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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Chemical potential in terms of temperature and pressure

For part (a), I know how to take the partial derivatives of S to get chemical potential, pressure. But there seems that I still need one equation to correctly express chemical potential in terms of ...
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1answer
84 views

Can water evaporate when frozen?

If an ice cube is stored in a freezer could it evaporate given enough time? Is there a temperature below which water cannot evaporate (even just a little)?
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16 views

Water Displacement in the Oceans As a result of Global Warming [duplicate]

Not sure if this is the right place to ask this but here goes. If the north pole ice sheets melt, everyone agrees this would be a bad thing, however one of the reasons they state for this being a bad ...
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2answers
50 views

Does the ice melt faster when breaks free from larger sheet and drops into Antarctic Ocean waters?

My question is, when Ice is intact with the large sheet and exposed only to air, it melts at some pace. But does it melt faster or slower when the big piece breaks free from the sheet and drops into ...
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2answers
123 views

Thermo-Emf variation with temperature

In the following experiment for seebeck effect After a certain temperature, the thermo-emf begins to fall. Why does this happen? What is happening microscopically at this level to cause such an ...
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2answers
359 views

If temperature is average KE per particle, and heat is total KE of all the particles, how can molar heat capacity vary?

If temperature is defined as the average kinetic energy per particle, and heat energy is defined as the total kinetic energy of all the particles (or more strictly, heat transferred is the total ...
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36 views

How to calculate the amount of energy in joules/s that gas oven uses?

I know there may be missing information, but my question is really simple and yet I haven't found an answer to it. To make things easy, let's assume we have a $40×40×40$ cm oven that we want to keep ...
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2answers
128 views

Description of the heat equation with an additional term

I have the following equation: $$\frac{\partial U}{\partial t}=k\frac{\partial^2 U}{\partial x^2}-v_{0}\frac{\partial U}{\partial x}, x>0$$ with initial conditions: $$U(0,t)=0$$ $$U(x,0)=f(x)$$ ...
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34 views

Would adding water after heating decrease the overall heat, when compared to adding the water before heating for the same period of time?

I was rather cold last night, and warmed up a cup of water to drink in the microwave. I put it in for 60 seconds, but it came out boiling hot, so I put a bit of cold water in with the hot water, and ...
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341 views

Why does a water drop on a hot plate at $150^o C$ evaporate faster than on a plate at $200^o C$?

I recently read that: "A drop of water landing on a hot plate at $150^o C \:(300 F)$ evaporates in a few seconds. A drop of water landing on a hot plate at $200^o C \:(400 F)$ survives a whole ...
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First law of thermodynamics applied to atmospheric fluid

I was reading an article that talks on a climate prediction model. This article proposes the following equation (energy balance): $$\rho_0 c_v\left( \frac{\partial T}{\partial t} + \sum^{3}_{j=1} ...
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How come evaporation is possible? [duplicate]

If I have wet clothes and put them on the ground and let the Sun shine on them, they dry as water evaporates. But water should evaporate at 100 degrees Celsius so how come they go dry if it's just ...
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7answers
3k views

Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?

The oil, vinegar and other liquids in homemade salad dressing separate into layers after sitting for a while, making the mixture become more organized as time evolves. Why doesn't this violate the ...
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1answer
59 views

What causes a heat generating source to stabilize at a certain temperature? (Answered by myself, I think)

For example, we out a heat sink on a microprocessor to keep it cooler. I understand that if we run 100 watts of electricity through the microprocessor, it will generate 100 watts of heat, or 100 ...
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3answers
229 views

What makes now special?

I recently came across the paper Relation between the psychological and thermodynamic arrows of time (arXiv). Their argument makes sense to me, however their concept doesn't seem to address what ...
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0answers
15 views

Understanding how clouds form: warm air near the earth's surface?

I'm trying to understand how clouds are formed. I've read that it begins with air near the earth's surface heating up. But I'm hearing two different reasons for how this happens: Air pressure near ...
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1answer
45 views

Heat generated on thin disc plate in magnetic field [closed]

There are the eddy currents in thin circular copper plate thickness h and radius a, in a harmonic magnetic field which is perpendicular to plate and the effect of auto-induction is negligible. Now we ...
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2answers
141 views

Is there an equation to calculate the average speed of liquid molecules?

