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Questions tagged [terminology]

Use this for questions relating to the proper use of physics terminology or nomenclature.

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59 views

Terminology: Infrared and Ultraviolet

I am new to high energy physics and string theory. I keep reading the terms infrared and ultraviolet in papers. I assume they aren't talking about electromagnetic radiation. For example, one paper ...
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1answer
59 views

“Pure” Yang-Mills and the absence of light matter

I am researching various models of Neutral Naturalness which involve the addition of an additional gauge group whose matter content is uncharged under SM color. Many of these theories state that their ...
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1answer
27 views

Do even modes exist for e.g. pipes closed at one end?

This is really a question about terminology, The wavelength of a standing wave in a e.g. pipe closed at one end and open at the other is said to be $\frac{4L}{n}$, where $L$ is its length and $n$ is ...
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62 views

Why optical phonons are called “optical”? [duplicate]

In diatomic lattice vibration, acoustical phonons correspond to vibration. But I could not understand the relevance of term optical in this context.
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1answer
85 views

Transmission coefficient and transmission probability

Are transmission coefficient and transmission probability the same terms? If not, could you please explain how they are related to each other?
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154 views

Why do we say that a photon is a particle if it is massless?

If light is made of photon particles and the photon doesn't have any mass but it is a form of energy (according to my thinking) then why do we call photons particles?
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2answers
165 views

Why is the ground state of a particle in a box called $n=1$?

For a quantum harmonic oscillator, the ground state in most sources is referred to as $n=0,$ and this state has zero nodes. For a particle in a box, the ground state in most sources is called $n = 1.$...
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1answer
86 views

Is a bound state a stationary state?

In Shankar's discussion on the 1D infinite square well in Principles of Quantum Mechanics (2nd edition), he made the following statement: Now $\langle P \rangle = 0$ in any bound state for the ...
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44 views

Name of real-valued representation of density matrix?

This is a specialization of my question https://math.stackexchange.com/q/3157300/ on math.SE. There are many ways to write the density matrix $\hat \rho$ as vector $\vec \rho$. In the Liouville space,...
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2answers
74 views

Nature of motion between comoving observers; What is the common time that they agree on?

This is a set of follow-up questions regarding this post. The following four queries are very closely related and needed to asked at the same place. Question 1 Is it really possible to regard the ...
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2answers
71 views

Name of the matrix that appears in matrix form of Hamilton's equations of motion

Consider a harmonic oscillator described by the second order differential equation $$\ddot{\phi} + \omega_0^2 \phi = 0 \, .$$ Defining $v \equiv \dot \phi$ we get two simultaneous equations \begin{...
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1answer
84 views

What is topological material?

Recently, topological material has been a hot topic in condensed matter physics, but I don't know what is topological material and how to distinguish topological material from band diagram. And how ...
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2answers
346 views

What is meant by “collective behavior” in the definition of plasma?

"Plasmas are many-body systems, with enough mobile charged particles to cause some collective behavior ." [M.S. Murillo and J.C.Weisheit Physics Reports 302, 1-65 (1998)]. In the above definition ...
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3answers
91 views

Summing up very basic terms in basic electricity [closed]

My attempt to define following terms as per my understanding. I am currently at high school. Electromotive force (EMF): Potential between two terminals when open circuited. Wikipedia's ...
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1answer
97 views

What is the difference between Closed and Bounded surface?

When I was going through "The Feynman's Lecture on physics" Volume-2 , I found the line "It is useful to speak of the flux not only through a completely closed surface, but through any bounded ...
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1answer
215 views

What is Snell's window?

Why is it that an underwater observer can see only a circular "window" and also can't see anything above the separating surface? Does the "window" depend on the depth?
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2answers
52 views

Ought we say 'body mass', rather than 'body weight'?

I'm asking in the context of medicine, where you're "massed" (or is it "weighted"?) on a scale. This answer beneath insinuates that 'mass' may be the preferred term, but it doesn't outwardly clarify ...
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85 views

What do we mean by curly braces in an atomic configuration?

What do the '{` mean in atomic configurations e.g: 1s(2)2s(1)2p(2){3P}3p(1) 1s(2)2s(2)2p(3){4S}3p(1)
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317 views

What's the difference between linearly polarised and plane-polarised waves?

To explain polarisation, my book gives an example of a transverse wave in a string, and explains as: Since each point on the string moves on a straight line, the wave is also referred to as a ...
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2answers
99 views

Newton's Second Law of Motion - Net Force Vs. Velocity

I am wondering about a question regarding Newton's Second Law of Motion. For an object to have a constant velocity, it means the total net force is 0 since there is no acceleration. Does that mean ...
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1answer
118 views

What's the difference between a generating function and a generator?

Usually in physics we use the notion generator to describe the infinitesimal elements associated with any finite Lie group transformation. But in the context of the Hamiltonian formalism, all authors ...
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1answer
102 views

Different Schwinger-Dyson Equations

In the literature on QFT there are a lot of different equations that are all called "Schwinger-Dyson equation" so I wanted to know how are they related and if they have proper names. The first ...
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2answers
60 views

Is there a name for the un-integrated Lagrangian?

The "action" is a functional of fields and their derivatives integrated over a space-time volume. A Lagrangian is just integrated over the space dimensions. But what is the name of the thing to be ...
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1answer
96 views

What is energy in quantum mechanics?

Is it wrong to say energy is the expectation value of Hamiltonian? Or should I say energy is the eigenvalue of Hamiltonian?
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2answers
121 views

What's the name of the symmetry $ L \to L + \frac{d \Lambda}{dt}$?

