0
votes
1answer
235 views

How does one come up with the Coulomb's law?

My teacher mentioned that field line density = no. of lines / area and the total area of a sphere is $4\pi r^2$ and so an electric force is inversely proportional to $r^2$. Actually, why can the total ...
0
votes
1answer
2k views

Ball rolling down an inclined plane going in to a loop

I apologize if this question is not up to par. When I was doing exercises in basic mechanics I checked the answers and I can't seem to find what I'm doing wrong. Suppose we have a ball with mass $m$ ...
2
votes
2answers
299 views

Rigid body dynamics of tossing of a coin

While tossing a coin, it is commonly experienced that you get a head, if you toss it up with the head side up, and a tails if you toss with the tails side up. Is there a mathematical proof of this ...
2
votes
1answer
101 views

Constraints on open strings absent at the perturbative level

Studying Disappearance of moduli for condensate of open strings and Negative open string norms after BRST cohomology? gave me a huge huge shock! Suppose we have N completely wrapped Dp-branes over a ...
1
vote
2answers
1k views

What does the general solution of the Schrodinger equation represent for the particle in a box problem?

For the particle in an infinitely deep potential well, I have an intuitive picture of the separable solutions of the Schrodinger equation as being the wavefunctions for the different allowed energy ...
6
votes
5answers
921 views

General relativity and the microscopic/macroscopic distinction

Here is Wikipedia's diagram of the stress-energy tensor in general relativity: I notice that all of its elements are what would be termed "macroscopic" quantities in thermodynamics. That is, in ...
2
votes
2answers
2k views

Artificial planetary magnetic field

I wonder how difficult it is to create an artificial planetary magnetic field with generators? What power they would need? The question is inspired by thinking about possible colonization of ...
0
votes
2answers
158 views

Energy Question

Carl throws 100 g of Bohrium-262 (Half life: 0.10 seconds, undergoes alpha decay) to Sukhdeep with a initial horizontal velocity of 20.0 m/s at an initial height of 2.00 m above the ground. What is ...
2
votes
1answer
217 views

DIfference in Pitch Caused by Water Temperature?

I have recently been intrigued by the following question: What is the difference between the pitch of the noise of dripping water between hot and cold water? For example, would cold water create a ...
15
votes
7answers
5k views

How can kinetic energy be proportional to the square of velocity, when velocity is relative?

Let's start with kinetic energy (from los Wikipedias) The kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a ...
6
votes
3answers
7k views

What are good books for graduates/undergraduates in Astrophysics?

There are no book recommendations for Astrophysics here. I will write my own answer, but I am also interested in what are others' views on the question (I will NOT mark my own answer as the best one). ...
2
votes
1answer
265 views

How does light travel create time travel violating causality?

Saw a question about faster than light travel... I still have the same question though none of the answers offered any resolution for me. It is so summarily assumed by all physicists and commentaries ...
3
votes
3answers
381 views

Would it be possible to create a hadron collider in space?

Would it be theoretically possible to create a hadron collider in space by orbiting particles around a planet?
1
vote
1answer
125 views

boundary limit conditions in 3D water surface simulation

As is discused on this post, taking some assumptions, the water surface can be simulated by a discrete aproximation of a grid of heights using this formula Where: HT is the new height grid HT-1 ...
1
vote
2answers
250 views

A step in the derivation of the magnetic moment of the electron in Zee's QFT book

In chapter III.6 of his Quantum Field Theory in a Nutshell, A. Zee sets out to derive the magnetic moment of an electron in quantum electrodynamics. He starts by replacing in the Dirac equation the ...
1
vote
1answer
406 views

Can high charges (like $1\times 10^{-3}$ coulomb) be acheived?

How can we charge a metal electrode with large charges ? When i saw a video about measuring a charge using a visiostat on a balloon , the charge was 0.6 nano-coulomb. Is the charge of 1 coulomb ...
5
votes
3answers
812 views

Why does the electric field dominate in light?

I read a book on the wave property of light where the author mentioned that the electric field, instead of magnetic field, dominates the light property. I don't understand why. In Maxwell's theory, a ...
2
votes
4answers
306 views

The requirements for superconductivity

Which properties are sufficient evidence for a material to be not superconducting? I am looking for a set of statements like If the material is semiconducting, it is not superconducting Edit: I ...
3
votes
1answer
173 views

What does Metric Transitivity Mean?

