0
votes
1answer
10 views

Entropy $S$ for canonical (NVT) and isobaric (NPT) ensemble

In case of non-isolates system (NVT or NPT ensemble), I learned I can calculate the entropy, $$S=-k_B\sum_jp_j\ln(p_j)$$ where $p_j$=probability at $j$ state. but I saw that the entropy is also ...
0
votes
2answers
13 views

Centre of Mass and tangential velocity star and planet

We have two objects - one massive star, and one planet which has a considerably smaller, but non-negligible mass, in a circular orbit about a common centre of mass. Using equation $F$=$GMm$/$r^2$ ...
0
votes
0answers
7 views

Anomaly for Majorana fermion?

In 4-spacetime dimension, is there U(1) gauge field chiral anomaly associated with Majorana fermion (or I am not sure if it is equivalent, majorana representation)? Besides, I have read from several ...
0
votes
0answers
13 views

Creating a realistic simulation

I've recently read an article from I believe it was Cambridge or something, where they created an extremely detailed simulation of bubble interaction. I've come here to ask what are some common ...
1
vote
0answers
8 views

Centripetal force on a charged particle in a uniform electric field?

My teacher was showing us the factors that affect the motion of a charged particle in a uniform electric field. He derived an equation by equating force due to electric field and centripetal force ...
0
votes
3answers
20 views

How can be effect of electric and magnetic fields on the motion of a particle be distinguished?

It's a conceptual question about magnetic field: Suppose a charged particle moves under the influence of an electric and a magnetic field, how do we distinguish the effect of the fields on the motion ...
0
votes
0answers
4 views

beta minus decay: expression for maximum electron energy

I'm having some trouble finding an expression for the maximum electron energy in beta minus decay. In the frame where the neutron is initially at rest, conservation of momentum reads: ...
1
vote
1answer
26 views

Electromagnetic braking hypothetical situation?

Let's say there is a conducting rod in space - with a constant external magnetic field. If you spin the rod - will electromagnetic braking make the rod stop eventually? I feel like there is a change ...
1
vote
1answer
124 views

Thermodynamic Internal Energy Reference States

The internal energy, $U$, of a given thermodynamic state, $\boldsymbol{R}$, as introduced in thermodynamics textbooks like Callen seems to be defined as: $U (\boldsymbol{R}) = \Delta U ...
1
vote
1answer
27 views

Can Tension between two blocks on a horizontal plane be discovered in these conditions?

the bodies are linked by an ideal string, one has m1=10kg & the other m2=20kg The force is known and is pulling horizontally, F=60N on the lighter object the coefficient of friction is said to be the ...
0
votes
0answers
26 views
+50

Viability of a Fayet Iliopoulos term in the MSSM

Why is a Fayet Iliopoulos term $-kD$ in the MSSM (Minimal Susy Standard Model) not relevant (or subdominant to an F-term)? According to Martin (A Supersymmetry Primer, p.70) it's because squarks and ...
0
votes
0answers
11 views

Particle-Wave Duality and the Quantum Uncertainty Principle United?

In a pretty recent research by Patrick Coles, Jedrzej Kaniewski, and Stephanie Wehner at the Centre for Quantum Technologies at the National University of Singapore,they came to the conclusion that ...
2
votes
4answers
110 views

Understanding the Quantum Vacuum State

In terms of the creation and annihilation operators $a_{j}$ and $a_{j}^{\dagger}$ (fermionic or bosonic, doesn't matter): Is the vacuum state $\ |\mathrm{vacuum}>$ exactly the zero vector on the ...
18
votes
1answer
205 views

Fluctuations of an interface with hammock potential

This question is related to that one. I ask it here since comments are too short for the extended discussion that was going on there. I am interested in a very simple interface model. To each ...
0
votes
0answers
19 views

Cosmological constant theories

Are there any hypotheses on the expansion of the universe, which have a cosmological constant, or some other parameter, that results in a universe with an ever increasing rate of acceleration for the ...
1
vote
2answers
142 views

Table of matrix elements of powers of r for radial functions in H atom

Im looking for some references here. I hope it is the right place to ask. I need to find a table of (or a formula from which to extrapolate) the matrix elements of the radial functions of the ...
2
votes
1answer
22 views

A question on the functional dependence of the Lagrangian density

I understand that in classical mechanics the state of a particle at a given instant in time is given by its position $q$ and its velocity at that point $\dot{q}$, and given that, for any given point ...
2
votes
2answers
39 views

Is it possible to block light pollution?

