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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26
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5answers
5k 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 ...
6
votes
1answer
266 views

How to derive a physical model of temperature above the earth surface?

At a point on the surface of the Earth, if I go straight "up" a distance $z$ (radially outward from the Earth), I'd observe a temperature profile $T(z)$. The conventional wisdom from the meteorology ...
0
votes
2answers
249 views

scaling of motor power

For car engines, the cylinder volume is often associated with the engine power, which suggests scaling of the power as $L^3$ where L is the linear size. Consider a system consisting of a motor and its ...
1
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0answers
59 views

Can I run a pulse tube cooler in reverse to generate pressure oscillations?

Since a pulse tube cooler is basically a Stirling engine without moving parts running "in reverse", does that imply that when I keep the cold end at ambient temperature and apply heat to the hot end, ...
1
vote
1answer
162 views

Dimensional analysis of magnetic energy: dimensions of µ0 and H

When calculating the energy difference between the normal and the superconducting state in a superconductor at zero magnetic field, the result is as follows: Now I'm quite confident of this result, ...
7
votes
1answer
279 views

How do ice spikes form?

I recently saw this picture posted on Twitter which shows a so-called ice spike rising from an ice cube tray. I have read the Wikipedia page, but it doesn't mean much to me. My instinct was that it ...
2
votes
1answer
112 views

Would a super-hot object launch itself into the air?

In this XKCD What If, an indestructible hairdryer outputs 2 GW of power, turning the earth under it into gas: Periodic explosions of gas beneath the box launch it into the air, and it starts fires ...
-2
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3answers
227 views

How “things” radiate electromagnetic radiation? [closed]

How things radiate electromagnetic radiation? I don't ask why they radiate (higher temperature than 0K) but how they radiate this electromagnetic waves?
2
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1answer
269 views

Is a tankless water heater more or less efficient than an electric stove at heating water?

Consider the following scenario that I actually encounter frequently: I just finished washing a pot in the sink, and now I want to boil some water for cooking noodles. If I fill the pot with hot ...
0
votes
1answer
467 views

Understanding Charles's Law

Charles's law states that, The volume of a given mass of an ideal gas is directly proportional to its temperature on the absolute temperature scale (in Kelvin) if pressure and the amount of gas ...
-1
votes
2answers
56 views

Paraphrasing speed and heat capacity [closed]

Can we call speed the change in distance per time? Further, would you phrase heat capacity as change in heat per temperature or change in temperature per heat? The reason for this question is that ...
1
vote
0answers
58 views

commutators in an uncertainty relationship derived from a partition function?

The maximum information principle for the discrete case gives rise to a partition function (>>> see details here) $$Z(\lambda_1,\ldots, \lambda_m) = \sum_{i=1}^n \exp\left[\lambda_1 f_1(x_i) + \cdots ...
2
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0answers
78 views

commutator to entropy in an uncertainty relationship?

Question: Does there exist a commutator to entropy in an uncertainty relationship? Similar Energy and time for instance.
1
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2answers
126 views

Extreme heating by Sun on Earth- Can eggs be fried?

Will it be possible to fry eggs in Sahara desert by just keeping them under the sun? If so, then will the radiated eggs be any different? Or will we have to use the solar cooking concept to some ...
0
votes
1answer
450 views

Calculating the amount of dissolved gases in a liquid?

The most basic situation, water at room temperature, has dissolved oxygen, CO2, and more. Why is this? How would one calculate how much gas should be dissolved in any given liquid?
1
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0answers
114 views

Traditional Transfer Matrix on the Potts model — how it grows for strip lattices?

What is the transfer matrix size for a strip lattice of width $n$ vertices, with arbitrary $q$?? I am not sure if it is $q^n$ x $q^n$ or something else. Any reference is also welcome.
2
votes
1answer
259 views

Where does additional heat energy come from in isothermal step of Carnot cycle

According to widipedia: During step 1 (isothermal heat addition or absorption) the gas is allowed to expand and it does work on the surroundings. The temperature of the gas does not change ...
-1
votes
1answer
618 views

Costant volume gas thermometer [closed]

I have two constant volume gas thermometers, one with an ideal gas $pv=RT$ and the other following the Van der Waals equation $(p+\frac{a}{v^2})(v-b)=RT$. They are calibrated using the freezing point ...
1
vote
1answer
582 views

How is the distribution probability in the canonical ensemble derived?

