-1
votes
0answers
23 views

Hexagonal shape of snow flakes

As we know snowflakes has hexagonal shape. My question is why is that? and Is there any mathematical model which can explain that particular geometric shape of the snowflakes?
-2
votes
1answer
39 views

What can shield a Ultrasonic Weapon? [on hold]

What can shield against a ULTRASONIC weapon? https://www.google.com/url?sa=t&source=web&rct=j&url=https://en.m.wikipedia.org/wiki/Sonic_weapon&ved=...
0
votes
0answers
20 views

Sound waves - physics [on hold]

A closed organ pipe of length L is in resonance with tuning fork. If a hole is made at a distance L/4 from the closed end will there be resonance again? If so when?
0
votes
0answers
22 views

How can I measure the security of Quantum Key Distribution (QKD)?

QKD protocol is a technique that allow two parties to share common secret key for cryptographic purpose and defined as being secure, by definition. But I am still wondering how can we measure that QKD ...
-6
votes
0answers
33 views

The origin of the universe and its current movement

Our universe started with the big bang, which was not within our universe, since it didn't exist. Let's assume it was the result of a quantum fluctuation in time. I have 2 questions: The common ...
5
votes
2answers
132 views

Gravitational waves in other dimensions

I know this question is purely speculative, as we don't know if more dimensions do exist and also we do not know if gravity is indeed stronger in other dimensions (if they were to exist). But, one of ...
-1
votes
0answers
51 views

Is there a fundamental picture for 'the speed of light'?

I am curious about the profound reason for the concept of 'the speed of light'. My considerations are: (1) It's related with the structure of spacetime (for example in Penrose's twistor plan),so ...
-3
votes
1answer
28 views

Will Project Avogadro introduce a new constant?

Will the Avogadro Project introduce a new constant? It seems to me that the aim of the project is to define the kilogramme as some constant number of silicon atoms. What would this constant be ...
4
votes
1answer
64 views

(Iso)spin coupling of three particles

I need Isospin calculations to predict the relative amount of strong decays, namely $D^{**0}\to D\pi\pi$, where the $D$ and $\pi$ can be charged or neutral. My problem is the order of contracting the ...
0
votes
0answers
22 views

Energy stored in a charged capacitor

There is a circuit with a 12.0 V cell and two capacitors with a switch, the switch in its initial position connects the cell and the first capacitor(4.7uF) (P) the switch in its second position ...
1
vote
0answers
14 views

Kerr Metric and Asymptotically Static Frame

Suppose we are given a Kerr spacetime (e.g. containing a single uncharged rotating black hole). How does one know that the coordinates chosen is rotating or non-rotating as seen from infinity? And how ...
-6
votes
0answers
12 views

How much heat does a Thermoelectric generater need to produce and how much would it produce

How much heat (Fahrenheit) does a Thermoelectric generater need to produce electricity and how much would it produce
1
vote
4answers
173 views

Why is the total potential difference in a circuit the sum of the individual potential differences?

I am having difficulty in applying my understanding of electrical potential to circuits. Why is the total potential difference in a circuit the sum of the individual potential differences among ...
1
vote
1answer
66 views

Where does the $0.61$ come from in $ R \sin \theta = 0.61\lambda $?

In my A2 Physics textbook it says that In the estimation of the nuclear radius by using electron diffraction the equation $$ R \sin \theta = 0.61\lambda $$ where: $R$ = radius of the nucleus $\...
0
votes
0answers
9 views

Do electronic energy levels of an atom effectively shift for scattering processes if the atom is moving in the lab frame?

When an electron of low energy scatters off an atom it interacts with one of the electrons in its shell and can transfer energy to it. The energy transfers would be discrete, since the shell electron ...
1
vote
2answers
171 views

Otto and Carnot efficiency comparison

Lets say both engines operate between same temperature limits. Carnot eff: $$ e_\text{Carnot} = 1-\frac{T_L}{T_H} $$ Otto eff: $$ e_\text{Otto} = 1-\frac{T_4-T_1}{T_3-T_2} $$ assuming ...
-1
votes
0answers
12 views

Excess pressure for a surface

Calculate the excess pressure for a surface located to plans a) $e_{1}$ b) $e_{2}$ for the flow specified by : $v_{1} =-c(x_{2} + x _{1})$ , $v_{2} = c(x_{2} - x_{1})$ , $v_{3} = 0$ where $c = 0,5 \...
0
votes
1answer
17 views

Are there interference effects for light that is reflected at an angle?

