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 does internal energy remains constant in isothermal system?

how to write this answer for 2 marks question simple and straight answer. Please
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2answers
24 views

Ice at zero gravity

I wish to know the behavior of ice at zero gravity, sound at zero gravity. How ice will behave when melted and how sound will break a closed glass at zero gravity vs g on earth? Thanks
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2answers
72 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
32 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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4answers
1k views

Which one true in First law of thermodynamics: $Q = \Delta U \pm W = \Delta U \pm p\Delta V$ or $\Delta U= \Delta Q + \Delta W $?

Which one true in First law of thermodynamics: $Q = \Delta U \pm W = \Delta U \pm p\Delta V$? (where $\Delta U$ is change of internal energy, $W$ work made by system and $Q=cm\Delta T $ heat made ...
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1answer
17 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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4answers
714 views

Why do high current conductors heat up a lot more than high voltage conductors?

120 volts x 20 amps = 2,400 Watts However, if I increased the voltage and lowered the current, you can also use a smaller wire size (more inexpensive), also have less heat and achieve the same watt ...
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31 views

Thermodynamics - Gas Laws [on hold]

Can anybody please help with the following problem? The compression ratio of an engine is 16:1. The volume of air in the cylinder is $0.5 \,\mathrm{litres}$ at a temperature of $30 ...
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2answers
44 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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12 views

Compute the temperature of the reservoirs between which the engine operates [on hold]

An ideal gas for which $c_v$ = 3R/2 is the working substance of a Carnot engine. During the isothermal expansion the volume doubles. The ratio of the final volume to the initial volume in the ...
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31 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
27 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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1answer
287 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
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1answer
29 views

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 ...
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1answer
37 views

Zero volume at zero Kelvin

Why does the volume of a gas become zero at 0 Kelvin? Can a Bose Einstein condensate be considered as matter? (I mean the volume becomes zero)
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1answer
65 views

Historical Survey of Statistical Mechanics

Statistical mechanics is a subject with a particularly rich history. I think of the early debates of Boltzmann and Loschmidt, the rather confusing differences between the approaches of Gibbs and ...
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1answer
29 views

Sufficient conditions for Equipartition Theorem to hold

I was wondering what are the sufficient conditions for the Equipartition Theorem. I know there is another question (For which systems is the equipartition theorem valid?) that somewhats answers this ...
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2answers
81 views

Thermodynamics : Work done on gas inside container by the force due to pressure exerted by external atmosphere

Suppose a container is fitted with a massless and frictionless piston lying on a table such that pressure due to gas is greater than pressure due to external atmosphere. Hence piston will move. Now ...
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1answer
16 views

Why is work done by an otto cycle along the 2 adiabatic curve negative?

I define the work done by the system as +dw and work done on the system as -dw. Looking through my notes on Otto cycle, I observed that the for the two adiabatic curves in a clockwise cycle such that ...
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1answer
144 views

Why is thermodynamic equilibrium not reached by the system during a thermodynamic irreversible process?

In reversible process,due to infinitesimal steps,the system remains in thermal equilibrium(why?) . But in irreversible process, thermal equilibrium does not exist. What is the cause for this ...
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2answers
33 views

Why is work done on the system considered when calculating the work output?

The thermodynamic efficiency $\eta$ is calculated by $\eta= \frac{W_{out}}{Q_{in}}$ Using the first law of thermodynamics we usually say that $W_{out}$ is $Q_c+Q_h$, where $Q_c$ is the heat ...
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0answers
23 views

Gas Pressure in Industrial processes [on hold]

Can anybody please help with the following? Ammonia is produced by the Haber process where nitrogen and hydrogen combine to form ammonia according to the equation: N2 + 3H2 == 2NH3 If 1 mole of N2 is ...
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1answer
142 views

Thermodynamics, chaperones : How to model polymer fragmentation

Living polymers are well described by equilibrium statistical physics. Now I would like to consider a case were living polymers undergo fragmentation due to chaperones. I can think of a kinetic ...
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5answers
145 views

Entropy Change in an irreversible process

I have just started learning thermodynamics and the concept of entropy confuses me. Suppose I have a gas in a cylindrical container fitted with a piston. I take it through an adiabatic irreversible ...
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3answers
67 views

At what energy consumption would we get a 1 degree rise in the Earth's temperature?

If energy consumption continues to rise at (say) 4% per year, how long before the heat dissipation seriously impacts climate?
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2answers
41 views

Any general method of determining changes in speed of sound with pressure?

I need to correct speed of sound measurements in various gases for changes in ambient pressure, typically 700-1100 mBar. Is there any general theoretical model available for this? Especially something ...
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1answer
32 views

Writing an equation for the INTERNAL energy for a BRAYTON cycle

I am trying to understand the equation for the change in internal energy in the Brayton Cycle. Both the websites below gave me this formula :Change in U=q1+q2−w=0 ...
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0answers
10 views

Thermodynamics of a heated enclosure

i have to maintain an aluminum enclosure of size 200x300x400mm at around 80 degrees Celsius, there for i need to calculate the thermodynamics of the system, ie what power of heater i need to achieve ...
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1answer
33 views

When does exergy destruction occur?

