# Tagged Questions

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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### Differences between eigenstates, bound states and stationary states [closed]

I am not very clear about the differences between eigenstates, bound states and stationary states.
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### Is the electric current a flow of charges?

Wikipedia defines charge as the fundamental property of forms of matter that exhibits electrostatic attraction or repulsion in the presence of other matter.Strictly speaking, while defining an ...
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### What is the difference between flow and expansion?

Fluids (both liquids and gases) will move from one point in space to another due to a potential gradient. Some examples may be: 1) horizontal pipe flow, a fluid will move from a region of high ...
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### Thermal diffusion and the 2nd law of thermodynamics

If we look at the definition of heat flux, $$\stackrel{\to }{J}=-\kappa\stackrel{\to }{\nabla}T \, ,$$ we may notice that it's defined to be a vector showing in the opposite direction of the ...
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### 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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### Does the term phase difference apply only for sinusoidal waves?

This question may sound dumb, (it will to me, hopefully, in a day or two!), but does the term phase difference apply only for sinusoidal waves? Wikipedia defines 'phase' as the following: Phase ...
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### Fermi energy on a “fermion pre-gas model”

I'm having serious trouble while trying to follow an example from Callen's "Thermodynamics and an introduction to Thermostatistics" regarding the definition of the Fermi energy. In said example one ...
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### Why are the quantum observables defined on opens sets a presheaf and not a sheaf?

In local quantum field theory or AQFT one can mathematically describe over each open set $U$ of a spacetime $M$ the quantum states or observables of the theory. This structure is commonly referred as ...
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### Does the definition of escape velocity apply strictly to an initial velocity of a ballistic projectile?

In Shivam Sarodia's answer to Escape Velocity question he states: "For a rocket launched exactly at escape velocity" This seems to be a repeated, and unclear way of discussing the matter of escape ...
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### Definition of a Supercluster

A group of astronomers in September 2014 redefined what classifies a supercluster. Before this, the supercluster where the Milky Way resides was the Virgo Supercluster. Now, the Virgo Supercluster &...
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### What's the difference between the Fermi level and the electrochemical potential?

I was asked in a Thermostatistics test to compute the electrochemical potential $\mu(T)$ and the Fermi level $\epsilon_F$ for a system of non-interacting fermions, with two possible energetic states ...
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### How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
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### What exactly is work?

What exactly is work? My book confuses me: a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the ...
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### What is the definition of time? [duplicate]

I wanted to know the definition of time just like as we define displacement, current etc. **Note:**There should be no mention of time period or time interval in the definition.
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### What is the defintion of a current-current diagram?

Right now I am facing some Feynman diagram calculations and in the instructions I am reading the phrase current-current diagram appears quite often so I wanted to know: What is the definition of a ...
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At the moment I am going to a physics camp. I also do vex robotics. I am trying to use the equations to help me build my robot perfectly. Right now I'm working on how fast the throwing wheels should ...