1
vote
0answers
103 views

Hydrogen 2p3/2 -> 1s1/2 transition polarisation and angular distribution

Could you please help me. I have to calculate the intensity angular and polarisation distribution in hydrogen electric dipole transition $\text{2p}_{3/2}\rightarrow \text{1s}_{1/2}$. To do this I ...
0
votes
1answer
491 views

Why do electric field lines never intersect [duplicate]

Electric field lines never intersect. We know that. So closely spaces field lines means a stronger field and fields lines farther apart means a weaker field. How are we really sure that they never ...
0
votes
1answer
58 views

I can make the mechanical energy 0 or in fact anything. Is this normal?

We let the rope fall with $\alpha = \pi/2$ (no initial velocity). if I choose the original of potential energy as the picture indicates there, this means that: $$E_m = E_{pe} + E_c = \frac12mv^2 ...
4
votes
2answers
212 views

Is a local Lorentz frame a coordinate chart on a spacetime manifold?

I am just starting to learn GR. I'm alternating between studying physics books and studying math books. I keep seeing the term Lorentz frame and I'm not sure what it means mathematically. Is a ...
0
votes
0answers
36 views

Ward Identity and possible Srednicki mistake

I'm trying to find an elegant way to prove Ward-Takahashi identity. I consulted many books (Srednicki, Peskin & Schroeder, Pokorski and many others). The most common way to prove it is to pretend ...
0
votes
1answer
60 views

Length of Focal Spot Along the Optic Axis

I am currently attempting a physics question on optics. A Fresnel Zone Plate has overall radius a and contains N half-period zones. The odd-numbered zones are open but the even -numbered zones are ...
1
vote
1answer
227 views

How do we normalize a delta function position space wave function? [duplicate]

I have a position space wavefunction $$\psi(x) = \delta(x-a) + \delta(x+a).$$ Now the question states to compute the following: The Fourier transform of $\psi(x)$. (Which invariably is the momentum ...
5
votes
1answer
226 views

Why do we need spontaneous symmetry breaking in Lagrangian formalism?

I have always struggled with the concept of spontaneous symmetry breaking. It seems to me that many others don't find it very intuitive as well, but that could be just me having difficulties with the ...
1
vote
0answers
71 views

Rayleigh criterion for sound and parabolic microphone

Currently I am developing a parabolic microphone for a study project. I've heard and read that the maximum wavelength of sound that the given diameter microphone can focus is determined based on the ...
0
votes
0answers
81 views

Is FTL information transfer possible in an experiment involving entangled particles and an “available” black hole?

We consider the classical entanglement experiments involving Alice and Bob, and their entangled particles. It is proved that nothing that happens at Bob's end has any immediate effect on Alice's ...
3
votes
1answer
319 views

anomalous chiral symmetry and the $\bar\theta$ parameter

I am studying anomalous $U(1)$'s, related to the strong CP problem, and I have some trouble with the origin of the parameter $\bar{\theta}$. We start with the QCD Lagrangian with the topological ...
0
votes
2answers
159 views

Electric Field lines that close on themselves

What causes an electric field line to close on itself as opposed to other cases?
1
vote
1answer
65 views

Type II supernovae explosions

I'm quite confused about the explosion of a Type II supernova. As far as I understand, when the Fe-56 core has been created, and the star has all the other layers around it, it starts to collapse, ...
1
vote
1answer
76 views

0+0 self interacting QFT - $ e^{-\sin^2 x}$ type integral — Bessel function expansion around infinity

In a physics paper (here) I found this variant of the Bessel function of the first kind. $$ \tag{1} Z(g) ~=~ \frac{1}{\sqrt{g}} \int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} e^{-\frac{1}{2g} \sin^2 x} \, dx ...
1
vote
1answer
186 views

Induced electric field due to a moving wire

An infinite wire carrying a constant current $I$ in the $\hat{z}$ direction is moving in the $y$ direction at a constant speed $v$. Find the electric field, in the quasistatic approximation, at the ...
1
vote
2answers
252 views

Is thermodynamic equilibrium static or dynamic?