I am imagining a glass substrate with a thin coating that has a 1/4th wave optical thickness. I understand how this acts as a basic anti-reflective coating for the one wavelength for which it acts as ...
5
votes
1answer
50 views

One particle states in an interacting theory

Question: What is the general definition of one particle states $|\vec p\rangle$ in an interacting QFT? By general I mean non-perturbative and non-asymptotic. Context. 1) For example, in Weigand'...
0
votes
4answers
2k views

Potential Difference in a wire with no current

Recently I encountered a circuit problem. Imagine, you have an ordinary circuit with a resistor and a battery($60\,\mathrm{V}$ emf and negligible internal resistance denoted by r) with a switch($S_1$) ...
0
votes
1answer
107 views

Pseudoscalar particle decay

Suppose I want to calculate amplitude of pseudoscalar particle decay into electron + positron. Interaction Hamiltonian is given by (ignoring the positive and real constants) $\mathcal{H} = \bar{\psi} \...
-1
votes
0answers
15 views

Difference between fermi energy level in metals and semiconductors

It is not exactly a question its a kind of confusion ... Here my confusion starts... what is meant by Fermi energy level?? The only definition that i found was the energy level at which the ...
-1
votes
0answers
4 views

Chromatic confocal microscopy (CCM) and stylus probe

I read research that compared between chromatic confocal microscopy (CCM) and stylus probe in wear test but the research didn't clearfield what is chromatic confocal microscopy and what is the stylus ...
1
vote
0answers
64 views

Are strings in string theory actually little black holes?

I sometimes read that strings in string theory are actually little black holes, or can be interpreted that way. Is this true? How is that consistent with that the particle that a string represents ...
-5
votes
0answers
35 views

Pendulum is symmetric

I need to find the plane phase for a pendulum of 0.8 joules of energy, is symmetric the figure that it shows? why? http://www.sc.ehu.es/sbweb/fisica/oscilaciones/pendulo2/pendulo2.htm
0
votes
1answer
38 views

How is a irreversible process (conventionally) represented on a $T-S$ plane and why cannot it be (really) represented?

A reversible process can be represented on a $T-S$ plane, and the area under the curve is the heat exchanged by the system. On $P-V$ plane a irreversible process is conventionally represented with a ...
0
votes
0answers
21 views

How to derive entropy from density of states?

I'm trying to derive the entropy of a black hole, given the density of states of a bosonic string (the details are not relevant). The density of states is $$ \omega(E) = E^\alpha e^{\beta E} $$ The ...
7
votes
1answer
90 views

Gauge transformation of connection of $\mathcal{O}(n)$

The holomorphic line bundle $\mathcal{O}_X(1)$ over a toric manifold $X$, admits a Hermitian connection, $A^{(1)}$, whose $U(1)$ gauge transformation in a local patch of the base space is $$ A^{(1)}...
6
votes
1answer
153 views

Theories that predict the number of space-time dimensions

My impression in that most theories assume three spatial dimensions and one temporal dimension, though could in principle be formulated in others numbers of dimensions without inconsistencies. I know, ...
0
votes
0answers
21 views

Graphene sheet “cuts”?

I'm no expert in physics at all, so this is probably a very simple question for this site's regulars. When reading a book or browsing paper sheets, I've sometimes had the skin of my finger cut (it ...
2
votes
3answers
69 views

The meaning of 'coupling'?

In quantum mechanics if two quantities $A$ and $B$ are said to be coupled what does this actually mean? I would guess that it means we have a term like $A\cdot B$ in the Hamiltonian but this is only ...
0
votes
1answer
30 views

Is Biot Savart Law valid for time varying currents unlike Ampere's law?

I have just finished learning the basics of magnetism, and it should be noted that I am not very familiar with all of Maxwell's equations. Consider an infinitely long straight wire, carrying a time ...
0
votes
2answers
57 views

Why is the magnetic force not (never) in the opposite direction

In this question I'm talking about the left-handed orientation for the direction of the $x$, $y$ and $z$-axis. This is the coordinate system at the left of the picture below. I learnt that when you ...
3
votes
1answer
131 views

A question on the Chern number and the winding number?

