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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Why is $c_p$ higher than $c_v$?

why is heat capacity at constant pressure higher than heat capacity at constant volume? It is supposed to be this way, since if you increase $C_p$ in volume work is being done, in other case not. This ...
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53 views

Does a closed system with fixed entropy imply an isolated system?

Just first to clarify, my university notation is $$\text{change in entropy} = \text{entropy flow} + \text{internal production of entropy}$$ I am confused with the term fixed entropy. Does that mean ...
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1answer
32 views

Electrical conductivity of metals on heating

What effect does heating have on metals (to be specific, on the electrical conductivity) ? And why does it have that effect?
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1answer
46 views

Paramagnetic/ferromagnetic transition under a magnetic field

The paramagnetic/ferromagnetic phase transition is an archetypal example of a continuous (or second-order) phase transition. When the temperature $T$ approaches the Curie temperature $T_c$, the ...
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12 views

Why is the cloth cooled to a temperature below that of the hot wind? [duplicate]

When a wet cloth is hung up in a hot wind in the desert, it is cooled by evaporation to a temperature that may be or so below that of the air. Discuss this process in light of the second law of ...
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131 views

Why is it impossible to build an air filter that lowers the average velocity of the air molecules in a house?

Imagine a special air filter placed in a window of a house. The tiny holes in the filter allow only air molecules moving faster than a certain speed to exit the house, and allow only air molecules ...
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3answers
74 views

Speed of heat / quantification of heat and other magnitudes

Is the speed of heat infinite? When solving the heat equation in a semi-infinite bar, we can see that a pulse in the finite end draws an immediate change in every point of the bar. So, at any given ...
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1answer
89 views

Area under temperature time graph

I have an open desiccant heating system which has a flow rate of $0.7$ litres/sec, I have recorded the temperature profile after the air has been heated and plotted it against time in seconds. My ...
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1answer
20 views

How to convert the molar attenuation coefficient, ie. molar absorptivity, to heat capacity?

In spectroscopy techniques, such as infrared spectroscopy, light of a certain wavelength is absorbed. I see parallels to the concept of heat capacity, i.e. the heat necessary to change the temperature ...
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70 views

Double Pipe Heat Exchanger Flow Hot Cold

Based on sources I referred, I got to know that a double pipe heat exchanger operates in a way where hot water flows in a pipe and comes out as cold water and cold water flows into another pipe and ...
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36 views

when a steam is being liquified, does its temperature change or not?

Here is a question: When ice is being melted, its temperature doesn't change. So, when a steam is being liquified, does its temperature change or not? And is the heat transferred here calculated by ...
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65 views

Why is heat transfer better from within circular tubes versus ex. square tubes?

It is claimed that heat exchange, through the tube-suface, is best from within circular tubes versus either (not sure which is correct): from outside of the tube itself other shapes like for example ...
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54 views

How to relate internal energy to atomic motion?

I am trying to conceptualize how atomic motion leads to the thermodynamically-defined internal energy (denoted as $U$ below) through some broad mathematical relationships. I get that the internal ...
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1answer
24 views

What causes the black shimmering bands on a sun-lit surface?

I can't figure it out. I thought it was the window causing it, but even without it it happened. It seems to be the motion of the air that causes it, but why shimmering black bands? Sometimes this ...
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35 views

Thermodynamics of a rubber band

I have a streched rubber band and I know that tension f is proportional to the temperature T when the length is constant. How can I proove that internal energy is only a function of temperature? I ...
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31 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
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1answer
25 views

Measured temperature (thermometre set to emissivity of 1) of smooth surface too high or to low?