Suppose, two parts of a system $A$ & $B$. They were at varying temperatures and hadn't achieved mechanical equilibrium. After the relaxation time, $A$ & $B$ were at thermal and mechanical ...
0
votes
0answers
45 views

Does this violate Stefan's law

Radiation energy per unit time is given Stefan-Boltzmann law as being proportional to temperature to the 4th power, and to surface area of the body. (For black bodies) This was told to me in our ...
1
vote
1answer
95 views

The concept of an electrically short, medium and long transmission line is primarily based on? [closed]

The concept of an electrically short, medium and long transmission line is primarily based on ? A. nominal voltage of the line B. physical length of line C. wave length of line D. power transmitted ...
3
votes
1answer
105 views

Trying to show that the current is conserved

$ \newcommand{\p}{\partial} $ I am trying to show that the current $J^{\mu} = (\gamma_{\nu}\partial^{\nu} \phi - m\phi)\gamma^{\mu}\psi$ is conserved for all fields that satisfy the Klein-Gordon and ...
2
votes
2answers
62 views

Why don't we have particles whose wavefunctions are symmetric wrt one exchange operator and anti-symmetric wrt other exchange operator?

Consider a system with $n$ identical particles. Let the wavefunction of the system be $\psi(r_1,\ldots, r_2)$. Let $P_{a,b}$ represent the exchange operator which exchanges particle $a$ with particle ...
3
votes
0answers
97 views

What're some criticisms of the paper “Six observations consistent with the electron neutrino being a tachyon with mass: mνe² = −0.11±0.016 eV²”?

Today I read about this paper making the case that neutrinos have imaginary mass and travel faster than light. I want to get excited, but I have no way to know how likely it is that this paper will be ...
3
votes
4answers
324 views

Entropy of the whole universe

In "Thermal Physics", Charles Kittel proves that entropy always increases in systems when the degree of freedom are increased (adding particles, adding energy, expanding volume, etc ). I started to ...
0
votes
1answer
57 views

Electron wave function question?

In interpretations of Quantum Mechanics that are Psi Ontic, in which the wave function is REAL ( Objective collapse theories, MWI, ect), does the wave function still physically spread to infinity? I ...
1
vote
1answer
32 views

Why does non-abelianity implies a single coupling constant?

Why does a theory described by a non-abelian group has only a single coupling constant $g$? While on the other hand in an abelian theory, as Electromagnetism, each charged particle has its own charge ...
0
votes
2answers
91 views

Why does the ray bend only in one direction?

By snell's law , the refracted ray bend away or towards the normal according to refractive index of the medium. But it can be seen that the refracted ray bends to the right by an angle when a ray of ...
1
vote
0answers
61 views

What's the physical or mathematical meaning of considering non-minimal coupling?

Why we still consider the case of non-minimal coupling? And I don't really understand the motivation of coupling. In general relativity, the non-minimal coupling violates the principle of ...
2
votes
1answer
89 views

planewave Ansatz for modelling phonon dispersion in crystals

From Ashcroft's "Solid State Physics", for one-dimensional monatomic Bravais lattice, the equations of motion of ions are: \begin{equation} M\ddot u(na)=-K[2u(na)-u([n-1]a)-u([n+1]a)] \end{equation} ...
0
votes
5answers
165 views

Is there a commonly used unit of measure (other than temperature units) that is not absolute? [closed]

I live in a country where we use Degree-Celsius(°C) to measure the temperature. Sometimes from one day to the other, the temperature rises from 10°C to 20°C and I hear people say, "Wow! Today is twice ...
2
votes
1answer
136 views

Can two distinct events occur at precisely the same moment in time?

I am writing a simulation and am having difficulty resolving the order in which two distinct forces occur. The simulation will give different results if the forces are applied to the state in ...
0
votes
1answer
50 views

Limitations of (non-lightfield) near-eye displays

The answer to Is it possible to blur an image in such way that a person with sight problems could see it sharp? suggest that you cannot present a "counter blurred" out-of-focus image such that it ...
2
votes
1answer
242 views

Combination of errors question [closed]

A resistance R is in series with an inductance L. At angular frequency ω the magnitude of the complex impedance Z of this combination is given by |Z|^2 = R^2 + (ωL)^2 . Find |Z|, and the error in |Z|, ...
2
votes
0answers
12 views

Reason for audio speaker diaphragm shape [duplicate]

Why are the diaphragms on audio speakers usually a cone with a dome in the centre? I don't know much about acoustics but my guesses would be: it just empirically sounds better, the design was found ...
1
vote
0answers
37 views

Compatibility of twin paradox with the time-dependent Hubble constant

The universe is currently expanding with a speed of about 70 km/sec/Mpc which is today's Hubble constant. As this expression includes two length units, it is also possible to use the unit: $sec^{-1}$, ...
14
votes
2answers
975 views