The old theory about seeing stars during the day if you stand i the bottom of a well or chimney is proven wrong because the atmosphere scatters the sunlight and makes it too bright to see the stars ...
0
votes
1answer
31 views

How can I add a sound wave on top of an existing one, without harming the original's loudness?

I'm working on a program that has to do with adding sound waves on top of sound waves. Currently what I'm doing is simply an average of the two waves. So if I have wave ...
0
votes
0answers
300 views

How much force is required to hold an umbrella?

Assuming a small umbrella (e.g. http://www.amazon.com/ShedRain-WindPro-Umbrella-Close-Size/dp/B001DL5WN0). What are the factors that need to be considered? I assume where I hold the umbrella might ...
0
votes
2answers
14 views

How can I add two sound waves without reaching distortion - always keep them under a certain value?

I'm working on a program that adds sound waves on top of each other. I read that the best way to do that (correct me if I'm wrong) is to simply add them together. However, this way I easily reach ...
0
votes
0answers
21 views

Where can I learn about Motors and Generators?

` Where can I learn about the functionality of motors and generators, so I can answer questions such as these? I need a good textbook that starts from the basics (eg faradays) then moves up with ...
0
votes
1answer
28 views

Using the Fourier transform to find the natural frequencies of coupled oscillators

How can I find the natural frequencies of a system consisting of a pair of coupled oscillators using Fourier transforms? The System consists of two masses and three springs. One of the springs ...
0
votes
2answers
43 views

Why do i get a shock if i touch a live wire and my feets are on ground?

I understand that there is a large potential difference but i guess we humans offer a very large resistance.So,shouldn't the current be very small .Small enough not to kill us?
2
votes
3answers
41 views

movement of particles in electric field

I am confused about a homework problem. Let's assume we have two electrically charged particles of which we know the charge and mass respectively. Let's say that at first they are fixed at some ...
1
vote
1answer
27 views

Engravings in “Wandering the Immeasurable” sculpture outside the CERN globe?

Does anyone have a PDF or a file that shows all of the engravings on the "Wandering the Immeasurable" sculpture by Gayle Hermick outside of the CERN globe of science and initiative?
0
votes
1answer
130 views

Calculate orbit height from tangential velocity

Is it possible to calculate the altitude of a satellite orbiting a planet, just from the planet's mass and the satellite's velocity, assuming that the satellite is in a perfect circular orbit? If so, ...
5
votes
5answers
739 views

Why does measuring the spin of an entangled particle cause it to become unentangle?

I've been taught that measuring the spin of an entangled particle causes it to become unentangled, but not how or why, so I'd like to know by what process this occurs. Is the cause known? If so, ...
0
votes
0answers
24 views

The effect of multiple Alcubierre rings

In all of the descriptions and visualizations I've ever seen of the Alcubierre drive but one, it takes the form of a single ring or toroid surrounding a spherical volume of flat space. The exception ...
3
votes
5answers
334 views

What is the mechanism behind the wave - particle duality

I'm not exactly sure how to phrase this question; I've been reading about wave -particle duality, its history and how it works. But it's really bothering me, whenever I watch YouTube videos about it ...
0
votes
1answer
20 views

X-ray background radiation

I'm running an experiment in gamma-ray imaging (although the main emission from the decay of Am-241 is ~60keV, so much more in the range of x-rays). I'm curious as to the sort of sources that would ...
1
vote
0answers
56 views

Basic question about Magnetism and Right hand rule? [on hold]

In our physics class we had a brief introduction to magnetism - the very basics, but I don't understand the right hand grip rule. Here is the question I'm stuck on: "a negatively charged object ...
41
votes
3answers
4k views

How small does sand have to be to get wet?

I think of sand as a lot of very small rocks. Suppose I have a pile of rocks, each about 1cm in size, and the pile is a meter tall. If I pour a bucket of water on the rocks, most of the water will ...
1
vote
2answers
109 views

How to use the first law of thermodynamics for simple mechanical systems?