I am doing a project on developing a code for the first and second law analysis of the Brayton Simple and Modified cycles. The first law part is simple. But I have run into a roadblock when I started ...
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0answers
9 views

Can an intercooler be analysed as any other heat exchanger?

I am doing this project on developing a code for the first and second law analysis of a practical Gas Turbine Cycle. It includes a two-stage compression process and thus, involves an intercooler, ...
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2answers
77 views

How long does it take for water to boil when subjected to intense heat?

I have a rather odd question that may just boil (sorry) down to a fairly simple problem I can't solve. The scenario is this: A person is testing the intensity of a super-focused beam of sunlight in a ...
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0answers
21 views

a physical model for pde [on hold]

Consider the initial boundary value problem $$u_t=a(t)u_{xx},\,\,\,0<x<1,\,\,\,t>0$$ $$-ku_x(0,t)=hu(0,t),\,\,\,t>0$$ $$u(1,t)=u_0,\,\,\,t>0$$ $$u(x,0)=f(x),\,\,\,t>0$$ where ...
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32 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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When obtaining the thermodynamic entropy (e.g. by differentiating F) the average entropy is being found. In what sense is this an average?

If I have some expression of the entropy (or another thermodynamic quantity of a system (e.g. pressure) obtained from the Helmholtz free energy, F. Is this the mean (average) or the modal (most ...
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15 views

How to design a radiator to dissipate heat? [on hold]

I am making heat radiator that dissipates the heat from water coolant lines coming off of another project of mine. The coolant lines will flow into a barrel, radiate as much heat off as possible, and ...
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3answers
190 views
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Causality principle and Entropy (Second Law)

I was reading about the light cone in relativity and I got to the point where in order to avoid paradoxes one can introduce the causality principle: Causality Principle: For every inertial ...
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1answer
31 views

What are the state variables like temperature after the system has done an adiabatic irreversible process? [on hold]

Consider a system containing ideal gas which is initially at a volume $V_{1}$ and then suddenly its volume is increased to a volume $V_{2}$. What is the final temperature of the system if the initial ...
5
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1answer
255 views

Thermodynamic relations from Gibbs-Duhem

Given the Gibbs-Duhem relation $V dp = N d \mu + S dT$, I am having trouble deriving the following identity: $\ \left(\frac{\partial N}{\partial \mu}\right)_{V,T} = N \left(\frac{\partial ...
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1answer
141 views

Does air conduct heat better than saturated steam?

This engineering toolbox table shows thermal conductivity of steam at 0.016. I understand that water is better in conducting heat than air, but if I read this correctly, steam is worse in conducting ...
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21 views

Is $\mathrm{d}H = C_P \mathrm{d}T$ and $\mathrm{d}U = C_V \mathrm{d}T$ always true?

Is $\mathrm{d}H = C_P \mathrm{d}T$ and $\mathrm{d}U = C_V \mathrm{d}T$ always true for ideal gases?
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13 views

How to find heat transfer and released heat? [on hold]

Given the sterling cycle with the following processes 1-2 isothermal expansion - heat addition from external source 2-3 constant volume heat transfer - internal heat transfer from the gas to the ...
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0answers
17 views

Heat capacity of a gas in gravitational field

How does one calculate the heat capacity of an infinitely long column (of constant cross-sectional area) of ideal gas in a uniform gravitational field? I tried using the lapse rate $dT/dH$ and putting ...
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20 views

Hot air particles

I have a question- albeit random one!. I recently visited a friends place who used a standard shovel from the shed as a tool for moving hot charcoals around a pizza oven. Unfortunately the shovel was ...
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32 views

Square of velocity = 2 times temperature times specific heat capacity ; seems too tidy [on hold]

So I did some algebra and came up with the following $v^2 = 2Tc$ where $ v = $ average velocity of the particles $ T = $ tempreture $ c = $ specific heat capacity but this seems too tidy
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0answers
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Finding the temperature needed to have speed of gas atom equal to Ve [on hold]

We are given n moles of a monatomic gas Argon Molar mass 6.4*10^-26. Pressure equal to 101300 pascals. Temperature = 300 K Need to find the average speed of one of the atom of the gas. Secondly I ...
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1answer
40 views

To find average speed of gas molecule when the temperature is incresed

We are given moles of gas let say $n$. Temperature is increased from $T_1$ to $T_2$. Volume is held constant at $V_0$. We need to find the average speed of gas molecule when the temperature $T_2$ is ...
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1answer
58 views

How can i turn home gas from liquid to gas [on hold]

I hope i am not too off topic, couldn't find a more suitable stack-exchange forum for this, if there is a better one, please point me to it, Well my question is the following, I am working on a ...
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0answers
11 views

How to calculate how much energy is needed to fuse makro particles such as a certain type of plastic? [on hold]

As the title suggests, how do I calculate that? I would like to fuse plastic particles of the size around 0.1 millimeter using ultrasound. What equations do I need?
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3answers
2k views

How can there be heat in a vacuum?

I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc. If heat is caused by thermal energy being radiated from particles ...
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30 views

Legendre transformation: non-convex/non-convave functions

The Legendre transformation is used to derive the Hamiltonian from the Lagrangian, and it finds many applications in thermodynamics to convert between the different potentials. $ f(x) \rightarrow ...