The definition tag is used in situations where the question is either about how some term or concept is define 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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5answers
465 views

Definition of entropy in thermodynamics

In most textbooks, the definition of entropy in reversible processes on a system $S$ is given simply as $$d S=\delta Q/T.$$ It seems to me this definition is insufficient since it does not specify ...
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3answers
519 views

What exactly is the “coherence” between waves?

I know, by definition, that coherence means that a pair of waves have constant phase difference. What does this mean? Does it mean they always have a 360 degrees, or 0 degrees phase difference? Or ...
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2answers
880 views

Can we define tension in a string as the reactive force produced in a string being pulled at both ends?

In my textbook, the definition of tension was given that Tension is the reactive force which exists when string is being stretched at its both end. After it there was a case given that to calculate ...
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votes
1answer
458 views

Hamiltonians, density of state, BECs

When working with Bose-Einstein condensates trapped in potentials, how can one tell what the density of state of a system of identical bosons given the Hamiltonian, $H$? (I have been told that it is ...
3
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1answer
100 views

Rigorous definition of degrees of freedom

According to this Wikipedia article, the definition of degrees of freedom is: The degree of freedom (DOF) of a mechanical system is the number of independent parameters that define its ...
2
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1answer
3k views

Why is the mechanical advantage of a wedge = length of slope/ width?

Mechanical advantage is defined as Force Output/Force Input For a symmetrical wedge with the length of the slopes being equal and the width being the distance between the end points, the articles ...
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1answer
190 views

What is many-body bound state?

Bound state by definition is a state when particles are bounded together, so then "many-body bound state" would be bound state for a system of many bodies. Then I have several puzzles: 1. is the state ...
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1answer
65 views

What does degrees of freedom mean in the context of vibrations?

If you have an $N$ degrees of freedom system what does this mean? What is the difference between a 1 and a 2 degrees of freedom system?
0
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1answer
140 views

Is displacement in circular motion a chord or an arc?

When taking the displacement between two points along a circular path to calculate its velocity, do you take the length of a chord connecting the two points or do you take the length of the arc ...
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1answer
43 views

How to implement the form of current density in a Hall Effect related calculation?

Please consider the following; Question. A rectangular plate of semiconducting material has dimensions 10mm x 4mm x 1mm. A current of 3 mA flows along the length and a Hall Voltage of 13.6 mV is ...
0
votes
1answer
165 views

Degrees of freedom in double Atwood machine?

Why the degree of freedom in double Atwood machine (one block on one side and a pulley with one block in its each side on other side) is 2 and not 1? According to the formula $s=3*n-m$; where ...
0
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1answer
310 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
3
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0answers
98 views

What are Killing spinors?

What are Killing spinors? How can they be motivated? Are they directly related to Killing vectors and Killing tensors and is there an overarching motivation for all three objects? Any answer is ...
3
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0answers
34 views

Is renormalization associated with a volume scale or with an energy-momentum and length scale?

Given that real-space renormalization blocks together small volume elements to construct larger volume elements, is it more appropriate/helpful to consider the renormalization scale to be a volume ...
2
votes
0answers
45 views

Regular initial data

I have a very basic question. What exactly is meant by "regular" initial data in general relativity? Does it mean smooth? at least $C^{2}$? All literature on the subject just uses this term without ...
2
votes
0answers
124 views

Holonomy twisting

There is Witten's topological twist of standard SUSY QFTs with enough SUSY into Witten-type TQFTs. What is a holonomy twist?
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0answers
44 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
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0answers
108 views

How is Infinitesimal coordinate transformation related to Lie derivatives?

I am reading the book "Gravitaion and Cosmology" by S. Weinberg. In section 10.9, while discussing Lie derivatives of tensors of different ranks, he makes a general comment: The effect of an ...
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0answers
82 views

Should Brillouin zone be a continuous object rather than a discrete one in the thermodynamic limit?

For example, just consider a 1D atom chain with $N$ sites and lattice constant $a=2\pi$, under periodic boundary conditions, the crystal momentum reads as $k=\frac{n}{N}\frac{2\pi}{a}=\frac{n}{N}$, ...
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0answers
2k views

Definitions in thermodynamics: temperature, thermal equilibrium, heat

I'm currently reading Fermi's "Thermodynamics" and I'm trying to grasp the (possibly different) right definitions for temperature, thermal equilibrium, heat. To clarify, I'm looking for definitions ...
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0answers
507 views

How is the term “Born level” usually defined?

How is the term "Born level" usually defined, e.g. in talking about the $pp\to Z/\gamma^*\to e^+e^-$ cross section at Born level?
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0answers
22 views

What exactly is wavefield extrapolation?

I am trying to understand what exactly wavefield extrapolation is. I can understand extrapolation of a function, 'wave' and 'field' as well; but could not understand the meaning or the problem ...
0
votes
0answers
40 views

What are non-local charges?

In integrable systems, for example in the XXX spin chain, one encounters non-local charges (that form a Yangian). They are fine since the Yangian generate an infinite number of them, which gives us ...
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0answers
90 views

Transverse Trace-less quadrupole

In Gravitational radiation, it is convenient to work with "transverse traceless quadrupole tensor". However there are three terms: "quadrupole moments" , "reduced quadrupole moment" and "transverse ...
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0answers
78 views

What are the Fermi and Debye temperature constants?

What are the Fermi temperature and Debye temperature constants? We were discussing these in class and I don't fully understand what these constants are or why we have them. Can anyone explain?
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0answers
51 views

The relationship between the two statistical mechanical definitions of entropy

It seems like similar questions have been asked here; hopefully my question is not a duplicate. I am reading my textbook on the statistical mechanical definitions of entropy, and I am very confused ...
0
votes
0answers
142 views

Streamlines tangent to velocity vector

As from the title, I'm not too sure how they are related. Definition is that streamlines are instantaneously tangential to the velocity vector of the field. Why would a streamline that shows direction ...