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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Electromagnetic radiation and health issue

A lots of article even wiki tells that Cell phone radiation is very dangerous for health. Some people tell that it can be reason for brain cancer. A article Mobile phone subsides man’s sperms! ...
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51 views

Measurement of heat in electrons

Is there any method to measure the heat of an electron and if there is; then is it a constant or a variable.
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84 views

Can we apply $pV^\gamma$=const only for quasistatic adiabatic process?

But If this is so, I have often seen people applying this formula for quick processes where no heat exchange is possible. Here is an example from where I am quoting the following: we will assume ...
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1answer
21 views

Is heat added to an air bubble rising in water?

An air bubble was initially released from the bottom of an ocean. Assume that the air in the air bubble is an ideal gas and its temperature remains constant at 25 degrees Celsius. Is heat added or ...
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1answer
28 views

Spherical Shaped Electrical Leads for Thermal Conductivity Mitigation?

I am designing a thermionic converter and one of the biggest inefficiencies is the thermal conductivity and limited electrical conductivity of the leads. I'm trying to mitigate the loss of heat ...
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78 views

Why did everything in space cooled out?

Through my research, I learned that; According to thermophysics, heat always moves from and area of high heat to an area of low heat. Space has no heat at all. It is extremely cold However, ...
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1answer
31 views

Why is the outside run of high presure line on a ductless mini-split airconditioner insulated?

On every ductless mini-split air conditioner I've ever seen, both the high and low pressure lines are insulated between the compressor and the building. It seems like the liquid refrigerant coming ...
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1answer
35 views

Vapor-compression refrigeration

In a vapor-compression refrigeration system I would like to understand the following : Why is there a need for the compressor ? Can't the saturated vapor from the evaporator be cooled directly in ...
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2answers
34 views

What caused a fluctuating cloud to form in a jet engine intake on a humid day?

I was on a commercial flight in a 737 stationary at idle on a taxiway. It had recently stopped raining so the relative humidity was likely near 100% and the air temperature was about "light jacket" ...
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73 views

Units kT = 1… why?

Why is it convenient to choose units kT=1? It came up in this paper: http://jfi.uchicago.edu/~leop/SciencePapers/scaling%20and%20universality%20in%20statistical%20physics.pdf in page 4, equation ...
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1answer
69 views

Can you extract energy from “hot” things without a temperature differential?

I've been reading about extracting energy from heat, particularly Sterling engines. There's always a temperature gradient. Heat flows from the hot side to the cold side through the working fluid. As ...
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1answer
17 views

Perfect Ideal Gas Modelization of Air

I'm solving a Thermodynamic problem. I have Air at temperature of 293.15 K, and pressure of 20 MPa. I would understand if is possible to consider this an Ideal Gas or not (and if is possible which are ...
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How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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1answer
41 views

How much electricity could be generated by cloths made of thermocouples?

Lets say that we made a glove, shirt, pants and a hat out of the most effective thermocouple material available today. How much electricity would be generated by each, by a healthy person, on a cool ...
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3answers
2k views

What is the minimum pressure of a medium for which a sound wave can exist?

At what pressure will be particles in a medium be unable to form a sound wave when disturbed? How can this pressure be described mathematically? My guess is that this would correspond to the point at ...
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0answers
38 views

Free energy a continuous function of temperature but may not be differentiable everywhere?

So according to my understanding, the free energy of the system should be a continuous function of temperature. This is because if the free energy is not continuous at temperature T, then at this ...
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5answers
629 views

Why can't a gas be liquified by pressure above its critical temperature?

What is the cause behind a gas being difficult to liquify above its critical temperature no matter how much pressure is applied on it?
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1answer
42 views

Are all means of heating equally efficient? [duplicate]

In terms of cost of electricity, does it matter if I heat my room using a space heater, an open oven, a flood light, an ASIC? Assume no energy escapes the room, that the heat quickly becomes uniformly ...
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1answer
45 views

is boiling of water an isobaric process?

Is the conversion of water into steam at 100°C an isobaric process? It is an isothermal process, but does pressure rain constant during this process?Please explain as well..
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72 views

Boiling Pasta resulting in a Torus like shape?

I noticed when I was boiling pasta the other day that the pasta uniformly spread out and formed a donut like torus. Why does this happen? Does it have to do with the shape of the pot? I tried to take ...
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1answer
60 views

Why are ceramic containers used for hot beverages?

Why are ceramic containers used for hot beverages? For example, is it dangerous to use plastic? Are there any other reasons other than to protect hands from heat?
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1answer
36 views

What does adding a visible light blocking IR filter do with heat?

Lets say I have a strong halogen light source which has a lot of IR radiation (e.g. a construction lamp). If I change the transparent front glass from the enclosure with a IR filter that blocks ...
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0answers
27 views

Cost vs. purity producing liquid oxygen [closed]

We are a group of rocket amatures who build rockets using LOX and ethanol as propellent. We normally buy the LOX from supplier. But lately we have been discussing if there is an easy way to produce it ...
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1answer
17 views

Efficiency of a thermal reactor

I was told that the efficiency of any thermal reactor increases if it is operated at higher temperature- in this case, nuclear reactor was referred to. But I cannot seem to understand why...
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4answers
4k views

Why does cold metal seem colder than cold air?

