3
votes
1answer
144 views

Why is orbital angular momentum quantized according to $I= \hbar \sqrt{\ell(\ell+1)}$?

I simply have no idea how this result is found $$I=\hbar \sqrt{\ell(\ell+1)}.$$ The result seems to just be dumped in textbooks rather than explained. I can get the result that $I_z=\hbar m_j$. ...
1
vote
1answer
68 views

Amount of entanglement in terms of greatest eigen value for hermitian matrices?

I was reading the paper No Universal Qubit Flipper. In this the paper they show inability to create a universal flipping machine. The method they follow is they take an entangled state between Alice ...
0
votes
1answer
45 views

Negative wavelength in the double-split experiment

In the double-slit experiment, according to Wikipedia, the spacing of the fringes ($w$) at distance $z$ from the slits is given by $\displaystyle w = z\frac{\lambda}{d} \quad (\Leftrightarrow wd ...
1
vote
2answers
161 views

Does mass curve space?

Just to be sure, according to the theory of General Relativity, my understanding is that mass curves space-time. My question is, can mass also curve space?
3
votes
1answer
266 views

Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on ...
10
votes
3answers
925 views

Would a spinning, evenly charged sphere generate a magnetic field?

I could see how it would go either way. On the one hand, there IS moving charge; on the other hand, it is not discernibly moving.
2
votes
1answer
77 views

If I were to keep increasing the mass of particles I throw at a double slit, at what point would it stop creating an interference pattern? [duplicate]

Why don't things like tennis balls create interference patterns when thrown at double slits? Where's the limit where it stops interfering?
4
votes
3answers
134 views

How can I find the angular and linear velocity of a 2D body that breaks into two bodies?

Afternoon. This is my first question, so do let me know if I'm doing anything wrong. Looking for help on building a 2D physics game engine with bodies that split in half: I have a two dimensional ...
1
vote
2answers
110 views

Is there an electric field due to current?

Is there any electric field associated with current? If yes, then charge particle passing through magnetic field due to current should also experience electric force along with magnetic force.
0
votes
2answers
73 views

Find max height [closed]

I have stucked with finding max height of an $m$, given only $m, M$ and initial velocity of $m$ - $\vec{V}$. There is no friction in the system. As I understood I need to find $\vec{V_0}$ - velocity ...
2
votes
1answer
96 views

Meaning of “vacuum state”?

I just learned about $|0\rangle$ and siblings $|0_\gamma\rangle$ and $|0_\infty\rangle$ while studying coherent and squeezed states in a QM class, and I have a question about the meaning of ...
7
votes
2answers
274 views

Why does the minus sign in the Minkowski metric mean that nothing can move backwards in time?

I just watched this video: http://www.youtube.com/watch?v=GkCWywO93b8#t=27 and there Mr. Cox states that because of the minus sign in the Minkowski metric nothing can move backwards in time. It's ...
5
votes
3answers
828 views

How can I relate linear and angular motion using a single formula?

I want to relate linear and angular motion using a single formula. Assume I have a 10m rod, and I apply a force of 5N on it, 2.5m away from the axis of rotation for 1s. How can I determine the ...
1
vote
1answer
167 views

Why is gravity viewed as a curvature of spacetime and not the electromagnetic force? [duplicate]

There are four known forces in the universe. Two of these forces are the force of gravity and the force of electromagnetism. The first is the result of the mass of the object that has the gravity. The ...
-1
votes
1answer
49 views

Specific heat ratio range [closed]

I know that the specific heat ratio, $\gamma$, exists in the range $1 <\gamma< 2$, and I am required to demonstrate a proof of this. I have come across the following proof (but I don't really ...
5
votes
1answer
537 views

Speed of sound of a gas mixture

Is there a general mixing rule for estimating the speed of sound of a gas mixture, given the speed of sound in the components? From the ideal gas relation: $$c = (kRT/M)^{1/2}$$ (where k is the ...
-3
votes
2answers
384 views

Could Quantum Entanglement be related with gravitational interactions? [closed]

Particles are entangled when they share the same state and their properties become correlated. Interaction with one of them, by say measurement, is experienced instantly by the other. If we measure ...
1
vote
1answer
81 views

Would light from the Sun necessarily reach Earth after 8 minutes if the Sun was switched off?

