All Questions
17,220 questions
1
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Doubt with Heat and Potential Energy. (Warning: Many Assumptions) [closed]
I had a question in my Textbook which reads as follows,
Before that, we have to assume that the flowing water is ideal.
So, here we have to equate Change in Potential Energy to Heat Energy/Internal ...
0
votes
0
answers
21
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Is there a forumla to estimate the rate of evaporation rate in grams per hour given the speed of wind passing over the surface?
I am doing an experiment, where I investigate the effects of different wind speeds (1,2,3,4,5 $ms^{-1}$) on the evaporation rate of distilled water. I am trying to calculate the theoretical ...
32
votes
10
answers
5k
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Why does the motion of a gas never stop?
It is said that if a container is filled with gas, the gas molecules perform random motion in every direction.
Pressure should be exerted on the walls of the container due to the collision of gas ...
- 608
3
votes
2
answers
115
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Pressure of mixture after mixing [closed]
An insulated rigid tank is divided into two compartments by a partition. One compartment contains $3 \,\text{kmol}$ of $\mathrm{O}_2$, and the other compartment contains $5 \,\text{kmol}$ of $\mathrm{...
- 31
2
votes
1
answer
200
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Why doesn't gas usually contract in volume?
I am very new to this business about entropy, so I came up with the following experiment to make sense of what I understood.
A gas in some volume $V$ initially expands into a gas in volume $2V$. We ...
- 435
0
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0
answers
44
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Why don't we take into account the change in kinetic energy in the isentropic efficiency?
Steam enters an adiabatic steam turbine at $6\,\text{MPa}$, at $600^\circ\text{C}$, with a velocity of $80\,\text{m}/\text{s}$, then exits at $50\,\text{kPa}$, at a temperature of $100^\circ\text{C}$, ...
5
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1
answer
242
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How does the lifetime and temperature of a black hole scale with mass in universe with more then 3 spacial dimensions?
I've tried to find out how the lifetime and temperature of a black hole scale with mass in a universe with more then 3 spatial dimensions. I've spent a while trying to look up an answer to this ...
- 3,001
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1
answer
72
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Entropy in a thermally isolated system
In page 141 of the book "Concepts in thermal physics" it is said that for a thermally isolated, the change in entropy is bigger or equal to 0 since $dQ=0$.
But since the system is thermally ...
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3
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2
answers
340
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Understanding the definition of the covariant derivative
I'm currently working my way through the book "Mathematical Methods for Physics - An Introduction to Group Theory, Topology and Geometry" and I think I have a very fundamental ...
- 61
-2
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1
answer
59
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Need help in understanding Tangential Acceleration [closed]
I am studying Circular motion and I am confused about tangential acceleration and tangential velocity. I am studying uniform circular motion and it says the tangential acceleration is $0$ in uniform ...
1
vote
0
answers
76
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Are we able to compute electrochemical potentials of metals?
When we put into contact a copper and a zinc plate some electrons will move from one metal to the other due to a difference in the electrochemical potential of the two metals (see for example the ...
- 206
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votes
1
answer
50
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Entropy generation in an expanding universe?
If entropy being generated in a system is given by
$$
S = \frac{dQ}{T} = \int \left( \frac{dQ}{dt} \cdot \frac{1}{T} \right) dt
$$
One could have the limit $S = \infty$ if $T \to 0$, so as the ...
- 2,878
3
votes
2
answers
116
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Clarification of notions regarding kinetic energy and kinetic theory of matter
To give a background of what I have been taught in school, I am currently in 9th grade. Last year in chemistry, we were taught about the 'kinetic theory of matter', which stated that all matter is in ...
- 143
1
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0
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15
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Different trends of thermalization in a collision of electron-ion
I performed a collision of electron-ion with using initial tmeperature of electron as $T_{e0}=$ 20 eV, ion as $T_{i0}=$ 10 eV and distributing with Maxwellian distribution of velocity. The density of ...
- 31
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0
answers
16
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Modular Hamiltonian of Thermal States
In this notes in Remark 20 (page 40) the author states that if a density matrix $\rho$ is thermal, then the modular Hamiltonian is just given by the physical Hamiltonian, i.e. modular time evolution ...
- 527
3
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1
answer
67
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"Deriving" the covariant derivative
Suppose we are working in scalar QED with Lagrangian
$$\mathscr{L} = (D_\mu \phi)(D^\mu \phi)^* - \frac{1}{4}F_{\mu\nu}F^{\mu\nu}.$$
I now want to find the form of the covariant derivative $D_\mu$ ...