(I apologize for this elementary question. I don't know much about physics.) Let's say that I put a metal pot in the refrigerator for several hours. At this point, I guess, the pot and the air (in ...
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1answer
68 views

Why does water freeze from top to bottom

I was wondering why water freezes from up to bottom and not the other way around. The reason I question this is because in a Video I came across, I discovered water freezes from top but surely with ...
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51 views

Building free energy directly from Lagrangian

Energy can be built from Lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. Free energy is a generalization of energy when the system exchanges heat with the ...
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153 views

Question on entropy

All of my textbooks mention, that entropy-change of all spontaneous physical, and chemical processes is positive, and that such processes need another condition to fulfill- decrease in the net ...
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I need to calculate the temperature of some flat copper wire as it loses contact with a chilled capstan roller

I need some help in designing a system for cooling wire as it comes off a resistance annealer. I need to calculate the temperature of that flat copper wire as it comes off a chilled roller (call it a ...
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85 views

How much energy does it take to cook a steak?

Grilling in the park today I started to wonder just how implausible a portable battery-powered grill would be. There are of course a lot of parameters in this question, so let's narrow it down for ...
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Effusion of particles from one box to another - pressure calculation

Suppose we have a container divided into equal halves. Right half is fixed at temperature $T$, volume $\frac{V}{2}$. Initially it has pressure $P_0$, a hole of area $A$ is opened between them. I ...
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3answers
113 views

Why can the entropy of an isolated system increase?

From the second law of thermodynamics: The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems always evolve toward ...
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1answer
58 views

Self Stirring Boiling Liquid

A couple of weeks ago, a friend and I were brewing a new batch of beer. We boil our wort in a turkey fryer. Pretty standard setup for beginners. Anyway, our wort was getting pretty close to boiling ...
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1answer
28 views

Thermodynamic potentials and approach to equilibrium

I have seen some material which tries to show that when approaching equilibrium upon different constraints, the changes in some thermodynamic potential is always positive or negative (for example, ...
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4answers
51 views

Why does my house seem to warm faster in summer than it cools in winter?

In summers when we switch off the air conditioner, the room seems to instantly get hot again. But in winter, when we switch off the heater the room seems to remain hot for some time. Why this ...
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761 views

How does heat actually stay kept in the carbon molecules in the atmosphere? [duplicate]

We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their ...
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60 views

Heat equation : boundary conditions?

Say we have a bar centered at $x=0$, that is heated. We have the 1D Heat equation which we can solve to find a parabolic temperature profile : $$\kappa \frac{d^2 T}{d x^2}=-\frac{Q}{L S}$$ with ...
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2answers
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If black and white object are in isolated space will the black absorb heat from the white?

This question has come to me from my friend in fact: he noted that the heating in the pub is painted black. I replied that it's better for heat emission. I don't know where did I know that from. And ...
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107 views

What would be non-ergodic physics processes?

As the title says, what would be non-ergodic processes that occur in statistical physics? Many textbooks do not really cover ergodicity really well so I ask this question. I can't suddenly remember ...
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2answers
58 views

Will a water-cooled system heat up a room less than an air-cooled system?

Recently - motivated by the recent heat where we live - an acquaintance argued that a water cooled computer will not heat up the room as much as an air cooled computer will. His reasoning was that the ...
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Thermodynamics of binary symmetric channels

I am reading this very interesting paper: http://m.iopscience.iop.org/1751-8121/41/40/402002/pdf/1751-8121_41_40_402002.pdf about thermodynamics of channels in information theory. More generally, ...
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2answers
80 views

Entropy was created after inflation?

I'm puzzeled by a statement in Big Bang Cosmology-review about the reheating phase subsequent to the exponential expansion during inflation: In this reheating process, entropy has been created ...
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1answer
47 views

How to prove R value for insulation?

I ran some tests on different types of insulation. I heated water, and placed it into an insulated box. The temperature was recorded every minute, for the water, as well as the air. The insulation ...
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1answer
78 views

Problem about thermodynamic relations

We know that for constant pressure thermodynamic processes, $dH=dQ_p$. My question is, does it implies that only reversible work is possible in this processes so that $dw=0$ because $dv$ is zero? In ...
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34 views

Irreversible heat engines strictly less efficient than reversible ones

I undertand how Canot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it isless clear why they need to be less efficient, as I have seen stated in ...
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Thermal Conduction through sphere

In general, a sphere with conductivity $\kappa$, heat capacity per unit volume $C$ and radius $R$ obeys the differential equation at time t: $$C\frac{\partial T}{\partial t} = \kappa \frac{\partial^2 ...
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2answers
41 views

Not Quasi-static, yet reversible process? Is this a valid example?

Imagine a gas (at room temp. and pressure) enclosed in a thermally insulating spherical container. At some instant, the container instantly expands symmetrically (radially outward) to, say, twenty ...
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2answers
66 views

Is every material able to exist in every state of matter?

I was shocked while reading Kittel's "Introduction to Solid State Physics", that the solid state of noble gases is a well described and makes one of the fundamental achievements of solid state ...
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19 views

How to calculate net power output of heated, expanding air?

I'm interested in designing and building a Stirling engine which uses air that has been heated, which expands and then acts upon a piston producing power. There is a fixed amount of air inside the ...
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Is tea weaker if you make it in a half full cup of water?

Imagine you put a tea bag in a cup and half fill it with boiling water. Then after one minute you take the tea bag out and then fill the cup up to fill with hot water. Will the tea be weaker than if ...