Let $\mid \psi(x,y) \rangle$ be a normalized wavefunction living in a $d$-dimensional Hilbert space and depend on two real parameters $(x,y)$ that belong to a closed surface (e.g., $S^2, T^2$, ...). ...
3
votes
2answers
132 views

Numerical Tools to find Braiding Statistics of Quasiparticles

While certain classes of systems that exhibit topological order can be solved exactly (such as the Toric Code, Abelian FQH Edges, etc.) there also exist systems (think of perturbed versions of the ...
1
vote
1answer
130 views

Interesting Hamiltonian System [duplicate]

The definition of a Hamiltonian system I am working with is a triple $(X,\omega, H)$ where $(X,\omega)$ is a symplectic manifold and $H\in C^\infty(X)$ is the Hamiltonian function. I am wondering if ...
1
vote
0answers
38 views

$\left< \frac{\partial (xp)}{\partial t} \right> = 0$ When is this true?

Is this always true in quantum mechanics? $$\left< \frac{\partial (xp)}{\partial t} \right> = 0$$ I encountered this when working problem 3.31 in Griffiths Introduction to Quantum Mechanics II....
0
votes
1answer
33 views

What is the difference between worldsheet supersymmetry and spacetime supersymmetry?

What is the difference between worldsheet supersymmetry and spacetime supersymmetry? For worldline formulation of fermions quantum mechanics, there is a supersymmetry. But the corresponding spacetime ...
0
votes
0answers
13 views

Why must the separation constant be real in a time dependent wave function?

I'm not sure if I'm asking this right. I'm reading ''Introduction to Quantum Mechanics'' by Griffiths and in the chapter 2 exercises he asks to prove that the separation constant, $E$, must be real. ...
4
votes
1answer
49 views

Dynamics of pairwise distances in the $n$-body problem

Consider the $n$-body problem where we are interested in describing the time evolution of $n$ masses interacting through a potential $U$. Let $D$ be the matrix containing all pairwise distances ...
85
votes
2answers
4k views

Why is a laserpointer able to “erase” a glow-in-the-dark sticker?

a while ago I tried to charge a glow-in-the-dark sticker using a simple red laser pointer. It was a large sticker, of the type used to mark emergency exits and fire extinguishers here in Germany. I ...
2
votes
2answers
50 views

Why isn't proton radiation by decay on earth known in nature?

Perhaps asking for why isn't appropriate in physics, but as there is neutron and alfa radiation what causes proton radiation not to be very common in nature (in laboratory it is seen although)
1
vote
2answers
37 views

Is the energy needed for a current through a straight and a coiled wire different?

When you add current to a straight piece of wire does it use less electricity than if it was coiled? Does the curve of the wire and proximity to itself make a difference in energy consumption?
0
votes
1answer
13 views

By which equivalent circuit (RC serie or RL serie) can I substitute the following circuit?

I was trying to solve the following question: "Assuming that 𝐑 = 𝟏𝐤𝛀, 𝐂 = 𝟏𝛍𝐅, 𝐋𝟏 = 𝟔𝐦𝐇, 𝐋𝟐 = 𝟑𝐦𝐇, 𝐞 𝛚 = 𝟏𝟎𝟒 rad/s, tell if the circuit can be substituted by an equivalent RC ...
1
vote
1answer
47 views

How do gravitational waves transfer momentum?

In Electromagnetism I understand it in terms of the Lorentz force: the E-component of the field causes the charge to respond infinitesimally with a $\vec{v}$ in the E-direction such that the $\vec{v}\...
-5
votes
0answers
20 views

symetric of lissajous figure

I want to know if this lissajouss figure is symmetric with phase between 3-5 and angle between 35° and 70°
0
votes
1answer
128 views

Induced charge due to charge distribution between two plates

I am trying to work through this problem: given two parallel square conducting plates (side w), one grounded(at x=0) and the other held at +V (at x=L where L < < w), and there is a charge ...
0
votes
2answers
44 views

Accelerated frames conceptual doubt

This thing has baffled me for a very long time and therefore I had to ask it here. I was thinking about accelerated frames. Lets assume I am sitting in an elevator going upward with some acceleration ...
0
votes
0answers
11 views

Trace of raman tensors

A raman tensor $\gamma_m$ is defined as the derivative of the polarizability tensor $\alpha$ with respect to a raman mode $Q_m$, so $$ \gamma_m =\frac{\partial\alpha}{\partial Q_m} $$ $\gamma_m$ will ...

15 30 50 per page