# 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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### 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) ...
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### 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 ...
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### 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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### 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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### 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: $$e_\text{Otto} = 1-\frac{T(4)-T(1)}{T(3)-T(2)}$$ ...
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### 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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### 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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### 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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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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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 ($U = 4(\... 1answer 62 views ### “Big Crunch” Ending of Universe? So, I am reading Introduction to Modern Cosmology by Andrew Liddle and have just learned that the universe is cooling as it is expanding. Now, I am mathematician knowing very little about physics, but ... 2answers 35 views ### Compressibility factor and deviation from ideal gas behaviour I have recently started to study the deviation of ideal gas behavior. The source from which I am reading doesn't give me an intuitive understanding of the compressibility factor. I dont understand how ... 1answer 45 views ### What is the relationship between Maxwell-Boltzmann statistics, Boltzmann distribution and Maxwell-Boltzmann distribution? [on hold] I have recently been studying some statistical thermodynamics and I am currently trying to understand all the different concepts of the course. I was wondering about differences between MB statistics, ... 7answers 14k views ### Recommendations for Statistical Mechanics book I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly I just want it to be thorough and to include all the math. And of course,... 0answers 17 views ### Landau Diamagnetism and Pauli paramagnetism In the conventional definition of Landau's diamagnetism we ignore the effect of spin-electron coupling and vice versa for the derivation of Pauli's paramagnetism. I want to know what would happen if ... 1answer 47 views ### An ideal black - body at room temperature is thrown into a furnace. It is observed that? An ideal black - body at room temperature is thrown into a furnace. It is observed that? (A) initially it is the darkest body and at later times the brightest. (B) it is the darkest body at all ... 1answer 62 views ### Specific heat capacity for Adiabatic process We can define infinite number of specific heat capacities between two temperatures(e.g$c_p ,c_v$) . Could we do that for an adiabatic process. As for adiabatic process heat addition or removal is ... 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 ... 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, ... 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 ... 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 ... 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 ... 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 ... 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? 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) (... 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 ... 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 ... 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 ... 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.... 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 ... 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 ... 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 ... 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) ... 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 ... 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 ... 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 ... 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 (... 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 ... 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 ... 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 ... 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 ... 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, ... 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$P_1 = 1atm$and$T_1 = 25°C\$. If we add an electric resistance to heat the water inside, we go through ...
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 ...