Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (3)

2
votes
1answer
2k views

How relative humidity and temperature affect rainfalls

The question is simple as stated in the title. How relative humidity and temperature affect rainfalls? I can't find a satisfatory answer in the web. Who can help me to understand me this relation?
2
votes
1answer
188 views

Minimal Maxwell's Demon

I would like to understand where the waste heat is generated in the Maxwell's demon problem. To this end I've come up with the simplest scenario I can think of. If my scenario is workable I am hoping ...
2
votes
1answer
312 views

Gas pressure equalisation: Where does the excess energy go?

Assume for purposes of discussion a closed container with a concentration of gas on one side and near-vacuum on the other. We could let the gas pressure equalise naturally, or we could construct a ...
2
votes
1answer
177 views

can hydrogen stay frozen in vacuum?

I've look into the hydrogen state diagram, and it seems that it can be frozen under pressure. Question: Does this mean that hydrogen cannot be kept frozen in a vacuum chamber?
2
votes
1answer
1k views

Physics of the electric hot plate

For an electronics experiment, I began wondering about the electric hot-plates (specifically the temperature dependence over time). If I were to measure the given temperature over time, I assume that ...
2
votes
2answers
761 views

Is it Possible to have Adiabatic Processes other than $PV^\gamma$ for the ideal Gas?

Is it possible to represent an adiabatic process for an ideal gas by a formula other than $PV^\gamma=Const$?: Relevant Considerations: We always need to connect a pair of arbitrary points/states $A:(...
2
votes
2answers
603 views

Demonstrate magnets adhere to conservation of energy pursuant to the laws of thermodynamics

I am looking for a way to demonstrate that magnets adhere to the laws of thermodynamics, in particular the requirement that energy in a closed system be conserved. To adhere to the requirement that ...
2
votes
2answers
6k views

Why I will feel colder when I get out from a swimming pool? [duplicate]

A friend of mine told me that because water heat capacity is higher. He also mentioned that it was similar to alcohol on skin effect. Assume that there are 3 situations. 1. I did not get wet 2. I got ...
2
votes
1answer
317 views

Man on treadmill and energy/mass conservation

Suppose we put a very obese man inside a large air tight isolated room with a treadmill and he runs on the treadmill for 24 hours and at the end of the day he sees his weight has come down (mostly ...
2
votes
2answers
719 views

how does heat energy start to speed up a gas molecule?

If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero. What would the molecule do as it thawed out? Would it translate the heat energy into it's electrons ...
2
votes
1answer
235 views

Is a closed system receiving heat guaranteed to have entropy below maximum?

Isolated system will preserve its entropy unchanged (for fully reversible system) or it will increase its entropy (for system with irreversible processes). For a closed system, it can receive energy ...
2
votes
1answer
2k views

Understanding the Seebeck effect

Thermoelectricity is, as I understand it, the difference in voltage between the hot and cold ends of two dissimilar materials. If two materials are connected at two different junctions, the hot ...
2
votes
1answer
1k views

Heat exchange depending on coolant flow direction

Consider a simplest case of a heat exchanger - two parallel pipes of flowing liquids (say, hot and cold) that have physical contact along some part of their length. Hot water of a certain temperature ...
2
votes
2answers
89 views

In a gas of particles, how is the displacement vector related to the number density?

Suppose I have a gas of particles that is initially uniformly distributed so that the number density is $n_0$ (number of particles per unit volume), and then I displace the particles by the vector ...
2
votes
1answer
2k views

time dependence of temperature equalization

Suppose you have two thermodynamical systems $X_1$ and $X_2$ (for example water and air) with different temperatures ($T_1 > T_2$). Now put them into thermal contact. Is there a formula which ...
2
votes
1answer
64 views

Entropy change of an irreversible process

I know that there's a lot of questions about this subject but I couldn't find specifically what I want to ask so here it is: One of the consequences of Clausius's theorem is the fact that for any ...
2
votes
2answers
72 views

Will a glass of water left in the fridge evaporate?

