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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1answer
55 views

An ideal black - body at room temperature is thrown into a furnace. It is observed that? [on hold]

An ideal black - body at room temperature is thrown into a furnace. It is observed that? (A) initially it is the darkest body and at later times the brightest. (B) it is the darkest body at all ...
7
votes
1answer
1k views

Inflating a balloon (expansion resistance)

I am doing a quick calculation on how to calculate the pressure needed to inflate a perfectly spherical balloon to a certain volume, however I have difficulties with the fact that the balloon (rubber) ...
22
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5answers
1k views

What is the status of Mpemba effect investigations?

There is this puzzling thing that is called Mpemba effect: paradoxically, warm (35°C) water freezes faster than cold (5°C) water. As a physisist, I've been asked about it several times already. And I ...
2
votes
3answers
68 views

Thermal energy of a system

If I had a hot cup of tea and I added to it cold milk, what would happen is that tea will lose some of its thermal energy to the milk. But why do we notice that our liquid is no longer as hot as ...
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2answers
112 views

If you lift something does the internal energy increase or remain unchanged?

So change in internal energy $\Delta U = q + w$; so in lifting an object you do work on it, thus increasing its internal energy. Is this correct? Sorry if this is a stupid question.
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2answers
166 views

Otto and Carnot efficiency comparison

Lets say both engines operate between same temperature limits. Carnot eff: $$ e_\text{Carnot} = 1-\frac{T(L)}{T(H)} $$ Otto eff: $$ e_\text{Otto} = 1-\frac{T(4)-T(1)}{T(3)-T(2)} $$ ...
4
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3answers
433 views

Distinguishable, Indistinguishable Paramagnetic Ideal Gas

In the canonical ensemble, the partition function for an ideal gas is given by: $$\frac{Z}{N!}$$ The factor $N!$ accounts for the indistinguishability of the particles of the ideal gas. What ...
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0answers
25 views

How is a irreversible process (conventionally) represented on a $T-S$ plane and why cannot it be (really) represented?

A reversible process can be represented on a $T-S$ plane, and the area under the curve is the heat exchanged by the system. On $P-V$ plane a irreversible process is conventionally represented with a ...
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0answers
8 views

I can't get the right solution to this thermal expansion problem [on hold]

The problem : A glass flask is filled to 'the mark' with 60 cm3 of mercury at 20 ºC. If the flask and its contents are heated to 40 C ºhow much mercury will be above the mark? $\alpha$ for glass : 9....
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4answers
1k views

Must a reversible engine be a carnot engine?

I have this homework question: "Show that any reversible engine operating between T1 and T2 is a carnot engine." I think I have a solution, but it feels very hand-wavy. We know that any process that ...
2
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0answers
189 views

Is Carnot engine the only reversible engine? [duplicate]

Is Carnot engine the only form of reversible engine? Is it possible to have a different form of reversible engine that goes through different processes? For a standard Otto cycle working with ideal ...
0
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2answers
43 views

Relation between entropy and internal energy

I am confused as to what is the relation between entropy and internal energy. Entropy is always presented as a measure of the randomness in a system. So when we supply heat to a well insulated system ...
2
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1answer
187 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
9
votes
2answers
255 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = 4(\...
-1
votes
1answer
62 views

“Big Crunch” Ending of Universe?

So, I am reading Introduction to Modern Cosmology by Andrew Liddle and have just learned that the universe is cooling as it is expanding. Now, I am mathematician knowing very little about physics, but ...
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2answers
36 views

Compressibility factor and deviation from ideal gas behaviour

I have recently started to study the deviation of ideal gas behavior. The source from which I am reading doesn't give me an intuitive understanding of the compressibility factor. I dont understand how ...
0
votes
1answer
45 views

What is the relationship between Maxwell-Boltzmann statistics, Boltzmann distribution and Maxwell-Boltzmann distribution? [on hold]

I have recently been studying some statistical thermodynamics and I am currently trying to understand all the different concepts of the course. I was wondering about differences between MB statistics, ...
10
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7answers
14k views

Recommendations for Statistical Mechanics book

I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly I just want it to be thorough and to include all the math. And of course,...
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0answers
17 views

Landau Diamagnetism and Pauli paramagnetism

In the conventional definition of Landau's diamagnetism we ignore the effect of spin-electron coupling and vice versa for the derivation of Pauli's paramagnetism. I want to know what would happen if ...
2
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1answer
62 views

Specific heat capacity for Adiabatic process

We can define infinite number of specific heat capacities between two temperatures(e.g $c_p ,c_v$) . Could we do that for an adiabatic process. As for adiabatic process heat addition or removal is ...
2
votes
2answers
66 views

How is one element capable of radiating (almost) every wavelength? [duplicate]

Black bodies are considered as emitting all wavelengths. A incandescent light bulb has (nearly/almost) also the continuous blackbody spectrum near-perfect color rendition. In this bulb is only one ...
2
votes
3answers
63 views

Flame shape and size(length) depending on gravity

How would the shape and size of a flame(from a simple candle for example) depends on the gravity? Suppose all the relevant information is known, like candle dimensions and its chemical composition, ...
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0answers
28 views

Problem in thermodynamics [on hold]

There is a 500 watt heater and a ton of wood. How much will the temperature of the wood increase over the course of 6 hours? P = 500 W m = 1000 kg t = 6 h = 21600 s c_wood= 1700 J/kg E = P * t ...
0
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1answer
31 views

Calculate how much air will cool from an amount of ice? [closed]

So, there are $3kg$ of ice at $-18$ degrees Celsius and $50kg$ of air at $30$ degrees Celsius. I need to calculate how much the air will cool by the time the ice reaches its temperature. I thought I ...
0
votes
1answer
110 views

Thermodynamics - mass of gas expelled

Question: An open vessel contains 200 mg of air at 17 degrees Celsius. What percentage of weight of air would be expelled if the vessel is heated to 117 degrees Celsius if the pressure is to ...
9
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4answers
11k views

What equation of state is needed for liquid states?

