# All Questions

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### Initial conditions of the origin of the universe [duplicate]

I'm not quite sure this question fits the format of this site but I try to word it the best I can to comply the rules. The question is simple: How far can we go talking about the origin of the ...
137 views

### Magnetic monopole

I've been watching a lot of videos claiming to make monopoles either by dropping the temperature to 5k (-268° C) and splitting the magnet or by pouring molten metal through an induction system and was ...
130 views

### How to prove the relations between the variables in bispherical coordinates?

When I was reading papers about the forces between two charged spherical conductors in a uniform electric field, I was confused with bispherical coordinates the author used to describe the spherical ...
32 views

### velocity function in slip effect

$$\frac{dp_l}{dx}-\mu_l\frac{\partial^2 u}{\partial y^2}=0$$ where $\mu_l$ and $p_l$ is the liquid phase viscosity and pressure, respectively; and $u$ is the flow velocity. The boundary ...
70 views

### To all experienced theoretical physicists out there, what is the step by step process in your math education? [duplicate]

I am not doing a physics degree but an engineering degree but i am planning using my free time to self study all the math in preparing myself to self study subjects in theoretical physics. (I've ...
380 views

### Entropic force in polymers

According to my textbook, the elastic force in a rubber is caused to the tendency of the polymers to return to their initial disordered state of higher entropy. But isn't this looking at entropy on ...
62 views

### Large-N critical NLSM (equation 13.115 of Peskin and Schroeder)

Any opinions if the equation 13.115 of Peskin and Schroeder is true on arbitrary manifolds in arbitrary dimensions for the same Lagrangian? I a priori see no problem. The point I also want to ask is ...
41 views

### resistance in a dc circuit [closed]

Herein is my question. On my gm vehicle, I replaced the dash gauges with aftermarket gauges. So, I replaced the battery light with a volt meter. I have burned up several alternators.. Have been told ...
131 views

### Calculating the height objects fall from [duplicate]

Imagine an object of a given mass. The object falls from a certain height. On contact with the ground, the object has a certain force. If the force of the object and the mass of the object are ...
79 views

### Application of wavelets in computational electromagnetics

I am a first-year graduate student (electrical eng.); wavelets is one of the courses that I am taking presently. As part of the course, I plan to explore application of wavelets in computational ...
146 views

### Do photons interact only with single particles or can a single photon be absorbed by 2 or more particles simultaneously?

Say I have 100 particles in a vacuum that are spread out such that their movement caused by a time variant electromagnetic field does not have an effect on each other. That is the particles can not ...
41 views

### How is the formula derived for finding the field of view given drift time and declination of a star?

How is the formula for field of view derived given the drift time of a star and its declination? $FOV = (drift\ time \cdot \cos(declination)\cdot360 ) / 86164$
155 views

### Does charge of a metal charged by induction determine by which ends of the metal is grounded to?

Does charge of a metal charged by induction determine by which part of the metal is ground to? I draw a diagram to make it simple to understand: Right diagram: When ground is touched with the ...
170 views

### Reissner-Nordström Black Holes

The Reissner-Nordström black holes are described by the metric, \begin{align} ds^2 = -\left(1-\frac{2M}{r}+\frac{Q^2}{r^2}\right)dt^2 + \frac{1}{1-\frac{2M}{r}+\frac{Q^2}{r^2}}+r^2d\Omega^2 ...
505 views

### What is dimensional units/quantity and dimensional state

First, I am not a native English-speaking student so I am not good at physics definitions in English. I participated in the MIT e-learning course on classical physics. The 1st lesson is about 3 ...
47 views

### Electron and photon interaction

Assuming I shoot a beam of light to an electron, the electron will take the energy and reemit EMR at all direction randomly? If it will, is it happening at the same time?
34 views

### Efficiency increase via ducting a fan - why is this more in viscous media?

I am looking at mixers for liquids like water or slurries. This brochure claims the following: With the optional jet ring, it is possible to increase efficiency by up 15% in water - even higher in ...
103 views

### Basic concepts in quantum theory to start learning semiconductor physics [closed]

What basic concepts in quantum theory one must known to start learning semiconductor physics?
92 views

### group velocity VS probability current

Think about an electron been accelerated from rest in a static electricfield. If we treat the problem classically, in which the electron is just a point charge. The velocity of the electron would ...
292 views

### Time dilation in special relativity?

I'm trying to understand the concepts of time dilation and spatial compression. I've been using the classic example of firing a photon of light inside a ship (spaceship, boxcar, etc.) moving at a ...
106 views

### Energy in a Solenoid?

Consider a circuit consisting of a battery, a resistor and a solenoid inductor. Then, the emf $\mathcal{E}$, is defined as: $$\mathcal{E} = L\frac{di}{dt} + iR$$ Multiplying both sides by ...
31 views

