Questions tagged [definition]
The definition tag is used in situations where the question is either about how some term or concept is defined or where the validity of an answer depends on a subtle definition of some term or concept used in the question.
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By what units is 'degradation to ozone layer' measured?
From Wikipedia:
The ozone depletion potential (ODP) of a chemical compound is the relative amount of degradation to the ozone layer it can cause, with trichlorofluoromethane (R-11 or CFC-11) being ...
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Normalization Factor and Sign of Exponential Term in Fourier Transform [closed]
I have two questions regarding the Fourier transform:
Normalization factor: Some texts use no normalization factor in the definition of the Fourier transform, while others use $1/\sqrt2\pi$. What is ...
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Confusing definitions of EMF
I was studying about EMF (electromotive force) recently but had trouble connecting the two definitions of the topic. Here are the two definitions of EMF listed in my book (The book I've referred is: ...
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In layman’s language what is the difference between stopping potential and work function?
In layman’s language what is the difference between stopping potential and work function? It feels like both the things mean the same thing, if I am wrong please explain the things to me.
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What is charge on a fundamental level and what is it caused by?
On bigger bodies, I've learnt so far that charge is caused by a lack or excess of electrons or protons but when you look at an electron or proton, how are they charged? what is the cause of their ...
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Definition of entropy and microstates (Huang)
The definition of Boltzmann entropy given in Ref. 1 appears to be different from most sources I've seen up to this moment. Let me start from the latter: typically textbooks assume that in a given ...
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How to state that a function has a certain andament in a limit? [migrated]
Assuming we have a function $f(r)$ that has the following limit
$$ \lim_{r\to0} f(r) = \frac{5}{3 r^2} \,.$$
What is the correct symbol to express that the denominator goes like $r^2$?
Is the ...
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Confusion on the definition of dielectric permittivity
I don't understand how we're defining the dielectric permittivity, sometimes it's defined as the ability of the material to resist the electric field and sometimes as the ability to permit the ...
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Meaning of of inertial frames in special relativity [duplicate]
One of the postulates of special relativity is
The laws of physics are the same in all inertial frames
There is a mention of inertial frames in the postulate. But the predictions of relativity are ...
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How can I call a transformation where only the $z$-axis is modified by a function in each point?
What is called a transformation that maps $z \rightarrow |f(z)|\, z$, while the other axis stays the same? Is it a conformal transformation?
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Intensity of light - questions about the particle standard definition and concerning the units [duplicate]
In the $5.111$ MIT class, lecture $3$, it is written on the last slide "intensity of light = photons per second". Intensity is previously defined in the lecture as the square of the ...
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How to use the definition of a rank-$2$ tensor for this kind of examples?
Suppose that, a rank-$2$ tensor transforms as
\begin{align}
T'^{ij}=\frac{\partial x'^i}{\partial x^k}\frac{\partial x'^k}{\partial x^l}T^{kl}.
\end{align}
How to use this criterion to investigate if ...
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What is the connection between moments in probability theory and the moment of inertia?
My question arises as the moment of inertia (MOI) has been described as a second moment.
In my understanding if the MOI is indeed a second moment of a distribution of mass, this suggests the MOI could ...
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Photoelectron and electron in photoelectric effect [closed]
Could you please help me find some answers, as I have been stuck in this for a while and didn't get understandable answers.
what is the difference between the photo electron and an electron.
The ...
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The Legendre transform is a convex function [migrated]
I am new at the study of Hamiltonian Mechanics and I am facing the definition of Legendre transformation. I know that the Legendre transformation of a convex function $f:\mathbb{R} \rightarrow \mathbb{...
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What exactly is equivalent resistance?
We all know the basic example of school with series and parallel resistors, so they might be a good place to start.
Given two terminals $A$ and $B$ from a circuit, if the current that exists $A$ is ...
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What does the $F$ in Newton's second law equation mean?
This is a super simple question: does $F$ represent the net force exerted on an object or the force it exerts on another object as a result of momentum? Say a ball is rolling. In this specific ...
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What are internal and external forces?
what is internal and external force? How do I decide what forces are internal and external?
in work-energy theorem and conservation of mechanical energy, do we consider internal, external, or both ...
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Why is warming food in the microwave work and not heat? [duplicate]
In Schroeder's An Introduction to Thermal Physics, heat is defined as the "spontaneous flow of energy from one object to another" and work is defined thermodynamically as any other transfer ...
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Second derivative of energy with $k$
In solid-state physics, we often encounter the velocity operator (e.g. this post) which the eigenvalues can be written as
$$
V^\mu(\vec{k}) = \frac{1}{\hbar} \frac{\partial E}{\partial k^\mu} \biggr|_{...
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Meaning of $n$-critical point
My lecture notes about field theory refer to a tricritical point as a point in which a continuous phase transition line meets a discontinuous phase transition line.
In the following it refers to a ...
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Is the definition of geodesics different if the electromagnetism is added to GR?
In plain GR, geodesic are defined by:
$$ \nabla_{u} u^{\,\mu} = 0 $$
where $u^{\,\mu}$ is the four-velocity of the particle.
Now, I don't understand if this holds true also in the electromagnetic case,...
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What is the relationship between Clausius Inequality and 2nd Law?
I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles.
I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
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Clarifying the definition of pressure in statistical physics
I am studying David Tong's lecture note on statistical physics, and I have a question regarding the precise definition of pressure. I checked other postings in this community, but was unable to get ...