I'm confused about what exactly is $Q$ and $U$ and their signs. Consider a block initially having some kinetic energy which we stop and we want to find by how much amount its temperature increases. ...
-2
votes
0answers
13 views

Problem involving a rigid body in equilibrium [on hold]

A uniform rod rests in equilibrium with one end against a smooth vertical wall and the other against a smooth plane inclined at 30 degrees to the horizontal. Find the inclination of the rod to the ...
0
votes
0answers
19 views

proper time according to rocket frame [on hold]

A space traveler with a wristwatch started from the origin and traveled a distance of 2.5 years with a constant speed of 0.357 according to the lab frame. What is the time recorded by the space ...
0
votes
0answers
20 views

Applying force to Keep constant velocity [on hold]

An object with mass 1kg is moving on an even plane. The plane has kinetic friction coefficient of 0.5. Gravity is pulling the ...
0
votes
1answer
9 views

Searl effect generator simulation

This is an scheme of SEG: https://www.youtube.com/watch?v=pUUvhuQtba4 https://www.youtube.com/watch?v=wAMrTxMzrds This mechanism change the electrons around the conversor. Would be really nice to ...
1
vote
1answer
12 views

Repelling a weak permanent magnet with an electromagnet

I have a question about magnetic repulsion. Suppose I have a permanent magnet (axially magnetized) placed on top of the iron core of an electromagnet. I want to switch on the elctromagnet to repel the ...
0
votes
0answers
26 views

Help a layperson out here [on hold]

Lately I have been at it, from my completely laypersons understanding of QM with what I see si fi wooers simply replacing a God watchmaker with a cosmic Bill Gates in place of this. Help me clear this ...
2
votes
1answer
34 views

In general, can a Lagrangian density depend on space-time explicitly?

In an exercise on classical field theories, I'm trying to derive the general formula of the Energy-momentum tensor. According to the formula in the lecture notes, this tensor includes a term of minus ...
0
votes
0answers
13 views

Magnetic susceptibility in ising model as magnetization change

Let's say I have a standard 2D Ising model with $$ H(\sigma) = - \sum_{<i~j>}\sigma_i \sigma_j - h\sum_{j} \sigma_j $$ With the metropolis algorithm, I can compute various things like energy ...
2
votes
1answer
12 views

How to build a MOKE (magneto-optic Kerr effect) magnetometer at home?

I'd like to build a magnetometer at home. The type does not matter actually that much but it should be doable at home. The MOKE (magneto-optic Kerr effect) magnetometer at least appears to use ...
1
vote
1answer
13 views

Significance of colours in photoelasticity

I already checked similar question at Physics SE, but none gives me a clear answer, also it is a bit difficult for me to understand it from wikipedia as I couldn't find relating material to my ...
0
votes
2answers
307 views

Magnification in compound microscope

I was studying about compound microscope here I don't see why we multiply linear magnification of objective with angular magnification of eyepiece. Shouldn't it be both angular or both linear? Can ...
-1
votes
0answers
28 views

$n^\text{th}$ operation of creation and annihilation operators on vacuum

My question is similar to the one that has been posted on this link. In particular I would like to express the following expression in the most compact form: ...
2
votes
1answer
22 views

Electric field in space created by intersection of spheres of charge

I am trying to calculate the electric field in space created by a body assembled by the intersection of 2 spheres. The upper sphere, its center is at $\frac{d}{2}\mathbf{\hat{z}}$ with radius $R$ and ...
0
votes
3answers
138 views

Is a nuclear bomb in some sense a bullet travelling at the speed of light, but along time rather than along space?

Apologies if this is a silly or perhaps obvious question, but $E=mc^2$ just looks so much like classical kinetic energy (except for the factor of 2). So I'm thinking of the to-be-fissioned-away ...
0
votes
0answers
51 views

Why do we use Fourier transforms in QFT? [duplicate]

I ask this question, as someone has recently asked me this and I'm not sure I gave them a satisfactory/correct answer. I explained that in QFT we describe particles (and there interactions) in terms ...
0
votes
0answers
9 views

Measuring electrical conductance (resistance) of ice and water

What is the standard method of measuring conductance of ice and water? The reason I ask is that apparently one has to take account of the fact that both of them conduct electricity protonically ...

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