Questions tagged [terminology]

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

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3
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6answers
16k views

What is the difference between conventional current and electronic current?

what is the difference between conventional current and electronic current? How are they linked to one another?
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1answer
340 views

Mutually Commutative

What is the definition of a Mutually Commutative set of operators? I've found articles describing a complete set of mutually commutative operators, but I can't actually find what mutually commutative ...
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1answer
42 views

What is the difference between “Inverse source problem” and “inverse scattering problem”?

As above in the title. I know the inverse scattering problem problem in the context of recovering dielectric profile of imaging domain from scattered fields measured at certain locations. But, what is ...
3
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1answer
1k views

What is a Witten diagram?

Recently I heard the terminology of Witten diagram. Studying QFT, I frequently see Feynman diagrams and use them to compute scattering amplitudes, one-loop corrections and so on. In string theory ...
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1answer
191 views

What are $S$ and $L$?

In a helium atom, the total spin of the electrons is 0, suggesting that the total spin quantum number S is the sum of the ms quantum numbers (1/2-1/2=0). However, many sources say that the total spin ...
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2answers
2k views

What is atmospheric stratification?

In the context of atmospheric stability, what are the meanings of stable or unstable stratification? What is stratification?
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2answers
49 views

What is baking and what are the effects?

In their experiment, Davisson and Germer had to bake the nickel mass because it was oxidized. What is baking and what does it do to the lattice of the metal?
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3answers
4k views

Why is static electricity called static?

They called it "static" because "it doesn’t go anywhere". In order to create static electricity, you have to rub two different materials. When you rub them, the electrons move. So, why is it called ...
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0answers
28 views

What's the difference between decay width and canonical decay width?

As I mentioned, I see this conception of "canonical decay width" in a paper, I looked up in the Wiki, but I can't find any thing could interpret this or any thing special about this, so I'm wondering ...
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1answer
50 views

How is $\delta \theta$ related to angular resolution?

Does the expression $\delta \theta \sim 3 ^\circ $ have a special meaning other than about 3 degrees? I was searching for the angular resolution of neutrino detectors and looking at the Super-...
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0answers
36 views

Is the ‘diffracting angle’ talking about the first minimum or first maximum?

So when we talk about diffraction for single slits, we refer to the first minimum as the ‘diffracting angle’. However, in other experiments with wave particle duality (for example electron ...
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1answer
170 views

Physical meaning of the space-space components $T^{ij}$ of the stress-energy tensor $T^{\mu\nu}$

The time-time component $T^{00}$ and the time-space components $T^{0i}$ of the energy-momentum tensor $T^{\mu\nu}$ are respectively called the Hamiltonian (energy) density and the momentum density. ...
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2answers
70 views

Precise definition of the vertex factor

Just a short question about the vertex factor in QFT. When I have an interaction Lagrangian $$\mathcal{L}_{\mathrm{int}}=-\frac{\lambda}{3!}\phi^3$$ with a real scalar field $\phi$, is the vertex ...
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2answers
123 views

What are $a$ and $a^*$ called in the context of a classical harmonic oscillator?

Consider a harmonic oscillator defined by the coupled differential equations \begin{align} \begin{split} \dot{X} &= \omega Y \\ \dot{Y} &= - \omega X \, . \end{split} \tag{1} \end{align} ...
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1answer
48 views

Lifetime definition

In Walter Thirring book Quantum mechanics of Atoms and Molecules he says that the probability that a initial state $\Psi$ be again measured at later time is $|\langle \Psi|\exp(-iHt)\Psi\rangle|^2$ ...
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1answer
38 views

Spacelike separation, special case

This is merely a terminology question. Consider two events A and B. Now suppose A and B happen in two different black holes, i.e. there is no way from A to B (or B to A). Is this fundamentally ...
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1answer
39 views

Going from wavepacket to wavefunction

Suppose we have a one-dimensional wave packet $$\varphi(p)=A\Theta[(\hbar/d)-|p-p_0|]. $$ I want to, at first, determine the constant of normalization, and the wavefunction $\psi(x)$. However, there ...
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1answer
51 views

Is it, in general, better to speak of potential energy density or of energy density? [closed]

I read in this article: Antimatter And here we are: at the very end of the feasibility spectrum into the fantastic. Antimatter is made of antiparticles, which have the same mass as particles ...
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7answers
982 views

What is motion?

