1
vote
2answers
212 views

Faraday's law and “infinite induction”

I may have confused after thinking too much about Faraday's law. If an emf is induced in a circuit due to some changing magnetic field, the induced current will be in a direction such that the ...
0
votes
1answer
3k views

Determine the maximum height a pump can suck up water

I am working on a homework problem that presents the scenario of trying to raise water from a small reservoir of depth 8 m whose surface is 25 m below a pump that can maintain a pressure differential ...
1
vote
2answers
126 views

Basic rule for diffraction

I'm a high school student. I still don't understand the reflection, diffraction and refraction of light. It seems to me that in concept of quantum physics, reflection is just a process of object ...
11
votes
3answers
7k views

Turning Jupiter into a star

So, I've heard from various works of science fiction about the prospect of turning Jupiter into a star. From what I know about the physics of such a task, it would require somehow condensing Jupiter ...
1
vote
2answers
70 views

Anyonic braiding statistics from density matrix renormalization group (DMRG) simulations

How does the ground state energy of the system change when we braid two anyons? Can the braiding of anyons be simulated with a computational method such as the density matrix renormalization group, ...
6
votes
1answer
260 views

What is many body localization?

Is there any good definition of many body localization? It is the property of one state or it is the property of a Hamiltonian? Why does disorder play an important role in many body localization? ...
1
vote
1answer
508 views

Density of classical states in quantum theory

Let's first treat electrons as classical objects. I can evaluate the classical energy of each state in a configurational space (3N real numbers and, say, spins) using just Coulomb's law. Then I ...
1
vote
1answer
71 views

Reduction of Nambu Goto action to true degrees of freedom

First consider the particle $$S=m\int\sqrt{-\dot{X}^2}d\tau$$ if you choose the static gauge $\tau=X^0$ and replace it in the action you get $$=m\int\sqrt{1-\dot{X}^j\dot{X}^j}d\tau$$ So now, you ...
0
votes
1answer
141 views

How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
0
votes
1answer
26 views

Helmholtz Free Energy vs Gibbs Free Energy in Landau Theory

When I was studying thermodynamics potentials for the first time, I learned that keeping the pressure and the temperature constant, the Gibbs Free Energy is a minimum, also, if we maintain the ...
1
vote
2answers
28 views

Neutron antineutron reaction documentation

Has neutron-antinutron reaction been observed? If so, can you please provide a documentation (experimental observation) for neutron antineutron reaction?
3
votes
0answers
57 views

Fermionic path integral on the disk - Recovering the vacuum state

I'm trying to get a better feel for the operator to state map in quantum field theory. There is a general claim for 2d theories that doing the path integral on a disk with no operator insertions gives ...
0
votes
0answers
21 views

observational-astronomy

I am looking for the current location of the line of apsides in tropical astrological coordinates; I tried using the sun's position at the time of earth's perihelion, but the results vary too much. ...
-3
votes
0answers
36 views

Le Sage gravity [on hold]

Is there a definitive reason that Le Sage's theory of push gravity, or push gravity in general, can be ruled out as possibility?
1
vote
1answer
78 views

Can Bosons couple to gravity? Why do we need vielbein?

It is said that In theories such as Supergravity where there are fermions coupled to gravity, one must use an auxiliary quantity, the frame field (vielbein). In supergravity, can a boson be coupled ...
1
vote
0answers
38 views

Why do decompositons like $16 \otimes 16 = 10 \oplus 120 \oplus 126$ tell us which Higgs representations we can use?

This line of thought is used everywhere in Grand Unified Theories, but I can't figure out why this works and it must be very obvious because no one seems to offer an explanation. Commonly the ...
0
votes
1answer
78 views

Isolation of a Physical System and Energy

I'm trying to grasp basic concepts of energy and i have a little doubt regarding conservation of energy. According to Feynman book and Wikipedia, the Law of Conservation of Energy states that ...
0
votes
0answers
32 views

Find distance vs. time for a space ship moving through cloud of dust of uniform density

Here's a problem: We have a cylindrical spaceship with cross-sectional area $A$ moves through a stationary cloud of dust of uniform density $\rho$. Initially the ship has some speed $v_0$ and some ...
0
votes
1answer
19 views

What does “simultaneously” mean in relation to a detonation shockwave?

I understand that the difference between a deflagration and a detonation is that the reaction front of a detonation moves faster than the speed of sound in the material, which means that the pressure ...
0
votes
0answers
17 views

How to calculate g-force of a vehicle in an accident through accelerometer values?

i'm developing a crash notification android application.i want to calculate the g-force at the event of car crash.which is detected by the accelerometer of the smartphone.so far my code is as below, ...
1
vote
1answer
139 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
1
vote
1answer
28 views

What would cause an orange sky?

(I was recommended to ask this question here by the guys on World Building) I'm starting a whole new planet for a story and would like it to have an orange sky during the day. At a basic level (I am ...
1
vote
2answers
37 views

Electric field on the surface of a charged sphere

We know that the electric field for a point charge is $$ E = \frac{KQ}{R^2}. $$ If $R$, i.e. distance from the electric field producer to the point where we want to find the electric field becomes ...
0
votes
2answers
39 views

Stopping a nuclear missile

I had been thinking about whether it is possible to stop an incoming missile or not. I found something quite interesting here. So, there many people said that it will be possible to stop an incoming ...
1
vote
1answer
309 views

Theoretically if you passed the speed of light in a medium, would there be a sonic boom equivalent?

