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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What is 't Hooft-Veltman gauge? What are the interactions in SM in 't Hooft-Veltman gauge?

What is 't Hooft-Veltman gauge? I can't really find any suitable answer online. If we introduce this gauge in SM, then what becomes interactions?
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What is rational CFT?

The definition of rational CFT was rather confusing. There's were many references saying the different definitions: $c$ to be a rational number. the representation of CFT have finite primaries. (...
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What is the meaning of flavor-scheme?

When they make simulations to predict cross-sections or differential cross-sections, they say events simulated in the 5FS and 4FS (Flavor scheme). What are these flavor schemes?
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4 answers
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What is constant in an isobaric process, internal pressure or external pressure?

I was taking a course in thermodynamics, where the instructor started to derive the formula for work in case of isobaric process for an ideal gas It stated W = -∫ P_ext dV And then equated it with -∫...
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Why is bulk modulus positive in equilibrium?

$B=-PV/\Delta V$ The negative sign indicates that when pressure increases, the volume decreases. That is, if $P$ is positive, $\Delta V$ is negative. Thus for a system in equilibrium, the value of ...
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1 answer
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Name in common to refrigeration and heat pumping

I'm struggling while re-visiting gas laws and some of their applications. Graduates and Googling explain refrigeration and heat-pumping, as if dependent on the refrigerant's gas-liquid changes of ...
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What's minimal model?

Minimal model In Francesco conformal field theory page 210 only $$ c=1-\frac{6}{p(p+1)} $$ was the representation without the nonunitary representation. However, for the theory to be unitary, it only ...
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1 vote
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What is minimal model, unitary, rational, and irrational CFT? [closed]

Minimal model In Francesco conformal field theory page 210 only $$ c=1-\frac{6}{p(p+1)} $$ was the representation without the nonunitary representation. However, for the theory to be unitary, it only ...
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1 answer
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In functional derivative the starting point confusion

how can one define the functional derivative $$\delta F= F[f+\delta f]-F[f].$$ Is it by definition or any physical reason holds for it.
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Why are there two definitions for the angular momentum of a particle with respect to a moving point?

There seem to be two definitions for the angular momentum of a particle with respect to a moving point. See the figure below. Let $O$ be the origin of a coordinate system in an inertial frame. Let $Q$...
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What is the correct definition of EMF in a circuit?

The EMF $\mathcal{E}$ in a closed circuit $C$ is defined as the closed line integral of the electric field ${\vec E}$ around the loop: $$\mathcal{E}=\oint_C{\vec E}\cdot d{\vec\ell}.$$ But in Section ...
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3 answers
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Understanding the definition of a path integral

In the Book "Quantum Mechanics and Path Integrals" by Feynman & Hibbs the path integral is approximated (page 32 and following) by $$ K(b,a)\approx\int...\int\int\phi[x(t)]dx_1dx_2...dx_{...
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-4 votes
1 answer
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Derivation of Fourier Transform in Quantum Mechanics [closed]

I recently came across an expression for Fourier Transform in Quantum Mechanics given by: I tried to derive with starting with the Fourier Transforms, and it went like this: I'm not able to find a ...
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What is the difference between electrostatic and electric potential energy? [duplicate]

In circuits what is the difference between electrostatic and electric potential energy? Side question does electrostatic potential energy even exist in a circuit?
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4 votes
4 answers
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What is the difference between electrostatic and electric potential?

What is the difference between electrostatic and electric potential in a circuit?
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When we say a rigid body is a system of particles, what exactly are 'particles' here?

In Newtonian mechanics, a particle (in my knowledge) is a point-like mass with no shape and size, deformation, rotation and internal movements, which is an idealized model of an object which does have ...
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-1 votes
1 answer
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Is electric field lines always towards the negative charge?