I seem to remember from first year physics that we can calculate the RMS speed of a stationary, ideal gas with $v=\sqrt{\frac{3RT}{M}}$. Does a similar equation exist for liquids?
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3answers
75 views

Is it possible to have $\Delta T\neq 0$ with no heat exchange $Q=0$, no work $W=0$ done, and no change in internal energy $\Delta E=0$?

Is it possible to have $Q=0$, $\Delta E=0$ and $W=0$, but $\Delta T\neq 0$? In particular, if there is no change in internal energy, doesn't that imply it is an isothermal process, and therefore that ...
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0answers
64 views

How to design a house to be cooled passively? [closed]

I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about ...
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3answers
920 views

How does cold air move through a room

If you turn on a fan in a warm room, it feels as if cold air is being pushed from the fan out in the direction that it's facing, but what's actually happening on a molecular level? When an object is ...
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3answers
235 views

Thermal physics question, final temperature of ice and water

Here is the question from my textbook: "In an insulated vessel, 250g of ice at $0^{\circ}$C is added to 600g of water at $18^{\circ}$C. What is the final temperature of the system?" The solution ...
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2answers
257 views

Chemical potential in Thermodynamics

In many scenarios, on computing the partial derivative of the internal energy (U) with respect to mole number (N) is negative. This implies that adding more moles of the substance decreases the U of ...
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1answer
36 views

Thermal Physics, Specific Question [closed]

Question: The melting point of copper is 1080 degrees Celsius and its heat of fusion is 200 kJ/kg. If a copper coin at this temperature is completely melted by the absorption of 2000 J of heat, what ...
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40 views

Given partial derivatives find the state function

I have to find the state function of a gas (which under very low pressures behaves as an ideal gas). So, first I tried writing it as part of an equation $ dV = \dfrac{\partial V}{\partial T}\ dT + ...
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3answers
75 views

Gas vs electric cooking

I've heard it said many times that you're more likely to burn food on an electric stove than a gas one, but I can't tell a difference. This seems to me to be a fallacy perpetuated by the natural gas ...
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2answers
136 views

Entropy $dQ=TdS$ and Work $dW = -pdV$ conditions?

What are the conditions in order for the equations: Entropy $dQ = TdS$ and Work $dW = -p dV$ to work? I think for $dQ = T dS$, it must be a reversible process? But for $dW = -p dV$, shouldn't it ...
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52 views

Do reversible processes exist in Nature?

Classical thermodynamics always discusses entropy in the light of reversible processes, and it lies at the heart of the definition of entropy. But do these reversible processes exist in Nature, or are ...
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20 views

Snowmaking in the tropics - an estimate of water evaporation

If I set up a snowmaker in the tropics and sprayed water with it how much water would I evaporate? How would I calculate?
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2answers
70 views

What is $k$ in Newtons Law of Cooling? [duplicate]

I am writing the definition of quantities for Newton's Law of Cooling and am not sure what to actually call k$,$ or its units. This is what I have so far $$\frac{dT}{dt}=-k(T-T_s)$$ Where ...
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1answer
21 views

Rate of radiation of infra-red ray from a hot body?

I have the equation $\frac{dE}{dt}=a(\tau^4-\tau_s^4)$ however I can't find anywhere what E is supposed to be. It is not pointed out anywhere in the text and what is confusing is that in engineering E ...
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4answers
2k views

Where does deleted information go?

I've heard that, in classical and quantum mechanics, the law of conservation of information holds. I always wonder where my deleted files and folders have gone on my computer. It must be somewhere I ...
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1answer
86 views

How hot does the upstairs need to be before it will heat the basement through convection?