- 283
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1
answer
53
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Derivative for the Maxwell field [closed]
I'm struggling with the following expression, which occurs in the derivation of the Maxwell Lagrangian in field theory.
$$\frac{\partial(\partial_{\mu}A^{\sigma})}{\partial(\partial^{\nu}A_{\lambda})}...
3
votes
3
answers
81
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Equilibrium in a reversible process
My lecture notes state the following (albeit in a very hand-wavy way):
If we
are gentle and careful however, we can change the state of the system slowly, making sure that while
the state is changing ...
- 33
0
votes
1
answer
86
views
Why is the number of accessible microstates obtained by summing over each microstate?
I am studying statistical mechanics, and I am trying to understand an example used in my lectures to explain the canonical ensemble.
The example involves a system ($S$), submerged in a heat bath ($B$)....
- 474
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1
answer
80
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The definition of the Lie Derivative
I am aware that an answer to an almost identical question already exist, however, I found the already existing answer not helpful (at least to my current question).
Carroll defines, in his book, the ...
0
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1
answer
24
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Comparison of processes for a thermally insulated chamber containing hot gas and some metal [closed]
I have the following problem from a textbook on thermodynamics:
A thermally insulated chamber contains some hot gas and a lump of metal. Initially the gas and the lump are at the same temperature $...
- 3
0
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0
answers
22
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What gas-law-related experiment (or experiments) might this description refer to?
Somebody on Hacker News described an experiment they performed as a teenager:
Back in high school, I built (with some parental assistance) an
apparatus to measure how quickly the pressure would drop (...
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-1
votes
0
answers
56
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Does Maxwell's demon violate Heisenberg's uncertainty principle?
Suppose we have two containers with the same gas but at different temperatures. The containers are separated by an ideal frictionless door Maxwell's demon can open and close at the very right moment ...
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1
answer
70
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Why are Weyl's Equations composed of only first-order derivatives?
I'm studying the Weyl's Equations from Section 1.5 of Perkins' Introduction to High Energy Physics.
The author says this:
Dirac set out to formulate a wave equation symmetric in space and time, ...
- 1,637
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votes
1
answer
37
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RMS Velocity of Gases
Whenever we have to find the RMS velocity of gas we use the formula √3RT/M, where R is the ideal gas constant, T is the absolute temperature and M refers to the molar mass of that particular gas. ...
0
votes
2
answers
39
views
Placing a mass on a piston in a heat sink
Imagine a problem with a piston filled with an ideal gas placed in a water bath. The gas is initially at a temperature equal to that of the water bath $T_1$ with volume $V_1$. A mass is then added to ...
- 3
1
vote
2
answers
79
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Dark baking pan versus light baking pan
There are a ton of articles on baking websites that state baking in a dark colored pan works different than using a light colored pan.
The only thing I can think of is that the pans are of different ...
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0
votes
1
answer
21
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Linearized or nonlinear least squares for Arrhenius: mitigating heteroscedasticity
I have a question that is essentially expanding on this older question, but digging into a specific aspect of it that was not directly discussed
Suppose I have data points that fit an Arrhenius trend:
...
- 968
0
votes
0
answers
44
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Event Horizon vs. "Interior" of a black hole from perspective of distant oberserver
From the perspective of a faraway observer watching an object fall into a black hole, they will see the object approach the black hole's horizon at a slower and slower rate until eventually "...
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6
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2
answers
490
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What is the purpose for the blackbody radiation graph to be graphed using the below parameters?
If you observe the above graph, for y axis, "intensity per wavelength" is used as the parameter. I am aware we use "per wavelength" because it is hard to measure and graph isolated ...
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votes
0
answers
22
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Latent heat transfer coefficient over the ocean?
I'm currently calculating for the surface turbulent latent heat flux over the Pacific. The formula I have needs a $C_E$ which is the latent heat transfer coefficient.
I've read several studies that ...
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2
votes
0
answers
56
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Conceptually understanding microstates
I had learned about microstates in my thermodynamics class, but I am having trouble understanding the probabilistic property of them. My teacher had told me that every microstate is equally probable, ...
- 263
9
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4
answers
4k
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Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant but acceleration is constant?
Is it ever possible that the object is moving with a velocity such that its rate of change of speed is not constant, but rate of change of velocity is constant?
Like speed is only the magnitude, so ...
4
votes
4
answers
558
views
Does a packed fridge cost the same as an an empty fridge? (Electricity cost) [duplicate]
Discounting initial power to bring an item into a frozen state, then is the electricity cheaper to leave my fridge empty; or is the cost the same for it being packed with frozen foods?