I know that it is technically impossible to reach the speed of light in vacuum since the mass of the object traveling would reach infinity. However in a medium, would there be some sort of theoretical ...
0
votes
1answer
44 views

which are the non-abelian anyons for universal quantum computation

I am trying to get a list of non-abelian anyons that can be used for universal quantum computation by implementing gates via braiding. I found that Majorana fermions and para-fermions (not sure about ...
1
vote
0answers
6 views

How does voltage sensitive dyes actually determine neural network in foetus?

In research topics of neurophotonics, the best way of determination of neural network in foetus is by using voltage-sensitive dyes instead of placing diodes. But how does it actually work? Sorry if ...
1
vote
1answer
28 views

Time for two relativistic objects to meet

How do you prove that the time for two objects traveling towards each other at relativistic velocities is still d/(v1+v2). Answer seems to have something to do with velocity addition but I'm ...
1
vote
2answers
14 views

Resultant half life of sample which contain more than one type of radioctive element.

If a sample is mixed with more than one radioactive elements - for example Ra-226, Po - 210 and Cs -137, then how to estimate the resultant half life of the sample? Is there any general formula to ...
3
votes
1answer
226 views

Least Action Principle (Classical and Quantum Theory)

I) My first question would be "why should classical systems obey the principle of least action ?" When we find out the propagator in quantum physics, we find the amplitude to be equal to the sum over ...
3
votes
2answers
281 views

What is conformal gauge?

I often see in physics articles on gravity such notion as conformal gauge and Weyl transformation. They use Conformal gauge to change coordinates to transform metrics from arbitrary $$ds^2=g_{\mu ...
0
votes
3answers
101 views

How exactly does wave theory of light fail to explain blackbody radiation? [duplicate]

I don't really understand the reason why wave theory of light fails to explain the blackbody radiation. My textbook says the Planck's quantum theory explains blackbody radiation. It says "If we ...
1
vote
2answers
211 views

Confused about elasticity and collisions

I was solving the following problem and the explanation to it confused me. There are two objects with mass $m$ and $M$, respectively. The object with mass $m$ has a velocity of $\sqrt{2gl}$ and ...
0
votes
1answer
26 views

In a spherical distribution the charge density varies as ρ=A/R [on hold]

ATTEMPT: The entire sphere be divided into infinite concentric spherical shells of thickness $dx$. Considering one such shell with radius $x$. volume of the spherical shell = $4πx^2dx$ charge ...
3
votes
2answers
66 views

Sign of momentum in fermion propagator

Thinking of a process like Compton scattering, where we have an electron as a propagator, I would typically write down the propagator as $$i \frac{\not q+m}{q^2-m^2}.$$ If I were to replace the ...
0
votes
2answers
15 views

Why do electric field lines point in the direction of decreasing electric potential?

Why do electric field lines point in the direction of decreasing electric potential? I came across this sentence in my school book but am trying to understand this ever since. I know that dV=-E.dr ...
3
votes
2answers
285 views

Is there a way to calculate the photoelectric effect in QED via a Feynman diagram?

The photoelectric effect is the historic origin of the quantum particle description of light. From it we learn that when light is shone onto a metal single photons interact with single electrons in ...
0
votes
2answers
41 views

generating heat using IR radiation

I have come to know that infrared radiation can generate heat in an object .Suppose if am using an optical fibre of very thin diameter (similiar to human hair) & when an IR source is passed ...
5
votes
1answer
53 views

What is the curve described by the water of a wet spinning tennis ball?

I'm looking at this picture from this site and I'm curious about what is the curve described by the water. The involutes $$x=r\left[\cos(\theta+n)+\theta\sin(\theta+n)\right]\\ ...
0
votes
1answer
170 views

Is something beyond the material needed to solve the Von Neumann Chain?

A problem has been presented that goes like this: Particles normally exist as several mathematical possibilities rather than one actual object. It is said that in the absence of observation, ...
0
votes
0answers
20 views

Vector fields corresponding to null geodesic congruences in general relativity

I'm working in Minkowski space, and I'm considering some 2D surface, $S$. On each point of the surface, I've computed a null vector, $k^a$, which is orthogonal to it. There will be a unique null ...
3
votes
4answers
56 views

What is the lowest level things have temperatures?

Something can be cold. If you split it in half, it will still be cold, keep doing that and it will still be cold. My question is, what is the lowest level things can have temperature? Do atoms have ...
0
votes
1answer
154 views

Sun's tidal force on earth

My question is regarding effect of sun's gravity on earth. I want to know that if sun's gravity can change earth's landscape in long duration (i.e. billion of years ) or not?? Means if earth is dead ...
0
votes
1answer
55 views

What physical properties can we measure most accurately?

As far as I am aware, frequency is the most accurate physical property we can currently measure. This has led us to very high standards of experimental verification of e.g QED predictions and the CMB ...
0
votes
1answer
49 views

Shape of galaxies [duplicate]

i want to know why galaxies are spiral in nature.. let us say there is some sort of intense mass (black hole?) at the centre of our milky way galaxy. the intense gravitaional pull is keeping evey ...
0
votes
0answers
23 views

When a charged insulator is touched by a conductor, What really happens?

1-how does the conductor get charged although the electrons in the insulator are not free to move? 2-If the conductor material is connected to the earth, Will the insulator be discharged?
1
vote
2answers
100 views

Origin of cusps in simulated dark matter halos

I keep reading that cusps are one of the most "robust" predictions of N-body simulations of dark matter halos. But papers I've found on the topic make it sound like these simulations are complicated ...
-1
votes
1answer
37 views
-2
votes
0answers
20 views

3 point masses;circumference [duplicate]

3 gravitating mass points of mass m are on the circumference of a circle with the same distance r to each other. At $t=t_0$ one lets go of the mass points and each of them moves within the ...

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