All Questions

-1
votes
1answer
114 views

Is there any defect in Rutherford's atomic model according to quantum theory?

According to quantum mechanics charged bodies do not emit energy continuously . Then why the atomic model of Rutherford has the defects of collapsing nucleus, continues spectrum.
1
vote
1answer
421 views

Centripetal force and circular motion

When a body moves in a circular loop, there are basically two types of acceleration acting on the object. One is the linear acceleration which is basically tangent to the circle, and there is an ...
0
votes
0answers
25 views

Quantised Angular Momentum?

So when learning about the Bohr model of hydrogen and de Broglie waves, it was shown that treating the electron of hydrogen as a de Broglie wave results in the relationship $$L=n\hbar$$ However, when ...
0
votes
0answers
28 views

Quantum mechanics, operator commutes with Hamiltonian

My textbook said, if an operator $\hat{O}$ commutes with the Hamiltonian, then we can use the eigen vectors of the Hamiltonian as a basis of the Hilbert space, then express the operator $\hat{O}$ in ...
0
votes
0answers
20 views

Why is radiance a measure for how bright an object appears if it is constant regarding the distance to the light source?

Radiance is flux per solid angle per unit area normal to the beam. Let’s say, you look at a piece of paper that is lit by the sun. Now you move twice as far away, the flux is then reduced by four due ...
0
votes
2answers
18 views

Quantization conditions/ Real Scalar field

It is often written in books, the quantization conditions for classical field theory leading to Lagrangian of a real scalar field and thus to Klein Gordon equation. And these are introduced by ...
0
votes
0answers
14 views

Can we calculate L-S coupling without Dirac equation?

It is known that there exists an orbital and spin angular momentum coupling for an electron moving in the atom. And the Hamiltonian can be directly derived using Dirac equation. I want to use a ...
4
votes
1answer
281 views

Can a relativistic quantum particle be completely confined into a finite hole?

If we write the Klein-Gordon equation in this form \begin{equation*} c^2 \hbar^2 \nabla^2 \Psi = \hbar^2 \ddot{\Psi} + 2i\hbar (U - mc^2) \dot{\Psi} + U (2mc^2 - U) \Psi \end{equation*} we have a ...
10
votes
3answers
590 views

How to prevent water droplets becoming larger on the tip of a nozzle?

I use an ordinary syringe to generate a single water droplet. However, it is not usually able to make a droplet smaller than 1 mm (because of surface tension forces, inner diameter of needle, etc.) ...
0
votes
1answer
21 views

Does the medium matter when calculating Optical Period?

If I consider the optical period $T$ for a given wavelength $\lambda$ in vacuum, I can calculate it as: $$ T = \frac{1}{f} = \frac{\lambda}{c} $$ However, in a particular material/medium, I am not ...
0
votes
1answer
47 views

Force-carrying particles instead of forces

Are there physical theories in which notions of particle are used without the concept of force? I know about gauge bosons, see: http://en.wikipedia.org/wiki/Force_carrier and ...
0
votes
2answers
101 views

What determines the magnitude of force of an electromagnet?

Let's assume that there is an electromagnet with $B = 1 Tesla$ , what is the magnitude of the force it could generate on other dipoles equal to it's surface area? Can the magnitude of force (in ...
0
votes
1answer
41 views

Get angle to hit (x,y) with vertex [on hold]

In a projectile trajectory, I'm using the following equation to get the angle required to hit a target in x,y coordinates: This works great, however, it implies that the target is reached by one of ...
5
votes
1answer
291 views

Why is UV index so high when storms are announced?

Everytime I check the weather news and storms are announced, the UV index is very often (if not always) "very high" or "extreme", why is that?
1
vote
2answers
67 views

Mathematical Definition of Locality

What is the mathematically precise definition of principle of locality in physics for a continuous space-time in the sense that an object is only directly influenced by its immediate surroundings?
0
votes
1answer
28 views

Covariant derivative tensor [on hold]

Given that $T^{αβ}{_γ}^δ{_σ}$ is a tensor, I worked the covariant derivative as: $T^{αβ}{_γ}^δ{_σ} + Γ^{α}{_{ρσ}}T^{ρβ}{_γ}^δ + Γ^{β}{_{ρσ}}T^{αρ}{_γ}^δ - Γ^{ρ}{_{γσ}}T^{αβ}{_ρ}^δ + ...
1
vote
2answers
106 views

Does $R=\dfrac{4q^2}{\pi^2a^2gH^2}$ suggest a square root relationship?

