4
votes
1answer
100 views

Yang and Mills' (and others') justification for local gauge invariance

In most physics textbooks, local gauge invariance is simply postulated---you start with a global symmetry, e.g. the global phase, then allow it to depend on the spacetime point, make the necessary ...
2
votes
0answers
65 views

QFT: What does “finiteness” mean?

As above: what is the definition of a QFT to be "finite"? That all UV corrections are finite and there are no divergences at all? That there are divergences, but these divergences can be absorbed ...
13
votes
0answers
167 views

Synthesis of Fe-based superconductors

Polycrystal cuprate superconductors are generally prepared by solid state reactions: Starting reagents are in powder form, they are mixed to each other and placed into furnace on high temperature ...
5
votes
3answers
768 views

What does it mean to “bin” in a spectroscopy context

In the following online article http://www.star.le.ac.uk/~sav2/stats/a.html I see the word "bin" used, in relation to x-ray spectroscopy, both as a verb and as a noun (people both "bin" things and ...
1
vote
1answer
48 views

What laws of physics apply when a flow of air is divided?

The question is rather simple, but I'm not sure if there is a simple answer to it. Let`s say I've got a flow of air (5 bar, 25 l/min) running through a 6mm hose. Then this flow hits a branch dividing ...
0
votes
3answers
174 views

Are there any well-known large body objects moving at a significant fraction of the speed of light relative to earth?

Introduction I've been reading a book called PsychoPhysics, part of the "Illuminati God Series" by Mike Hockney (a pseudonym). Without getting into too much detail, they basically believe that the ...
2
votes
2answers
144 views

How to prove $\mathrm{Tr}\left[|\alpha\rangle\langle\alpha|\hat{A}\right]=\langle\alpha|\hat{A}|\alpha\rangle$

For a coherent state $|\alpha\rangle=e^{-\frac{|\alpha|^2}{2}}\sum\frac{\alpha^n}{\sqrt{n!}}|n\rangle$, please show me how to prove, $$ ...
0
votes
1answer
65 views

Why does the stiffness of organic polymers (plastic) change so much with small changes in temperature?

This is on the borderline between Physics and Chemistry, but I would like a Physics perspective. I am guessing that plastics are a glass-like phase, rather than a true solid.
0
votes
2answers
83 views

How energy of a photon or EM wave has something to do with frequency?

While I was thinking what exactly meant by energy in quantum mechanics, I was quite shocked by the fact that it is proportional to frequency. $$E=hf$$ Given the fundamental definition of energy in ...
1
vote
1answer
36 views

Why is metal stiffer at lower temperatures?

Each morning I cycle to school and lock my bike with a thick steel wire (about 8 mm thick). I noticed that it's much harder to change the shape of the wire in the morning when it's much colder than ...
3
votes
3answers
187 views

Angular velocity of a fluid element

If we have a fluid element that is subjected to: Translation Rotation Extensional strain (dilatation) Shear strain As in this picture starting from time $t$ it can be shown that angles ...
1
vote
2answers
45 views

Is there a formulation for (self-)accelerating fluid flow through permeable medium?

I have a permeable system where is an accelerating fluid flow. Imagine a sponge that is squeezed. The fluid starts at rest, accelerates and flows out from the sponge. How to calculate the fluid speed? ...
1
vote
0answers
80 views

Numerical Calculation of the Second Harmonic Generation in the Nonlinear Media

Recently I am working on the Numerical Calculation of the Second Harmonic Generation in the Nonlinear Media. I refer to the Book ...
2
votes
3answers
295 views

Sign of torque when rolling an object down an incline

Suppose you have an object rolling down the incline at 30 degrees. Given the point of contact is instantaneously at rest, I decided to analyse torques at that point. Therefore, the only force ...
1
vote
1answer
80 views

When to use a whole vector approach vs an energy approach?

My professor has just introduced two new ways to solve projectile motions. One approach involve using trigonometry and vectors and the other involves using the idea of conservation of energy. My ...
0
votes
2answers
35 views

Filament lamp $(V,i)$ behavior between 0 and 1V

I was wondering why the behavior is more "chaotic" at 0~1V when compared to 2V+ (which is when it starts to glow).
0
votes
0answers
30 views

Approximation for rotational drag on a box?