In the Lagrangian formulation of Classical Mechanics, we have the freedom to add a total time derivative of an arbitrary function $\Lambda$ to the Lagrangian: $$ L \to L + \frac{d \Lambda}{dt} . $$ ...
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1answer
118 views

What is the relation between incompressible flow and laminar flow?

I have a small question about dynamics. My textbook shows me the velocity profile for an incompressible flow, which has a parabolic profile. Does this automatically mean it's laminar flow? I don't ...
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1answer
79 views

“Killing leaves” in General Relativity?

I now about Killing vector fields in GR but recently stumbled upon the notion of "Killing leaves" and couldn't find any simple explanation of this notion. For example, this paper writes: "integral ...
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2answers
174 views

Meaning of the term $V(x)$ in the Schrodinger equation [closed]

I'm new to quantum mechanics and I am currently trying to understand finite potential well (although my question is not specific to finite potential well ). In the Schrodinger equation, many texts ...
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1answer
38 views

What is the difference between supersymmetry and MSSM?

What is the difference between supersymmetry and MSSM? Please explain in a simple language i am just a beginner of supersymmetry
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2answers
79 views

What does Dirac mean by “proximity”?

I was reading Dirac's "The Principles of Quantum Mechanics" and on page 7 he makes the following statement: "Like the fundamental concepts (proximity, identity) which everyone must learn on his ...
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1answer
68 views

What are three-point functions?

I came across this term while I was trying to read this paper related CFT correlators. Can some please take some time out to explain what does it mean in general?
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27 views

I want to know the name of a type of cable

I was doing an experiment on photoelectric effect. The photocell had a cable from which both the anode and cathode wires came out. I was told to find out the name of the cable. here's a skillfully ...
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0answers
59 views

Is the work function a function? [closed]

The work function is the energy an electron needs to leave the metal. Why is it called a function? Its value is different for different metals, but that doesn't make it a function; density and melting ...
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2answers
219 views

Can magnitude be negative?

My teacher told that magnitude is the positive value of that quantity or the modulus of that quantity. he also told that vector quantities have both magnitude and direction and scalar quantities have ...
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2answers
2k views

Can two atoms be a crystal?

In the physics literature, you can often find the term "two-ion crystal", when talking about two ions that are confined in a e.g. Paul trap. How is this possible? Shouldn't a crystal be a structure ...
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1answer
212 views

What is clean limit and dirty limit?

In superconductor there has two limits, one called as clean and other one called dirty limit. But what are that meaning? What means clean and dirty? How the coherence length depends on the electron ...
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0answers
47 views

Is there a difference between false (metastable) and local equilibria?

Or is it permissible to use the terms interchangeably? If there is a difference, what is it?
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2answers
470 views

What are “large hadrons”? Are there also “small hadrons”?

The BBC News article Cern plans even larger hadron collider for physics search says: The difficulty with Cern's proposals for a larger Large Hadron Collider is that no one knows what energies will ...
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1answer
77 views

Meaning of ft-values in nuclear physics

What is the "physical" meaning of the ft-value for a decay channel? From what I understand, the ft-value is inversely proportional to the square of the matrix element, hence I would expect a larger ft-...
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1answer
51 views

What does the term “no slipping” mean in mechanics?

Say, I have two blocks. One block is on top of the other. Suppose friction is present everywhere. What is the condition for no slipping?
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1answer
60 views

What does $\mathcal{N}$ refer to in Gauge theories?

Context: I am a second-year (undergraduate) physics major applying for a summer research position. The investigator is working on Quiver Gauge Theories and in response to my inquiry email he told me ...
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4answers
837 views

What are the differences between specific latent heat and latent heat?

What are the differences between specific latent heat and latent heat? As far as I know, latent heat is the heat required or released during the change of state, without change of temperature. So ...
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2answers
69 views

Angular Momentum of a Rigid body

When defining angular momentum or rather calculating angular momentum what is the difference in the use of the terms "with respect to" , "about a point" or "in the frame of" ? Are the angular ...
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1answer
46 views

Are Generations and Families of elementary fermions one and the same?

I've seen both terms being used in papers and it seems to me they essentially mean the same thing referring to three generations of leptons and quarks as families. Is this true or are there some ...
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1answer
80 views

What is 'definite' variable in QM?

I have gone through a few of the questions on the website regarding this particular query, but I have not understood what they meant. When a question says that a particle has definite momentum, are ...
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1answer
36 views

Name of measurement expressed as the sum of different units

In a paper I'm writing, I want to make a comment about errors in an old paper made when doing arithmetic with measurements expressed as as the sum of quantities with two or more different units, for ...
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4answers
1k views

What precisely is a *classical* spin-1/2 particle?

I was recently having a Twitter conversation with a UC Riverside Prof. John Carlos Baez about Geometric Quantization, and he said (about his work) that "Right. For example, you can get the ...
16
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3answers
2k views

Is the second law of thermodynamics a “no-go” theorem?

As defined here, there are several no-go theorems in theoretical physics. These theorems are statements of impossibility. The second law of thermodynamics may be stated in several ways, some of which ...
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1answer
196 views

Difference classical and statistical thermodynamics

What should I read to link between classical thermodynamics or engineerig thermodynamics and statistical mechanics?
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2answers
280 views

Normal force not perpendicular to the surface

In my class about mechanics i had to solve this problem, but it was never really explained. The solution is found beneath in a picture. In the solution they also calculate the angle of the normal ...