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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84 views
Math for Thermodynamics Basics
I am studying Statistical Mechanics and Thermodynamics from a book that i am not sure who has written it, because of its cover is not present.
There is a section that i can not understand:
...
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2answers
96 views
Why is Entropy expressed in terms of Enthalpy?
Why does ${\Delta}S_{m(fusion)} = \frac{{\Delta}H_{m(fusion)}}{T}$ ?
I always thought ${\Delta}S = \frac{dQ}{T}$
In this case does it mean $dQ = {\Delta}H$ ??
Why is it so?
4
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3answers
320 views
Is there a mechanism for time symmetry breaking?
Excluding Thermodynamic's arrow of time, all mathematical descriptions of time are symmetric. We know the arrow of time is real and we know the equations describing physics are real so is there any ...
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1answer
35 views
Can Joule's First Law of Thermodynamics be Applied to Atomic Charges?
James Joule established that all forms of energy were basically the same and interchangeable. My question is if thas law is relevant in particle physics. Can a positive charge and a negative charge be ...
4
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2answers
147 views
Dispersion relation and Heat Capacity
I have seen case studies of the 3D Debye model where the vibrational modes of a solid is taken to be harmonic with dispersion relation $\omega = c_sk$. It is said that for temperatures much less than ...
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3answers
163 views
Human as a heat engine
humans are heat engines. heat engines can't operate when the source and the sink are at the same temperatures and also if the temperature of the sink is higher than that of the source. in humans' ...
4
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1answer
108 views
Maxwell demon : how can the demon move the door without doing any work ?
Here is something that I never understood about Maxwell's demon paradox : in order to contradict the second law of thermodynamics, the demon must open and close the door without doing any work... But ...
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0answers
36 views
Relation for Temperature and Pressure starting from chemical potential
Assume we have a system filled with a specific substance. Inside the system there is a small box with an opening. Usually this would mean $T,p,\mu$ would all be the same inside the box and outside. ...
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2answers
78 views
Temperature change inside pressure chamber
Let's say there is a pressure chamber with some sort of sample / specimen (e.g. protein crystal) in it. Now I apply a certain amount of gas pressure, e.g. 10 or 20 atm. Let's say I use xenon as a gas. ...
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6answers
610 views
What are the various physical mechanisms for energy transfer to the photon during blackbody emission?
By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
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0answers
31 views
What is the meaning of $h_L - h_H$ for a heat engine?
My problem gives me a Carnot cycle heat engine with water as its working fluid, with $T_H$, $T_L$, and the fact that it starts from saturated liquid to saturated vapor in the heating process.
I need ...
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1answer
56 views
In $PdV$, what is the value of $P$? $P_1$ or $P_2$?
Say I have an ideal gas that has a known $P_1$, $P_2$, $T_1$, and $T_2$ undergoing a reversible adiabatic process. I want to find the work done so I must use $PV = RT$ to get the change in $V$, so ...
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0answers
97 views
Difficulties with understanding total entropy change and unavailabillty
Of course, I know the fact that the entropy of an isolated system never decreases. Neverthless what makes me confused about the entropy(or change of entropy) of an isolated system is the explanation ...
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1answer
66 views
Information bearing degrees of freedom of a quantum simple harmonic oscillator
I am trying to make sense of arXiv:physics/0210005. I am confused with the concept of information bearing degrees of freedom of a system mentioned at the very beginning. To verify the arguments of the ...
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1answer
58 views
Why is the equation for Entropy of an ideal gas that undergoes reversible change in T at constant Pressure like this?
Why is the equation for change in Entropy for a reversible change in $T$ at constant $P$ described as
$$\Delta S = n C_p \ln\frac{T_f}{T_i}$$
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1answer
58 views
Landauer's principle vs Wien's displacement law
Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of kTln2? If it is so, can we also argue ...
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0answers
35 views
Landauer's principle vs Rayleigh–Jeans law
Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of $kTln2$? If it is so, can we also ...
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1answer
82 views
Funny classroom experiments [closed]
I'd like to perform some weekly classroom experiments to keep my students interested and curious about everyday physics. Those experiments have to be quite easy to set up and not too easy to ...
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2answers
140 views
Behaviour of individual terms in Einstein-Smoluchowski fluctuation-dissipation relation
Consider a bath of Brownian particles at temperature $T$. If we sprinkle some larger particles in this (eg: pollen grains in water or dust motes in air), they'll diffuse with diffusion constant $D$ ...
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0answers
77 views
Rotational Constant and Moment of Inertia of Fluorine gas
I have come across some homework question on thermodynamics which needs me to calculate $B$ of $F_2$
My attempt:
$B= \frac{h}{8\pi^2cI}$ where $I=\mu r^2=\frac{m_1m_2}{m_1+m_2} r^2$
Atomic mass of ...
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1answer
75 views
Is there a relation between supersymmetry and entropy?
Considering that entropy denotes the level of order/disorder in a system, would it be possible for entropy and supersymmetry to exist at the same time? Or, are they entirely unrelated?
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3answers
234 views
Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?
Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
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2answers
87 views
How long will a water drop exist until it evaporates based on ambient conditions?
How long will a water drop exist until it evaporates based on ambient conditions? I am looking for a simple equation or table that would tell me how long a water drop may exist until it evaporates ...
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1answer
91 views
Sensible heat question (solving for temperature)
If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water.
Using $Q = mc(t_2-t_1)$ or ...
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2answers
122 views
Have negative pressures any physical meaning?
Some cubic thermodynamical equations of state predict negative pressures, have negative pressures any physical meaning? Could they be related to negative mass?
