All Questions
17,220 questions
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Why do only the eigenstates of the Hamiltonian follow a boltzman distribution
Suppose I had a system with e.g. conserved impulse p, but no thermal equilibrium/fixed energy. Why is only the entropy of the distribution of eigenstates of the hamiltonian being maximized? (if p and ...
1
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1
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51
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Entropy driven production of antimatter at high temperatures
Might be a stupid question:
The condition for spontaneous change under constant pressure is dH - T*dS < 0. If one took a bunch of matter and heated it to a arbitrarily high temperature, would 50% ...
-2
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1
answer
99
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Is interpreting information conservation as time reversibility non-mainstream physics?
I understand the following as standard results in modern physics.
Black holes evaporate over time via Hawking radiation.
Small black holes evaporate over very short times.
There is an "...
- 931
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0
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Explosions in high viscosity liquids
I was watching The Score (2001) in which De Niro manages to make a hole in a cobalt and titanium infused steel safe. he fills it with water. inserts an explosive and boom! the safe is open.
It made me ...
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51
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Solid to liquid transition second order, but has latent heat?
I always thought that first-order transitions cannot have symmetry breaking. But the water-to-ice transition seems to break this idea. We do know that it has a latent heat of freezing, but we also ...
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65
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Question regarding Principle of Corresponding States
This is one of the excerpt from Modern Thermodynamics by Ilya Prigogine where he talks about Van der Waals' equation.
Van der Waals showed that if his equation is re written in terms of reduced ...
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2
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27
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Physical Significance of power density of a point source of heat
What does the power density of a point source of heat signify?
I'll illustrate this with the help of an example
Consider a sphere of radius R and thermal conductivity k with a point source kept at ...
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Cooling due to evaporation
I'm reading "The water wizard" by Callum Coats ed. Gill Books. At page 9 I read:
Terracotta exhibits a porosity particularly well-suited to purposes of water storage. This is because it ...
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2
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59
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Thermodynamic quantities during free expansion and joule Thomson expansion
What happens to thermodynamic quantities like internal energy, heat, work done and entropy during free expansion and joule Thomson expansion of both ideal and real gases. I always find this very ...
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70
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Which of the following processes (a) isothermal, (b) isobaric, work done will be maximum?
Sir i am facing very difficultly in this following question. It will be so kind of you if you can explain this question to me:
This question is about the thermodynamics from the applications of 1st ...
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Why is the specific heat capacity of water greater than that of ice? [duplicate]
My powerpoint at school says the following:
how can this make sense if the rate of temperature change is inversely proportional to the specific heat capacity, wouldn't that mean that the specific ...
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Why is the Einstein Field Equation relevant in the area theorem?
I am studying Area theorem and the first assumption is as follows :
If Einstein equation holds satisfy null energy condition...
I don't understand in general, what does it mean to satisfy Einstein ...
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480
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Second derivative of unit vector
We know that the second derivative of unit vector (the vector from a point toward the source) is proportional to the Electric field caused by the source in a particular point.
If we imagine that our ...
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47
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Quasistatic and Reversible thermodynamic processes
A quasistatic process is a process where all intermediate states are in equilibrium. A reversible process is a process where no entropy (of the universe) is generated (and thus can be reversed to its ...
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1
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96
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Why does ethanol, despite having a lower boiling point than benzene, has a higher heat of vaporization?
At 1 atm of pressure, ethanol boils at 78.37°C with a heat of vaporization equal to 39.3 KJ/mol, and Benzene boils at 80.1°C with a heat of vaporization equal to 31.0 KJ/mol.
Here are my assumptions:
...
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Does closing a jar instantly change the temperature? [closed]
Temperature is the derivative of energy with respect to entropy. I say derivative and not partial derivative because the defining property of temperature is that heat flows from hot to cold, and this ...
- 1,276
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Relationship between covariant derivative and metric tensor
In general relativity, the covariant derivative of the coordinate vector is a tensor, equal to $$x^{\mu}_{:\rho} = x^{\mu}_{,\rho} + \Gamma^{\mu}_{\rho\nu}x^{\nu},$$ is it meaningful to equate this ...
