All Questions

0
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1answer
10 views

Understanding angular velocity in spherical polar coordinates

I'm a first year physics student and i've just learnt this equation for angular velocity in spherical polar coordinates: $\omega=\dot{\phi}\mathbf{e_z}+\dot{\theta}\mathbf{e_\phi}$ The diagram i ...
0
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0answers
7 views

$T \bar{T}$ OPE

In page 157 of Di Francesco (Conformal Field Theory) it is said that the holomorphic and antiholomorphic components of the energy-momentum tensor have the trivial OPE $T(z) \bar{T}(\bar{w}) \sim 0$....
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0answers
16 views

Signal / electromagnetic wave propagation

The question is rather an everyday question: Think on an electromagnetic wave (e.g. let's say 60 GHz) and I would like to know how to absorb it such that there will be no transmission (through a wall) ...
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0answers
14 views

Are there any formulas that calculate the stopping distance of a car on different surfaces that include deceleration?

I already found the formula d = v^2/2ug where 'v' is for velocity, 'u' is for the coefficient of friction between the tires and the road surface, and 'g' is the acceleration of gravity. Are there any ...
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0answers
6 views

A problem involving Radiance and Fluence definition

In the book I'm reading the Radiance is defined in this way: $$I=\frac{dP}{d\Sigma'd\Omega}$$ where $d\Sigma'$ is the projection of the surface $d\Sigma$ on the plane perpendicular to the photons flux ...
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0answers
33 views

I am confused about moment of inertia

Question There is a homogeneous and nonelastic (solid) rod on the frictionless line with mass M, length L and velocity V. Then line becomes a circle with radius L and our rod starts turning around it. ...
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0answers
24 views

What would happen to the water bodies if gravity ceased to exist on Earth?

If water stopped flowing (it would stop flowing downwards from mountains and all) then, would it start rising upwards? If it floats on the space ( I say space because there'd not be any atmosphere) ...
0
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0answers
29 views

Newton's second law in non inertial frames: why am I getting $r_x = 0$?

Consider the following system: and the following frame: A rotating frame $x^{\prime} y^{\prime} z^{\prime}$ whose origin coincides with the inertial frame $x y z$ and the $z^{\prime}$ and $z$ ...
3
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0answers
24 views

Characteristics of the Navier-Stokes equations as a set of PDE's

I am not entirely sure if I should ask this question here or not, but here goes: can anyone suggest any reference (book, article, etc.) about the Navier-Stokes equations from a mathematical point view?...
0
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1answer
44 views

Facts about element 173

I am watching a video about element 173 being the biggest and last element that can ever be assembled. The reason given as the last element that can be created is that the electrons would have to ...
0
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0answers
18 views

Can we exploit non-conservative field forces?

If a body is revolving in a constant non-conservative field and a non-zero work is done on it. Can we repeat the cycle infinite times and get more and more energy there by creating a free energy ...
2
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0answers
37 views

Reason for repulsion of like charges

Like charges repel and unlike attract. Like magnetic poles repel and unlike attract. Since electricity and magnetism are fundamentally linked , is this attraction/repulsion due to the magnetic fields ...
0
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0answers
24 views

Dimensional analysis of Clausius and Clapeyron equation

proof that the following formulas unit are consistent using dimensional analysis.
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4answers
29 views

Finding the charge on a capacitor (RC circuit)

I am having trouble finding the charge on the capacitor for $t\rightarrow \infty$ after the switch has been closed at $t=0$. I already know the current $I$. I also have to find out on which sides the ...
2
votes
1answer
29 views

Thermodynamical conjugate variables

In thermodynamics the potentials are typically only a function of 2 variables, say $$U=U(S,V)$$ with entropy $S$ and volume $V$. I see that conjugate pairs $S,T$ or $p,V$ always have the unit of ...
1
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0answers
19 views

Constraints on the $(4^n-1)$-dimensional Bloch vector

I'm interested in the constraints on the $(4^n-1)$-dimensional generalized Bloch vector (the Bloch vector for $n$ qubits). To the best of my knowledge, these are not analytically characterized for ...
-1
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0answers
23 views

Understanding The Electric Globe Valve

To begin, we need to look at the everyday "globe valve," to see how it actually functions. Mainline(constant pressure lines), are coupled with inlet of Valve. Typically flow will stop there when ...
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0answers
27 views

How do I derive the relationship between the classic magnetic field and the electromagnetic tensor?

