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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How to measure the energy consumption class of a home appliance?

Some of you may be familar with the EU energy consumption classes for domestic appliances (or equivalents in other areas). Let's say we have a dometic appliance which was made before the energy ...
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1answer
10 views

Total multiplicity and entropy of Einstein solids

This is really a question to get a little more insight about a homework exercise. 1. In my text book, the sum of multiplicities for all possible macrostates is given to be: $$\sum ...
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0answers
28 views

Are temperature increases discrete?

Are temperature increases ever discrete in nature, or is it a continuous variable? If a discrete case exists, is there any material that exhibits particularly strange behavior?
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1answer
33 views

Making fire using a filled water bottle

I have seen videos where a fire was started using a water bottle filled with water. I guess the bottle acts like a convex lens that converges light to a focal point to start a fire. But why does water ...
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6answers
479 views

Why is it natural to look for solutions involving dimensionless quantities?

While studying the Heat Equation, I got stuck in a statement in my book. It says "We have seen that the combination of variables $\displaystyle \frac{x}{\sqrt{Dt}}$ is not only invariant with respect ...
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1answer
44 views

Why is density an intensive property?

I am still trying to understand what are intensive and extensive properties. Possibly someone can give a pointer to a decent text (preferably on the web), as I am not too happy (to say the least) with ...
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0answers
18 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
41 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 ...
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1answer
31 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 ...
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1answer
50 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
24 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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26 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. ...
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2answers
69 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
34 views

Given the Gas, Temperature and Pressure find Volume? [on hold]

Give the specific volume of carbon dioxide at -20 C for 2000 kPa and for 1400 kPa. I am getting ready for Thermodynamics class so I've been reading the textbook and doing some questions, I can ...
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0answers
37 views

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

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
81 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 ...
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1answer
19 views

Is average air temperature related to near shore water temperature? [on hold]

Basically my wife booked to go on a beach based holiday but cloudy and only warm conditions are predicted for the area- does that mean the water is likely to not warm?- we are sensitive to cold. Its ...
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0answers
49 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 ...
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2answers
42 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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4answers
75 views

Entropy and dark matter structure

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 ...
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1answer
68 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 ...
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3answers
82 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 ...
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0answers
36 views

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

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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8answers
1k 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
58 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 ...
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55 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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3answers
372 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
164 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 ...
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2answers
54 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 ...
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1answer
25 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?
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1answer
85 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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0answers
24 views

What is the “cold accumulator” liquid that is ruined at hot-room temperatures? [closed]

There are a few kitchen gadgets which use a liquid (or gel?) as a heat buffer. A class of them warns never to warm the gadget above 35 Celsius. I have an ice cream maker whose bowl is filled with this ...
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1answer
59 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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13 views

Heat transfer through a slab with both conduction and radiation [closed]

A solid slab made of Tantalum of dimensions l(length)=15cm, b(breadth)=6.25cm and t(thickness)=0.5mm , is heated from the side txb (Thickness x Breadth) using some electrical energy of 6 x 10^4 ...
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2answers
63 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 ...
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3answers
732 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 ...
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1answer
32 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, ...
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2answers
278 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
67 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 ...
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2answers
40 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 ...
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1answer
52 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 ...
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2answers
53 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
86 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?
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1answer
97 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
31 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
26 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
30 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
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2answers
128 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?
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1answer
71 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 ...
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3answers
134 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 ...