2
votes
1answer
47 views

Are there any experimental tests of non-locality / Bell inequalities that do not rely on spin?

All the experiments I know, which have been performed to test Bell inequalities, are somehow based on measuring the spin degree-of-freedom of some particle (usually photons, sometimes electrons). I ...
3
votes
0answers
46 views

meteorite-like impact of a drop of yogurt

When I throw a drop of Yogurt (through spoon) into a dish of Yogurt, it caused something like a meteor hitting the earth and something occurs similar to the place a meteor hitting the earth(Barringer ...
1
vote
1answer
20 views

Accelerated wedge [on hold]

Consider the following figure, where a mass $m$ is placed on a wedge which is accelerated to the right ($\vec a$) which could be negative. The coefficient of friction between the mass and the wedge ...
0
votes
1answer
55 views

Green function for simple harmonic oscillator

I'm interested in examples on how to use Green function (GF)for simple harmonic oscillator (SHO)? I am from undergrad physics, so I need a fundamental math and quantum mechanical application of GF ...
0
votes
1answer
34 views

A problem regarding equivalent resistance between two points [on hold]

I came across this problem in a book which has solutions for all questions except this one. I can't get how to do this partly due my doubt whether the R and 4R resistors will get short-circuited or ...
1
vote
2answers
54 views

Could a trial wavefunction providing exact eigenenergy differ from the exact eigenfunction by a zero measure function?

Given the eigenequation of a Hamiltonian $$ H |n \rangle = E_n |n \rangle \tag{1} $$ We write it in the position representation $$ \langle x | H | n \rangle = E_n \langle x | n \rangle \tag{2} $$ ...
0
votes
3answers
34 views

What is the net force experienced (at the lowest point) by a wire being rotated in a vertical circle with a mass 'm' at its free end?

A metallic wire is being rotated in a vertical circle with a mass $m$ fastened to its end. My understanding says that the net force experienced by this mass should be the centripetal force: $T - mg ...
1
vote
1answer
27 views

How to get the direction of bending light?

When light passes from a more dense to a less dense substance, (for example passing from water into air), the light is refracted (or bent) away from the normal. My question, is there any ...
0
votes
1answer
55 views

Why does the magnetic force exerted by two charged particles on each other do no work?

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. ...
0
votes
1answer
26 views

Working of fusion reactor

The present type fusion reactors use the magnetic confinement technique for the production of energy. Moreover only 48% for the energy is only absorbed and converted into useful energy . Why we are ...
0
votes
1answer
19 views

Does no variables change in an adiabatic + isothermal system?

Adiabatic + isothermal = no heat and temperature change. Does that mean the system will remain as it is? If it is adiabatic + isovolumetric or adiabatic + isobaric , is it as well no change in any ...
0
votes
0answers
27 views

Do all atoms get accelerated in a synchrotron? [on hold]

How does an electron accelerator work? I have been going on the accelerators and I have lots of doubts on how to minimise the cost and size of the accelerators.
0
votes
1answer
28 views

What is the difference between reversible and irreversible adiabatic expansion?

What is the difference between reversible and irreversible adiabatic expansion? Is it true that the work done by the gas is the same but the pressure applied externally differ between two process? ...
2
votes
1answer
22 views

question about ICRF/J2000 equinox orientation

The DE406 ephemeris data and the NASA Horizons website all report the Earth's current coordinates on 2014 Sep 27, a few days after the Fall equinox, as approximately [1,0,0] AU. However every ...
0
votes
1answer
18 views

Direction of friction force between two boxes

There are two boxes on top of each other. The bottom box is dragged right by a constant force. What is the direction of friction of the top box against the bottom box?
2
votes
2answers
137 views

Confusion between magnetic field and magnetic flux

I've been learning about electromagnetism and Maxwell's equations (in integral form), and I'm slightly confused. The Ampere-Maxwell law (as I know it): $$ ...
5
votes
1answer
165 views

Why is wet paper transparent? [duplicate]

When paper get wet, it becomes transparent. How does this happen? Is it because of refraction, or bcause water extends the space between molecules that consist of the paper? I have no clue.
5
votes
1answer
79 views

What is the meaning of a state in QFT?

I guess this may be more of a mathematical than a physics question, but it comes down to physical interpretations, so I'm posting it here. In classical Quantum Mechanics, we can define a state ...
2
votes
2answers
61 views

Where does the $\partial \vec{E}/\partial t$ term from Maxwell's equation go in Ampere's Law?

