0
votes
0answers
25 views

Global and local symmetry for Isospin/Strangeness etc

Why some symmetries $ \big[SU(3),SU(2)$ and $U(1)\big]$ of the Standard Model are local, and some others remain global, like Isospin and Strangeness. Is there a fundumental reason for that? Doesn't it ...
2
votes
1answer
76 views

Electronic spectroscopy question in a more physics oriented view. What is the operator that describes relaxation pathways?

Recently I was studying spectroscopy in Symmetry and Spectroscopy: An Introduction to Vibrational and Electronic Spectroscopy p.357-358 as shown in the image http://i.stack.imgur.com/LSLyZ.jpg The ...
0
votes
0answers
50 views

The commutator between observable and unit radius vector

As I encounter the commutator relating to unit radius vector, I am quite confused. I have just started the learning of quantum mechanics and all I know about the commutator is based on two identities: ...
3
votes
1answer
58 views

Expectation of energy?

Suppose we have a hydrogen atom in a specific state $\psi_{nlm}$. Of course, the state is given by $$\psi_{nlm} = Ce^{-r/na}r^l L_{n-l-1}^{2l+1}(2r/na)Y_l^m(\theta, \phi) $$ I am being asked to ...
0
votes
1answer
942 views

Jumping from a moving train

If you were to jump from a moving train at 20 km/h, would it be better to run in the direction of movement before jumping to maintain inertia or in the opposite direction of the train ?
1
vote
0answers
37 views

Induced charges, electric potential

Consider a solid spherical conductor with charge Q on it, a charge q is placed at a distance r from the centre of sphere. Find the electric potential at the centre of sphere due to induced charges on ...
1
vote
1answer
48 views

Hamiltonian average of energy of two stationary states

In quantum mechanics, the description of the infinite square well is given with the potential energy defined as $$V(x) = \begin{cases} 0 & \text{if } 0 \leq x \leq a,\\ \infty & \...
-2
votes
1answer
77 views

How do you detect the colors of a traffic light? (exam question) [closed]

I just took an exam where the question was: give three ways you can detect the colors of a traffic light given only a gray scale camera. You're allowed to use any optical devices. We learned about ...
0
votes
1answer
98 views

The minimal knowledge required for theoretical research in Quantum computing & AMO physics [duplicate]

I'm a senior undergraduate student and I have chosen my future Ph.D research area in {Quantum Computing}$\bigcap${AMO physics} (e.g. design a new experimental realization of QC or propose a new way to ...
0
votes
0answers
47 views

Is Feynmann gauge reduce always physical gauge?

Is Feynmann gauge reduce always physical gauge? I heard in QCD, Feynmann gauge does not always give correct physics. The lecture says, "Fenymann gauge gives physical gauge, if the theory contains ...
-2
votes
0answers
108 views

Which light bulb will burn out? [closed]

We have 5 light bulbs connected in series assuming all bulbs have identical characteristics. The environment is identical for all bulbs. Wire is superconductor (0 Ohm) and is thick enough to deliver ...
2
votes
2answers
192 views

Elongation and tensile strength of rubber

I want to do some experiments on a neoprene rubber sheet (ex. supplier). When I went to order the sheet I was confused because the listed elongation and tensile strength for all sheet sizes (with ...
0
votes
0answers
85 views

Calculating Microcanonical Entropy in Molecular Dynamics

As a beginning, I am simulating Argon liquid at 94 K and characterising as it is done by the Rahman's first paper on Molecular Dynamics. After going through the first two chapters of Art of Molecular ...
2
votes
1answer
46 views

Surface energy of water [closed]

If $10^3$ small drops of water each of radius $10^{-7}\,\mathrm{m}$ combined to form one single large drop then what should be the energy ? If the surface tension is equal to $0.07\,\mathrm{N/m}$ . I ...
1
vote
2answers
175 views

Finite temperature correlation functions in QFT

Suppose that we want to calculate this imaginary time-ordered correlation function for an interacting system (in Heisenberg picture) : $$\langle \mathscr{T} A(\tau_A)B(\tau_B) \rangle =\frac{1}{Z} Tr\...
2
votes
1answer
32 views

The validity of constitutive diffusive fluxes

In transport phenomena the diffusive fluxes for mass, energy and momentum are the constitutive laws: $$\boldsymbol{j}_c=-D\boldsymbol{\nabla}c \quad \boldsymbol{j}_T=-k\boldsymbol{\nabla}T \quad \...
0
votes
1answer
49 views