I am trying to derive the relationship between the components of the electromagnetic field tensor and the components of the magnetic field by inverting $F_{ij} = \epsilon_{ijk}\beta_{k}$. The ...
-4
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0answers
43 views
0
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0answers
39 views

What's does square root of number of atoms mean?

Number of atoms $N$ was counted in 3 dimension. $x,y,z$. However, when calculate it, i.e. in many cases such as refractive index , people take the square root of it, i.e. in reflective index $n=\sqrt{...
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0answers
3 views

What are ways or methods to calculate or measure the thermal conductivity of a hybrid nanoparticle?

I'm looking for ways of estimating or approximating the value of the thermal conductivity of two nanoparticles added or combined. Creating a hybrid nanoparticle.
0
votes
1answer
33 views

Maximum value of speed of sound in a medium?

I read somewhere that speed of sound in a medium cannot be greater than rms velocity of medium particles. But why?
0
votes
1answer
23 views

Why isn't Argon's heat capacity ratio constant with temperature?

The Wikipedia Heat Capacity Ratio page claims that Argon has a different ratio at -180°C, that would make it the only noble gas that doesn't always hold a ratio of ~1.660, why is that ?
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0answers
7 views

Axion CDM analogous to reheating?

In a paper on Axions Peccei writes: When the Universe goes through the PQ phase transition at $T ∼ f_a > > Λ_{QCD}$ the QCD anomaly is ineffective. As a result, early in the Universe $< ...
-1
votes
1answer
46 views

Would protons in a straight line ever break their alignment?

Let any amount of arbitrarily spaced protons appear along a line segment of length $x$ in an otherwise empty universe at $t+0$ What mechanism, if any, could cause the breaking of said alignment ...
0
votes
2answers
31 views

How can magnetic fields be used to stop a rotating wheel?

How can a rotating wheel stop using magnetic power? For example, consider a rotating iron wheel: can it be made to stop suddenly with using magnetic power? If so, how?
0
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0answers
28 views

Does the 2nd law of thermodynamics hold inside the event horizon of a black hole?

Suppose I am an observer inside the event horizon of a black hole, and I am part of a system comprising myself, an object and a singularity. Now I throw the object towards the singularity; what ...
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0answers
3 views

What is Incoming wave boundary condition (IWBC) in context of nuclear fusion reaction?

For calculation of fusion cross section at sub barrier energies, instead of regular boundary condition we impose Incoming wave boundary condition (IWBC). How does this different from normal boundary ...
-1
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0answers
16 views

Information across the event horizon and the implications of Entaglement

What would it imply if Entagled particles remained entangled after one of the elements of the set crossed an event horizon.
0
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0answers
11 views

Combine coherence tomography with second harmonic generation

I was given the task to combine the OCT procedure with second harmonic generation. Problem is I am completely new to this stuff. Could anyone give me a few proposals which I could use as starting ...
0
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0answers
11 views

Underwater Photography

An underwater camera has a lens with focal length in air of $35.0mm$ and a maximum aperture of $\frac{f}{2.80}$. The film it uses has an emulsion that is sensitive to light of frequency $6.00\times 10^...
-1
votes
1answer
48 views

In quantum entanglement, can their share 'information' beyond speed of light?

If we have two quantum things and they are entangled, and then we separated them at more than 299 792 458 meters, does their share information instantaneously? If yes, are they breaking the speed-of-...
-1
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0answers
17 views

Wave interference: two antennas

I have a question, that I cannot answer so I need help with this, please. It goes: two radio antennas are 600m away from each other. One is in the north the other in the south, and they are ...
0
votes
1answer
53 views

Moving moon explanation

I saw the moon moving in a fast pace several times with the naked eye, even during day time when its cloudy. How is that possible? I asked my teacher about it and he said its just an illusion, but ...
0
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1answer
19 views

Cavity mode counting

I am reading the book "Laser Fundamentals" by William T. Silvast and he mentioned that the number of cavity modes can be calculated as an octant of a spherical volume, i.e. $M=\frac{1}{8}\frac{4\pi}{...
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3answers
66 views

How is it possible that doubling a force on a fixed mass causes its acceleration to triple?