Jaynes In his paper "Information theory and Statistical mechanics" says "Previously, one constructed a theory based on equations of motion, supplemented by additional hypothesis of ergodicity, ...
1
vote
1answer
196 views

Minimum time required to reach a point [closed]

A police inspecter P is at point $ (\acute{x},\acute{y})$ and a thief X is at point $(x, y)$. X has a constant velocity $V_x\hat{i} + V_y\hat{j} $, where $\hat{i}$ and $\hat{j}$ are unit vectors in ...
0
votes
1answer
204 views

About interchange phase of identical particles in Weinberg's QFT book

In Weinberg's textbook on QFT(google book preview), he discussed the phase acquired after interchanging particle labels in the last paragraph of page 171 and the footnote of page 172. It seems he's ...
2
votes
1answer
749 views

Is it possible to increase refractive index at lower densities?

Are there any materials for which the refractive index decreases with density? It seems that for most materials we would expect there to be a positive correlation between density and refractive index, ...
5
votes
1answer
4k views

Phase and Group Velocity of Electromagnetic Waves

Moving charges produce oscillating electric and magnetic fields -we have an electromagnetic wave. In terms of moving charges or at the level of charges, what is phase velocity and group velocity of ...
1
vote
3answers
186 views

Constructing Supersymmetric Lagrangians

It is a very trivial doubt but somehow I am not able to figure it out. While constructing a supersymmetric lagrangian we always even number of fermionic fields. One reason is of course the product ...
5
votes
1answer
559 views

Lotus effect dust removal

I have found hundreds of papers describing the contact angle of water droplet sitting on hydrophobic surface and the change between Wenzel Regime and the Cassie-Baxter regime. Now, as I understand ...
7
votes
2answers
407 views

Scattering states of Hydrogen atom in non-relativistic perturbation theory

In doing second order time-independent perturbation theory in non-relativistic quantum mechanics one has to calculate the overlap between states $$E^{(2)}_n ~=~ \sum_{m \neq n}\frac{|\langle m | H' ...
2
votes
0answers
951 views

Electrostatic Dust Removal

I have been recently reading a paper on dust removal and I have a few basic questions regarding it. First off, I am citing this paper - "Dust removal system with static electricity" Basically, an ...
1
vote
1answer
77 views

Schrödinger operator with a potential defined implicitly

let be the problem $$ -\frac{d^{2}}{dx^{2}}y(x)+f(x)y(x)=E_{n}y(x)$$ however we have a problem, we do not know the potential but its inverse $$ f^{-1}(x)=g(x) $$ we know $ g(x) $ but not $ f(x) $ ...
1
vote
2answers
476 views

Proca equation question

i'm having trouble understanding the Proca equation $$(g_{\mu\nu}(\Box+\mu^2)-\partial_{\mu}\partial_{\nu})\varphi^{\nu}=0$$ where $g_{\mu\nu}$ is the metric and $\mu$ is a parameter. Where is the ...
3
votes
1answer
111 views

If the observable universe keeps expanding would we eventualy see light 24/7… clouds permiting? [duplicate]

If we can see more observable universe could there be a time when day and night looked the same?
2
votes
2answers
332 views

Could dark energy be heat? Could dark matter be stuff that is not seen because of its refraction limits?

Heat has to go somewhere. Would the light and heat of the stars in the universe amount up to being dark matter ...and dark energy ... Dark matter would just be small pieces of stuff. Dark energy ...
2
votes
0answers
189 views

Where can I find a complete list of metamaterials up to today?