Plateau–Rayleigh instability for liquids with low $Re$ number

I'm working on a project about Plateau–Rayleigh instability for liquids. But I've a question. we can examine the fluids with high $Re$ number that the influence of viscosity is negligible, but what ...
2
votes
1answer
105 views

Understanding rocket equations [closed]

I'm doing a science project where I have to explain the physics behind a trip to an exoplanet and I also have to explain about rocket equations while doing so. I know that a trip to an exoplanet is ...
1
vote
1answer
63 views

Rotational equilibrium Paradox

A block of mass M and height h is moving on a rough surface of coifficent of friction 0.5 .The block is moving with a velocity v at some instant. if we balance the torque due to frictional force and ...
0
votes
0answers
22 views

How atmospheric pressure affects liquid but not solid? [duplicate]

The barometer indicates a difference in elevation of liquid mercury level due to the effect of atmospheric pressure. For 1 square cm of surface the atmospheric pressure exerts what is equivalent to ...
1
vote
1answer
78 views

Physical interpretation of the constant coefficient appearing in solution to the Schrodinger equation

The product solution to the Schrodinger's equation is $$\Psi_{n} \left ( x,t \right )=\psi\left ( x \right )\phi\left ( t \right )$$ By superposition, the solution becomes $$\Psi \left ( x,t \...
0
votes
0answers
47 views

Deriving Maxwell's equation from the Lagrangian of an electromagnetic field with a charge density $\rho$

I want to derive Maxwell's equation from the Lagrangian of an electromagnetic field with a charge density of $\rho$ The Lagrangian is given by $$L={1\over2}(\epsilon_0E^2-{1\over\mu}B^2)-\rho\phi+\...
0
votes
1answer
89 views

Angular momentum of a rigid body about any points

Is angular momentum about all points same if the body is rigid and is rotating/translating/rolling with a constant velocity? Why? No external force is acting on the body.
1
vote
1answer
53 views

Difference of water pressure

We know that $P = \rho gh$, so is it true that water pressure at 2nd floor will be higher than water pressure at 9th floor of a 12 story building?
1
vote
2answers
53 views

What is the purpose of the directions for vector quantities such as angular velocity and torque?

Looking at just both angular velocity and torque, many other exhibit this same property. What is the purpose of and usefulness of having a direction that is in the Z-direction? (assuming that, in the ...
1
vote
1answer
79 views

At a fixed inital velocity, What throwing angle will give the projectile the most trajectory length? [closed]

This is a diagram of a projectile motion: Given a constant initial velocity, What angle gives the most trajectory length? By length I mean the length of the parabola from the point the ball is shot ...
0
votes
0answers
42 views

What is the probabililty that a fair coin lands on its side?

This is a popular gag in movies, but I wonder how likely it really is. What is the probability that a uniform cylindrical coin (with radius $1$ and height $h$) lands on its side? If the ground were ...
0
votes
3answers
144 views

What is physical significance of energy?

John Rennie said, actually all particles are basically energy in the sense that they were created by adding energy to a quantum field. This applies whether you're creating a photon, an ...
4
votes
1answer
82 views

Is it a law of physics that all machines will break?

The question sounds kinda dumb when I say it out loud but at the same time I'm very curious. When things break, is it solely due to an intrinsic design flaw or is it due to entropy? And is the ...
0
votes
1answer
23 views

Changing angular momentum with no forces to do torque

Suppose a particle of mass $m$ moves in a straight line at velocity $v$ some distance away from an axis, as shown here at times t1 and t2 (where the axis of rotation is located at the origin of the ...
2
votes
0answers
34 views

How fast does water have to be moving for it to gain a lot of heat? [duplicate]

A random question popped into my head a few minutes ago: objects, when moving fast enough, start to get resistance from the air. Since there is friction between the air and the object [water], there ...
2
votes
2answers
450 views

Why does the pressure of fluid increase when the diameter of the pipe increases?