One of Maxwell's Equations (ME) is: $$\nabla\times\vec B = \mu_0\vec J+\epsilon_0\mu_0 \frac{\partial \vec E}{\partial t}.$$ While Ampere's Law (AL) is: $$\nabla\times\vec B = \mu_0\vec J.$$ ...
1
vote
1answer
26 views

Diffraction and Shape in the grating

Suppose, I use a laser with a known wavelength of 650 nm through a "opaque grating" that has a pattern of holes of same shape and size. We can see the pattern on the screen. We know the distance ...
-1
votes
0answers
36 views

Show that any rotation can be represented by two successive reflections [on hold]

Show that any rotation can be represented by two successive reflections in two planes, both of which passing through the axis of rotation with the planner angle $\phi/2$ between them
0
votes
0answers
31 views

Will there be an induced emf in this situation?

Here is a (horrible) illustration: The first ring has a voltage $V_1$ applied to it through the voltage source on the left. Ring 1 has resistance $R_1$ whereas ring 2 has resistance $R_2$. Will ...
4
votes
2answers
92 views

When does a singularity start to exist during a black hole formation?

Excuse me if the question is naïve. I am not a physicist. Let's imagine formation of a black hole from a homogeneous collapsing star. At certain moment when enough of matter is inside of a small ...
0
votes
0answers
18 views

Find the angle and force constituent [on hold]

See picture for the problem description. I know of one way to solve this problem: Use the law of cosines to obtain: $$ 500^2=F^2+750^2-2 \cdot 750 \cdot F \cdot \cos(30°) $$ Rearranging and ...
0
votes
1answer
23 views

Is it only possible when 600J of heat is exhausted and 400J of heat is converted into work? [on hold]

Is it only possible when 600J of heat is exhausted and 400J of heat is converted into work? Is the 600J heat will enter the cold reservoir and available to do work again? q1/T hot + q3 / T cold = 0 ...
5
votes
1answer
53 views

What's the definition of incompleteness of a coordinate system and a spacetime?

I always see in GR textbooks that some coordinates or some spacetime is incomplete, such as Rindler spacetime and spacetially flat FRW universe with only positive cosmological constant. This ...
3
votes
0answers
34 views

Does Hawking radiation need an apparent horizon and when does it switch on during stellar collapse?

I've read that Hawking radiation is implicitly linked with the existence of an apparent horizon (1). This seems a slightly less onerous than linking Hawking radiation with a genuine bona fide event ...
1
vote
1answer
59 views

Do Photons Accelerate Upon Creation? [duplicate]

Of course the speed of light is constant relative to everything. Its frequency can change, but its speed is constant. Photons may be absorbed by atoms or release by atoms as energy, but as soon as it ...
2
votes
0answers
23 views

What happens to a particle in the exact center of a Kerr black hole?

Kerr black holes (and Kerr-Newman black holes), instead of the "point" singularity theorized in spherically symmetric black holes, instead have a "ring" singularity, spread along the equatorial plane ...
1
vote
0answers
36 views

Potential due to a Uniform Ring [on hold]

Consider a uniform ring of mass $M$ and radius $a$ (?). I would like to prove that for $r > a$: $$\Phi(r) = \frac{GM}{r} \sum_0^\infty[P_n(0)]^2 \left(\frac{a}{r}\right)^n $$ Where $\Phi(r)$ is ...
1
vote
2answers
41 views

Why won't the efficiency of a heat pump increase when $T_\mathrm{cold}$ decreases?

Why won't the efficiency of a heat pump increase when $T_\mathrm{cold}$ decreases? In the carnot cycle, efficiency increases when $T_\mathrm{cold}$ gets colder and $T_\mathrm{hot}$ gets hotter. Are ...
2
votes
1answer
33 views

Nails and Screws without Friction

In my physics class we're just starting the chapter on friction, and our book began the chapter by describing what a world without friction would be like. Among other examples, it said "nails and ...
2
votes
2answers
257 views

If conservation of energy was wrong, how would we know about it?

Suppose you just started learning physics and you've been introduced to conservation of energy and kinetic energy. Apart from those concepts you know next to nothing. Then you observe an inelastic ...
1
vote
2answers
102 views

What is the expectation value of the 3D delta function for the Hydrogen atom ground state?