I'm familiar with the ideal gas law $$PV=nRT$$ but I don't think it applies to liquids like water. If I'm wrong, please correct me! If I'm right, then what equation of state applies to liquids such ...
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2answers
37 views

Is the top of an iceberg floating above the waterlevel equal to the expanding of the whole iceberg?

When water freezes it expands and is getting less dense. But is this expansion of the total iceberg equal to the top of an iceberg floating just above sealevel?
0
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1answer
22 views

At what rate does a wet clothing decrease the temperature of a human body?

The question is required for my project, but it is frankly too hard for me... The variables that I consider are: Human Body: 36.5(C) Air: 20(C) Sunlight Intensity: 1,368(W/m^2) Wind Speed: 20(km/hr) (...
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1answer
1k views

Otto cycle efficiency described in pressure ratio (instead of compression ratio)

The Otto cycle's thermodynamic efficiency is often described using the compression ratio: $$\eta_{th} = 1 - \left( \frac{1}{CR} \right ) ^ {k-1},$$ (where CR is the compression ratio, and k the ...
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vote
2answers
50 views

Why don't air cool over time?

Say you have a balloon full of a type of gas, it is completely isolate from everything else. Let the temperature of the gas be 20 degrees (or any temperature, it doesn't matter) Now, the ballon is ...
2
votes
2answers
117 views

Why does pressure decrease as velocity increases?

Bernoulli's principle states that as velocity increase pressure decreases. But higher the velocity, greater is the temperature and pressure must be high. Can you explain the situation in both the ...
3
votes
2answers
67 views

What is the time required for water at 10 deg C to reach room temperature?

I have a small container (100mm X 80mm X 60mm) filled with water at 10° C. The container is made out of Aluminum and is not insulated, and is resting on a wooden table. Room temperature is about 27° C....
8
votes
3answers
2k views

Is cooling really exponential?

I did the following experiment: I took boiling water, put a thermomenter (from Vernier hooked up to a TInspire calculator) into it and pulled it out. Then we started measuring the temperature it read ...
5
votes
2answers
57 views

Books on entropy [on hold]

What books introduce entropy in a intuitive, elementary way (at most, for a person with undergraduate physics studies)? The book should not necessarily introduce entropy in relation only to ...
4
votes
3answers
93 views

Is reversible work a point function?

The potential of a conservative force is equal to the reversible work done on or by a system. But since the potential of a conservative force is represented by a point function, this would seem to ...
1
vote
2answers
141 views

Rankine Cycle pressure

I don't understand why in (Ideal) Rankine Cycle we assume that pressure remains constant at the boiler and the condenser. Shouldn't water pressure change, when water goes from liquid to vapor (boiler) ...
3
votes
1answer
331 views

How to calculate the heat transfer rate between the liquid and the gas?

Let water (liquid) be in a chamber (with no heat transfer to the walls). The gas is the residual space above the liquid, meaning that the contact surface is the surface of the water. Given the gas ...
1
vote
1answer
215 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 ...
0
votes
1answer
62 views

Using the ideal gas law to figure final pressure [on hold]

I'm studying for the GRE and I'm happy with Charles', Boyle's and Gay-Lussac's laws. I'm doing some questions on the ideal gas law. Please hear me out. This may come across as a homework style ...
2
votes
3answers
128 views

Work done by an ideal gas expressed as change in potential energy of fluid

I get confused in problems where it is necessary to evaluate the work done by a gas that someway moves a mass. I'll make an example. Consider the tube containing mercury and an ideal gas in A (...
30
votes
6answers
14k views

Why does wet skin sunburn faster?

There is a popular belief that wet skin burns or tans faster. However, I've never heard a believable explanation of why this happens. The best explanation I've heard is that the water droplets on the ...
-1
votes
0answers
39 views

Does modern science discussed the concept of knowledge and the process of gaining it? [on hold]

I though of an idea is some extrapolation of the law of conservation of energy, and the second law of thermodynamics. It may come a bit philosophical, and I'm really interested if there is any field ...
4
votes
3answers
67 views

Enthalpy of condensation

suppose we have one mole of an ideal gas undergoing a phase change at constant temperature. we know that enthalpy change is given by the formula $n\cdot Cp\cdot\delta(T)$. since there is no ...
0
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0answers
28 views

Specific Heat of tissues vs kcal (Weird Thermodynamics question)

I'm a YouTuber who over-examines video game physics for the purposes of both education and entertainment, and I've run into a bit of a snag while researching my next video. I'm looking into heating ...
5
votes
2answers
380 views

Why did our universe become transparent to light approx. 300,000 years after the Big Bang started?

Most books say that at age 300,000 years, our universe had cooled to approx. 3000 degrees Kelvin, which allowed free-electrons to bind with atomic nuclei, which allowed light to travel, unimpeded, ...
1
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0answers
79 views

How much time it takes to boil water in a rigid body?

I have a question that bothers me. If we have a rigid container containing water at $P_1 = 1$ $atm$ and $T_1 = 25$ $°C$. If we add an electric resistance to heat the water inside, we go through ...
3
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2answers
99 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?
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0answers
12 views

ploting probability distribution of energy in Canonical ansambel [on hold]

To reproducing fig3.3 statistical mechanics pathria, probability density function of energy: $$p(E)\quad \alpha \quad e^{-\beta E} g(E) = e^{-\beta (U-TS)}~ exp{(-\frac{(E-U)^2}{2KT^2C_V})}$$ . I ...