiators have a single pipe connected to them. The steam comes to the radiator and the water leaves in the same pipe. The steam and the water are both at a temperature of 100°C. Where ...
-5
votes
0answers
53 views

Why does hot food give off vapor?

Does your food melt and then boil to give off this gas? What is the vapor here?.
2
votes
1answer
33 views

Thermodynamics - ideal gas [closed]

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
45 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
55 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
49 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
34 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 ...
18
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
21 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
54 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
18 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
787 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
43 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
729 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?