Tagged Questions

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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37 views

Energy from the Feynman-Kikuchi Partition Function

The Feynman-Kikuchi Partition function is given as $$Z_{FK}=K_\beta \int dx \eta(x) \exp \left(-\frac{x}{\beta}\right) $$ where $K_\beta$ is a normalization constant and ...
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0answers
44 views

How much energy would the Human Torch need? [duplicate]

I wasn't sure whether to put this in the SciFi section or here, but since I'm interested in a physical quantity,so I decided to ask it here. I was wondering about approximately how much energy would ...
1
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1answer
41 views

Capacitor-like-thing for controlling temperature of fluid?

I want to minimise the Gibbs' phenomenon like thing i.e. sudden peaks (temperature peaks here) in a container. Assume you have a cone where you want to block the transmittance of the temperature into ...
0
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1answer
53 views

Dark Matter as possible an explanation for Coronal Heating

It's my understanding that the mechanism behind Coronal Heating - why the Corona is so much hotter (> 1,000,000 K) than the surface of the Sun (6,000 K), and the mechanism by which the energy gets ...
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0answers
31 views

Simple Conduction Simulation

What is the simplest way to simulate heat conduction on a 2D plane? What I want to do is have 1024x1024 2D plane of uniform temperature 0°C and specify the temperature of a cartesian coordinate. ...
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1answer
67 views

Calculating height and evaluating the vicinity of a peak in a multiplicity function for a two-state paramagnet

I have to calculate the height and width of the multiplicity function for a two-state paramagnet. I'm supposed to do this analogously to the method in the text book, which I will try to outline below. ...
2
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3answers
104 views

Mixing mild and cold water, which one to pour first?

Suppose for example that a person like me likes his water in-between. A bit colder than the room temperature but not very cold. If you have a water dispenser that pours rtp water and cold water, which ...
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0answers
46 views

Is there an efficiency-optimizing layout of items in a refrigerator? [closed]

Is there some optimal layout of items, or types of items (characterized by size, shape, density, solid/liquid, etc) that will allow a common household refrigerator to function with optimal energy ...
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2answers
131 views

What to do when you are sitting in a closed room without any fan or AC

I suffered this today, when the solar panels of our college stopped to work. Imagine a situation in which you are sitting in a botany lecture conducted by a 73 year old man, who cannot speak loud and ...
2
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0answers
90 views

Why is thermodynamic equilibrium not reached by the system during a thermodynamic irreversible process?

In reversible process,due to infinitesimal steps,the system remains in thermal equilibrium(why?) . But in irreversible process, thermal equilibrium does not exist. What is the cause for this ...
0
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2answers
75 views

Liquid Nitrogen Expansion to Desired Temperature

I want to take liquid nitrogen in a pressurized container and spray it through a hose onto objects in a room. The container has a pressure regulator so I can adjust pressure as desired. The ...
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5answers
222 views
+100

How does dark matter collapse?: Entropy considerations

Inspired by this question. I believe that the usual explanation that preserves the second law of thermodynamics as an astrophysical gas cloud collapses under gravity is that the gas must heat and ...
4
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1answer
124 views

Why does the majority of smoke leave when flames appear?

When I burn wood, paper, or other plant matter, where there is a flame, there generally isn't too much smoke, but it I blow the fire out, smoke starts billowing up. It billows thicker and thicker as ...
3
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3answers
143 views

Are galaxies, stars, planets, and ultimately life in violation of the second law of thermodynamics? [duplicate]

How can we think about entropy in these situations? To my knowledge all of these structures are born out of gravitational interaction. However, it would seem that the formation of these more organized ...
1
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0answers
37 views

Heat transfer to a cube from one of the faces [closed]

Heat Flux= 10 MW Inlet water temperature = 28 degree centigrade for cooling purpose through a tube passing through the centre of retangular block of length 50 mm,height 30 mm and width 30 mm inner ...
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9answers
2k views

What is entropy really?

On this site, change in entropy is defined as the amount of energy dispersed divided by the absolute temperature. But I want to know: What is the definition of entropy? Here, entropy is defined as ...
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2answers
69 views

What is entropy of the universe? [duplicate]

What is entropy of the universe? What is the change in entropy of our universe? Is this change increases or decreases? If the entropy of universe keeps on increasing then what are the consequences? Is ...
1
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0answers
77 views

Milk-First School

I have always been struck by the huge amount of different arguments about the issue: When you make a cup of tea, the milk should be poured first or added to the cup after the tea? Wikipedia, ...
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5answers
556 views

Is speed an intensive property?

I remember being taught in elementary physics that while it makes sense to add volumes, masses, or heat, it makes no sense to add temperatures. As I wanted to use that to illustate some other issue, ...
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2answers
180 views

Thermal superconductivity

I have heard several times of the concept of "thermal superconductivity" (As opposed to "electrical superconductivity"), but I am unclear on exactly what that could mean. It turns out to be really ...
2
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2answers
69 views

Is enthalpy also valid for liquids and solids?

The definition of enthalpy is $$H=E+PV,$$ is it only valid for (ideal) gas? As this naturally comes from the first law of thermodynamics, $$dE=dQ+PdV$$ for a enclosed system of gas. Can we talk ...
2
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1answer
36 views

can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
3
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1answer
143 views

Why does the thermal conductivity of water decrease with increasing salinity?

Intuitively I would expect the thermal and electric conductivity to be positively related, and since electric conductivity increases with salinity, so should thermal. But according to this table ...
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1answer
71 views

Relationship between temperature and energy

What is the definition of temperature in relation to energy? I'm mostly interested in general dimensional terms. Is temperature the kinetic energy per mass? Or kinetic energy per volume?
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2answers
76 views

What's the difference between energy and temperature in field theory?