I'm confused by the derivation of the canonical ensemble, namely the origin of the probability density, that is the Boltzmann factor. Here's what I have: We have a system of particles with ...
8
votes
1answer
2k views

Are two thin blankets significantly warmer than a single thick blanket?

Almost every source I can find online maintains that two 0.5 cm blankets are significantly warmer than a single 1cm blanket due to air trapped between the thin blankets. However, the thermal ...
-1
votes
1answer
147 views

Heat Sink Design-Choice of Material [closed]

I am currently designing a heat sink for OPA 549. Among the many considerations, for example, the choice of material, the geometry of heat sink, the design of fins and all the parameters that come ...
3
votes
2answers
148 views

The heat equation in relation to smoothing algorithm

Recently I learned about a technique in image processing, which has its roots in something called the 'heat equation' from physics. The original creators of this technique were inspired by the physics ...
7
votes
4answers
4k views

Can you make ice red hot?

This video clip allegedly shows an otherwise unspecified ice cube that turns red hot (and burns) due to induction heating. Can somebody explain how this works?
3
votes
2answers
1k views

Simple thermodynamics basics - can internal energy be calculated?

Well this got me stumbled, because I've been wondering what the "question" is. One of the example examns got the following question (strangely there are no supplied solution books): A $0.2 {\rm ...
6
votes
1answer
233 views

Can solar furnace achieve higher temperature than sun surface? [duplicate]

Can solar furnace achieve higher temperature than sun surface? I guess not, but I'm not sure about that. Can you check my reasoning: -------- My reasoning ----------- Consider Sun as a black body ...
-1
votes
1answer
131 views

Heat preserving performance of container relative to content

This question has been addressed in the case of a thermos bottle: Performance of a thermos bottle relative to contents I am asking the question again without the hypothesis that it is a thermos ...
11
votes
1answer
518 views

Thermodynamically possible to hide a Dyson sphere?

You build a Dyson sphere around a star to capture all its energy. The outer surface of the Dyson sphere still radiates heat at much higher temperature than the cold space background, so you're easy to ...
0
votes
1answer
46 views

What is the limit of vanishing density?

I've been asked to examine the limit of vanishing density for the virial equation of state derivation of $\left(\frac{\partial U}{\partial V}\right)_T$ and quite frankly, I have no idea what this is ...
-1
votes
2answers
164 views

Conditions for heat exchange and evaporation

I wonder if there is any law for heat exchange. I have learnt that heat exchange between systems occurs when the temperature of respective systems differ. But in case of evaporation, the process ...
0
votes
2answers
125 views

Temperature in a calorimeter [closed]

A closed calorimeter of negligible water equivalent contains 1kg ice at 0 degree Celsius. 1kg of steam at 100 degrees Celsius is pumped into it. Find the resultant temperature of the mixture. I ...
8
votes
2answers
262 views

radiation thermodynamics paradox

This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape. Consider two nested shells that are axisymmetric ellipsoids with the same ...
0
votes
1answer
80 views

Monotherm cycle, negative $Q_{net}$

In the demonstration of the Clausius theorem in classical thermodynamics my book uses the fact that $Q_{net}\le0$ is negative in a cyclic monotherm (meaning with one heat reservoir) transformation. ...
1
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0answers
61 views

Does time stand still at a phase transition?