If my fridge is ...
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2
votes
1
answer
76
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Thermal expansion and stress analysis of rigidly joined rods
I’m working on a problem involving two steel rods and one aluminum rod of equal length and cross-section rigidly joined at their ends. And the overall rod, made by joining them is overall free. When ...
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11
votes
3
answers
1k
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How can water go below zero and still be liquid? [duplicate]
I recently had seen an interesting experiment where a water bottle could be placed in a freezer for a while and would retain its liquid state until someone tapped on it, where it would quickly ...
- 263
1
vote
1
answer
50
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Grassmann Numbers, anticommutation and derivative rules
If $\psi(t)$ is a complex Grassmann number and $\psi^*(t)$ is its complex conjugated. The following is true:
$$\frac{\partial (\psi^*\psi)}{\partial \psi}=-\psi^*\frac{\partial \psi}{\partial \psi}=-\...
- 1,628
0
votes
1
answer
83
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Is the product of pressure and volume of an ideal gas equal to its energy?
While solving a physics problem book (Narayana coaching material Physics for Jee advanced volume 4), I came across this question.
An ideal gas undergoes a process in which $PV^{-a} = \text{constant}$,...
1
vote
1
answer
40
views
Equilibrium partitioning between two domains with different mobility
Imagine a random walk in a system consisting of two adjacent phases. In one of the phases the walker has a high mobility, and in the other low mobility.
If I'm not mistaken, the walker will in this ...
-2
votes
0
answers
70
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Use of $dv/ds$ in defining acceleration [duplicate]
We can write acceleration as either
$dv/dt$ or $v dv/ds$.
And surprisingly the work-energy theorem arrives from the second definition.
I feel it would be fundamentally understanding towards work ...
1
vote
1
answer
30
views
Under what circumstances is "equality of osmotic pressure" functionally equivalent to "equality of osmolarity"?
Consider the classical U-tube, semi-permeable membrane experiment. Assume I define osmotic pressure as $\Pi=\frac{RT}{V}\gamma$, where $\gamma$ denotes the number of total solute particles (across all ...
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1
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80
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Chemical potential, zero of energy, extensivity
It occurred to me today that I cannot reconcile the notion that the chemical potential, $\mu_i$ of a species in solution is, like energy, defined only up to an additive constant. This is implied in ...
0
votes
2
answers
60
views
Generalization of Heat input in a $pV$ curve for a reversible process
I was wondering, is there a way to generalize by just looking at a PV curve for a certain process that heat flows into it or out of?
For example, for a cyclic process if the process is "clockwise&...
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1
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0
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23
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Can I use the sollution to the heat equation for a 1D diffustion problem like I have?
So, I have some source of heat at point $x=0$, from which i don't know the temperature as function of time $T(0,t)$, I do however have $T(x_{NTC},t)$ and i want to know the temperature at some point x....
2
votes
1
answer
89
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Einstein Solid: Density of States vs. Partition Function
This question probably has a straightforward answer. The density of states in a 3D Einstein solid is
\begin{equation}
D(\varepsilon) = 3N\delta(\varepsilon-\hbar\omega_E)
\end{equation}
where $\...
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-1
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0
answers
17
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How to prove that a Lie algebra-valued differential form is exact for the covariant derivative [migrated]
Given a differential $p$-form $\omega^A$ over a smooth manifold with values on some Lie algebra, I wanted to know how could one prove that it can be written as an exact form for the exterior covariant ...
- 381
2
votes
1
answer
56
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The origin of Joule heating from scattering
My understanding is that Joule heating originates from the transfer of electronic energy to the lattice. This post states that impurities contribute to the dissipation of electrical energy. However, ...
- 143
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0
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59
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What's the difference between $dx$ and $\delta x$? [duplicate]
In the process of defining crystal momentum $\hbar k$, I found these formulas below.
By the definition of group velocity,
$$v_g=\frac{d\omega_{nk}}{dk}=\frac{1}{\hbar}\frac{dE_{nk}}{dk}$$
Also if an ...
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0
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1
answer
66
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Is Stress a Derivative?
On page 289 of the text "Fundamentals of Fluid Mechanics" by Munson et al., the authors give the following definition of the normal stress acting on the surface of a fluid element:
At any ...
1
vote
0
answers
53
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Temperature dependence of heat capacity
Sometimes I find a graph of Cp/T vs T, where Cp is a heat capacity of a material and T is the temperature. What is the physical meaning of this graph? Which property can you know from the plot?
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