All Questions

3
votes
4answers
88 views

Is rotation absolute? [duplicate]

I was reading an article that rotation instead of linear motion is absolute. Can anyone explain why? Shouldn't an observer (A) moving in a circle around a point in an object that rotates (with respect ...
0
votes
0answers
21 views

See-saw with springs attached on both ends [on hold]

Hello, I have question regarding following task; we have see-saw that weighs 2kg and on each end there is a spring that is connected both to the ground and see-saw. Coefficient of the spring is 10000 ...
-1
votes
0answers
9 views

lux intensity meaured through the maxima and minima of a 15000 per inch diffraction grating [on hold]

What is the lux intensity measured through the maxima and minima of a 15000 lines per inch diffraction grating?
1
vote
0answers
27 views

How does Alain Connes NCG compare phenomenologically with superstring theory?

In Veltmans book on QFT, diagrammatica, the full SM Lagrangian is published. There are more than a hundred terms and it looks pretty uninspiring and not quite the kind of equation one would want to ...
3
votes
1answer
59 views

Lagrangian equations of motion for ball rolling on turntable

The equations governing the motion of a ball of mass $m$, radius $R$ rolling on a table rotating at constant angular velocity $ \Omega $ which are derived using Newton's laws are: (I present these for ...
-2
votes
1answer
39 views

Electromagnetic waves in an arbitrary direction

I have been reading Griffith's electrodynamics and I get how EM waves travelling in z direction $e^{ikz-wt}$ can be represented but what about a wave travelling say 45 degrees from x axis.$\vec{k}=k(\...
-4
votes
1answer
20 views

Some physics problems from teacher [on hold]

** I'm stuck in the question no 4.** **Also help me how i improve my problem solving skills for solving this type of problem **
1
vote
1answer
24 views

What are the main physical consequences of supergravity?

String theory in some limit becomes supergravity. This is the super generalisation of gravity where instead of taking the Poincare symmetry as the local symmetry of spacetime we take the super-...
-1
votes
0answers
14 views

Does domestic source is pure AC or not? [on hold]

Do we get pure AC or not? If not then what type of AC do we get? Please get it with graph diagram.
0
votes
2answers
44 views

Is it correct to say that a smartphone cable is only a “1A” cable?

A store owner said that some lower quality smartphone charging cables are only "1A cables", so if you want 2A, those cables won't do the job. Is it correct to say a cable is only 1A? Does the metal ...
0
votes
0answers
16 views

What causes a 3m or 10 feet lightning cable to charge an iPhone or iPad slower than a 1m cable? [on hold]

In Asia, there are many varieties of lightning cables. The store owner said it is better to get a 1m cable. Otherwise, get a 2m one. He said the 3m is going to charge up the phone quite slowly. What ...
1
vote
1answer
29 views

Commutation relations of symmetry generators in SUSY

It is well known that the generators $$ Q_\alpha = \frac{\partial}{\partial \theta^\alpha} - i \sigma^\mu_{\alpha \dot \beta} \bar{\theta}^\dot{\beta} \partial_\mu $$ and $$ \bar{Q}_\dot{\alpha} = -\...
-1
votes
0answers
16 views

Equations 3 & 4 in J.S. Bell 1980 “Bertlmann's Sox … Reality” Paper

J.S. Bell's 1964 "On the Einstein Podolsky Rosen Paradox" is a world-famous paper related to the interpretation of the EPR paradox and QM. In 1980, Bell wrote Bertlmann's Sox and the Nature of ...
0
votes
0answers
13 views

Question about Spinors and Probability Densities

So I was toying around attempting to simulate some relativistic wave equations for a recreational project. Now I have never studied spinors in dept and the knowledge I have is from reading online (...
0
votes
1answer
41 views

$dS^d$ and $AdS^d$ are conformally equivalent

I have seen in the book by Zee (Einstein Gravity in a Nutshell) the following metric for $dS^4$: $ds^2 = \frac{1}{\cos^2 \tau} \big( - d\tau^2 + d\psi^2 + \sin^2 \psi \, d\Omega_2^2 \big) $, (Eq. IX....
2
votes
0answers
46 views

Feynman prescription in path integral by adding an imaginary part to time

It is known that the well-definiteness of the path integral leads to the Feynman's $i \varepsilon$ prescription for the field propagator. I've found many ways of showing this in the literature, but it ...
0
votes
0answers
10 views

Is the Euler-Eytelwein equation also applicable for sliding friction?

Is the Euler-Eytelwein equation also applicable for sliding friction? Does this hold true if you just replace the coefficient of static friction with the one of sliding friction? I'm working on a ...
0
votes
0answers
38 views

Is there a difference between false (metastable) and local equilibria?