During the winter we keep the basement door closed so that the cold air from upstairs won't flow into the basement. Then we heat the basement and the upstairs gets heated partially by conduction ...
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1answer
37 views

relation between isothermal process and its surrounding

"In an isothermal process the temperature of a system remains constant but may or may not be similar to temperature of surroundings" How is this possible ??
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93 views

Information or Matter or Energy

Which one is the most fundamental of the universe? What it is made of? Physicists are searching for unique and fundamental form. The question is , information is more fundamental than energy ? ...
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1answer
166 views

What does 1/k represent regarding Newtons Law of Cooling?

What does 1/k represent regarding Newtons Law of Cooling? I know k represents the cooling constant. I think the inverse of k is the time taken for the liquid to cool from its maximum temperture to ...
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1answer
48 views

Suggest why electrical power input P1 differs from power used P2

We have done an experiment heating water with a wire element and have determined it takes 21.5964 watts to heat 200ml of water to a specific temperature in 10 minutes. However the power of the ...
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2answers
54 views

Why does hydrogen give up its electron to a platinum catalyst?

All descriptions of a Hydrogen fueled fuel cell (such as this one) Start with $H_2$ giving up its electrons to a platinum coated anode. Then the $H^+$ ions (protons really) travel through the ...
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Do COBE, WMAP, and Plack have design flaws? [duplicate]

MRI expert Pierre-Marie Robitaille on the design flaws of COBE, WMAP, & Planck and the violation Kirchhoff's Law: Here are his talks: Pierre-Marie Robitaille: The Cosmic Microwave Background ...
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Does transverse flow always assist in mixed convection?

I am dealing with both natural convection and transverse forced convection over a flat plate. There are 4 different situations: Upward-facing cold plate Downward facing cold plate Upward facing hot ...
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1answer
68 views

Using Jacobians to prove an identity

I have to prove the identity $$ \left(\frac{\partial U}{\partial V}\right)_T=T\left(\frac{\partial p}{\partial T}\right)_V-p $$ I know how to do this using Maxwell's relations, but the assignment ...
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2answers
126 views

$E,H,\rho,\vec{j}$ intensive? $B,D,\Phi,\vec{A}$ extensive? Why not $ DdE,BdH ,\Phi\delta\rho,\vec{A}\cdot \delta \vec{j}$ as infinitesimal work?

$u$ is the e&m field energy $\frac{\partial u}{\partial t}=H\cdot \frac{\partial B}{\partial t}+E\cdot \frac{\partial D}{\partial t}$ Compared with thermo physics: $PdV,TdS,\mu dN$ ...
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0answers
29 views

Cooling - in vs out? [closed]

Suppose I have a 20x20x20 c"m plastic box where the top cover is open. On the top cover there is a fan ( 20x20 cm) which suppose to cool a cpu which is in the box . At the bottom there is a CPU ...
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0answers
40 views

Landau free energy

I am reading the statistical mechanics by Pathria in Chap 12. I have a question about the Landau free energy. What is the physical reasoning for that the free energy could be a functional of the order ...
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1answer
90 views

Why a mono-atomic crystal layer (2D) can't be stable?

According to Peierls and Landau, 2D crystals were thermodynamically unstable. They can't exist! Of course, this theory was disapproved in 2004 (example: graphene). What is the general definition of ...
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51 views

Heat transfer in infrared

Why does the most of the heat transferred on Earth come from infrared part of electromagnetic spectrum?
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1answer
51 views

When the matter is heated does the photon absorbed by electrons of atoms or by atoms themself?

When the matter is heated does the photon absorbs by electrons of atoms or by atoms themself?
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29 views

Heat energy in special theory of relativity [duplicate]

Is heat energy invariant under Lorentz transformation? If so then how?
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3answers
473 views

Would being underwater help survive a nuclear bomb?

If I jump in my pool, on the river near my house knowing that a nuclear bomb, or atomic or H-Bomb exploded around 10 km from my house, would I survive? The way I see it is that water will protect me ...
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1answer
67 views

Why are intensive variables easier to control than extensive?

In a IUPAC Technical Report (Alberty, Use of Legender Transforms in Chemical Thermodynamics, pdf) I have found the following assertion (p. 1359): "Intensive variables are introduced because they ...