# All Questions

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### Calculating the total energy required to deform a material [on hold]

How do you calculate the energy required to elongate a material by 10mm. The initial diameter was 56mm, initial length 143mm, final length 146mm and the maximum load was 93kN.
14 views

### LArTPC muon sign determination

What are some techniques for muon sign determination (w/o magnetic field) for fully contained muons, using statistical analysis? Especially because liquid Argon time projection chambers' sign ...
589 views

### Why should Conservative forces have their curl equal to zero?(intuition)

There are several conditions that must be met in order for a force to be conservative. One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If ...
17 views

### Photoelectric effect and work function relation

Let's consider the graph above for two metals $M_1$ and $M_2$ showing relation between photocurrent and potential. First question that I want to ask here is that how do you relate stopping ...
26 views

### Question from Griffith's E&M chapter 7 [on hold]

Estimate the induction current in the copper tube assuming the magnetic field of the permanent magnet to be 1.2 tesla, the weight of the permanent magnet to be 20 grams, the diameter of the copper ...
30 views

### Every Galilean transformation can be written as the composition of rotation, translation, and uniform motion

Having heard many good things about Arnold's Mathematical Methods of Classical Mechanics, I picked it up and started going through it. While I think I understand all of the definitions he makes, the ...
173 views

### Infinite Resistive lattice problem

While there have been many discussions regarding the solution(say using the Fourier transform or the lattice Green's function approach) to the two-point resistance of an infinite-square resistive ...
59 views

### Deriving the Lorentz factor

Recently, I learned how to derive E = mc^2. However, to do so, one must accept the relativistic mass equation. How does one derive this?
100 views

### How does electrostatic force affect electronic devices?

How does electrostatic force generated by two seperate plates having opposite charges affect electronic devices? I know that magnetic fields have some harmful effects to electronic devices but I am ...
55 views

### Are black holes an infinite source of energy?

Black holes are considered particularities because in a determined point in time they are pointless, as consequence there are some mass in a null space so the density become infinite. Finally if ...
43 views

### What is the direction of the magnetic vector potential in an electromagnetic plane wave?

The vector potential $A$ is perpendicular to $B = \nabla \times A$, by definition, and hence, in a plane wave, it is either in the direction of $E$ or the direction of propagation. I suspect it is in ...
252 views

### Why is there a voltage drop across a superconducting inductor?

If there is no electric field inside a perfect conductor, then why is there a potential difference across an (superconducting) inductor?
5k views

### Why doesn't light affect a compass?

In our daily life a lot of photons of visible light, infrared and radio etc move around us. We know that light is an electromagnetic radiation. So why doesn't that electromagnetic radiation affect a ...
445 views

### Momentum of stationary electron in a curl free vector potential

The essence of this question is simplicity itself: There is an electron in a curl-free $\vec{A}$ field. The electron is stationary so its m$\vec{v}$ momentum is 0. However, it has "momentum" from ...
67 views

### Magnetic flux of a loop due to another loop

The scenario is the following, I am given 2 loops with the same radius, r, a distance of d, and same current of I. In the left loop the current goes counter clockwise, in the right loop the current is ...
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+50

### How does Dirac define the representative of $\{\langle\phi\frac{d}{dq}\}\psi\rangle = \langle\phi\{\frac{d}{dq}\psi\rangle\}$

On pate 89 of Dirac's book, The Principles of Quantum Mechanics, he writes: Let us treat the linear operator $\frac{d}{dq}$ according to the general theory of linear operators of section 7. We ...
30 views

### Condition on $U_{eff}$ for a mass to get trapped in orbit around a heavier mass

this question is now solved, and I have already edited the wikipedia page The wikipedia page on Effective Gravitational Potential states that $$U_{eff} \leq E$$ is a condition for a free mass getting ...
53 views

### Covariance of the Dirac Equation

i want to show that the following equation holds: $$\frac{1}{8}\left[\gamma^{\mu},\omega_{\mu \nu} [\gamma^{\mu},\gamma^{\nu} ] \right] = \omega^{\mu}_{~~~\nu}\,~ \gamma^{\nu}$$ $\gamma^{\mu}$ ...
7 views

### Faraday induction for seawater flow system

Magnetic flow meters use Faraday induction to produce a voltage across a channel in which a conductive fluid is flowing. The basic relationship (using convenient geometry so that the cross products ...
22 views

### In a Stern-Gerlach measurement, does passing particles through the B field influence their spin state?

This question is similar to this post and was influenced by this discussion as well. Assume a Stern-Gerlach apparatus oriented along the z-axis acts as a measurement on the basis of the z-component ...
38 views

### Formulating a symplectic integrator for a non-local Hamiltonian

I recently asked two questions, Q. [1] and Q. [2], regarding reformulating non-local Lagrangians as Hamiltonians. In these questions, the Hamiltonian is formulated as an integral because of it's ...
65 views