I never thought of this before but when an $8^{th}$ standard student asked me to explain what momentum is, I simply said that it the amount of motion contained in a body and tried to explain that how ...
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3answers
90 views

What x20 x40 x100 magnification means?

I want to buy a biologic microscope for fiber analysis, thus I need to see details of a fiber of around 20μm. Could you please explain what "x20" magnification means? I understand that it will not ...
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1answer
59 views

What is a cold black hole in astrophysics?

I found the word 'Cold Black hole' in some academic papers. I think it is concerned with thermodynamics of black hole but I don't know exactly what is cold black hole. Please help me to understand ...
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4answers
1k views

What is the difference between the valence shell and the valence band?

What is the difference between the valence shell and the valence band? The valence band is usually defined as the highest filled band whereas Wikipedia defines the valence shell as the outermost shell ...
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2answers
916 views

What is the difference between sound and vibration?

As far as I know, the only difference between sound and vibration is that sound propagates but vibration does not. In most cases, they are the same. Please help clarify these concepts.
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2answers
1k views

Difference between Oscillatory motion and vibratory motion

What is the difference between oscillatory motion and vibratory motion. I have read in my book that "If the amplitude of oscillatory motion is extremely small,the motion is called vibratory motion". ...
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1answer
174 views

Spring constant, but intrinsic to material, not rest length

If you have two metal springs that are coiled in the same way, but one is twice the length of the other, the spring constant will be half as large for the longer one. That makes sense of course. What'...
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1answer
62 views

Decomposition of a Cartesian tensor

In "Modern Quantum Mechanics" by Sakurai J.J. he gives an example of a Cartesian tensor of rank $2$ which is a dyadic formed out of two vectors $\mathbf{U}$ and $\mathbf{V}$, i.e. $T_{ij} \equiv U_i ...
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3answers
52 views

Why is $m_{\ell}$ called the magnetic quantum number? What is its association with magnets?

I am going over my quantum lecture notes and I can't seem to link the quantum number $m_{\ell}$ with any magnetic property. It just seems to specify the shape of an orbital with a particular principal ...
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2answers
1k views

Confusion with partial derivatives as basis vectors

So I have seen that the directional derivative can be written as $$ \frac{df}{d\lambda} = \frac{dx^i}{d\lambda}\frac{df}{dx^i} $$ And we can identify $ \frac{d}{dx^i} $ as basis vectors and $ \...
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1answer
64 views

Thermal vs Thermic

Thermal vs Thermic Which one of this two terms is the most correct as an adjective meaning "relative to temperature" ? If neither are, which one is the most used in a scientific context ? Do they ...
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3answers
63 views

I can't understand one of deduction in Simple Harnomic Motion, can anyone help?

source:http://farside.ph.utexas.edu/teaching/336k/lectures/node18.html#e4.8 in order $x=0$ to be a stable equilibrium point we require both $$f(0)=0$$ and $$\frac {df(0)}{dx}<0$$ Now, our particle ...
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1answer
65 views

Why is it called “Conservative” field?

I understand -mathematically- what a conservative field is; it is a vector field that can be expressed a gradient of some scalar function OR it is a vector field whose line integral is path ...
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1answer
53 views

Is there a name for the repulsive force or pressure quality of energy that is harnessed to do work?

I read a book recently (The Information by James Gleick) that states energy is conserved. The author explained that the energy in gasoline used for driving still exists in the same amount although ...
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1answer
64 views

Why theoretical gravity reactors are often named “anti-gravity” reactors? [closed]

I know that to create gravitational waves that effect human bodies or devices such as spacecrafts, huge bodies of matter are required, such as a planet or a star, and at least in theory, also black ...
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1answer
1k views

What is a stoquastic Hamiltonian?