A commenter suggested that a glass of water left in a fridge would evaporate. I couldn't tell if this is true. I don't want to do the experiment since it would take too long; so I thought instead I'd ...
2
votes
1answer
93 views

Two conflicting forms of equation of state of non-relativistic gas

I've run into two conflicting derivations of the equation of state of a non-relativistic gas. However, the derivations of the relativistic equation of state of both sources agree. I think maybe the ...
2
votes
1answer
65 views

Is zero heat capacity possible without violating the third law of thermodynamics?

Suppose we have a gapped system i.e. no gapless excitation is possible. If the thermal energy is insufficient to excite atoms from ground state to excited state of any kind (of a single atom or of a ...
2
votes
1answer
30 views

Derivation of Apparent Expansion of Liquid

The formula for apparent expansion of liquid in a container is given as follows: $$\triangle V=V_0{(\gamma_{l}-\gamma_{c}})\triangle T$$ Where $V_0$ is the volume of the liquid as well as the ...
2
votes
3answers
69 views

Does “IF isentropic THEN reversible” only holds for adiabatic processes?

I know that: IF adiabatic and reversible THEN isentropic First question: does the implication IF isentropic THEN reversible hold for adiabatic processes? Second Question: if yes to the above, are ...
2
votes
1answer
40 views

Is saying that “Heat always flow from hotter to colder object in a isolated system” equivalent to the second principle?

In other words, can we make exactly the same predictions as the second principle (that involves entropy) by this phrase without ever introducing entropy ?
2
votes
4answers
51 views

$ P = \frac {v^2}{R} $ derivation confusion [duplicate]

I have always had a confusion of why we use $ P = V I $ or $ P = I^2 R $ and not $ P = \frac {V^2}{R} $ for relating to power loss due to heat in high tension lines. I know there are a lot of ...
2
votes
1answer
131 views

How to make Temperature vs. Energy graph representing a phase change?

As we know that phase change graphs generally show a variation in the Temperature and time.The graph roughly looks like this. I guess that the shape of the curve will be the same. This is because ...
2
votes
1answer
37 views

Coefficient of Linear Expansion (Formula)

Quoting directly from my textbook: We define average coefficent of linear expansion in the temperature range $\Delta T$ as: $$ \bar \alpha = \frac 1L \frac{\Delta L}{\Delta T} $$ The ...
2
votes
2answers
90 views

Internal energy, Enthalpy, and Heat

Setting a general background for my question: We know that the equation of state for an ideal gas is given by: $$pv=RT$$ where: $p$ is the absolute pressure of the gas. $v$ is the volume per ...
2
votes
1answer
67 views

Does a ceiling fan air heat up the air?

I was laying in bed one day, looking at my ceiling fan, when I wondered, "Doesn't the ceiling fan, because it makes wind, cause wind chill, which 'wicks' heat away from me -> making me feel cooler, ...
2
votes
1answer
59 views

Physic explanation of some property of heat equation? [closed]

When I compute the heat equation, I found that gross of heat do not change,it is same as our real world.But as I know , the heat equation is found according to the way of heat conduction. Why the ...
2
votes
1answer
69 views

Maxwell Boltzmann distribution: Going from momentum to energy

I am learning about the Maxwell Boltzmann distribution, and am trying to convert the equation from momentum into energy, but I'm stuck on changing $d^n p$ into $dE$. I have the equation: $$ E=\frac{|\...
2
votes
1answer
244 views

What is the significance of the Debye temperature from a materials perspctive?

If I look at a table of different metals and their Debye temperatures, what does the variation in these temperatures tell me about these materials?
2
votes
1answer
149 views

What is the physical implication of Clausius inequality?

Clausius inequality is given as: $$\oint \frac{\delta Q_\text{res}}{T_\text{res}} \le 0\;.$$ From Carnot cycle, we get the equality relation as the entropy lost by the hot reservoir is the same as ...
2
votes
2answers
61 views

What is the mechanism of heat exchange of a bouncing ball?