### How can we prove this system is in a stationary state?

I'm having trouble using the given hint to solve the problem. The problem statement is as follows: At instant $t=0$, the probability distribution of a particle under a potential $V(x)$ is ...
132 views

### Special relativity - twin paradox explored

A thought experiment. A person on the Earth has a clock. Another person who also has a clock is in a rocket ship passing the Earth travelling at 50% the speed of light. They synchronise watches as ...
111 views

### Legendre transform for non-local Lagrangians, or Hamiltonian of non-local Lagrangian and their properties

This is sort of a multi-part question, mostly dealing with how to treat non-local Hamiltonians and how the corresponding properties of Hamiltonians work in a non-local framework. I proposed an example ...
449 views

### Geodesic equation from Euler - Lagrange

There are several ways to derive the geodesic equation. One of which is the variational method which I seemed to understand it because it was written in great details. Then it was mentioned that the ...
30 views

### Ricci tensor of Metric black holes with nils and solv geometries of Horizon

The metric of black holes with nils and solv geometries of the horizon is generically represented by $$\mathrm{d}s^2=-r^{2z}\mathrm{d}t^2+\frac{\mathrm{d}r^2}{r^2}+\sum_{I=1}^3 r^{2q_I}(w^I)^2$$ How ...
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### Why is tree-level interaction between neutral scalar and photons non-renormalizable?

I've read that the decay of a neutral scalar particle into two photons, i.e., $$S(p+q) \to \gamma(p) + \gamma(q)$$ can't happen via tree diagrams and instead is caused by loop diagrams (such as a ...
28 views

### If a vehicle (bus, train) rapidly stops (or accelerates, or turns), why don't our hair or clothes move from the inertial force?

Many times I was sitting in a train, watching closely nearby people. If the vehicle changes it's movement rapidly (brakes, turns, etc), then obviously, people feel the inertial pseudo-force that ...
72 views

### What are the mathematical models for force, acceleration and velocity?

In mechanics, the space can be described as a Riemann manifold. Forces, then, can be defined as vector fields of this manifold. Accelerations are linear functions of forces, so they are covector ...
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### How can one reasonably theoretically model polycrystalline materials?

Many techniques are taught in advanced solid state courses but they are almost all derived for perfectly crystalline materials. For example, band structure really only appears theoretically when you ...
29 views

### Is there a friction or retarding force in creating spacetime?

As matter and energy expand with the big bang, they create spacetime (or so I've been told). Is there any evidence that this creation of spacetime has a retarding force on the expansion? If not, ...
29 views

### Electric Field At Centre Of Non Uniform Ring

In the above solved example why only the cos components have been taken for calculation of electric field at centre ? Why not the sine components ? BTW in case you say that the sine components ...
60 views

### Is density functional theory a mean-field theory?

Is density functional theory exact or just a mean-field theory?
100 views

### Question about Hartle and Hawking's universal wavefunction?

My apologies in advance if this question is poorly worded or doesn't make any sense, however I have just finished reading into this theory and it seems as though Hawkings No Boundary Universe is ...
51 views

### Does a source emitting visible light also emit infrared, microwave and radio waves?

I have a bulb which is hot enough to emit visible light and obviously it's hot enough to emit radiation which lies before the visible light temperature i.e. radio waves, microwaves, and infrared ...
87 views

### When the Cosmic Microwave Background radiation cools, where does the energy go? [duplicate]

I understand how photons can change wavelength via gravitational redshifting, but that doesn't seem to be what's going on with the CMB radiation. I've heard it explained as happening because of the ...
43 views

### Is the present state of our universe due to a bottom up or top down process, or both? [on hold]

Bottom up is the main stream science view. Most models of the universe are bottom-up, that is, you start from the well-defined initial conditions of the Big Bang and work forward. The other view is ...
1k views

### In circular motion, with a constant distance, why does the mass of the orbitting object have no effect on its revolution at all?

Using Newton's universal equation and some circular motion equation, the orbiting object's mass cancels out. But can someone please explain why this is without using pure algebra?
21 views

### Pressure in closed container [on hold]

I am wanting to figure out the pressures in my solar still so that I can figure out the volumetric flow rate(assuming no turbulence). For water to go 6 feet uphill it would require a lot of pressure ...
666 views

### Why do my ice cubes stick together? [duplicate]

When I put ice cubes in a glass of water, I find that sometimes they will stick together and form a sort of "bridge" between them as they melt. There is usually a visible line where one ends and the ...
25 views

### Metal Refractive index

I'm working on Fresnel equation for calculation of reflection of a light (532 nm) on Iron. I've got a question: Is metals refractive index always a real number or it can be a complex number?