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1answer
80 views
Rate of Cooling
I was given the following problem:
Two objects have a temperature difference of 20 degrees C at time 0. Two minutes later, they have a temperature difference of 18 degrees. How long does it take ...
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1answer
78 views
What pressure or tension occurs in a glass jar when I pour boiling water inside?
Sometimes it happens that when you pour a boiling water into a glass jar, it cracks. Since glass is very hard material and resilient to pressure, the tension must be very high. Is it possible to ...
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0answers
43 views
How to solve state parameters using these givens for an ideal gas?
In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
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3answers
97 views
Determine the Dependence of S (Entropy) on V and T
Why can the equation $$dS= \frac{1}{T} dU + \frac{P}{T} dV$$ be expressed as $$dS= \left. \frac{\partial S}{\partial T} \right|_V dT + \left. \frac{\partial S}{\partial V} \right|_T dV \quad?$$
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0answers
130 views
Simple thermodynamics simulation software [closed]
Just looking for some simulator that I can model a simple boiler with a heat source, overpressure valve and steam tap so I can play around with some parameters and learn the fundamentals of heat ...
3
votes
3answers
257 views
How can my water cool down more quickly?
I have a cup and I can only pour hot water inside, I wanna know whether the heat will dissipate more quickly with more water or less water?
How about the occasion when my cup is well covered?
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1answer
73 views
Sketch p-v and t-v diagrams [closed]
I have been trying to sketch this diagram for the thermodynamic cycle below but I'm not sure how to go about it. Any help is appreciated.
Sketch the cycle below on p-V and T-V diagrams, showing shape ...
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2answers
279 views
Most efficient type of heat pump
Can I make a heat pump beat the Carnot efficiency? Why is the Carnot process the most efficient one?
If I have a heatpump that is sphere shaped, and cascaded in layers like a onion can I beat Carnot ...
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1answer
147 views
A formal procedure for thermodynamic relations
This is my third time taking a thermodynamics course (two in undergrad, one in grad), and I've finally become frustrated enough about something to post on here.
A lot of thermodynamic questions want ...
2
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1answer
37 views
Reconciling Units in Jeans' Criterion Formula
In "Physics and Chemistry of the Solar System" Jeans' Criterion is given as:
$\frac{GmM}{R_c} = \frac{3mkT}{2}$
... To me this suggests that on the left we have Joules, and on the right we have ...
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0answers
36 views
State equations in magnetic systems
Assume there is an isotropic magnetic material in a homogeneous field $\vec{H}$ inside of a long coil. The work done to the material is given by $\delta A = H dM$, where $M$ is the magnetisation of ...
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1answer
50 views
How hot would a disc have to be to create strong drafts that lift it upward?
I read this article on xkcd.xom, from its spin-off blog "What If?" and that answer made me wonder.
It was mentioned in that article that a very hot but indestructible box would eventually be able to ...
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1answer
82 views
Thermodynamics and electromagnetic fields
The energy density in an electromagnetic field is given by: $u = (1/2) <\vec{E}^2 + \vec{B}^2>$ where $<,>$ denotes the average over time. In a cavity it holds that $u= u(T) = ...
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0answers
71 views
How much money does an unused but plugged-in cellphone-charger waste in a year, if its not getting warm?
Is it right as xkcd states:
You can use heat flow to come up with simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day.
Or, more ...
2
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2answers
134 views
Why the temperature is getting lower when the universe is expanding
As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the ...
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2answers
137 views
Is there a formal definition of a macroscopic variable in statistical mechanics?
Intuitively it's easy to accept that the usual variables like temperature, internal energy, etc. are 'macroscopic', but does there exist a formal definition of a macroscopic variable?
In other ...
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1answer
78 views
A simple thermodynamic question? [closed]
I tried this question a lot of time and few day's earlier I also solved it correctly but I don't know why I am not able to solve it now. I can't get what link I am missing.
ques: 2 moles of helium gas ...
6
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2answers
148 views
When should I take wine out of the fridge - transient heat transfer problem
I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around ...
3
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3answers
260 views
Formulae for Heat Change and Internal Energy Change in a Thermodynamic Process
Today, we were being given a lesson on Thermodynamics when my brain encountered an error.
It is easy to derive that, $\Delta U$, the internal energy change for constant volume process is given by,
$$
...
4
votes
1answer
143 views
Energy equation for an open system
I teach undergraduate thermodynamics and I was quite ashamed that I couldn't explain to a student, the following. I thought I'd bring it to physics.SE in hope of providing my student a good ...
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2answers
131 views
Can low temperature plasma exist?
Plasma is ionized gas which as far as I know only occurs at high temperatures. When plasma cools down it tends to recombine with the electrons present and turn back into gas. But what if the ...
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0answers
30 views
Will humid air mitigate airborn dust due to neutralization of static electricity?
I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces.
My first question: is this above statement true?
If the answer ...
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1answer
40 views
What controls the heating ability of steamers?
Pictured below is a standalone steamer used for foaming and heating milk for milk-based coffee drinks like cappuccinos and lattes. They can be filled with water up to the pressure relief incorporated ...
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votes
2answers
240 views
Why is there a Global Minimum for the Morse Potential?
For Diatomic molecules, the Morse potential describes their potential energy as a function of separation distance between the two particles.
My question is, what is the explanation of of the dip ...
25
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1answer
942 views
Rubber band stretched produces heat and when released absorbs heat.. Why?
I always used to wonder why this happens..
when one stretches a rubberband to nearly it snapping point holding it close to your skin - preferably cheek(helps feel the heat), it emits heat. While ...