- 562
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Nonlinear optics, nonlinear suscpebilities
I am very much new to nonlinear optics. The basic doubt I have is how KDP, BBO crystal exhibits both second-order and third-order susceptibilities. What does it mean that third-order susceptibility ...
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1
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58
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Heat current through a material with variable conductance
Can anyone explain how temperature at any point on the rod (or any material in general) varies with distance when conductivity is variable. This question came to my mind from my physics test last week,...
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2
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55
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Why do various materials have different specific heat capacities?
What physically determines the specific heat capacity of a material? Is there a combination of factors that determine this? For example what gives water an uncharacteristically high specific heat ...
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1
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35
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Reduce etendue by aperture
Lets look at a light source of area $S$ where each point on this surface emits light into a light cone with max. angle of $\alpha$. Then the etendue is -as far as I understood it- defined by $\epsilon ...
- 171
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Physics behind gold+silver space blanket placement
In the first aid and mountaneering, "space blanket" or "astro foil" is used for protection against cold enviroment or as first aid after burns. There are many different versions of ...
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60
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Thermodynamics, cooling curves
It is well known that temperature is a measure of the average kinetic energy of the medium particles. In the heating curve, when heat is added the average kinetic energy increases and the temperature ...
- 411
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2
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33
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Factoring the volume of the water inside the pipe in a heated pipe calculation
I have been using a formula to calculate how much heat needs to be generated by a heated pipe in order to raise the temperature of the water flowing through the pipe by a certain amount, e.g. from 10𝑜...
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Leibniz rule and Nakahara's definition for functional derivatives with respect to Grassmann variables
In Nakahara's book "Geometry, Topology and Physics" in section 1.5.7 (I'm reading the second edition) he defines the functional derivative with respect to Grassmann variables. He does so in ...
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Evaporation of water due to vacuum aspiration?
In my research, I have encountered the following problem:
I have a vacuum pump that I would like to use aspirate water from below an elastic surface. The water resides under the elastomere and a tube, ...
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A trick for derivatives of thermodynamic quantities [closed]
Starting from
$$dU=TdS-PdV$$
We can write, for instance $U(T,V)$ and $S(T,V)$ to obtain:
$$\left(\frac{\partial U}{\partial T}\right)_VdT+\left(\frac{\partial U}{\partial V}\right)_T dV=T\left(\frac{\...
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5
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Is a "hot cube" (analogous to an ice cube) a physical possibility?
Is it possible to fabricate a uranium or plutonium "hot cube" that could be used to keep a cup of coffee hot? Basically a piece of fissile material, shielded, and covered with a non-toxic ...
- 403
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3
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94
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How does a pizza heat up in the oven?
Sometimes if you bake a frozen pizza (and are impatient) it can happen that the center of the pizza is still cold while the edges are already burning hot. How is this possible?
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Equilibration/Thermalization in mean-field theory
Assume a scalar field in $D$ spacetime dimensions with a quartic interaction
$$H=\int d^{D-1}x\;\left(\partial_\mu\phi\partial^\mu\phi+\frac{1}{2}m^2\phi^2+\frac{\lambda}{4!}\phi^4\right)$$
This ...
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218
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Is temperature same for same final pressure and volume?
I have a doubt regarding temperature changes in various thermodynamic procces. Lets say if a gas has initial pressure p1 and volume v1 and has final pressure p2 and volume v2 then according to pv =nrT ...
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Is this mathematically correct that gradient of deformation gradient is equal to deformation gradient?
The deformation matrix is defined as follows, where $x$ is the current location and $X$ is the reference location. It shows the relationship between current $x$s with regard to original $X$s,
$$F = \...
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Conflicting Solutions for Calculating Apparent Speed of Jogger's Image in Convex Mirror
I’m facing a challenge with a physics problem due to conflicting solutions across different sources, and I'd appreciate some clarification.
Problem Statement:
Suppose, while sitting in a parked car, ...
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1
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81
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Why is heat flux said to be per unit area?
Heat flux is defined to be the flow of energy per unit area per unit time. But I do not understand where the "per unit area" comes from.
In Fourier's law, heat flux is modeled to be
$$
\phi=-...