So the suggested solution is A. But here's what I don't get, when the F is doubled, how is it possible that the acceleration(A) tripled? If the answer is m.a should the question be "a person needs ...
0
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0answers
16 views

QFT Complex scalar field and commutators

The conserved charge is $$Q=i\int\ d^3x(\phi\pi-\phi^\dagger\pi^\dagger)$$ Expressing this in terms of creation annihilation operators gives $$Q=i\int d^3 x \frac{d^3p d^3k}{(2\pi)^3(2\pi)^3}\frac{i\...
0
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1answer
13 views

Breaking wave behind a paddle steamer

While travelling on an 1890's paddle steamer (PS Marion) I noticed that the wake from the paddles consists of a series of waves from each paddle that progressively reduce in amplitude. Some distance ...
0
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0answers
24 views

What is the set of independent parameters that can be used to describe a quantum particle like photon or electron?

How many independent parameters are there for fully describing a quantum particle like photon or electron?
-1
votes
1answer
58 views

Thought experiment: if an observer can travel at the speed of light [on hold]

What would the observer see if he could travel at the speed of light and shot a photon beam at the same time?
-1
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0answers
43 views

Do photons have multiple peaks or only one? [on hold]

Energy of a photon is given by E = h x frequency Thus, if an photon hitting a detector delivers 10 peaks/ second, it will transfer 10 h/s per 1 photon (6.626x10^-33 J) I.e the EM wave delivers 6....
1
vote
1answer
56 views

Why is $\langle{\dot A}A^* \rangle=0$ for dynamical variable $A$?

In page 179 of Hansen and McDonald's book, Theory of Simple Liquids, 3rd edition, 2006, an identity of correlation functions was deduced. Here $C_{AB}(t)$ is the time correlation function between ...
1
vote
1answer
31 views

When air is ionised, which component gases are actually ionised?

Air is a mixture of O2, N2 etc. Which gases are ionised at STP, and is there a different level of ionisation for different gases?
0
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0answers
27 views

Which properties does tensorial product have with respect to scalar product?

Are the associative and distributive properties preserved? In Cohen-Tannoudji's Mécanique quantique vol. I, the scalar product in the $\epsilon=\epsilon_1 \otimes\epsilon_2$ space is defined as ...
0
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0answers
16 views

Introducing Spin operator in QM

What was the experimental facts used in the construction of spins in Quantum Mechanics? What forced W.pauli to invent the idea of spins ? Can there be other internal degrees of freedom yet to be ...
2
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0answers
39 views

What is going on in “nonlinear gravity from entanglement in conformal field theories”?

EDIT: I am now convinced that the sign of the logarithmic terms in the equations after 3.29 and 3.30 are wrong (unless I have missed something else). These identites come from looking at ...
0
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0answers
15 views

CFT in momentum space

Is there a way to see the conformal symmetry in momentum space in a CFT? I mean if I can recover the conformal group in some way in momentum space.
0
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0answers
10 views

Help me calculate the photons flux on Earth surface

I want to find the PFD in small intervals of wavelengths based on this dataset (https://www.nrel.gov/grid/solar-resource/spectra-astm-e490.html) see second link in Data Files. I did it and have my ...
0
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2answers
29 views

Understanding positive and negative shear strength sign

Shear strength is a force that tries to keep stuff in equilibrium, when another force tries to break/bend/modify a structure. This "another force" (external force) may also produce a moment. In the ...
-1
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0answers
15 views

If mass can not travel at the speed of light, what exactly is going on with black holes and their gravitational forces that not even light can escape? [duplicate]

I've seen people ask things like, what would happen traveling at the speed of light. I've seen the question put to bed with "mass can not travel at the speed of light." and an explanation about how if ...

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