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31 views

How a 'variation' $\delta x$ of an independent parameter differs from $dx$? [closed]

I have been reading the Classical Field theory part from The Quantum field theory book of Lewis H Ryder. After defining classical field $\phi(x^\mu)$ he says something about adding variations on both ...
0
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2answers
44 views

How do I find the ground state energy in this question?

I had the following question in my Quantum Mechanics test. A particle of mass m is subjected to a potential V(x) = β|x|, where β is a positive constant. Using the uncertainty relations (principle) ...
1
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3answers
32 views

How can we be sure that the equation of SHM that works for one dimension of an object moving in circular motion works for all SHM?

I have learned that a component of a uniform circular motion is an example of SHM. And I have no question about it, I totally understand that. I also understand how we can derive formulas like $\vec{...
0
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0answers
18 views

Dimensionality in Bistritzer MacDonald Hamiltonian

I was trying to understand the origin of flat bands for twisted bilayer graphene and had a basic misunderstanding. The starting Hamiltonian is $$H = \begin{bmatrix} -iv_0 \sigma_{\theta/2}\nabla &&...
2
votes
2answers
37 views

Galilean invariance of Newton second law with potential force

Let's consider particle in some potential $V(x)$. Newton law: $$m \ddot x= -\partial _x V(x)$$ After Galilean transformation: $$ x^\prime = x -vt \;\;\;\;\;\;\;\;\;\; t^\prime = t $$ Form of equation ...
2
votes
4answers
52 views

When a train starts, the head of a standing passenger seems to be pushed backward. Can we consider it as pseudo force?

Pseudo force always acts in a non-inertial frame and it is always opposite to the direction of the body's acceleration. The backward push is of course inertia, but can we consider it in this manner (...
0
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0answers
7 views

How to prove symmetry of stress tensor using torque equation?

** You have to write the angular momentum equation i.e. Torque = (Moment of Inertia)x(Angular Acceleration) for an infinitesimally small 3D element (about any axis of your choice). Finally, you have ...
1
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1answer
38 views

Why do we insert the Lagrangian with some Lagrange multipliers into the Euler-Lagrange-equation?

Let's assume that we have two coordinates $q_1$ and $q_2$, a Lagrangian function $\mathcal{L}(q,\dot{q},t):=\mathcal{L}(q_1, q_2, \dot{q_1}, \dot{q_2},t)$ and a constraint $f(q,t) = 0$. Then I ...
-1
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0answers
14 views

Why refractive index contrast is important?

I have been studying total internal refraction in waveguides and fibers. And to my understanding the higher the refractive index contrast is, the better the confinement of the modes propagating inside ...
1
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1answer
40 views

Quantum Mechanics Spectral decomposition misunderstanding

My notes state that the spectral decomposition formula is of the form: $$ \hat{A} = \hat{A}\hat{1} = \sum{\hat{A} } |A_i\rangle\langle A_i | = \sum{A_i } |A_i\rangle\langle A_i | $$ Now consider the ...
1
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2answers
56 views

How to make sense out of Potential Energy?

My teacher says that Energy is in the form of Electric field. I've also seen the mathematical prove. (The amount of work done in bringing a charge from infinity to that point in the Electric Field) ...
1
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1answer
43 views

What is the possible changes in law of gravitation [closed]

Can someone figure it out for me how this formula arrives Provide derivation courtesy HC VERMA vol 1
0
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1answer
20 views

Derive non-relativistic equation from relativistic equation using series expansion

For a free particle of rest mass m moving at speed v, the total energy (E), momentum (p) and kinetic energy (T) can be written in the relativistically correct forms: $E=γmc^2$, $p=γmv$, $T≡E-mc^2=(γ-1)...
0
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1answer
3 views

Transformation operator in Sequence of linear QND measurements

I am following the book Braginsky and Khalili. Consider a measurement scheme where we connect a object to be measured to another quantum system which is then measured by classical devices.(Example: ...
0
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2answers
19 views

Magnet size vs field strength

Why is a compass not significantly affected by nearby (less than a couple meters) powerful magnets (such as those located inside home appliances and electronics) given Earth's magnetic field is just ...
0
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0answers
12 views

Central force problem, Bertrand's theorem [duplicate]

How can you explain the statement that "the only central forces that result in closed orbits for all bound particles are the inverse square law and Hooke's law."
0
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0answers
18 views

Null geodetic on different metric relation between affine parameter

If i have a null geodetic on a $g_{\mu \nu}$ metric, it's also null in a generic $\hat{g}=\exp{2\omega(x)}g_{\mu \nu}$ for any $\exp{2\omega(x)}\geq 0$? What's the relation between affine parameter?
0
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1answer
28 views

Is this why a satellite ejects mass (decreasing its mass) into space so that its orbital radius decreases?