Or is it permissible to use the terms interchangeably? If there is a difference, what is it?
2
votes
1answer
24 views

Can we always find a Quasi-Probability distribution representation for density operator of any physical system?

For a pure, quantum optical system, the QPD formalism is straightforward and possible because of the existence of coherent states. The question is whether we can find coherent states for any quantum ...
0
votes
3answers
75 views

Why are Spin 1/2 particles invariant to $4\pi$ rotation loops while Spin 1 particles are invariant to $2\pi$ loops?

Why do Spin 1/2 particles when turning them by 360 deg get a phase factor of -1 and a loop of 720 deg leads to the identity while for spin 1 particles a loop of 360 deg gives already the identity?
0
votes
0answers
24 views

Derivation of the BCS Hamiltonian

$$ \hat{H}_{\mathrm{BCS}}=\sum_{k \sigma} \varepsilon_{k} c_{k \sigma}^{\dagger} c_{k \sigma}-\sum_{k k^{\prime}} G_{k k^{\prime}} c_{k \uparrow}^{\dagger} c_{-k \downarrow}^{\dagger} c_{-k^{\prime} \...
-1
votes
0answers
6 views

Atmospheric Optical Thickness from flux

Is it possible to calculate or estimate the atmospheric optical thickness given a measured flux? And if so, how?
1
vote
0answers
33 views

What is torsion physically in the Einstein-Cartan theory?

In Einsteins theory of gravity the metric gives a unique torsion free connection called the Levi-Civita connection. In the Einstein-Cartan theory we allow any connection compatible with the metric ...
0
votes
2answers
82 views

Why is the direction of net force on an object and the direction of acceleration of that object different in this problem?

A $ 2.0 kg $ box of cucumber extract is being pulled across a frictionless table by a rope at an angle $ \theta=60° $ (from positive direction of $ x $ axis, we have taken horizontal surface of table ...
0
votes
0answers
21 views

What would happen to a vibrating string moving forward at relativistic speed?

Suppose a physical string set in a frame vibrating with enough frequency and amplitude that the middle point of the string reaches 25% of the speed of light. Now suppose that the entire frame with the ...
0
votes
1answer
61 views

Why do I see two versions of Planck's law?

There's a version here: $$E_{\lambda}=\frac{8\pi hc}{\lambda^5}\frac{1}{\exp(hc/kT\lambda)-1}$$ And here's another version: $$B_{\lambda}(\lambda,T)=\frac{2\pi hc^2}{\lambda^5}\frac{1}{\exp(hc/kT\...
-1
votes
1answer
32 views

How do I get energy distribution of radiation (Planck's Law) in terms of frequency?

I have $$u(\lambda) d\lambda = \frac{8\pi hc\lambda^{-5}}{e^{hc/\lambda kT} - 1}d\lambda$$ I want this in terms of frequency. I can start with $\lambda =c/f$ but I will end up with $u(c/f)$ rather ...
0
votes
1answer
34 views

Potts model equivalent to Heisenberg model

The mean-field equations for the three-state Potts model $$ \mathcal{H}=-J\sum_{\langle ij \rangle}\delta_{\sigma_i\sigma_j}\:,\qquad\sigma_i=1,\,2,\,3 $$ is equivalent to $$ \mathcal{H}=-J\sum_{\...
0
votes
1answer
22 views

For a volume charge distribution, What is the electric field intensity of a solid hemisphere at radius = 0 [on hold]

The problem: The textbook I am following for the course is Guru's: https://www.amazon.ca/Electromagnetic-Field-Theory-Fundamentals-Singh/dp/0521116023 My attempt at a solution: The equation that is ...
1
vote
1answer
45 views

Where does the factor of one half come from in the delta-vector equation involving the Riemann Curvature Tensor?

In Einstein's Theory, A Rigorous Introduction for the Mathematically Untrained, by Grøn and Næss: The change of the covariant components a vector by parallel transport around an indefinitely small ...
-2
votes
1answer
23 views

will the polarized beam get diffracted when passed trough diffraction grating [on hold]

Source of light after polarization is passed through diffraction grating.will the light get diffracted?
0
votes
1answer
20 views

The need for coherent sources for interference

I already know that the pattern created by non coherent sources will constantly change ( from the other answers). I want to understand why this is so My explanation (which I want to confirm): ...
0
votes
1answer
43 views

double-slit experiment showing faster than light information transfer?

