# All Questions

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### What is the mathematics behind artificially generated plasmas via electric fields?

The ionization degree of a plasma is given by the Saha equation, which depends on the temperature and the particle specific ionization energy. In thermal equilibrium, the relation between ionization ...
64 views

### Unknown quantum state with promise of classical data

I am trying to solve a problem in the measurement and identification of quantum states with a promise as to what states it could be. Here is the problem. Imagine a system that produces qubits in ...
104 views

### Formula for potential for 2 coaxial tubes

Could someone remind me of the formula for potential function for a system consisting of 2 coaxial tubes maintained at a fixed potential difference and the in between medium has uniform conductivity ...
505 views

### Double image in binoculars

How can I reduce the double image seen when looking through binoculars? I recently got a new pair, but have been having troubles using them because I am seeing double...
61 views

### A nice overview (and maybe derivation) of the Poincaré transformations of the Vector Spherical Harmonics

With $Y_{lm}(\vartheta,\varphi)$ being the Spherical Harmonics and $z_l^{(j)}(r)$ being the Spherical Bessel functions ($j=1$), Neumann functions ($j=2$) or Hankel functions ($j=3,4$) defining ...
746 views

### Question involving Vectors and Forces

This is a question I found in Mechanics for Engineers by Beer & Johnston. A 600-lb crate is supported by the rope and pulley arrangement as shown below. Write a computer program which can be ...
6k views

### Why is oxygen in a triplet state and what are the consequences?

From Wikipedia here and here: ''Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception.'' ''The unusual electron configuration prevents ...
858 views

### Quantum perpetual motion

Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, ...
815 views

### What's the importance of Noether's theorem in Physics

The Noether's theorem that I want to mention is the following: Noether's theorem. I know the importance of Noether's contribution to modern algebra. Can anyone write about Noether's theorem in ...
11k views

### Are all metals good conductor of electricity?

I am writing an article for kids, which is on conductors and insulators of electricity. If I make a statement that "All metals are electrical conductors and all non-metals are electrical insulators" ...
2k views

### Oil drop experiment--How was the result so accurate?

I remember while learning about Millikan's oil drop experiment and being pretty skeptical about the setup. I know that there is a lot of controversy regarding manipulation of data, but the fact is; he ...
503 views

### Good theoretical physics introduction for 6 year old very advanced in math? [duplicate]

I think now is a good time to introduce my son to theoretical physics. He asks so many questions about the universe, black holes, gravity, atoms, molecules, light, etc. He's borderline obsessed with ...
308 views

### Correlation Functions, Symmetries and Measurements

Is there a book that goes deep into correlation functions? What I'm interested in a book/article that explains in the detail the relation of the correlation functions with symmetries and how one can ...
672 views

### Bra space and adjoint vectors

If I'm not wrong, a bra, $\langle \phi_n |$, can be thought as a linear functional that when applied to a ket vector, $| \phi_m \rangle$, returns a complex number; that is, the inner product it's a ...
385 views

### Calculating spacecraft water leak flow rate

A large container of heated water is floating in space. How can I calculate leak rate if a small puncture is opened? I'm assuming the water is kept at 298K and in the liquid state inside the chamber. ...
1k views

### How does the Milkovic Two-Stage Mechanical Oscillator Pendulum-Lever System work?

See http://peswiki.com/index.php/Directory:Milkovic_Two-Stage_Mechanical_Oscillator The Two-Stage Mechanical Oscillator Pendulum-Lever System is very simple, yet very puzzling because it appears ...
468 views

### In-flight damage to a supersonic jet

I'm doing some research for a book I'm writing, and, as the title implies, I'm looking to understand what happens when a supersonic jet sustains in-flight damage. Specifically, what happens to the ...
1k views

### What happens when a supersonic airplane flies through a cloud?

What happens when a supersonic airplane flies through a cloud? Will it punch a hole or is it more like a bullet through water (= hole closes immediately after the aircraft has passed)? Is there some ...
1k views

### Example in the book: A simple accelerometer

A simple accelerometer You tape one end of a piece of string to the ceiling light of your car and hang a key with mass m to the other end (Figure 5.7). A protractor taped to the light allows you ...
378 views

### How is it that some nebulae are rotating and others are not?

First, I should make it clear that this isn't a question about angular momentum (unless I may have completely missed something). It is my understanding that a nebula must have some inherent initial ...
383 views

### How does one interpret the Dirac equation with a self-field potential?

EVERY QFT text I've ever examined states that if there is an external vector potential, $A_\mu$, then one writes the Dirac eq.(or Klein-Gordon eq.) using a covariant derivative to include this U(1) ...
1k views