Would light from the Sun still reach Earth if there was a hypothetical event that shut off the Sun? The time taken by light to travel from the Sun to the Earth is 8 minutes. Couldn't a catastrophe in ...
0
votes
1answer
91 views

Type of spring used in recoil system

What type of coil spring is used in systems like rewind type measuring tape or lawn mower starter mechanism or wristwatch? Is it constant force, constant torque or constant power? And what equations ...
1
vote
1answer
136 views

Covariant formulation of physical equations?

Is it possible to rewrite equations like the Klein-Gordon, the Dirac or the Proca equation in a generally covariant way? And if yes, how and how can the general covariance be shown? (I searched ...
2
votes
0answers
59 views

How did Lord Rayleigh find the volume fraction of argon to air?

In order to isolate for pure nitrogen, Lord Rayleigh and his colleagues took some air and removed oxygen, carbon dioxide, and water vapour, leaving behind what he believed to be pure nitrogen. In ...
-1
votes
1answer
26 views

Explain an experiment: airstream between two hinged curved surfaces

Please, see the following video (the experiment starts at 3:40 and ends at 3:55): https://www.youtube.com/watch?v=7pB6q_bH35s&feature=youtu.be&t=216 The basic idea: given 2 curved surfaces ...
7
votes
1answer
757 views

What is a 'turning point' in WKB and why does it fail at that point?

What is meant by a classical turning point in quantum mechanics and why does the WKB approximation fail at that point?
1
vote
2answers
145 views

Negative pressure

How is negative pressure created in a fluid system?Isn't it counter intuitive that we are reducing the pressure of a system containing no molecules(zero pressure) to a lower value?
0
votes
0answers
58 views

A rod on an inclined plane

(55th Polish Olympiad in Physics) A rod of length $l$ and mass $m$ was lain on an inclined plane of angle $\alpha$, on the altitude $h$ above the floor. (while $h \gg l)$ Describe the rod's ...
3
votes
1answer
333 views

Why are we allowed to spontaneously break the Higgs field symmetry?

In the lepton Lagrangian there are no mass terms allowed for the gauge bosons, due to gauge symmetry. To fix the problem of existing gauge boson masses, we introduce another field (Higgs) and say that ...
1
vote
1answer
29 views

Mass dimensions and weak interaction

The Fermi constant has a mass dimension of $-2$ and a value of $10^{-5}GeV^{-2}$. How can I infer from this information that the mass scale of the weak interaction is about $10^2 GeV$?
0
votes
0answers
42 views

Charge conjugation of gauge field

In some QFT lecture notes read that "under charge conjugation, a matrix gauge field should transform into minus its transpose." What is the reason? Charge conjugation is $\psi \rightarrow i\gamma^2 ...
0
votes
0answers
35 views

Spinors and asymmetry of wave function

A spinor is a mathematical entity which changes sign if it is rotated by $2\pi$. Is this connected to the asymmetry of the spinor wave function?
2
votes
0answers
45 views

Do quasiparticles have antiparticles?

Bosons (except for W) are their own antiparticles, since they have no electric charge. Charged fermions have antiparticles differing from the particles. Now my question is: has a charged ...
0
votes
1answer
163 views

second variation of the action for 1-d lagrangian

i know that the first variation of the action integral yields to the euler lagrange equation by setting $ \delta S [y(x)]=0 $ however given a Lagrangian in the form $$ \frac{1}{2}mv^ {2}-V(x)$$ how ...
1
vote
3answers
673 views

How do these factors affect the free fall of objects?

Take an example of two balls of different masses being dropped from about 250 meters from the ground. How do the following factors affect free fall: Air resistance. Absence of air resistance. ...
0
votes
0answers
176 views

Self-made air pump - What does it take to pump up a balloon?