We want to measure the temperature of a smooth flat surface with a thermometre based on absorption of thermal rays. The emissivity setting of the thermometre is set to 1 (same as a black surface), ...
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2answers
106 views

Thermo - Plotting constant pressure and temperature on a Pv and Ts diagram

I was just curious what the saturation curve for water (plotting pressure versus specific volume) would look like if you drew both a line of constant pressure as well as constant temperature. I am ...
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1answer
178 views

Newton's law of cooling for the heat equation boundary condition

Newton's law of cooling says the temperature of an object satisfies $$ \frac{dT}{dt} = -k(T(t) - T_0),\tag{1} $$ where $T_0$ is the surrounding temperature. See these HTML notes for example. Now if ...
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1answer
67 views

Second law of thermodynamics (in terms of entropy)

Is the second law of thermodynamics (in terms of entropy) for closed systems or isolated systems? I thought it must be valid for isolated systems, such as the Universe. But the book Fundamentals of ...
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1answer
47 views

Does it mean the molecules of all matter above absolute zero temperature are moving? [duplicate]

According to my knowledge, heat is the energy that is stored in form of kinetic energy of molecules in Brownian motion. However, in a macroscopic view, a rigid body seem to be "stable" but still store ...
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4answers
243 views

Where does air pressure come from?

Where does air pressure come from? I thought it was from gravity or the speed of the gas resulting from its heat. However, analyzing my own hypotheses, I think that my 'heat conjecture' is probably ...
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1answer
58 views

Could you make a system that exchanges matter but no thermodynamic energy?

Normally we distinguish between open, closed and isolated systems, assuming that the 4th possibility does not exist, as an exchange of matter presupposes energy exchange. Could it be nevertheless ...
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32 views

Charles Law inverse for cooling?

Is the inverse of Charles law also true? If I double the volume, the temperature will be halved? In the fire service we ventilate a structure by opening up the ceiling to the attic. If the volume of ...
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3answers
120 views

Is heat from a stovetop, transfered through convection, radiation or conduction?

It doesn't appear to be convection, as there are no moving objects (or are there); probably not radiation (?), so it is conduction? I really don't know much about heat transfer and thermodynamics, ...
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2answers
309 views

Why energy at room temperature $= kT$ and not $(3/2)kT$ [duplicate]

I always see that a room temperature of $T=300\,\text{K}$ corresponds to an energy of $k_BT \approx \frac{1}{40}\,\text{eV}$. But shouldn't it be $\frac{3}{2}k_BT$ since the molecules in the air have ...
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Heat transfer coefficients

I am trying to make a model of non-stationary heating on a plate and I have questions considering coefficients. I am using explicit method to solve it (have to use it). I am not sure if I am using the ...
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1answer
27 views

Monoatomic fluids and free space around atoms

In monoatomic fluids the atoms can move quite freely around each other. Is there any thermodynamic/statistical mechanic equation how much free space there is between the atoms? This has to be ...
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1answer
82 views

Internal reversibility

The concept of reversibility always gives me a hard time.In a reversible process the change of entropy is zero. On the other hand for irreversible process it is not.But there comes another topic which ...
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40 views

Confusion regarding latent heat of fusion

During vaporizing there is higher increase in internal energy (higher positive $\Delta U$) and more work is done by the liquid (higher $W$) as molecules become widely separated. During melting, there ...
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1answer
1k views

How long would it take for a smelly object to evaporate?

This question is a follow on from this deleted one: http://physics.stackexchange.com/q/177894/26076 as I was writing what I thought to be a valid physics answer to it. Version 1 of this question ...
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1answer
55 views

Is the Landau Free Energy U-TS or βH?

I'm having a hard time figuring out the physical meaning of the Landau Free Energy density: $$f(\phi,\nabla\phi,T) = \frac{1}{2}|\nabla\phi |^2 + \frac{a(T-T_c)}{2}|\phi |^2 + \frac{b}{4}|\phi |^4$$ ...
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1answer
30 views

A question about Thermodynamics [closed]

Burning fuel in car engine produce more heat or burning that fuel in free space?
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47 views

What--is the Ultimate Limit of heat based off c? [duplicate]

As heat goes up, molecules start moving at a faster rate. A gas molecule, if unhindered, could speed across the United States in three hours. I don't even want to know about plasma. But if heat ...
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1answer
23 views

If Ionic crystals are heated up, where does the energy go?