### Velocity dispersion of galaxies

I couldn't find on web how can I get the velocity dispersion and velocity maps of galaxies from the 3D data cube I get from integral field spectrograph.
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Feynmann Lectures Vol 3 Ch 8 Sec 6 describes how an ammonia molecule can have two definite energy states. If the amplitudes of the base states are $C_1(t) ... 1answer 39 views ### Differentiating between mass number (A) and activity (A) in a nomenclature/glossary [closed] I'm not sure if this is the best place to ask this question, but as it's related to the terminology of nuclear physics I thought it would probably be a logical place to start. I'm currently writing ... 0answers 106 views ### about orthogonal catastrophe I am reading Wen's book, QFT of many-body systems ( @Xiao-Gang Wen ). I am a little confused about the orthogonal catastrophe introduced in Chap.5. Below Eq.(5.1.6), it is stated that the influence ... 0answers 26 views ### How does beta+ decay actually occur? [duplicate] I'm having difficulty in understanding beta plus decay. How can a proton which has slightly less mass than neutron transform into a neutron, positron and neutrino? Form where does the extra mass for ... 1answer 571 views ### Where do these formulas for an object being pushed up an incline come from? [closed] An object on an incline with an angle$\theta$is being pushed at constant speed. Constant speed implies$a = 0$. Because$F=ma$and the object must have mass greater than 0. If I want to find the ... 0answers 51 views ### Coherent State in 2 dimensions I am looking at a 2D harmonic oscillator $$H=\frac{1}{2m}(p_x^2+p_y^2)+\frac 12m(\omega_x^2x^2+\omega_y^2y^2)$$ Where$\omega_x=5\omega_y$. I am told that the oscillator is prepared in a coherent ... 0answers 161 views ### Correct way to include constant external force in virial and pressure calculation Halo, given a simulation cell with N particles where particles interact only with bond and pair potentials and periodic boundary conditions (minimum image convention) are used. On a subgroup of ... 0answers 50 views ### Change in Angular momentum of a spinning superball I throw a superball towards the ground and when I do I intentional induce a spin on the ball so that the ball is spinning towards me on the descent. As soon as the ball hits the ground and comes back ... 2answers 791 views ### Magnification in compound microscope I was studying about compound microscope here I don't see why we multiply linear magnification of objective with angular magnification of eyepiece. Shouldn't it be both angular or both linear? Can ... 0answers 85 views ### Derivation of cylindrical line heat source problem? I have a line heat source embedded inside a cylinder and I am trying to find the temperature distribution T(r,t). By using the similarity variable, the solution to the differential equation is ... 1answer 393 views ### Energy difference between symmetric and antisymmetric wavefunctions [closed] Is there any energy difference between a particle in a symmetric wavefunction and an identical particle in an identical potential but in a state with an anti-symmetric wavefunction? Or is it ... 0answers 567 views ### Conformal maps and flow around corners The complex potential$\Psi = \psi + i \phi$($\psi$is the velocity potential,$\phi$the stream function) is an analytical function for an irrotational inviscid flow, since its constituents in this ... 0answers 50 views ### Personalized “anthropic principle” and many-worlds divorce between Shroedinger's cats Anthropic principle, at least in laymen explanations that I have encountered so far, sounds something like "the physical universe suits us exceptionally well because among all the possibilities we, ... 0answers 225 views ### Different phase in capacitively coupled RLC circuits I was trying to work with some data for a lab report I'm writing about capacitively coupled RLC circuits. The setup is pretty simple and looks like that: Where$C^{'}$is the coupling capacitance. ... 0answers 64 views ### Loaded die problem A loaded die has an uneven mass density distribution. A given die is constructed from a square pyramid of material with mass density$\rho_1$whose bsase lays on the face marked "1",with the rest of ... 0answers 31 views ### electric charge is a intrinsic property how is there a prpoer way to explain electric charge? [duplicate] how to define electric charge ? How to explain this term ? As learned by me electric charge is an intrinsic property of atoms like mass of different atoms. 0answers 277 views ### Orbital angular momentum selection rules for three identical particles I'm trying to figure out if there are selection rules for the total orbital angular momentum for a system of three identical particles, say bosons. For two identical bosons one can argue that the ... 0answers 64 views ### Vacancy Generation / Annihilation Time (Relaxation Time) Vacancy Generation/Annihilation Time, Recombination Time and Relaxation Time ($\tau$) are all synonymously used in atomic physics literatures. They're defined as the time that it takes for vacancies ... 2answers 51 views ### Infinite heat from gas? Does any type of gas keep the same temperature if is constantly exposed to same force? In other words, must we change the applied force in some moment to get heat again, or is the same constant force ... 0answers 98 views ### Integral of energy-momentum tensor On Weinberg's Gravitation and Cosmology section 8 chapter 2, he introduced the energy-momentum tensor of a system of$n$particals: $$... 0answers 155 views ### Is strictly harmonic 2D lattice made of Hooke springs possible? If we connect a set of point masses in a 1D lattice with Hooke springs and consider longitudinal oscillations, we'll have a strictly harmonic system, for which there exist eigenmodes and the frequency ... 1answer 75 views ### twin paradox inferring cosmic speed limit As I understand it, the twin paradox was integral to Einstein's conclusion that nothing can travel faster than the speed of light. Why wasn't there a similar conclusion for a hypothetical scenario ... 0answers 59 views ### How to work out bubble size and rising velocity in turbulent flow? Is there a way to determine bubble size and rising velocity in turbulent flow? I know stokes law but this is only valid for laminar flow. 0answers 51 views ### Information paradox and spacelike slices I'm reading S. Mathur's paper on the information paradox and I can't seem to understand the reason why we choose spacelike slices. Is it because we want to have a global timelike vector so that we ... 0answers 191 views ### Electric field produced by a charged ring I have a question I couldn't find an answer for anywhere. There is a ring of radius R which is charged uniformly with linear density \lambda, and I have to find the electric field on any point of ... 0answers 86 views ### What are characteristic ranges of time, distance, energy regions for physics and chemistry? [closed] I've constructed such table from many different sources for my thesis introduction: I'm trying to make a bit of philosophy it the thesis first chapter. Are they realistic or not? Could you make any ... 0answers 68 views ### Meaning of k in Sachs-Wolfe formula for angular power spectrum I've seen the formula for the angular power spectrum of the CMB written as$$C_\ell = \frac2\pi \int\left|\Theta_\ell(k) \right|^2 k^2dk,$$where$\Theta_\ell(k)$is the temperature contrast at a ... 0answers 445 views ### Partition Function of a three state particle system I've just finished studying the partition function of a two-state particle system, where particles can have a 0 energy value or E energy value . That is: Where$t_j\$ is a variable of value ...

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