1
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0answers
19 views

Ising model. What is large fluctuations of magnetization?

My background is in mathematics. I have studied the Ising model in $\mathbb{Z}^2$. The main model of statistical mechanics. Yesterday, I was reading the preliminary notes of the book Statistical ...
1
vote
1answer
10 views

What are threshold corrections?

As the title goes, what are threshold corrections in Quantum Field Theory? In particular, I would be glad if a good reference is provided. Standard QFT books such as Peskin, Weinberg, etc seem to ...
0
votes
0answers
2 views

Properties of 3D waves

I have a few questions about 3D waves: Are all 3D waves types of electromagnetic radiation? Are all 2D waves mechanical? Thx and regards,
2
votes
1answer
27 views

An identity for spinor helicity formalism

I have a question about the spinor helicity formalism from arXiv:1308.1697 Denote the massless spin-1/2 fermions as Eqs. (2.10)-(2.11) in that paper $$v_+(p)= \begin{pmatrix} |p]_a \\ 0 ...
0
votes
0answers
7 views

Fraunhofer Diffration using Lenses

I've come across a question that I don't know how to tackle: An alternative way of observing Fraunhofer diffraction uses lenses to provide appropriate conditions. Sketch an optical configuration ...
0
votes
1answer
8 views

Can't virtual images be put on a screen?

Apparently the plane mirror makes virtual images, and virtual images cannot be projected onto a screen. If you look below, it is? If the eye is basically a screen of rods and cones, then everything ...
0
votes
0answers
3 views

Law of Gauss. Electrostatics

I have seen on the internet that many times people assure that inside a cilindric condenser the electrostatic field is null due to the fact that the Gauss flux inside is null. But I wanted to make ...
0
votes
0answers
9 views

How to find out the electric field intensity between the plates of this Capacitor? [on hold]

I am preparing for my final and it seems that i cannot get the answer to this question, any tip will be really helpful thanks. Prove that the electric field intensity between the plates of Capacitor ...
1
vote
1answer
29 views

Is cosmic background radiation absolute

Now that we don't have permeating Ether anymore, why don't we consider the omnipresent Cosmic background radiation in place of it? and measure Speeds with respect to the CMBR? In that way an object ...
0
votes
1answer
9 views

What is the difference between virtual object and virtual image?

What is the difference between virtual object and virtual image?
10
votes
6answers
6k views

How do moving charges produce magnetic fields?

I'm tutoring high school students. I've always taught them that: A charged particle moving without acceleration produces an electric as well as a magnetic field. It produces an electric field ...
19
votes
5answers
6k views

Why does GPS depend on relativity?

I am reading A Brief History of Time by Stephen Hawking, and in it he mentions that without compensating for relativity, GPS devices would be out by miles. Why is this? (I am not sure which relativity ...
0
votes
1answer
41 views

Estimating the number of atom/nuclei in a single quantum dot

I often read in introductions about quantum dots that depending on the fabrication method, a single dot contains about 100 - 100000 atoms. Assuming a self-assembled dot of lens or pyramid (cone) ...
0
votes
0answers
4 views

Charge distribution inside a parallel plate capacitor

I'm having difficulty deriving a known expression for the magnitude of the Electric Field within a parallel plate capacitor with applied potential difference $V$ and an immobile charge distribution ...
6
votes
4answers
113 views

What is difference between Inertial mass and gravitational mass [duplicate]

I recently read that the mass we deal with in Equation $F=Ma$ is called inertial mass and the mass we deal with in $F=Mg$ is gravitational mass. Suppose I am taking a same ball in a free fall and in ...
0
votes
0answers
9 views

Forces, symmetry, and asymmetry

The concept of symmetry is one of the most promising and misunderstood concepts in physics. If one consider Hermann Weyl ("Symmetry"; ISBN-13: 978-0691023748), "As far as I see, all a priori ...
1
vote
0answers
9 views

Some question about symplectic transformation

I read Arnold's book Mathematical Methods of Classical Mechanics and come across with three problems in page 229. 1.Let $\lambda$ and $\bar{\lambda}$ be simple (multiplicity 1) eigenvalues of a ...
0
votes
0answers
13 views

Converting between (abstract) linear operators and their position representations

Just as we have an abstract state vector $|\psi\rangle$ and its position representation $\psi(\vec{x}) = \langle \vec{x} | \psi \rangle$, how do we transform between a linear operator, say $H$, that ...
0
votes
0answers
7 views

How did the hard boiled egg get hard?

I know it's the proteins that somehow change their properties at some temparature. But what kind of change, in terms of molecule-level structure?
0
votes
1answer
38 views

What is concept of temperture in ion trap?

As only several thousands of particles are holding in the ion trap, how can we understand the temperature?
0
votes
2answers
20 views

How does ultrasonic horn produce a convection current in the water?

When I was using ultrasonic horn in a beaker, I notice that there are convection currents in the beaker and stir up my substance. I don't understand why it produce water current, I thought that it ...
3
votes
3answers
85 views

Is a particular force different in different frames

Can a particular real force have different magnitude in different frames?
4
votes
2answers
727 views

How is dark energy consistent with conservation of mass and energy?

I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is ...
0
votes
0answers
6 views

What determines the speed required to pull a table cloth?

I was watching this show "Street Genius" on National Geographic and the host Tim Shaw demonstrated an experiment about Inertia, What he did was, He tied one end of a table cloth to a car through a ...
2
votes
1answer
30 views

A single valued function from a multi-valued function

In Schrieffer's book "Theory of Superconductivity", there is said when he deals with multiple connected superconductors (and discuss London equations), that if one takes the line integral of the ...
15
votes
5answers
1k views
+50

Why do nearsighted people see better with their glasses *rotated*?