I did an experiment involve how R scales with q (the other variables are constant), and I got a relationship like $R\ \propto \sqrt q$ I have been told to evaluate my findings with those in ...
0
votes
1answer
34 views

Force on ball going around loop [on hold]

Suppose I have a ball of mass m going around a loop. It is radius $r$, and rolling without slipping. Half way up the loop, what is the force in the $x$ an $y$ direction if it is at velocity $V$? I ...
0
votes
2answers
41 views

Twinkling in sunlight reflections

A question that covers optics and possibly biology/physiology: looking out my window, I see the Sun reflecting off car windshields in a distant parking lot. The very bright reflections are distinctly ...
0
votes
1answer
43 views

how can an egg be balanced on a nailhead on equator [on hold]

How can an egg be balanced on a nail head on equator? Why only on equator and not on different latitudes?
0
votes
0answers
19 views

Voltage changes under load across parallel pack [on hold]

I have 97 LiFePO cells in parallel. They've been sitting for days so the average cell voltages is 3.19v. I put a 5A load on the pack at "B". I measure V across "B": 2.80V. I measure V across "A" ...
0
votes
1answer
22 views

Lubrication Theory

Basically, I'm modelling the flow of a "coating" process -- a fluid flow between a flat moving plane and a stationary cylinder, 2D, cartesian coordinates. Subscript 0 is the at the minimum height b/w ...
1
vote
0answers
30 views

Is There A 'Leading Edge' to the Universe? [duplicate]

Is there a center to the universe? Did the Big Bang happen at a single location, spreading outwards? Or, was the Big Bang more of a state-change, in which the universe went from super-dense and ...
0
votes
2answers
29 views

Using Coulomb's law to solve for a continuous charge distribution [on hold]

I have been trying to evaluate this specific integral and have been completely stuck. $\frac{1}{4\pi \epsilon_0} \int^L_0 \frac{2\lambda z}{(x^2+z^2)^\frac{3}{2}}dx$ I am a freshman and have been ...
2
votes
1answer
36 views

Uniqueness of representing POVM using projective measurement

$\newcommand\tr{\operatorname{tr}} \newcommand\ket[1]{\lvert#1\rangle} \newcommand\bra[1]{\langle#1\rvert} $[Skip to the conjecture for a self-contained mathematical formulation of the question.] ...
0
votes
1answer
22 views

two bodies are travelling with equal acceleration

two bodies are travelling with equal acceleration in the same direction and are in contact with each other. What will the force exerted by 1st body on second be? By taking an example of masses 5 and ...
2
votes
0answers
58 views

Physical interpretation related to a non-linear partial differential equation

I am doctoral student in pure mathematics working on a particular problem. My question is if this problem has applications to real world phenomena. I will try to explain the direct problem starting ...
0
votes
1answer
79 views

Verifying a solution to Einstein's vacuum field equations

I need to verify a solution to Einsteins vacuum field equations. I have the solution as follows $$ds^2=a\,dt^2+b\,dr^2+\cdots$$ Is the following the right approach? Einsteins equation reduces to ...
2
votes
1answer
176 views

Sufficient conditions for the energy to be not conserved?

I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics. Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. ...
5
votes
1answer
43 views

To what extent can the superconducting order parameter be thought of as a macroscopic wavefunction?

I know that the order parameter does not obey the Schrodinger equation; it instead obeys the Ginzburg-Landau equation. However, I am unclear as to the situations under which the view of the ...
1
vote
2answers
22 views

Negative frequency contributions for very short pulses?

I am wondering if very short optical light pulses can have a Gaussian envelope? When I describe the pulse shape with a Gaussian than the frequency distribution has also a Gaussian shape. But if the ...
1
vote
0answers
22 views

Area moment motivation

I have some intuition about the (second) moment of inertia, and there is some motivation to define this concept if we think about the $KE$ of a rotating body or the torque $\tau$ applied, for example, ...
2
votes
1answer
57 views

Representations of Galilei group

Show that the operator $U(\alpha, \beta) = e^{i(\alpha \hat{x}^2 + \beta \hat{p}_{x}^2)}$ can represent the space reflection of the 1D Galilei group: $x \to -x; t \to t$. I don't really know ...
1
vote
3answers
72 views

Point, bar and a mass

This question is a simplified down version of my first question to understand the core essentials of my question. The question now stands with the simplified diagram: There are three things in the ...
21
votes
5answers
4k views

Why are a motorcycle's front brakes more effective than back?