The drag equation gives us an approximation for the drag on an object caused by its velocity in a fluid: $F = \frac{1}{2} \rho A v^2 C_d$ Is there any similar approximation for the rotational drag ...
1
vote
2answers
75 views

Configuration manifold of a rigid body

As I know, a rigid body is a set of $N$ particles in three-dimensional space subject to the following constraint: if $b_1,\dots,b_N\in \mathbb{R}^3$ are the initial positions of the particles and if ...
0
votes
2answers
49 views

Stored Energy in My Badge Reel Finds Equilibrium With Centrifugal Force?

Probably a most horrible question title, please respond with suggestions for a better one. In the example of my badge reel, I grab hold of my badge itself and pull on the reel until the string is ...
5
votes
3answers
147 views

How do shock waves form in space?

Today my aerodynamics professor mentioned that the equations we were learning for atmospheric shock waves can also be applied by astrophysicists to study black hole-related shock waves in space. How ...
0
votes
1answer
52 views

How much time would have to pass for a blackbody object at 0.1 K to emit a single infrared photon? [closed]

My understanding is that blackbody radiation occurs on a curve that depends on the temperature of the object - as the temperature increases, the area under the curve increases, and the peak of the ...
0
votes
3answers
97 views

Equal and opposite reaction at light speed

My knowledge of physics is very limited. And this question is only really to help me put to rest a question i have had for some time. I would like the answer to be a simple one as i am not really in ...
2
votes
2answers
83 views

Is it possible to mix a drink with a non-standard phase of ice?

Would it be possible to safely cool and drink a glass of water with anything else than the Ih form of ice? Here and here you can see that some alternative forms of ice have a higher density than ...
0
votes
1answer
68 views

State of academic fields of analytic mechanics and Multi Body Dynamics (MBD)

My question essentially contains two parts: one practical question and one philosophical question. Background I am an engineering student working in the field of Multi Body Dynamics (MBD). My ...
1
vote
2answers
2k views

Why do voltmeters and ammeters have high and low resistance respectively?

I understand why voltmeters are connected in parallel and ammeters are connected in series, but why is it that to measure voltage, you must have high resistance, and to measure current, you must have ...
1
vote
0answers
66 views

Funnel theory exists?

I have a funnel and I notice when I try to pour powdered sugar through it, it blocks up unless I tap it. If I put sand in the funnel, it goes through. Is there a theory of funnels that can predict ...
1
vote
0answers
67 views

Correspondence between variational method and Feynman diagrams

There are two ways to look at the Hartree or Hartree-Fock equations. One method relies on the variational method for a particular type of the probe function and the second one originates from ...
-1
votes
2answers
86 views

cm^-1 and ns^-1 relationship

In my last Phys.SE question Emilio Pisanty mentioned this relationship $1 cm^{-1} = 10^n c^{-1} ns^{-1}$. I was wondering where this relationship came from. Does anybody know? Second of all, I am not ...
1
vote
2answers
148 views

Rabi problem for a spin-1 particle

I'm trying to solve, analitically, the transition probability of a spin-1 particle in a magnetic field $$ \vec{B}=B_0\hat{k}+b(\cos{\omega t}\hat{i}+sin{\omega t}\hat{j}). $$ In particular I want to ...
3
votes
3answers
252 views

Perturbative series for bosons

I have recently read that ... the perturbation series ... is valid only when the perturbed state is qualitatively similar to (or ‘has the same symmetry as’) the unperturbed state. This means ...
1
vote
0answers
63 views

semiconductors extrinsic and intrinsic carriers concentrations equations

I get why $n \cdot p = n_i^2$ in intrinsic semiconductors, but why is that equation also true in the case of extrinsic semiconductor? Here, $n$ is the charge density of the negatively charged ...
1
vote
3answers
78 views

Is there a dynamic prelude to the state equation?