Let an electron be placed at a distance from a $-q$ charge. We learned that electric field lines are into the negative charge. But here direction of force on electron due to negative charge is away ...
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-2 votes
1 answer
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Distinction between mechanics and thermodynamics [closed]

I claim to be able to put the distinction between mechanics and thermodynamics as follows: "In mechanics, energy is related to mass, whereas in thermodynamics, energy is related to a particle or ...
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What is a current?

I am confused. One GCSE video on YouTube says it is a flow of electrons around a circuit; while, my textbook says it is a flow of charge around a circuit, carried by electrons. Since charge can be ...
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2 answers
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On mathematical level, what exactly is time in Newtonian mechanics?

One easy answer would be that in practical purposes, it is a very special sort of parameter. This point comes up quite clearly when we do the derivation for the work-energy theorem: $$ W = \int\mathbf{...
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3 votes
1 answer
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What were the $r$ and $n$ of $\theta$s (Polchinski String theory section 8.6 page 265)?

In the Polchinski String theory section 8.6 page 265 In generic backgrounds, all the $\theta$s are distinct and the only massless vectors are the diagonal ones, $i = j$. The unbroken gauge group in ...
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What is the difference between equation of motion, equation of change and momentum equation in transport phenomena?

What is the difference between equation of motion, equation of change and momentum equation in transport phenomena?
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Why is it said that the lightest neutrino is relativistic?

The neutrinos from the cosmic neutrino background have a temperature of $T_\nu=1.945K$, that is an energy of $E=\frac{3}{2}k_BT_\nu$. If the neutrino's mass is around $0.1eV$ $$ \frac{3}{2}k_BT_\nu<...
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Mechanical hysteresis

can someone explain what hysteresis is in a mechanical system. I briefly think I understand, say we have a rubber cylinder and compress it with 15N then to 30N when we reduce the force back to 15N ...
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1 answer
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Renormalization Group Flow

I am reading a book on effective field theory where the following "renormalization group equation" is given: Now a quick search on google shows a bunch of interesting pictures of "...
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2 answers
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Evaluating conjugate momentum from a given Lagrangian density

I have the following Lagrangian density $\mathcal{L}$ where $$ \mathcal{L}=\frac{1}{2}\left(c[\partial_{t}\phi(x,t)]^{2}-\frac{1}{l}[\partial_{x}\phi(x,t)]^{2}+\frac{1}{\omega_{J}^{2}l}[\partial_{x}\...
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1 answer
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What does Penrose mean when he talks about topology of spacetime?

Let us now set aside the question of the submicroscopic structure of space-time and concentrate, instead, on its large-scale properties. In this case, we may imagine that the smooth manifold picture ...
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0 answers
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Is it a pre-requisite for something to have constant mass to be a 'system' in Mechanics?

I deal sometimes with control volumes, and we have closed systems, in Newtonian mechanics we often just describe a 'system' without defining if it's closed or open, if we have a 'mass flow' such as a ...
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0 answers
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What exactly is energy self-shielding in nuclear physics?

I have recently been trying to understand self-shielding, both energy and spatial self-shielding. I am having a particularly hard time understanding energy self shielding. Thus far, everything I’ve ...
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What is a "massive phase" in the string theory or CFT?

When reading through some articles, one encountered a vocabulary termed as a "massive phase" in the string theory or the CFT, in the case where a theory followed an RG flow between UV and IR....
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0 votes
1 answer
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Arbitrarity of $i$ in the propagator

My question is simple: how arbitrary can the factor in front of the propagator be? What I mean by that is, if we call the wave operator $K$ and the propagator $G$, I've seen different books use ...
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1 vote
4 answers
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What is the clear difference between interference and diffraction? [duplicate]

Richard Feynman said in his book. "No one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage, and there is no ...
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Parity and intrinsic parity definitions

The action of parity operator on wavefunctions is defined as a reflection in the origin $$\hat{P}\Psi(\boldsymbol{r},t)=\Psi(\boldsymbol{-r},t)$$ In particle physics, though some books define its ...
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0 answers
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What is the difference between photoelectric effect and photo-ionization?