Recently, I've often read about the term 'stoquastic Hamiltonian'. But I couldn't find a precise definition anywhere. I found that the Ising-Hamiltonian is a stoquastic Hamiltonian, but that does not ...
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4answers
2k views

Why do we say “Spacetime Curvature is Gravity”?

Although "Spacetime Curvature is Gravity" is the first statement that is told to an infant by the "popular science", I believe that really really misrepresents what GR has to say. I am posting this ...
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2answers
114 views

What are laws in physics? [duplicate]

Many times a precise definition of something in physics is not available but yet there exist some rough definitions that guide us through. I need the same rough (if not precise) definition of physical ...
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5answers
3k views

Velocity is to speed as acceleration is to ________? [duplicate]

Vectors give both magnitude and direction, whereas scalars can be thought of as magnitude without direction. So, velocity is a vector since it is speed with direction. Similarly, what is the scalar ...
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3answers
60 views

Are absorption and attenuation the same thing?

Are absorption and attenuation different words for the same thing? Wikipedia separate has articles on Absorption (Acoustics) and Accoustic Attenuation. I don't see a clear physical distinction between ...
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4answers
3k views

The notion of an adiabatic process in thermodynamics -vs- quantum mechanics

I'm confused about the terminology in the two contexts since I can't figure out if they have a similar motivation. Afaik, the definitions state that quantum processes should be very slow to be called ...
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2answers
368 views

What does it mean when we say 'The difference between two quantities is of first order'?

This question is about the explanation below Eq.(6.19) of Modern Quantum Mechanics by Sakurai Nepolitano (2nd edition) Let ${\bf j}(dx)$ be an operator that translates a point $x$ to $x+dx$. jf(x) = ...
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0answers
19 views

Approximating the wave functions of multiple electrically charged elementary particles as a function of time and position

As I understand it the wave function of a free particle in natural units is defined by the equation $$\Psi(\vec{r},t)=\left(\frac{a}{a+it/m}\right)^\frac{3}{2}e^{-\frac{{\vec{r}}^2}{2(a+it/m)}}$$ with ...
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1answer
76 views

What is the term for “shock” absorbed by car suspension?

I’m looking for the correct term to find equaltions for car shock absorber physics. Searching for “shock” returns a lot of irrelevant results. What is the correct term for the force exerted by a road ...
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1answer
160 views

What are the boundary conditions simply?

I don't know what are actually boundary conditions for incompressible fluids (I don't really understand what they are.) So may you give me a simple explanation in the incompressible fluids only?
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6answers
28k views

What is the difference between Raman scattering and fluorescence?

What is the difference between Raman scattering and fluorescence? Both phenomena involve the emission of photons shifted in frequency relative to the incident light, because of some energetic ...
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0answers
33 views

What is the name of the thermodynamic potential $U - \mu N $?

It is the exponent of the terms in the summation for grand canonical partiton function. What is its name?
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2answers
48 views

How can two forces be in the same direction AND be of the opposite sign?

In his book "Einstein's Theory of Relativity" (1962 edition) on page 147 Max Born wrote: "We next take two such test bodies P1 and P2, bring them in turn to the same point in the vicinity of M, and ...
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3answers
839 views

What vector field property means “is the curl of another vector field?”

I'm an undergraduate mathematics educator and I teach a lot of multivariable calculus. I posed this question on MSE over four years ago and I haven't gotten any definitive answers (despite 12 upvotes ...
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2answers
76 views

Feynman Probability lecture 6 - probability density graph

I'm trying to understand the 6-7 graph in the Feynman lecture 6 on Probability chapter (6–4) A probability distribution He says: "We plot $p(x)$ for three values of $N$ in Fig. 6–7. You will ...
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0answers
17 views

Can lead field be a scalar field?

In electrophysiology it is common to use lead (vector) field to describe relation between an electric dipole and a measured potential. Can the lead field be generalized as a tensor field? I am mostly ...
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1answer
28 views

Fluids mixture density prediction

As you know 100 ml of H2O mixed with 100 ml ethanol is not 200 ml What is the official name of this 'volume loss'? Is it possible, and if so, how, to calculate, before mixing, what the density of a ...

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