I'm familiar with the formalisms for both zero temperature and finite temperature field theory, but (somewhat embarrassingly) I don't actually have a good physical intuition for when physical ...
5
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3answers
805 views

Didn't we mess up with the temperature?

The following passage has been extracted from the book "The Feynman Lectures on Physics-Vol l": The mean kinetic energy is a property only of the "temperature." Being a property of the ...
1
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1answer
35 views

How to transfer propane from a SMALL cylinder to a SMALL metal cylinder [closed]

I made a metal cylinder that is the SAME size as my 400g propane cylinder (picture: here). I want to transfer ALL (or almost all) of the propane from the propane cylinder to my metal cylinder, ...
10
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2answers
360 views

How can it be that the sun emits more than a black body?

As far as I know, a black body is an ideal emitter. So how can it be that a non-ideal emitter emits more radiation than a black body? This happens only in a very limited area at around 500nm, but it ...
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2answers
145 views

Relations between pressure and temperature

I have several questions concerning thermodynamics and I order them in 4 points that may be related: What's the difference between heat and work at the atomic level? Isn't heat simply work between ...
3
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2answers
62 views

What materials are used in non thermal plasma?

While reading about non-thermal plasmas, I came across their ionization potentials(~1%), and other capabilities, such as their non Maxwellian energy distributions. At what temperatures, and pressures ...
3
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2answers
113 views

How much work will a human do to lift a weight?

I saw a pretty simple homework question here that asked how much work it takes to lift a 200 kg weight, and while the math for a basic answer is simple the weightlifter in me instead wanted to ...
2
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2answers
102 views

What happens at the subatomic level when energy is added to an atom?

For the sake of simplicity I shall use the hydrogen atom. I know that adding energy to the hydrogen atom means bombarding it with photons. I am curious about what happens to the quarks and electron of ...
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4answers
98 views

The conduction electrons in metals is a thermal phenomenon?

When applying an external electric field in a metal at absolute zero, there is electrical current? There must be thermal fluctuations in the electron's band to be occurs current?
3
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1answer
129 views

Entropy of a two-level system

Consider a two-level system with energies and degeneracies $\epsilon_0 = 0, g_0=1$ and $\epsilon_1 = \epsilon, g_1=4$. I can show that the temperature at which both levels are equally populated is ...
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1answer
42 views

minimum possible absolute temperature in the universe? [duplicate]

Sorry guys i went wrong in my previous question , actually my question is what is the minimum possible absolute temperature in the universe of what ever substance...?
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0answers
32 views

Is It Possible To Have Temperature Below Absolute Scale? [duplicate]

Guys I have a doubt Is it possible to maintain the temperature of any Substance Below the Absolute Scale?
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0answers
33 views

White bread toasted seems hotter than brown bread?

Ok this is a bit of a random question but I 99% of the time use white bread for toast and I always toast my bread the same amount and every time I take it out it's too hot to handle and the butter ...
5
votes
2answers
131 views

Why does the second law of thermodynmics only occur in the time dimension?

If I break an egg, how broken it is depends on "when" I am not "where" I am. Why is the time dimension special?
-1
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1answer
85 views

Heating up a room to 50 °C

Suppose I have an empty room of $24 m^3$ and I want to heat it to 50 °C, assuming the current room is well isolated and the current temperature is 20 °C. How much power (in Watts) would a single ...
2
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3answers
149 views

Why doesn't Euler's theorem provide an *absolute* energy scale

we know that for a one component system $$U= TS - PV + N \mu$$ Now all terms on the right hand side have well defined zeros, but the internal energy is known to be a relative quantity, with no ...
2
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2answers
103 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...
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1answer
61 views

Does the energy required to increase a volume of water's temperature increase as that temperature increases?

Obviously in a simple, classroom style experiment the energy required to increase water temperature is a constant and thus wouldn't change, but what if we made the experiment just slightly more real ...
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2answers
359 views

Are isobaric, isochoric, and isothermal processes quasistatic by definition?

Let us start from definitions, as they are given in many sources. A quasistatic process is an idealized processes that happen out so slowly that a system go through a sequence of states arbitrarily ...
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2answers
156 views

What if an asteroid the size of the moon hitting earth

Would we all parish due to excessive heat? Or would that be only limited to the area near the impact while as the people on rest of the earth would die from other phenomenons such as mega earthquakes, ...
6
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0answers
104 views

What are the implications for the AdS/Cft program if AdS is unstable?

To my understanding recent progress in the study of the non linear stability of AdS spacetime suggest that $AdS$ might be unstable. If this is true, what are the physical and mathematical ...
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1answer
31 views

Does it take a lot of energy to heat metals up?

Why does it take a lot of energy to heat metals? And to do it quicker it requires much more energy? What about the use of lasers would that be an efficient process that is quicker and requires less?
2
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1answer
121 views

When Fire meets Water

To preface, I am not a scientific mind, but a writer looking for some validity to a possible scene. That being said, please forgive me! In my scene, huge masses of fire are raining from the sky and ...
1
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0answers
67 views

What algorithms can be used to compute the binodal in a ternary Flory-Huggins theory?

What are the most popular algorithms used to obtain a binodal curve for the ternary mixture (starting from Flory-Huggins theory)? I would like to obtain a plot similar to the one calculated here ...
1
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1answer
50 views

How can momentum changes from individual collisions be considered as a whole?

I have a question about deriving the equation of kinetic theory of ideal gas $$PV=\frac{1}{3} Nmc_r^2$$ where $N$ is number of atoms, $c_r$ is root mean square of atom speed and $m$ is mass of one ...
1
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1answer
65 views

Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...