I was doing a Physics question and the question was: How does a satellite reduce their orbital radius. The answer was by ejecting mass (thus decreasing the mass) but it didn't explain more. This is my ...
0
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0answers
14 views

Church–Turing–Deutsch principle

In what sense from the  Church–Turing–Deutsch follows that it is possible to simulate with one physical system all the other physical systems? I know that we can build logic circuits with a Toffoli ...
0
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0answers
13 views

Alternative formula for the affine connection in a new coordinate basis

In Hobsons's General Relativity: An Introduction for Physicists, pg. 64, he gave two different expressions for the affine connection $\Gamma'^a_{bc}$ in a transformed coordinate basis $x'^a$ (the ...
1
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2answers
27 views

What is the polarization of an EM wave after it suffers scattering?

If a linearly polarized classical monochromatic electromagnetic radiation undergoes a scattering, does the scattered electric field have the same polarization as the incident electric field? I am ...
0
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2answers
42 views

Velocity of a point in a massed spring [closed]

I got a Doubt that what if the spring has mass I found the following question When one end of a spring (of mass m and length l ) is pulled with velocity V1 and other and with velocity V2 then velocity ...
-1
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1answer
34 views

Moment of inertia of cone - What am I doing wrong? [closed]

Could you, please, spot my mistake? Thank you in advance.
1
vote
1answer
33 views

Why we cannot use Gauss's Law to find the Electric Field of a finite charged sheet?

I could not understand why we can't use Gauss's Law to find the Electric Field of a finite charged sheet?
-1
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0answers
23 views

Is it possible space could explain the dark energy in the universe? [closed]

I have kind of been thinking about it for a while now and this is what i came up with. in the beginning there was nothing but space, no matter, space has a charge though and it repels itself because ...
1
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3answers
36 views

Pair production in vacuum

So , everywhere I have looked for pair production it is stated that it cannnot happen in vacuum . Most proofs I have seen for that , state that the conservation of energy and momentum cannot be true ...
0
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1answer
33 views

Can a photons wavelength be independent of its associated temporal wavefunction?

Typically a traveling photon is described as being in a superposition of frequency modes $\hat{E} = \int g(\omega) a^\dagger_\omega d\omega + h.c. $ where often the $g(\omega)$ is some kind of pulse. ...
-1
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0answers
13 views

How to compute theoreticals related to the orbits of moon and sun based on historical mythologies?

Current, we say the earth on average is about 93,312,000 miles from the sun. And the sun has a diameter of 864,000 miles. Together they form a ratio of 108. Currently, we say the earth on average is ...
0
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5answers
88 views

Can two charged particles exert gravitational force on each other?

Consider two charge particles say Q1 and Q2 both are positive so they creates a electric field around it and both influence each other. Is it possible that both particles (or charge) creates a ...
0
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0answers
20 views

Prove Lagrange's equations of the 1st kind

Without involving Euler-Lagrangian equations. I wanted to prove the Lagrangian equation of the first kind. Basically, D'Alembert's principle says $$\sum_{i=1}^n (F^{a_i} - ma_{x_i})\cdot dx = 0,$$ ...
0
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0answers
6 views

“Crossover phenomena and Critical Behavior” [closed]

My Thermodynamics assignment is on this topic. Where do I start? My book does not cover the topic. Any reading material or any point to start with will be of great help!
-4
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0answers
30 views

Gas pressure without a container [closed]

Gas pressure needs a container for pressure. Yet science tells us that the atmosphere is the container. This impossible
5
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1answer
262 views

What is the explanation for the elevated levels of iodine-131 near Vermont shown in this video?