I'm trying to evaluate the expectation value of some perturbation Hamiltonian $$H=\alpha \delta^3(\vec{r}),$$ where $\alpha$ is a positive constant, for the ground state wavefunction of the hydrogen ...
0
votes
0answers
28 views

Problem in Solving an Equation in Quantum Mechanics [duplicate]

I am trying to reproduce this paper : http://www.ias.ac.in/pramana/v73/p573/fulltext.pdf But, somehow I am stuck at equation (7). The equation that I am trying to solve for particle outside the well ...
0
votes
0answers
18 views

Comparison between isobaric, isothermal and adiabatic expansion

Please check if my understandings of these terms are right because they are a bit confusing to me. For all three types of expansions, a change in volume means work is done by the system to the ...
0
votes
0answers
18 views

Relative humidity of an air parcel with decreasing temperature

I'm a bit confused while doing relative humidity calculations. To make the case simple: let's say I have my room temperature at 25 degrees with a 50% relative humidity (RH). If I take an air parcel ...
1
vote
0answers
86 views

Forced Quantum Harmonic Oscillator

I'm just starting my journey to QFT and Particles physics and I have a question about the problem of QHO witch we hit with a force $F(t)$ for $ t< t' $, for which the force is zero for $t>t'$. ...
0
votes
0answers
19 views

Property of mass moment about center of mass [on hold]

Can any one give the analytical (mathematical) proof of the following statement: "The summation of mass moment of all the component of the system about its centre of mass is always equal to zero."
-3
votes
0answers
40 views

Conservation Laws and relativity [on hold]

A 50 kg meteorite moving at 1000 m/s strikes Earth. Assume the velocity is along the line joining Earth's center of mass and the meteor's center of mass. What is the gain in Earth's kinetic energy?
1
vote
2answers
45 views

What “exactly” happens when a ray is incident at the critical angle?

The question arose when my physics teacher taught me geometrical optics and told that the phenomenon of both refraction and $reflection$ occur by change in medium. First of all, I'm not sure about the ...
5
votes
0answers
49 views

Fermions in Schwarzschild spacetime

To my understanding Geroch proved that on 4-dimensional non-compact manifold a necessary and sufficient condition for a manifold to have a notion of spinors is to be parallelizabe .1 (General ...
0
votes
0answers
6 views

Are there any potential pitfalls of deferring admission to a PhD program? [migrated]

I'm currently in my final year of undergraduate study, and will be applying to physics PhD programs (for condensed matter theory) soon. Without going into details, I am convinced that deferring my ...
1
vote
1answer
53 views

Deriving photon propagator

In Peskin & Schroeder's book on page 297 in deriving the photon propagator the authors say that $$\left(-k^2g_{\mu\nu}+(1-\frac{1}{\xi})k_\mu k_\nu\right)D^{\nu\rho}_F(k)=i\delta^\rho_\mu ...
0
votes
1answer
53 views

Help with equations for deflecting an asteroid

This is a homework assignment, but not the physics part. I have to write a python script to simulate the size of a warhead required to deflect an asteroid (parameters inputted by user) that is on a ...
0
votes
0answers
14 views

How big can be gradient of magnetic induction (in lab)

I'm thinking about magnetic levitation and how big force can push a diamagnetic when we put it in inhomogenious magnetic field. As far as I know, force exerted on a diamagnetic is proportionald to ...
1
vote
1answer
35 views

Symmetry transformation on Quantum Field

I stumbled upon this point several times, the latest beeing this question: Connection between conserved charge and the generator of a symmetry I want to understand, why Quantum fields transform under ...
0
votes
2answers
32 views

For change in entropy dS = dq/T, is T the temperature of system or surrounding or both?

For change in entropy dS = dqrev/T, is T the temperature of system or surrounding or both? I am confused about Thot, Tcold, Tsys and Tsurr. If qrev, are we talking about the reversible cycle such as ...
0
votes
1answer
26 views

Is there a simple explanation for the fact that the Lorentz transformation must be linear? [duplicate]

In my physics class, for deriving the Lorentz transformatuons my professor assumed that there is a linearity relatioin between the coordinates of the two systems. But why is that?? Can anyone please ...
-1
votes
0answers
21 views

Commutator of $SU(2)$ angular momentum operators [on hold]

Prove the following statement. $$[J_i,J_j] = i\hbar\epsilon_{ijk}J_{k}$$ using rotation operators.

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