Imagine a falling ball on a perfectly hard ground. The kinetic energy will be first converted into a deformation of the ball, then the ball will restore it into kinetic and heat energy and recover ...
2
votes
1answer
80 views

Our Perception of Heat [closed]

Our body temperature is roughly 37 degrees celsius (that is, when we measure our body temperature externally, by using a thermometer that measures the temperature of our skin usually between our arm ...
2
votes
3answers
1k views

How is the efficiency of a heat engine related to the entropy produced during the process?

I'm reading Schroeder's An Introduction to Thermal Physics. Regarding heat engines, it is stated: Unfortunately, only part of the energy absorbed as heat can be converted to work by a heat engine. ...
2
votes
2answers
67 views

Evolution of a system - Thermodynamic potential

There is something I don't understand about thermodynamic potentials. We know that the necessary condition for a system to evolve is an increase in entropy. For a system kept at constant volume and ...
2
votes
2answers
359 views

Why can't the Carnot cycle be used to operate automobiles, if its the most efficient?

Since the cycle proposed by Carnot (consisting of two isothermal and two adiabatic processes) is the most efficient one on which to run a heat engine, why do we use other, less efficient ones (like ...
2
votes
2answers
60 views

Quenching of binary alloy: Concentration equilibrium

I'm currently reading "Models for phase separation and their mathematics" by Paul C. Fife and there is a paragraph which I don't understand because I lack the necessary background in physics/...
2
votes
1answer
101 views

Black plastic balls on reservoir to reduce evaporation - why black?

The story is here It states: The balls sit on top of the water and block the sunlight from hitting it, helping to reduce water evaporation as well as natural contamination and certain ...
2
votes
1answer
80 views

Does relativity objectively define entropy?

In his undergraduate text "Spacetime Physics", Wheeler points out that there is always a fourth component to momentum and energy interactions, because the internal motion of the objects involved will ...
2
votes
1answer
856 views

Calculation of entropy change in irreversible cycles, meaning of $\delta Q/T$ in irreversible processes

Let's take the two cycles in the pictures working with an ideal gas. We perform one, and then perform the other. The cycle is made reversible by making the gas exchange heat with a heat bath having ...
2
votes
1answer
186 views

The outside of a steel teapot is hot to touch. Does this mean that the water inside is necessarily at least as hot?

Some teapots, like this one Are made from thin steel which conducts the heat of the teapot quite well, meaning that you can't comfortable hold the sides while they're full of hot water. Tonight I ...
2
votes
1answer
83 views

Finding the expression for the time it takes for a water tank to be half empty

The problem is to find an expression for the time it takes for a cylindrical water tank is half empty. I am given that the water tank has a diameter of $D_0$ and a hight $H$. The water outlet is ...
2
votes
2answers
1k views

what is the temperature (and pressure) of the oxygen inside an oxygen bottle?

In the hospital or in a lab, one can see the huge oxygen bottles. A question is, what is the temperature of the oxygen inside the bottle? And what is the pressure inside? We know the critical ...
2
votes
1answer
149 views

Why the heat capacity doesn't diverge in the Kosterlitz-Thouless (KT) phase transition?

The KT transition has a special properties that, during the phase transition the heat capacity stay finite (so the behaviour of the heat capacity cannot reflect any critical behaviours). However, the ...
2
votes
1answer
232 views

Why should slope of pressure versus volume always be negative?

I read that the slope of the pressure, ($P$), versus volume ($V$) graph should always be negative for thermodynamic stability, but there was no further explanation in the text. Could someone give an ...
2
votes
3answers
189 views

Feasible way to cool water (ice) to temperatures around -20 degree celsius

Is there an easy way to cool water to temperatures around -20 or -30 degree celsius that is economically and technologically feasible for a high school student. Can it be done using typical household ...
2
votes
1answer
108 views

2nd law of thermodynamics - thought experiment

I have designed this simple thought experiment that seems to contradict 2nd law of thermodynamics. Could you please find a mistake in my reasoning? ...
2
votes
1answer
181 views

Planck's postulate for oscillators or for light?

I know that Planck originally postulated that the energy of an oscillator in a black body was quantised to $E=nh\nu$ but did he know at the time that this meant the energy of light was also quantised (...