In the figure shown below, a laser sends a continuous stream of a large (almost infinite) number of photons per second at a double slit, and the photons are then are displayed on a screen. The upper ...
-1
votes
0answers
13 views

Difference between laminar and steady flow

I am having a hard time relating these five terms which describe the dynamic flow of a liquid: Laminar flow, streamline flow, transient flow, steady flow and turbulent flow. Which of these yerms are ...
2
votes
5answers
73 views

Why does air move from higher to lower pressure?

Somebody answered this question elsewhere and said it's because there is a higher force acting at the high pressure region compared to the low pressure region so a net force pushes it towards the ...
0
votes
0answers
39 views

Maximum number of electrons in a given atom that can have specific quantum numbers [on hold]

"What is the maximum number of electrons in a given atom that can have the quantum numbers $n = 3, \ell = 1$?" $n$: principal quantum number $\ell$: angular quantum number I found this question in ...
-2
votes
0answers
20 views

How to estimate the size of a molecule with examples [on hold]

The distance x is equivalent to the average atomic spacing between two atoms or molecules e.g butter has a density of 1000g/cm3 and a molar mass of 0.018kg/moo. Determine the average spacing of ...
0
votes
1answer
31 views

False solution of Landau Hamiltonian

The Landau Hamiltonian in 2D is given (in natural units $q=c=2m=1$) by $$ \hat{H} = (\hat{\vec{p}}-\vec{A}(\hat{\vec{x}}))^2 \,,$$ where $\vec{A}$ is the magnetic vector potential field. We know that ...
-1
votes
1answer
28 views

Particle collision and mass relation

Is mass important in calculations when two particles are collide? or is only the charge that matters? is collision in microscopic world the same with macroscopic world?
0
votes
0answers
10 views

Matching band momenta of zigzag and infinite graphene

Let's say the zigzag line is along the $x$-direction. The 2D 1st Brillouin zone (BZ) of an infinite graphene is a hexagon with inequivalent Dirac points located alternately at the 6 corners as shown. ...
-1
votes
1answer
50 views

Slater determinant in second quantization using the creation operators help

$$ \left\langle 0\left|\hat{\Psi}\left(x_{1}\right) c_{\alpha_{1}}^{\dagger}\right| 0\right\rangle=\left\langle 0\left|\varphi_{\alpha_{1}}\left(x_{1}\right)-c_{\alpha_{1}}^{\dagger} \hat{\Psi}\left(...
0
votes
0answers
33 views

Thermodynamics Heat Question [on hold]

Suppose 1300 kJ of heat is added to 1.1 kg of ice at -2.0 degrees Celsius. Compute the final Temperature. I am really confused on how to solve this. What do I do the compute the final temperature?
-2
votes
0answers
20 views

How magnets by range from 20 micro-tesla (20000nT) to 70 mT are built in the laboratory?

I would like to have examples of magnets of how they are built in the laboratory / by range from 20 micro-tesla (20000nT) to 70 mT. I would like to know if they are sold and where they can possibly ...
-6
votes
0answers
49 views

Is Casimir effect proof of God? [on hold]

Is the casimir effect proof that there is indeed a being that is out of time ( god ) that creates these particles and antiparticle pairs that appear out of literally no where ?
0
votes
1answer
18 views

How does the shell theorem play into two objects just outside of a planet's boundaries gravity towards each other?

So the scenario I envision to represent this would be two meteors on opposites sides of a planet heading directly towards the planet. How would the shell theorem play into the two meteors ...
3
votes
1answer
80 views

The origin of quantization

I will present a question which already is buzzing in my head for quite a time. Actually quantum physics developed as a interplay of empirical results and theoretical developments where it is ...
0
votes
1answer
38 views

Doubt in thermodynamics pressure volume work done

Why work done in irreversible process is not calculated as -$\int p_{internal} dV$ ?
0
votes
0answers
39 views

Lagrangian and vector potential

Known are ${\bf E}=- \nabla \phi - \frac{\partial {\bf A}} {\partial t}$, ${\bf B}= \nabla \times {\bf A} $, $U=q \phi - q {\bf A} \cdot\dot{\bf r}$. the Lagrangian is $$L=\frac{1}{2} m \dot{\bf r}^...
-1
votes
2answers
58 views

Weight of a person sitting on a spring kept on a weighing machine. What is the reading shown? [on hold]

In the above image, what would the scale reading be? Let scale reading be $R$. I was taught that the scale reading will always be the Normal force. Thus imagining the compression of spring to be $x$ ...
-1
votes
2answers
54 views

Differential Equations for Physicists

I find differential equations in physics to be quite challenging so I'm looking for a book to help me master them. I'm familiar with solving ordinary differential equations via seperation of ...

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