If I'm not mistaken, the state equation $$PV=nRT$$ also known as the 'ideal gas law' serves as a mathematical model relating pressure-volume-mass-temperature states of an assumed ideal gas. In other ...
0
votes
0answers
46 views

The dipole moment P in a metallic sphere

A metallic sphere is in a homogenous field $\vec{E}=E \cdot \vec{e_z}$. Put a dipole moment P at the origin, so the total potential is constant on a surface of a sphere with radius $a$. Which $p$ is ...
1
vote
1answer
137 views

What speed does a proton have with the energy 7 TeV?

So this is a question from the 2014 admission test for Chalmers University of Technology, Gothenburg. To clarify some rules (cited and translated from the test): Calculators and physics ...
-1
votes
1answer
105 views

Why does the water level go down when a dense object is moved from a boat to the bottom of the pool [duplicate]

Imagine you have a container ship with an extremely heavy mass on it. Why does the water level on the ship drop when the mass is placed in water?
2
votes
2answers
77 views

Do galaxy clusters follow De Vaucouleurs' law?

Do galaxy clusters follow De Vaucouleurs' law? If objects in the universe are built hierarchically, wouldn't one expect a galaxy cluster that is roughly spherical to follow the same profile as an ...
0
votes
1answer
85 views

Wave packet and group velocity?

While finding the wave function of a free particle say $\psi(x)$, my textbook says that this is nonphysical because the wave velocity is not same as particle velocity of the free-particle. I don't ...
2
votes
0answers
65 views

Is the current density ${\bf j}$ an observable?

The current density ${\bf j}$ is most easily defined from$$ I = \int_{\text{cross-section} \atop \text{of wire}} \textbf{j}\cdot d\textbf{S}, $$ where $I$ is the current flowing through the wire. From ...
1
vote
0answers
91 views

interaction of permanet magnetic field with electromagnetic field

I am working on non contact breaking system for a rotating permanent magnet in an electromagnetic field.so I would like to know if the interaction between the magnetic field and an electromagnet will ...
-4
votes
0answers
55 views

How to compare dimension of this with velocity [closed]

Prove that the dimensions of $\large \sqrt{\frac{1}{με}}$ are that of the velocity?
1
vote
1answer
174 views

What does the free body diagram for mass 1 look like?

In this situation: Enough tension is applied towards the right on $m_2$ so that $m_1$ starts sliding backwards. I am confused about what the free body diagram for $m_1$ looks like. Here is my ...
2
votes
0answers
29 views

How to mathematically model a realistic aperture illumination?

I want to know a mathematical expression that I can use to model a realistic aperture illumination to produce the primary beam of an antenna so that the radial distribution of this aperture ...
0
votes
0answers
24 views

Dark matter = neutral matter? [duplicate]

Could dark matter be a neutral form of matter between antimatter and matter, much like how neutrons are neutrally charged particles that keep protons and electrons stable within an atom?
0
votes
1answer
127 views

Quantum mechanics successive measurements (incompatible observables) [closed]

I started a "principles of quantum mechanics" course this year, and already have a problem with successive measurements (using Dirac notation). The question is about incompatible observables A and B. ...
-4
votes
1answer
97 views

What is the value of the Universe's acceleration? [closed]

Please read this http://www.researchgate.net/publication/282157370_VALUE_OF_THE_UNIVERSE%27S_ACCELERATION Your ideas are welcome.
0
votes
2answers
81 views

Mechanical equivalent to electric circuits

Could one build a mechanical equivalent to electric circuits ? I'm considering mechanical waves (like shock waves) travelling through a medium here. I'm aware that due to the high loss and practical ...
0
votes
2answers
150 views

Can mercury evaporate if it's covered by water?

I was recently watching a video about elemental mercury and how it's cleaned up in water (fish tanks), and it was mentioned how mercury can be toxic in vapor form. My question is, if I were to drop a ...
0
votes
2answers
148 views

In a nuclear reaction, where does the energy go?

Lets say two hydrogen fuse together, where does the energy released go? Is it carried away as momentum imparted on the helium atom? Is it carried away in neutrinos? Is it carried away as gamma rays? ...
0
votes
2answers
417 views

Electromagnet Electricity Consumption?

Wikipedia states that - The only power consumed in a DC electromagnet is due to the resistance of the windings, and is dissipated as heat. Is this true? So powerful magnets like junkyard magnets ...

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