Assuming mass flow rate doesn't change and it's a closed system. Why does going from a smaller pipe to a large pipe cause an increase in pressure? What is the kinetic energy converted to as the ...
0
votes
1answer
34 views

Data for Tully-Fisher Relation

I have a derivation of the Tully-Fisher Relation and I'd like to test it against some real data. Does anyone know of a catalog where I can find the maximum velocity ($V_{flat}$) and radius (of $V_{...
-3
votes
1answer
106 views

Which gives the most realistic pictures, Mirror, camera or their combination? [closed]

By googling, I have found several different opinions about how to take one's own facial images more realistically: Some said photos taken by cameras (smartphone's cameras, if specific) are more ...
-1
votes
3answers
66 views

how can you tell if liquids have different densities [closed]

help me i need an answer asap for finals
5
votes
1answer
104 views

Why quantum fluctuation existed before big bang?

I read somewhere that quantum fluctuation can give rise to a big bang and thus the creation of a universe which we know today, where do these quantum fluctuations come from if space is only created ...
1
vote
4answers
49 views

How do I figure out the totally airborne height for a given machine?

Technically "airborne" can just mean to move through the air, but I would like to know how high you have to be before you are entirely supported by air in a helicopter-like machine, as opposed to ...
0
votes
0answers
26 views

Is it possible to determine perigee distance from distance recordings from a spacecraft to Earth?

If you are on a spacecraft orbiting earth in an elliptical orbit and were able to take measurements of the distance between the spacecraft and earth as well as the time intervals between those ...
3
votes
1answer
63 views

Why Conserved Current Should Not Need Renormalization?

May be this is trivial but I need to understand why the renormalization of conserved current is not necessary ? As for example, in this paper, they demand (2$^{nd}$ paragraph of the 2$^{nd}$ column in ...
0
votes
1answer
89 views

How to proceed (Tough Problem) [closed]

The problem that I am considering is to find the shortest path (or geodesic) on a surface with the equation $z=f(x,y)$. The path is parameterized by $s$ so that the path goes from $(x(0)$,$y(0)$,$z(0))...
6
votes
1answer
159 views

Is there mechanical strain on a wire along the direction of current flow?

The (attractive) magnetic force on two parallel wires can be seen by the two wires bending towards each other. This can be explained by the Lorentz force acting on the charges and the charges "pulling"...
0
votes
0answers
46 views

Center of mass of a quantum field

In classical field theory the Noether conserved quantities associated to the translation symmetry are the momentum of the field $P^i = \int\! d^3 x\ T^{0i}$, where $T^{\mu \nu}$ is the energy-momentum ...
0
votes
1answer
58 views

Why not run a cable from the north pole to the south pole to access its energy (magnetic or electrical)

Would a cable tied to the North Pole around the curve of earth downwards to the South Pole give us access to a HUGE AMOUNT of energy (magnetic or electrical) by linking into it.
1
vote
1answer
38 views

Experiment to show $a \propto F$

I learnt about an experiment to show that acceleration is proportional to force. It was done by placing a trolley (like a toy car) on a smooth track. At the end of the smooth horizontal track was a ...
-4
votes
1answer
128 views

do we live in 3.5 dimension? [closed]

After watching interstellar movie i came to know that time is 4th dimension and watch some videos and read articles which says there is there is around 10 dimension(11 also). As x,y,z are 3 dimension ...
0
votes
1answer
56 views

How force is transmitted in Magnetic field (Quantum mechanically )

According to particle physics , every fundamental force has its force carrier particle. Photon is a force carrier particle of electromagnetic force but What is the process through which magnetic ...
0
votes
0answers
45 views

Doubt in Path integral equation

In Pokorski's "Gauge Field Theories" book, page 108 we find equation (2.87) $$\int{}\mathcal{D}\phi{}e^{iS_0[\phi]+iS_I[\phi]+i\int{}d^4y\,\phi(y)J(y)}=e^{iS_I[-i\frac{\delta}{\delta{}J(x)}]}\int{}\...
1
vote
2answers
57 views

What are the limitations of recording very faint sounds?

Is it possible to record very faint sounds like, say, the bending of a strand of hair? Part of the problem, I imagine, would be the need to find a way to isolate the target sound from other sounds. ...
0
votes
1answer
60 views

Liquid phase is a highly compressed gaseous phase

$\mathbf{Q:}$ While teaching "Real Gases", my professor remarked last day that "Liquid phase is a highly compressed gaseous phase." But he did not explain the reason behind it and left it as food for ...
0
votes
1answer
80 views

How to find potential energy per unit volume of a simple harmonic wave in a string?

How to derive the formula for potential energy per unit volume of a simple harmonic wave in a string? My book just states the formula as $\frac{1}{2} \rho v^2 (\frac{dy}{dx})^2$ without the proof. $\...

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