Why are electromagnetic waves not able to pass through a hole with a diameter smaller than the wavelength? [duplicate]

I am doing research on Faraday cages for school, and I want to know how it works. Faraday cages can have holes in them, and if the diameter is smaller than the wavelength of waves you want to block, ...
0
votes
1answer
161 views

Exact formula in simplest terms for Magnetic field at a point outside a solenoid [closed]

I need the COMPLETE formula for magnetic field outside the solenoid. So the situation I am stuck in is I have to solve this question: The magnetic field at the centre of coil of $n$ turns, bent in ...
0
votes
1answer
101 views

Configuration Space And Hilbert Space For A Physicist Without Knowledge Of Analysis

I have passed calculus course, have basic knowledge of complex numbers and passed introductory linear algebra course. I am trying to study Griffith Quantum Mechanics book, but I am also checking some ...
4
votes
4answers
117 views

Possibility of making an experiment in a classroom to simulate DNA diffraction

I am a TA in a structural chemistry class. The professor want me to show students how Watson and Crick determined the structure of DNA from X-ray diffraction results of DNA crystals. The professor ...
3
votes
2answers
237 views

Slater's determinant for Bosons/Symmetric Particles?

For Slater's determinant it is obvious how this describes two or multiple fermions/anti-symmetric particles. By definition the determinant introduces a negative sign in front of the second product. ...
0
votes
1answer
65 views

A parameter to quantify instability in flight

Suppose I have plotted the body angles of a flying aeroplane.I have two such plots. One of a normal plane, and the other plot in which a primary sensor of the aeroplane is removed. So with the absence ...
2
votes
1answer
168 views

If reality is relative, then what about Newton's bucket argument?

There is nothing outside the universe. - Lee Smolin So, there can't be any absolute frame. Everything must be measured relative to an entity that exists in the universe. Thus, space ...
0
votes
1answer
81 views

Is the speed of photon always $c_0$? [duplicate]

The propagation of light in medium is sometimes interpreted as the photons moving with $c_0$ (the speed of light in vacuum), occasionally absorbed by particles and released again by transition, ...
0
votes
1answer
56 views

does electron - positron pair annihilation occur when E is negative?

Suppose I release an electron-positron pair from rest at a distance of $r$. Then the particles attract each other and collide. The total energy $E$ is $$E = 2m_ec^2-\frac{e^2}{4\pi\varepsilon_0r},$$ ...
0
votes
0answers
41 views

Does the holographic principle imply that objects exist twice?

The surface area that surrounds a volume of space contains the same information that the volume has. My question is if we have Alice in a 3D space the 2D boundary should have all of her information. ...
1
vote
1answer
43 views

Does Poincare recurrence imply that a photon shot into a box will exit the way it came in?

If you have a big closed cube that has perfectly mirrored surfaces on the smooth flat walls or faces of the cube and only one corner has a tiny 'entrance' , a narrow hole at a specific angle , say ...
0
votes
1answer
32 views

Chrial multiplet's fundamental and anti-fundamental representation

Here i follow the notation in arXiv 9312104v1 (Witten's Verlinder algebra ~ paper) The usual kinetic energy for a chiral multiplet is given as (In 2 dimensional $N=(2,2)$ supersymmetry theory) ...
0
votes
1answer
797 views

How can a negative charge move towards a position of a higher electric potential but lose electric potential energy?

I understand that the equation is: change in electric potential = (negative)change in electric potential energy / unit charge. And I understand that if q is negative, then the change in electric ...
0
votes
1answer
59 views

Why $2j+1$ number of states?

In this statement from Modern Quantum Mechanics by J.J. Sakurai: If $j$ is an integer, all $m$ values are integers; if $j$ is a half-integer, all $m$ values are half-integers. The allowed ...
0
votes
1answer
184 views

charge distribution on three conducting plates [closed]

There are three parallel plates identical and equidistant. A charge q is given to the first plate.And then the second and third plate are connected with wire.Then how to find its charge distribution. ...
0
votes
0answers
27 views

If neutron would be lighter by 1 MeV, how stability of Hydrogen could be changed?

In current Universe proton is stable and the following reaction does not go $ p + e \rightarrow n + \overline{\nu_e}$ Currently proton is lighter than neutron by 1.293 MeV. If neutron would be ...
0
votes
2answers
80 views

Boy , Table and the Newton [duplicate]

Suppose a boy is trying to stand on a table. If the table can hold upto a particular force, the boy would fall on to earth. If he stands on the table and providing greater force than the table can ...

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