For second order phase transition thermodynamic properties can be described in very general terms by their critical exponents. So at every transition the correlation length $\xi$ should diverge as ...
-1
votes
1answer
161 views

Temperature loss of a moving object

I would like to know how to calculate the temperature change of a moving object. For example if I throw a ball that is warmer than the surrounding air, how much would it lose form it's temperature in ...
2
votes
1answer
814 views

Pressure derivatives of the bulk modulus of materials? (Solved) [closed]

Isotherm bulk modulus is defined by $$K=\rho\left(\frac{\partial p}{\partial\rho}\right)_T=-v\left(\frac{\partial p}{\partial v}\right)_T$$ wherein $v=\tfrac{1}{\rho}$ is the specific volume. Studying ...
2
votes
2answers
553 views

Doubt over Kelvin-Planck statement of thermodynamics' second law

I have a doubt over the Kelvin and Planck's statement of thermodynamics' second law, in particular applied to a cycle. Let's take a Carnot cycle as an example, and let's call the first two ...
3
votes
2answers
1k views

Performance of a thermos bottle relative to contents

I'm not a physicist but I majored it at high school (a long time ago) and I study university math. Me and my roommate discussed whether the performance of a Thermos bottle is influenced by how full ...
2
votes
1answer
135 views

Clarification on the Seebeck Effect

Alright, I've been interested in the Seebeck effect lately, so I've been trying to learn it. From what I understand, this is measured with the Seebeck Coefficient, which gives you the $\mu\textrm{V}$ ...
0
votes
0answers
121 views

Please correct my understanding of Clausius-Clapeyron and latent heat

As I work a problem set, I'm being asked to calculate the latent heat associated with a particular phase transition of $NH_3$ (solid -> liquid, liquid -> gas, solid -> gas). I'm being told to perform ...
7
votes
0answers
289 views

Is a venturi pump feasible at very low pressure?

I need assistance (or experience feedback) in estimating if a Venturi pump would work at low pressure. A boiler under vacuum (10% atmosphere) will produce steam (at a given speed depending on the ...
2
votes
1answer
1k views

Thermodynamic cycles, when is the work negative/positive?

ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is ...
1
vote
0answers
262 views

ideal gas law modelization in a vacuum chamber

I am trying to model a pressure sensor in COMSOL. The basic work is that there is current flowing inside it, if the pressure of the gas around it drops down, the temperature goes down as well (ideal ...
1
vote
1answer
122 views

What sort of thermodynamic process is this?

I have to calculate the work done in this thermodynamic cycle: LINK. But the bottom bit of the cycle is something I've never seen before. I guess the curve in $pV$ space is given by $$\left( V- ...
2
votes
2answers
155 views

Is an ice globe the worst possible way to cool a drink (with ice)?

Given an alcohol solution and a mass of ice in whatever shape you like, is shaping it into a sphere the worst possible way to cool your drink without diluting it? If the ice starts off at a sub-zero ...
0
votes
0answers
36 views

How to compute the change in entropy of s system when the temperature is decreasing?

How to compute the change in entropy of s system when the temperature is decreasing? Such a question may be too general,then we may ask a special case:How to compute the change in entropy of Annealing ...
-2
votes
1answer
118 views

How do I calculate the work of a gas showed up on a graph? [closed]

I have this graph of a gas: Now, I need to calculate work of it, based on ABCD cycle of changes (that's a bit confusing to me, do I calculate AB, BC, CD separately?). How do I do it? Also, how can ...
3
votes
2answers
174 views

What are the largest thermal gradients achievable in a lab environment?

I am looking for a system capable of creating a gradient of $100\, \mathrm{K}/\mathrm{\mu \textrm{m}}$ on a $30\, \mathrm{\mu}\textrm{m}$ spacing of a system mounted on a Si-N membrane. My so-called ...
-2
votes
1answer
164 views

How to multiply Celsius and kilograms? [closed]

I have something like this: $$\frac{0.04\,\text{kg} \times 90\,^{\circ}\text{C} + 0.06\,\text{kg} \times 50\,^{\circ}\text{C}}{0.1\,\text{kg}} = T_k$$ Where $T_k$ is a temperature, in Celsius. But ...
3
votes
2answers
3k views

Time required for water to freeze

recently I was wondering if there is any specific formula in order to calculate how long it takes for certain liquids to freeze (especially water). I know this depends on: the volume of the liquid, ...
2
votes
1answer
459 views

How much does sunlight affect inside temperature?

Suppose we have a $3\cdot 3\cdot 3\,m^3$ room of which one side is glass. And suppose that the other 5 sides have no effect on temperature (super isolation). We know from physics how to calculate ...