If you are nearsighted (like me), you may have noticed that if you tilt your glasses, you can see distant objects more clear than with normally-positioned glasses. If you already see completely clear, ...
3
votes
1answer
257 views

Surface gravity of Kerr black hole

I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand. Firstly, the metric is given by ...
0
votes
0answers
11 views

how do you work out the direction of an eddy current

I find it very difficult to work out the direction of the eddy current, can someone please explain the steps in working out the direction of it? there is a following question; I dont understand how ...
1
vote
1answer
17 views

Is work done by sound wave on air particles?

Is it possible for sound wave to do net work on air particles? As in can a sound wave make the air move in one direction so that it can for example move a sail boat ? I think since molecules gyrate ...
0
votes
1answer
21 views

What is the relevance of potential energy as a concept?

As far as i understand, for an object to have a fixed quantity of potential energy, it must be in current equilibrium and have no net force applied to it (otherwise the potential would convert to ...
2
votes
1answer
89 views

What the heck is negative effective mass?

I am reading this book:Solid State Electronic Devices by Ben G Streetman and Sanjay Kumar Banerjee. I have some doubts in the article 3.2.2 Effective mass. In this the aythors say that ...
4
votes
2answers
1k views

How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
2
votes
1answer
480 views

Why do people with bigger hands/wrists have bigger torque advantages in arm wrestling?

I have arm wrestled people with less strength than me who win simply because they have thicker wrists, or larger hands. It has nary to do with having better technique either, because their wrist size ...
2
votes
1answer
37 views

Goldstone couple to conserved current

The Goldstone in spontaneous symmetry breaking problem couples naturally to the associated conserved current of the broken symmetry. How can I see a rigorous (mathematical) derivation for that?
1
vote
1answer
33 views

Branch cuts in two-point function

The propagator of a QFT is known to have a branch cut as a function of the (complex) external momentum. The branch point (as done by, say, Peskin & Schroeder in eqn.7.19 section 7.1) is ...
2
votes
1answer
23 views

The Energy involved in the work done here?

When a wire that has current $I$ flowing within it and its in a magnetic field, the wire experience the Lorentz force, and that force moved the wire over a certain distance $x$(no matter how small), ...
1
vote
1answer
57 views

Point group symmetries and unit cell

I was wondering if the unit cell (of a given lattice) had to have every point group symmetries of the lattice it defines ? I guess there is no unique way to define a unit cell and that it may not have ...
2
votes
3answers
2k views

Rotating a stone with a string

Suppose we are given a stick and a stone tied to the stick by a string. Now if we rotate the stone around the stick the stone rises in height (see picture below). My question is which force accounts ...
1
vote
1answer
28 views

Formula for molar specific heat capacity in polytropic process

I found this formula for a polytropic process, defined by $PV^n = {\rm constant}$, in a book: $$C = \frac R{\gamma-1} + \frac R{1-n} $$ where $C$ is molar specific heat and $\gamma$ is adiabatic ...
0
votes
0answers
28 views

How come that an Infinite universe will collapse under gravity?

In this PSE post the issue is about the stability of an infinite universe under Newtonian gravity. Here I'will drop the Newtonian constraint because we know of the finite speed of interactions and I ...
0
votes
1answer
93 views

Surely force on shell can't be balanced by field momentum?

Imagine a particle with charge $q$ at rest at the origin. It is surrounded by a concentric spherical insulating shell, also at rest, with charge $Q$ and radius $R$. At time $t=0$ I apply a constant ...
7
votes
2answers
199 views

Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empircially privileged reference frame?

OK...before everyone blasts this with references to the relativistic invariance of the physical laws, time dilation, etc let me add some context. Also, I am an amateur with an interest in physics, so ...
2
votes
0answers
14 views

Off-diagonal terms of the Husimi $Q$ function?

The Husimi $Q$ function of a quantum state $\rho $ is defined as $ Q (\alpha)=\langle \alpha \vert \rho \vert \alpha \rangle $, where $\alpha = (x, p) $ is a phase space coordinate and $\vert \alpha ...
2
votes
3answers
38 views

electron levels in a high voltage conductor

what is the electron energy level in a 300,000 volt power line? This voltage is way above the ionisation potential but electrons are not emitted from the wire.
-2
votes
0answers
23 views

Calculating power [on hold]

I need some help and explanation with solving this question: What is the power required to give a body of mass m a forward acceleration of a when it is moving with velocity v up a frictionless ...
3
votes
2answers
139 views

Rocket propelled by a giant monochromatic laser

I am preparing for my quals and stumbled across the following problem, and although it only requires undergraduate-level physics, I feel I can't piece everything together. "A rocket of mass $m_0$ is ...
5
votes
3answers
168 views

How do charge carriers move thermal energy? (Peltier effect)

I am having hard time understanding how the charge carriers (electrons and holes) are able to move thermal energy. I am on a high school physics level, so I will probably have a hard time ...
0
votes
1answer
30 views

Kronecker delta in inertial tensor

I feel confused in (11.9) how does the book prove the following identity: $$\sum\limits_{i} w_{i}x_{\alpha,i} \sum\limits_{j} w_{j}x_{\alpha,j} = ...
0
votes
1answer
71 views

Dark energy and conservation of energy [duplicate]

With accelerated expansion of universe which is same in all direction we know that dark energy increase with time because space between any two point in space time increases with time. So after some ...
0
votes
0answers
8 views

Friction in Water - Conservation of Energy [on hold]

A 57.0 kg diver dives from a height of 15.0 m. She reaches a speed of 14.0 m/s just before entering the water. What is the force of friction underwater if she reaches a depth of 2.5 m before ...

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