We are building a simple altitude-controlled balloon (idea borrowed from Google Loons). As part of that, we need an air pump to inflate a balloon acting as ballast (which is called a Ballonet in ...
0
votes
1answer
81 views

Space-time translations and Propagator

Let us assume to have the following scalar field theory $$ {\cal A}=\int d^4x\left[\frac{1}{2}(\partial\phi)^2-\frac{\lambda}{4}\phi^4\right] $$ where I used a quartic potential to fix the ideas. ...
0
votes
0answers
198 views

Effect on Q factor and resonant frequency when scaling down a damped oscillator to micro / nano scales

I've always just accepted that as you scale down a mechanical system the frequency and Q factor both increase. But how exactly do they scale? Linearly? With the square of reduction in size? Or maybe ...
0
votes
0answers
41 views

Pressure change in throttling & flow rate reduction in a water circulation

If the pressure in a water pipe line is reduced from 7kgf/cm2 to 4 kgf/cm2, what is the % reduction in flow rate?
0
votes
0answers
52 views

Linear Perturbation theory in General Relativity, what to do with products of derivatives?

I'm trying to do a problem in which I am given the Einstein tensor for the following metric: $$ ds^2 = -e^{2\Phi}(d{x^0})^2 + e^{2\Psi}\delta_{ij}dx^idx^j, $$ And then asked to find the Einstein ...
6
votes
3answers
6k views

Why does red light travel faster than blue light?

I know that light of all frequencies travel at the same speed in vacuum. But I wonder why their speed differ in any other medium, why does red light travel faster if it has less energy than blue ...
0
votes
0answers
43 views

A free axis of rotation [duplicate]

It is claimed that the free axes of rotation of a rigid body are the ones with the smallest and the largest moment of inertia. Why? How can we determine which free axis of rotation will be used?
1
vote
0answers
45 views

Name for the transformation into an accelerated frame?

A transformation into a frame that looks at an experiment from a rotated perspective is called a rotation. A transformation into a frame that moves with a different constant velocity is called a ...
1
vote
1answer
47 views

Potential in uniform fields

First in a book I found that the electric field strength $\mathrm{E}$ of a uniform electric field from a charged plate is equal to $\frac{q}{2\times \epsilon_0 \times S}$ where $q$ is the charge of ...
0
votes
0answers
35 views

Radian Zeno-version paradox: Can a particle moving in the circular path reach the angular position of non-terminating decimal form radian value?

Consider a particle P moving in a circle of radius r as shown in the figure. Premise 1: Position of the particle can be described by the angle $\theta$. Premise 2: Particle reaches the position ...
0
votes
1answer
151 views

Oscillation of a vertical rod supported by horizontal spring [closed]

The system seems to oscillate with $\omega = \sqrt{\frac{\frac{3}{2}mgl + 3k a^2}{ml^2}}$ for small angle $\theta$, and in particular for whatever stiffness $k$ chosen relative to gravitational ...
0
votes
1answer
41 views

SR: constant acceleration wordline simultaneity

A worldline $W$ with constant acceleration $a$ is given parametrically by $$t=\frac{c}{a} \sinh(\frac{a \tau}{c}), \quad x=\frac{c^2}{a} \cosh(\frac{a \tau}{c}).$$ Let $E=(0,0,0,0)$. I showed that for ...
0
votes
0answers
41 views

Interaction rates from cross sections in a thermalized gas

Consider a target particle embedded in a gas with a thermal distribution of velocities. If we know the cross section $\sigma$ for interactions between the target particle and a gas particle, how do we ...
4
votes
1answer
342 views

Fire: Why is Carbon combustible and Why is Oxygen needed?

This question is about the requisites of fire and combustion. My physics learning is only high school level. In a nutshell, why are certain elements more susceptible to combustion while others are ...
1
vote
2answers
61 views

When was Electromagnetically Induced Transparency first introduced?

The oldest paper I know regarding this topic was published in 1997 by Stephen E. Harris. But I am not sure if he is the first to introduce this idea. Could you tell me when and by who did introduce ...
0
votes
0answers
40 views

What are non-local charges?

In integrable systems, for example in the XXX spin chain, one encounters non-local charges (that form a Yangian). They are fine since the Yangian generate an infinite number of them, which gives us ...
-1
votes
2answers
293 views

Acceleration of Simple pendulum [closed]

A simple pendulum starts its motion from one extreme when it left at extreme it starts its motion towards the extreme and its velocity become increase and become maximum at mean position and also ...
0
votes
0answers
127 views

Why is the electric field inside a solenoid tangential?

I have been looking at some derivations for the electric field inside a solenoid. I know how to find it, but I don't get the symmetry argument used. This is often of the form: Since if we choose ...

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