Ionic crystal are poor conductors of heat, due to lack of delocalised electrons. So if they are heard up where does the heat go? Does it get dumped in the potential well created by interatomic ...
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1answer
61 views

Double Pipe Heat Exchanger

I have a metal plate and I need to transfer heat out of the metal plate to the atmosphere. Hence, I can use a double pipe heat exchanger which contains 2 pipes. But what if I just use one pipe and let ...
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0answers
46 views

Canonical or microcanonical ensemble?

What of this ensembles is more honest with natural thermal equilibrium? In microcanonical ensemble the sample is isolated, and we don't now the precise value of energy. By this considerations we have ...
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Why the non-analyticity of free energy function implies phase transition? And what's its connection with other 'higher level' free energies?

I have seen 'free energy' arising from several contexts in very different forms, and each contains different amount of information. For example free energy is defined as the logarithm of the ...
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2answers
55 views

Internal Energy questions

The first law of thermodynamics states that $\Delta U=q+w$ where $ΔU$ is the increase in internal energy of the system, $q$ is the thermal energy supplied to the system and $w$ is the work done on the ...
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1answer
46 views

Can a solar panel work with heat?

As we know that a solar panels due to the energy of light, but can we run a solar panel with the same amount of energy provided as heat?
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3answers
52 views

How much work do I need to convert 300ml of water from 25°C to 3°C? [closed]

A question on how to apply thermodynamics principles to figure out how much work is needed to hold 300ml water in room temperature at 3°C. So far I have: 1Cal for each degree per g of water. We have ...
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2answers
96 views

Ice when melted at zero gravity [closed]

I wish to know the behavior of ice at zero gravity, how ice will behave when melted at g=0? Thanks
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2answers
182 views

How does temperature relate to the kinetic energy of molecules?

In ideal gas model, temperature is the measure of average kinetic energy of the gas molecules. If by some means the gas particles are accelerated to a very high speed in one direction, KE certainly ...
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1answer
36 views

Counting the number of microstates that there are for a given configuration. How to prove this result?

I'm doing some statistical physics and I came across a result which I'm not sure how to derive. Any help? The answer turns out to be: Can anyone help with this derivation? Thank you :D
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2answers
78 views

How is the work done by a system turned into internal energy according to the first law of thermodynamics?

I have several questions about the first law of thermodynamics: When we have a force over a piston of a recipient with an ideal gas inside and that piston moves, we have work associated with that. ...
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2answers
91 views

Which one is colder? Zero temperature ice or zero temperature water?

I like to understand that which one of the following items seems colder, when we touch them? zero temperature ice zero temperature water Why? Thank you.
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2answers
164 views

How to calculate temperature of an incandescent bulb filament?

Suppose we have a light bulb, for which we know its power rating, like voltage of $12\mathrm V$, and power consumption of $10\mathrm W$. We also know it's a halogen bulb with a tungsten filament ...
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40 views

Physical interpretation of legendre transformations in thermodynamics

I have found this question(Physical meaning of Legendre transformation) and I have some questions regarding the transformations in thermodynamics, In thermodynamics we have: $$H= U+PV $$ $$F=U-TS ...
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1answer
49 views

“Definition” of internal energy

Conversation of energy implies that if we have a thermally insulated system which goes from state 1 to state 2: $$\Delta E_{12}=E(2)-E(1)=\Delta W_{12}$$ and the 1st law of thermodynamics ...
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How does the second law of thermodynamics affect the efficiency heat-to-work conversion, at the molecular level?

I understand the second law of thermodynamics in terms of the improbability of the high--and-low-velocity particles of a gas to separate themselves so that at one moment they are at different sides of ...