### How long will my fridge magnet stay attached to my fridge?

I have a 500 gram neodymium magnet. It is stuck to my fridge. With the constant pull of gravity trying to pull it off how long would it stay attached to fridge? For arguments sake lets say my fridge ...
251 views

### How to define the required aspherical coefficients for a lens?

I would like to purchase my own aspherical lens for testing purpose. Then I need to define the required coefficients. But how? My known requirements are f=25mm F/# 2.0 and MTF 0.5 @ 120lp/mm with a wl ...
251 views

### what is a kink-kink-meson vertex?

These are questions I have after reading the Rajaraman's book "Solitons and instantons". So I think you must have read the book if want to answer. And also know about quantum solitons. Rajaraman ...
111 views

### Why does Omega Centauri have a distinct chemical signature from the rest of the Milky Way?

In answering a question about the orbital path of Omega Centauri, I learned that it has a distinct chemical signature from the rest of the Milky Way. Basically, it is very rich in s-process elements, ...
4k views

### Why do far away objects appear to move slowly in comparison to nearby objects?

When we are in a moving train, nearby stationary objects appear to go backwards. In Physics, relative velocity can be employed to explain the phenomenon: velocity of object w.r.t train = velocity ...
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### Square of Laplace–Runge–Lenz vector in Hydrogen atom [closed]

I have a problem. I've tried this question, but I don't get the correct expression. Can someone give me some ideas? Thanks! Consider the Hydrogen Atom Hamiltonian:  H = (\mathbf p^2/2 ...
386 views

### Some questions about the BCFW reduction

I am trying to give a fast sketch of what the BCFW reduction does and embed within it some questions at the steps which I don't seem to understand clearly. The first bullet point is sort of a very ...
273 views

### Raising a toolbox with a rope

Suppose you use a rope to hoist a box of tools vertically at constant speed v. The rope exerts a constant upward force of magnitude F_up on the box, and gravity exerts a constant downward force (the ...
514 views

### Equivalence principle and radiation from falling particle

I am currently having a hard time solving a problem of GR from Lasenby's book. I can't make it more clear than by quoting the exercise: 7.2 A charged object held stationary in a laboratory on the ...
340 views

### Potential energy conservation in traversable wormholes

Let's say I have a tube, of large radius (about 5 - 7 meters in diameter), with traversable wormholes at the ends. The wormholes are arranged as such that if something falls inside one hole from ...
386 views

### How are functional determinants of Laplace-type operators used in physics?

Many mathematical papers concerning the $\zeta$-regularized Determinant of Laplace-type operators refer for motivation to the broad use of such determinants in mathematical physics, especially in ...
703 views

### How should I draw this free-body diagram?

The horizontal force P acts on the rim of the homogeneous cylinder of radius R and weight W. Determine the smallest coefficient of static friction that enables the cylinder to start rolling up the ...
688 views

### Turn-on delay time for Laser diode

Do you know any simple explanation on the reason why the turn-on delay time on a laser diode is reducing while we increase the bias current? Turn on delay,is the time that the laser needs from the ...
264 views

### Find largest angle

The two homogeneous bars AB and BC are connected with a pin at B and placed between rough vertical walls. If the coefficient of static friction between each bar and the wall is 0.4, determine the ...
173 views

### Representation on Hilbert space of the product of two symmetry transformations

We know by Wigner's theorem that the representation of a symmetry transformation on the Hilbert space is either unitary and linear, or anti-unitary and anti-linear. Let $T$ and $S$ be two symmetry ...
778 views

### Unitarity of S-matrix in QFT

I am a beginner in QFT, and my question is probably very basic. As far as I understand, usually in QFT, in particular in QED, one postulates existence of IN and OUT states. Unitarity of the S-matrix ...
5k views

### Could a real-life X-Wing fly in Earth's atmosphere?

From an aerodynamic point of view, could a full-size aircraft of X-Wing design fly in Earth's atmosphere? Assuming you were free to add control surfaces here and there, could the wings in open ...
300 views

### What is electric/magnetic field in a medium?

One method of introducing electric field is based on the measurement of the force acting on moving charged particle. By equating F to qE we determine the electric field E if the electric charge q is ...
597 views

### Train crash: are these situations alike? [duplicate]

I was just wondering... I believe that if a car travelling 50 miles per hour crashes into a wall, the result should be the same as crashing to another car also travelling 50 miles per hour (but in the ...
481 views