I've noticed that when I apply the front brakes on my bike it stops quite quickly. If I apply the back brakes at the same speed, it skids rather than stopping quickly. Why?
0
votes
1answer
59 views

What is matter made of in the light of Quantum Mechanics? [on hold]

I've always wondered what matter (particles, force particles, etc.) was actually made of considering the fact that quantum mechanics has shown us that particles can actually act as a probabilistic ...
1
vote
1answer
95 views

NMR rotating frame

I'm reading about a linearly polarized field (in the context of NMR). The field is given by $$ {\bf H_{lin}}=2H_1({\bf i}cos(\omega_zt)).$$ This can be created by having a pulse field plus its ...
6
votes
3answers
624 views

Other explanation for cosmological redshift?

I'm interested if any of the following explanations have enough predictive capability to explain the observations we see today. The claim is that the Universe is not expanding, and that red-shift of ...
0
votes
0answers
10 views

What is the $g^2(0)$ value of squeezed light? [on hold]

$g^2(0)$ value of coherent light $= 1$ $g^2(0)$ value of chaotic/classical light $>1$ $g^2(0)$ value of quantum light $<1$ $g^2(0)$ is the second-order correlation function given by ...
1
vote
1answer
199 views

Intro to Solid State Physics

I didn't see this listed on the books page so here it is. I'm currently in an introductory Solid State course, and we are using Kittel's book. I have been having a rough time with this book although I ...
3
votes
2answers
128 views

Why can you touch two positively charged rods?

For a physics lab on the Triboelectric effect, we rubbed two rods with fur which gave both of them a positive charge. We then brought them close together, and they obviously repelled. We then held ...
1
vote
1answer
188 views

Frequency of rotating coil

Given a coil initially in the x-y plane, rotating at angular frequency $ \omega $ about the x-axis in a magnetic field in the z-direction. This uniform time varying magnetic field is given by $B_z ...
0
votes
0answers
41 views

Is a model of helium atom without electron-electron repulsion solvable analytically?

Consider the following Hamiltonian: $$\hat H=-\frac{\hbar^2}{m_n}\nabla_n^2-\frac{\hbar^2}{m_e}\nabla_{e1}^2-\frac{\hbar^2}{m_e}\nabla_{e2}^2-\frac Q{|\vec r_{e1}-\vec r_n|}-\frac Q{|\vec r_{e2}-\vec ...
0
votes
1answer
17 views

Optics simulation software for iypt #12 question thick lens

(As I'm writing these I viewed previous posts about optics simulation) me and some of my friends are working in iypt problems. one of the problem is named "thick lens" which says: A bottle filled ...
1
vote
1answer
47 views

Why do we use time-dependent regions in this derivation?

I'm studying fluid mechanics and I have the following doubt: on the book, the author first deduces the differential form of the equation of balance of momentum. First he argues that if the fluid is ...
0
votes
0answers
22 views
1
vote
0answers
26 views

Flow in the strip $0 < x < \pi/2$, $y > 0$ [on hold]

Could anyone please explain how to show that a complex valued function represents a flow? For example, how does one show that $\Phi(z) = \sec^2 z$, where $z = x + iy$ with $x, y \in \mathbb{R}$, ...
0
votes
1answer
28 views

Parallel Resistors (special cases formula)

1) A car's rear window defroster uses $n=15$ strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged ...
6
votes
5answers
23k views

Why a glass rod when rubbed with silk cloth aquire positive charge and not negative charge?

I have read many times in the topic of induction that a glass rod when rubbed against a silk cloth acquires a positive charge. Why does it acquire positive charge only, why not negative charge? It ...
4
votes
1answer
378 views

Tracking down the locality assumption in a CHSH inequality derivation

CHSH inequality requires both locality and realism. I will equate here realism with counterfactual definiteness. Now counterfactual definiteness tells us that given two different measurements on the ...

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