Where might I find a list of all the metamaterials up-to-date?
2
votes
2answers
748 views

Circular polarization: properties and detection

I am thinking about the property of circular polarization of light. I have two circularly polarized beams, one is rounding in positive direction, other is negative. My task is to figure out: if ...
0
votes
2answers
13k views

Confusion about P=VI and V=IR

If we look at $P=VI$, we see that if the current doubles then the potential difference is halved but this doesn't seem to make sense according to $V=IR$. If we look at that equation, since the ...
3
votes
1answer
251 views

$J_1$-$J_2$ Heisenberg antiferromagnet

In this paper, the authors solve for the excitation spectrum in a $J_1$-$J_2$ Heisenberg antiferromagnet using the modified spin-wave theory in the Dyson-Maleev representation. As an intermediate ...
2
votes
1answer
210 views

about polarization of light

In the course of circuits and electronics, I remember there is an experiment to show the polarization of the wave as lissajous figures. I am wondering for polarized laser, is there any way to ...
0
votes
1answer
90 views

What does Friedrichs mean by “Myriotic fields”?

I came across K. O. Friedrichs' very old book (1953) "Mathematical Apsects of the Quantum Theory of Fields", and hardly any of it makes sense to me. One of the strange things that he refers to are ...
3
votes
1answer
638 views

Can a blackhole eat a blackhole?

I'm not a physicist and I do not understand maths. But I watch documentaries about "how it all began", "the big bang", "What is time", etc etc just really fascinating. I was wondering if a blackhole ...
2
votes
6answers
2k views

Confused about unit of kilowatt hours

So I am a little confused on how to deal with the Kilowatt hours unit of power, I have only ever used Kilowatts and I have to design a residential fuel cell used as a backup generator for one day. ...
18
votes
1answer
946 views

Why does the spotlight reflected off of a rectangular mirror tend to become circular?

Background and setup When I was 12 I used to like a girl, we were almost neighbors and it was essential that our parents don't find out. So whenever one of us wanted to call the other they'd signal ...
3
votes
3answers
639 views

How to determine whether a large container is air-tight?

In constructing a kitchen-waste digester at home, I use a 50 Litre HDPE drum. The base of the drum is holed with a plug fitted to allow drainage when necessary. The top has two openings - one for ...
0
votes
0answers
219 views

How do I find the force on the charged sphere due to a dipole sitting inside?

I have a dipole sitting inside a charged sphere i.e. at the centre of the sphere. As far as I can see the force on the Dipole is zero because the external electric field on the dipole at $r=0$ is $0$. ...
4
votes
1answer
962 views

How do Einstein's field equations come out of string theory?

The classical theory of spacetime geometry that we call gravity is described at its core by the Einstein field equations, which relate the curvature of spacetime to the distribution of matter and ...
3
votes
1answer
154 views

What is the maximum mass of planet HD 40307 g

Recently discovered planet HD 40307g around HD40307 Star system is claiming that its inside a habitual zone of a solar system. Besides It has water where life could be evolved. I tried to calculate ...
0
votes
2answers
233 views

Force on a bar magnet

A bar magnet is freely falling vertically inside a conducting ring placed in horizontal plane. Will it fall with an acceleration equal to g, less than g or greater than g?
0
votes
2answers
1k views

Vector Nature Of Angular Velocity

I am currently reading about angular position, angular velocity, and angular acceleration. I came across this paragraph that was particularly confusing, and was wondering if someone could perhaps help ...
2
votes
1answer
123 views

Units of azimuthally integrated radiant intensity

If the radiant intensity $I(\phi,\theta)$ of electromagnetic radiation is given in spherical coordinates ($\phi$ the azimuth, $\theta$ the polar angle, indenpendent of $R$) with units $Js^{-1}sr^{-1}$ ...
6
votes
4answers
664 views

Quantum mechanics textbooks that use path integrals

I'm looking for a textbook in quantum mechanics that relies heavily on Green functions and the path integral formalism to supplement my QM books. I want to do some calculations using alternative ...
1
vote
1answer
2k views

Plane wave expansion in cylindrical coordinates

I am trying to solve scattering problem in 2D and got to expand the wave function in cylindrical system which comes out to be Hankel function. Can you tell me how to expand the plane wave $\exp(i ...
1
vote
1answer
232 views

Potential for charge distribution, finiteness

Consider a potential for charge distribution: $$v_H(\mathbf{r}) ~=~ \int \frac{\rho(\mathbf{r'})}{|\mathbf{r}-\mathbf{r'}|}d\mathbf{r'}$$ where $\rho(\mathbf{r'})$ is the charge density. This ...

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