Photoionization, ionization by a photon, and the photoelectric effect aren't they identical? If not then what is the phenomenological difference between them?
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2 votes
1 answer
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What is the difference between "cluster states" and "graph states"?

I wonder about the difference between the cluster state and the graph state. I guess the only difference is the graph of the cluster state is limited to a two-dimensional square lattice The concept of ...
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0 votes
1 answer
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What is $B(N)$ crystal structure? What does this nomenclature stand for

Is it basic cubic with 20 atoms? I can't find the explanation for this nomenclature online. Maybe I could find it in a textbook, but if someone answers it here, other people can just google it.
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0 votes
1 answer
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Can you explain me the definition of wave number as defined in theoretical physics? [duplicate]

Wavenumber, as used in spectroscopy and most chemistry fields, is defined as the number of wavelengths per unit distance. The corresponding formula is $$k=\frac{1}{\lambda}.$$ However, in theoretical ...
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2 answers
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What is an eigensystem? Could you provide a simple example? [closed]

Also, what is the difference between an eigensystem and the eigenspace?
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4 votes
3 answers
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What exactly is order of magnitude?

I am little bit confused with what order of magnitude is. In my book it says, when we write approximate values of quantities in powers of ten i.e $10^b$, then $10^b$ is the order of magnitude. But ...
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2 votes
8 answers
317 views

Are Newton's laws just definitions?

I have read a bunch of articles online regarding my question but none have helped. Newton's Laws: In an inertial reference frame, an object's momentum doesn't change unless the object is acted upon ...
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0 votes
2 answers
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Does Gas constant depend on molecular weight?

I came across the following question recently Calculate the difference between two specific heat of 1 g of helium gas at NTP. Molecular weight of helium = 4 and J = $4.186×10^7$ erg $cal^{-1}$ The ...
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Why can't we use integral of $x$, $y$ and $z$ in calculating moment of inertia

I've got no problems with calculating the moment of inertia/tensor of inertia of a cube using an integral over the lamina of a cube. However, I must be missing something obvious or making some sort of ...
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5 votes
2 answers
387 views

Why does the Strange Quark have Strangeness -1?

I have been trying to find an explanation for the strange quarks negative strangeness value, I understand the term strangeness predates the quark model, but I'm unsure if terminology carry over is the ...
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What is the meaning of a conductor in equilibrium?

Electric field lines are always perpendicular to the surface of a conductor in equilibrium. what is the meaning of a conductor in equilibrium?
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1 answer
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Radial position operator

While trying to find the expectation value of the radial distance $r$ of an electron in hydrogen atom in ground state the expression is: $$\begin{aligned}\langle r\rangle &=\langle n \ell m|r| n \...
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1 answer
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Definition of a wave packet

In Shankar's QM book page 168, the author stated a wave packet is any wave function with reasonably well-defined position and momentum. What does he mean by resonably well-defined position and ...
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Meaning of "$=$" in $\vec{F}=m\vec{a}$ (for example)

I don't understand how the two could really be one and the same. E.g. we can exert forces $\vec{F}$ and $-\vec{F}$ on a body and it's acceleration will not change. I don't think it makes sense to say ...
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Can a primary constraint contain spatial derivative of the field?

I am currently studying the Hamiltonian formulation of GR and I have problems understanding this definition of primary constraint. In the textbooks, primary constraint occurs when a momentum conjugate ...
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What's the definition of temperature ? What's the meaning of reaching a zero temperature and infinity temperature? [duplicate]

I'm taking a course about statistical mechanics and it is completely new to me . We've learned about entropy and how when 2 different sub-systems comes to contact the entropy of the whole system keeps ...
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2 answers
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What is a state function?

What is a state function? I've been briefly introduced to the idea in an introductory module, and I'm confused by the whole idea, I understand the 'path dependence' from line integrals, but is it ...
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