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.

2,187 questions
Filter by
Sorted by
Tagged with
51 views

Explanation for the $(a,b)$ Notation in Super Conformal Field Theories [duplicate]

In the literature, there are many theories and quantities which I usually seen in the context of conformal field theory that described via the notation of $(a,b);\quad a,b\in\mathbb{Z}$ for example: ...
8 views

• 39
1 vote
39 views

What is the formal definition of capacity fade?

https://www.ipaceforums.co.uk/threads/capacity-fade-vs-power-fade.6794/ According to this post capacity fade is defined as the percentage of total capacity left. So I'm assuming it would be calculated ...
• 39
235 views

How many significant figures does the speed of light have? [duplicate]

Since the speed of light (in a vacuum) is a constant, its number of significant figures should be infinite, right? But if I were to say that the speed of light $= 3\times10^8$, would the number of ...
• 21
46 views

What is the difference between loudness, amplitude and volume?

i'm confused because some websites I've seen they are not the same, while my textbook says they're the same, and I'm trying to find the distinction between amplitude, loudness and volume.
49 views

Strogatz's condition on definition of energy

In, Nonlinear Dynamics And Chaos, 2nd edition page 160, by Steven H. Strogatz, he writes Let’s be a bit more general and precise. Given a system $$\dot x =f(x),$$ a conserved quantity is a real-...
23 views

What is meant by optical density?

I’m trying to research about optical density for a school task, but the definitions online are confusing me. From what I’ve gotten, optical density is: how much the intensity of light is increased or ...
92 views

GR and Riemann Surfaces -- does the complex plane have anything to do with it?

I have only the vaguest understanding of Riemann Surfaces -- my sense is that Einstein used them in General Relativity because of their shape. But Riemann Surfaces I think are not just deformations of ...
• 2,258
1 vote
32 views

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 ...
• 379
75 views

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: ...
• 442
36 views

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.
128 views

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 ...
95 views

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 ...
• 1,989
89 views

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 ...
32 views

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 ...
36 views

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?
• 772
1 vote
39 views

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 ...
• 608
91 views

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 ...
111 views

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 ...
• 13
54 views

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 ...
• 11
55 views

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 ...
• 153
163 views

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 ...
• 539
106 views

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 ...
• 91
49 views

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 ...
58 views

52 views

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 ...
1 vote
58 views

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 ...
1 vote
96 views

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 ...
54 views

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 ...
• 914
92 views

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 ...
201 views

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 ...
• 305
45 views

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 ...
• 309
32 views

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 ...
1 vote
59 views

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 ...
19 views

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 ...
1 vote
66 views

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 ...
• 11