At 9:07 in the latest Veritasium video, we see a map showing elevated levels of iodine-131 in the United States. The big band through the mid-west makes perfect sense to me; nuclear weapons tests ...
0
votes
1answer
40 views

Magnetization subspace and Hamiltonian representation

A follow-up question of the subspaces of 4-electrons: assume the magnetization of the system is conserved (the number of total spin-up $(\uparrow)$ particles is conserved), say 1, for example. Then ...
0
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1answer
12 views

Rate of change between radius and temperature in a spherical balloon with difference of pressure proportional to the radius

I have an spherical ballon filled with an ideal gas such that the difference of pressure between the interior $(P)$ and the exterior $(P_0)$ is proportional to the radius of the balloon: $$P-P_0 = \xi ...
-1
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0answers
39 views

Is there other reason(s) why abstract simulated math concepts do work and in harmony with this physical world besides elementary explanation? [closed]

It's most accepted that numbers and most related concepts do not exist in physical world, for example, since there're no 2 exactly identical leaves in this physical world, so there's no real copy of ...
0
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0answers
21 views

How to obtain the quadrupole expression from the dipole expression?

I need to find the quadrupole expression from the dipole expression. I know that the dipole expression is $$V(\vec{r}) = \frac{1}{4\pi\epsilon_0}\frac{\vec{p}\cdot (\vec{r} - \vec{r}^\prime)}{|\vec{r} ...
2
votes
1answer
26 views

What does the prime symbol indicate in a nuclear reaction?

I've come across a reaction shown as $ ^7\text{Li}(\alpha,\alpha^\prime)^7\text{Li}^*$. I understand that the asterisk indicates that the final $ ^7\text{Li}$ is in an excited state, but what about ...
1
vote
1answer
69 views

What causes the non-arrival of the signal of my remote (infrared) control device for our TV?

Recently I made this video. It can be seen and heard that the remote control (MTLogic) of our TV doesn't work when I place an object between it and the TV. This is the remote control: It's obvious ...
-2
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0answers
26 views

Can anybody explain how to simplify the following system of capacitors given in the image below

Can anybody explain how to simplify the following system of capacitors given in the image below.
0
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2answers
29 views

Is acceleration in mutual attraction of two particle system is uniform

The gravitational force on a body due to another body is $\frac{Gmm'}{R^2}$ where the mass of the respective bodies are $m$ and $m'$ So the acceleration of one body (say mass $m$) be $\frac{F}{m}$ ...
16
votes
7answers
2k views

Why does holding a hot object with a cloth make it feel less hot?

Let's say that I held a hot object with a warm cloth. It instantly feels less hot and only warm to the touch. This is because the cloth is an insulator and doesn't allow as large a heat transfer as if ...
1
vote
2answers
50 views

How is Newton’s third law valid in the case of a charged sphere enclosed within another charged sphere?

Let's say we have two point charges q1 and q2 both of which are positive, according to Newton's third law the force one exerts on the othe is equal to the force the other exerts on the first. ...
0
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0answers
20 views

Can a body which is in pure rolling move forever?

Meaning of pure rolling here: Rolling without slipping. Now moving to the question: In pure rolling there is only one type of force which is static friction which helps to start the pure rolling ...
-1
votes
1answer
23 views

2D Motion Plane Problem - Problem with Vertical Component [closed]

Question: With its engine cut off, a small airplane glides downward at an angle of 15 degrees below the horizontal at a speed of 240 km/h b) If the airplane is initially at a height of 2000m above the ...
0
votes
1answer
25 views

Concentric Conducting Spheres and Gauss's Law

One of the things I am struggling with in working with electrostatics is in situations where a charge is surrounded by a concentric sphere, and Gauss's Law must be applied. Like if there is a metal ...
0
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2answers
54 views

Do gravitational waves change the color of light?

It stands to reason if gravity changes the color of light then the color will be affected by gravitational waves. My question is, when the waves pass, will the color change be permanent or will the ...
4
votes
3answers
580 views

Why doesn't Gaussian wavepacket broadening in position mean there will be a shortening in momentum?

Many sources that say in free broadening of a Gaussian wavepacket, the momentum uncertainty (I think defined in terms of the range of 'significant' momentum amplitudes) is time invariant even as the ...
0
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0answers
6 views

Experimentally measure penetration depth for metamaterials?

I have simulated a high penentration metasurface design and want to fabricate it. |E|^2 decays above the metasurface with very long ~ 1um decay length. What would be a good experimental way to measure ...
0
votes
1answer
46 views

Ladder Paradox and Understanding Space-time Diagrams

With the given details, An observer $O$ at rest relative to the garage with measured length $L_g$= 6.10 m. The garage is equipped with doors that can open or close instantaneously at a chosen time. ...

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