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49
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Why is the air speed of a general fan less than 500 meters per second?
I am confused. Since the thermal motion speed of air molecules is about 500 meters per second, why is the air speed of a general fan less than 500 meters per second?
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Can noninteracting Bose-Einstein condensate reach infinite density?
If particles are noninteracting, does it mean that the density can be infinite in the ground mode of the Bose-Einstein condensate?
For example, here they are investigating the photon condensate ...
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Why is steaming food not faster than boiling it?
A recent Physics SE question asked "Why is steaming food faster than boiling it?, and specifically why food heats faster in steam than in boiling water. As noted in my answer to that question, if ...
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Calculation of the diffusion coefficient of a Lennard-Jones fluid (liquid argon)
I'm trying to simulate with the code written by Professor Cameron Abrams(https://github.com/Abrams-Teaching/instructional-codes/blob/main/originals/mdlj_and.c), a set of argon atoms interacting via a ...
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Is it possible to create a Bose-Einstein condensate of ions?
The question is in the title. In my opinion, it can not be created, as ions have Coloumb interaction, while condensate is usually created from weakly interacting particles. However, some condensates ...
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Can nonimaging optics concentrate heat to a higher temperature than the source? [closed]
Practical goal:
I'd like to concentrate the low-grade heat from the back of solar panels, which I've measured is in the range of 20-50F greater than the ambient temperature throughout the day, and ...
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1
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What material removal mechanisms are present in a high RPM, nanometric thick, SiC circle saw?
There is a video of someone who cuts a circle out of a regular A4 paper. He then spins up this circle using the motor of a circle saw working bench. He shows that this thin, soft paper circle is able ...
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What is the minimum number of particles for which the ideal gas law applies?
The ideal gas law has in it the number of particles N, in PV=NKT. Now, if N=1, does the ideal gas law still apply?
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Planck's law in terms of flux [duplicate]
The Stefan-Boltzmann law describes blackbody radiation in terms of radiant flux per unit area i.e. how much energy passes through a 2D surface per unit time. I find this very simple and I understand ...
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Stokes–Einstein–Sutherland equation
I've been trying to understand how the diffusion coefficient of droplets, $D$, in a gas medium depends on its self-diffusion coefficient, $D_0$, assuming that the particle's friction against the ...
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Given an infinite amount of time, will every possible combination of matter pop into existence?
Apparently it is true that when the universe is in the state of heat death, quantum fluctuations will eventually produce every combination of matter, no matter how unlikely, given an infinite amount ...
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In a warm cup of tea, how substantial is the temperature difference between the surface and the bottom of the cup?
There are various questions around how cups of tea cool down, or why splitting a cup of tea helps it cool, and things like that.
Thinking about the various mechanisms - heat rising within or escaping ...
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Sign convention on thermodynamics - Problem 6.6 Heat and thermodynamics [closed]
I made the problem 6.6 of Heat and thermodynamics by Zemansky. But I have a question with the sign of the final result from section c). If I use $W= P \Delta V$ instead $W= - P \Delta V$, my answer is ...
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How to bends in a pipe influence the heat transfer rate?
We can calculate the energy required to heat water flowing through a pipe using the formula
𝑄˙=𝑚˙𝐶Δ𝑇
Where
𝑄 is the heat transfer rate (in watts, W), 𝑚 is the mass flow rate (in kilograms per ...
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Smoke simulations and how to render them
I recently began a real time smoke simulation system, and I need some help with the rendering. I didnt know if to ask here or on the game development stack exchange, but I decided here as it is ...
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What happens to $g^{\alpha\beta}_{,\sigma}=-g^{\alpha\mu}g^{\beta\nu}g_{\mu\nu,\sigma}$ when $g_{\mu\nu}\rightarrow \eta_{\mu\nu}$ (weak field limit)?
The equation
$$g^{\alpha\mu}_{\,\,\,\, ,\sigma}\,g_{\mu\nu} + g^{\alpha\mu}\,g_{\mu\nu,\sigma} = (g^{\alpha\mu}g_{\mu\nu})_{,\sigma} = \delta^\alpha_{\nu,\sigma} = 0 $$
gives the useful relation
$$g^{\...
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