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Two values of Rydberg Constant
In my textbook I came across two values of Rydberg Constant:
\begin{align}
R&= 109\,677\ \mathrm{cm}^{-1}
\\
R_h&= 2.18 × 10^{-18}\ \mathrm J
\end{align}
when we are calculating energy of the ...
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What is $r$ in a metric signature in general relativity? If $v$ and $p$ are the time and spatial coordinates?
The Wikipedia article on metric signatures says that the signature of a metric can be written $(v,p,r)$, where $v$ is the number of positive eigenvalues, $p$ is the number of negative eigenvalues, and ...
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Rest Mass Energy
What exactly is the Rest mass energy? I know the usual goes Like it is total energy stored in mass $m$ that is in Rest. so for someone moving relative to the frame that the mass $m$ is in (a rest ...
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What is the difference between Born approximation and tree-level processes?
The answer to this question says that Born approximation is essentially equivalent to the tree-level. This can be seen from the Feynman-diagrammatic version of Born series discussed in many NRQM ...
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What exactly are cohesive and adhesive forces?
Are cohesive and adhesive forces defined only when at least one of the interacting materials is a fluid?
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On the definition of topological order
I am currently reading the "Quantum Information Meets Quantum Matter -- From Quantum Entanglement to Topological Phase in Many-Body Systems". I am trying to understand the proper definition ...
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What is the so-called momentum density? [duplicate]
What is the so-called momentum density? I am reading the paper by Pitaevskii, in which he stated that it is well-known. He studied the nonlinear Schroedinger equation, but it seems that the concepts ...
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Is displacement vector always the shortest path?
I read that the displacement vector of a particle is the shortest path between its initial and final positions since it's a straight line joining the two points, this holds true for me till a 2D ...
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Is there a practical distinction between functions of state and functionals in thermodynamics?
In thermodynamics, and more precisely when talking about continuous systems, some sources [1, 2] introduce functionals of state:
$$F[s(x), \dots]:=\int_VdV(x)f(s(x),\dots,x)$$
In order to derive ...
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What does Density really mean? [duplicate]
We say that density is mass per unit volume and if an object has high density that means it has more amount of matter contained per unit volume but as we know mass is not the amount of matter ...
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Definition of “quasi-locality” in Wilsonian RG scheme
I’m studying about the holographic RG with this paper.
In that paper they say Wilsonian action expects quasi locality, but I’m not sure what “quasi-locality" exactly means.
If quasi-locality ...
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How were angles measured in ancient times?
What is one degree (angle measurement)? I know that we calculate one second using atomic clock, one kilogram using Planck's constant, one meter using speed of light but how do we define one degree? If ...
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What is the definition of a conformal symmetry? [duplicate]
I have been very confused by this after some recent reading. So as far as I know, a conformal transformation (according to the definition in di Francesco et. al.'s book on CFT) is an active coordinate ...
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What are regular event horizons?
I am studying uniqueness theorems of Black Holes and I often see the word "regular event horizon" instead only event horizon. Many textbooks and literature do not define this term. Please ...
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Where does the four-vector potential $A^\mu$ originate?
Now the default answer to this may be, "It has no origin because it's a definition", but let me just try to justify my concern here.
On page 842, equation (22.91) of "Modern ...
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What exactly is a brane? [duplicate]
what exactly is a brane? i know that in order to get the equations of motion of a relativistic string by varying the Nambu-Goto action one has to impose a Neumann boundary condition and a Dirichlet ...
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Pressure sensors vs. piezoelectric sensors
In simple terms, what is the difference between pressure sensors and piezoelectric sensors?
I did some google search online and could not come to a good conclusion.
Say you make a 'sensor' in the lab ...
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What stationary charges exactly mean?
When learning about magnetic fields, it is said that stationary charges do not have any effects due to magnetic fields. So when explanations are given, is the spin of the charges not considered?
And ...
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Precise Definition of Degrees of Freedom [duplicate]
I am taking Analytical Mechanics and while reading Goldstein's and LL something bothered me: can I say that a degree of freedom is an independent (generalized) coordinate?
What bothers me is that we ...
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Defining Nuclear Reaction and Beta Decay
I use a school textbook that defines nuclear reaction in the following way. I will go through what does make sense to me, and then point out the thorns.
"When an atom changes into a different ...
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Why is entropy defined in the way it is?
In thermodynamics course we were taught that in a reversible adiabatic process of an ideal gas the entropy change is zero.
Now what I didn't get intuitively is that if the system is compressed ...
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Is there a formalization of the butterfly effect?
According to my understanding, the butterfly effect says, very informally, that even a tiny perturbation in a physical system can lead to significant alterations in future states of the physical ...
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What are relativistic particles? [duplicate]
What are relativistic particles? I got it in a question of mechanics.
So, what is it about a particle that makes it "relativistic"?
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Can the composition law of a group be defined only when considering a representation or realisation of the Group?
When we talk about, lets say, the Lorentz group, we define the action of the Lorentz transformation $\varLambda$ on
\begin{alignat}{1}
x^{\mu} & \in\mathbb{R}^{1,3},\\
x^{\mu} & \rightarrow x'^...
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In what sense is $\int (u \cdot \nabla) u \cdot u dx$ an energy flux?
Due to the nature of this question I have have cross-listed it on mathSE.
Let $u$ be either a solution to either the Euler equations or Navier-Stokes equations over a domain $\Omega$. In fluid ...
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What is the name of the transformation from one harmonic oscillator basis to another centered elsewhere?
If I have a harmonic oscillator basis centered at $x=2$, how do I rewrite it in terms of the harmonic oscillator basis centered at $x=0$? To be more specific:
If $|\Psi_n\rangle$ is the $n$th ...
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