# All Questions

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### Acceleration in general relativity

Let's say that, from my point of view, another observer is accelerating. Now, from his point of view, he is standing still: all he feels is an overall fictitious force of gravity, which is just a ...
1answer
47 views

### Why does an electron or proton posses the property of a charge?

If seen, every property is caused due to some reason (eg: solids are hard due to strong force of attraction between its constituents particles), similarly what causes an electron or proton to posses ...
0answers
44 views

### Vacuum Energy in QFT under the Light of Divergence Invariance of the Lagrangian

The divergence invariance of the Lagrangian has been exploited many times, eg., for the purposes of obtaining a symmetric energy-momentum tensor --Belinfante-like-- consistent with GR. We know the ...
0answers
35 views

### Indistinguishability in statistical mechanics

I have two questions about using the concept of indistinguishability to determine the partition function in statistical mechanics, like for instance when determining the partition function of an ideal ...
0answers
19 views

### Gauge invariance prohibits the existence of other universes?

I'm only a student, so most likely misunderstood. The Wikipedia article on Relational quantum mechanics says: "The universe is the sum total of everything in existence with any possibility of ...
1answer
19 views

### Is the speed of an air bubble in a fluid equal to the fluid's speed?

The liquid (water) in a closed pipe system is pumped around. There are some air bubbles in the system. Do the air bubbles travel with the same speed as the fluid in the pipes?
1answer
81 views
+50

### Entropy and the brain

Maximum entropy is equivalent to minimum information in statistical mechanics and quantum mechanics and the universe as a whole is tending towards an equilibrium of minimum information/maximum entropy....
1answer
282 views

1answer
83 views

### What is the work done by friction on a body which is rolling with slipping?

A hollow sphere is released from the top of an inclined plane of inclination $\theta$. (a) What should be the minimum coefficient of friction between the sphere and the plane to prevent sliding? (b) ...
0answers
25 views

0answers
4 views

### Axis to take when finding time period of oscillation after perturbing a dipole in an external electric field

Suppose I have sum of forces is zero, this means that torque is independent of the origin I take the torques around, but then there is a problem here, the inertia about any particular point is ...
4answers
284 views
+50

### Free-body diagram of a rack of blocks revisited a.k.a. if it were on top of lava, which block would you choose to stand on?

This question is a follow up to the following question asked by esdoublelef Free body diagram on a rack of wooden blocks To repeat, consider a rack of blocks (each block is a cube), that are held up ...
1answer
103 views

### Ising model: How is $|\langle\sigma\rangle|^{2}=\lim _{r \rightarrow \infty} G^{(2)}(r)$?

In the book of Statistical Field Theory by Giuseppe Mussardo, on page 51, it is given while talking about Ising model that One arrives to the same conclusion by analysing the possibility of a non-...
1answer
15 views

### Current flowing in a circuit made up of ideal conducting wires

Taking a simple circuit with a battery to provide a potential difference and some resistance across, also our circuit is made up of an ideal conducting material so $\sigma$ is infinity. Now I have ...
0answers
9 views

### What are the basic principles of experimental electromagnetism? [closed]

I want to learn about experimental physics in the context of electrodynamics and electrostatics. Basically I'd like to know how we are able to measure different quantities in this field (electric ...
6answers
692 views

### Can acceleration depend linearly on velocity?

Is it possible that acceleration may vary linearly with velocity. Is it practically possible, if so is there a practical example of it? By integration I was able to verify that for the above case to ...
1answer
55 views

### A Doubt on Hawking Radiation: What Birrell wants to say here?

Well, I know basic General Relativity but I still learning the basics of Quantum Field Theory (therefore without mentions on curved spacetimes). But, I'm trying once and a while to become more used to ...
2answers
27 views

### Gravitational potential energy in a system of two particles

if we have $m_1$ and $m_2$ as two particles separated by a distance $r$, then gravitational potential energy of this system is $-Gm1m2/r$. why do we not add their gravitational potential energies ...
0answers
4 views

### DPDT relay and H-bridge [closed]

I am trying to make a circuit so I can use an arduino to change the rotation of a dc motor , so I am thinking about using an H-bridge made of a DPDT relay connected to the arduino. Would it work? Also ...
6answers
532 views

### How to find the falling time of an object when acceleration is not a constant? [closed]

Let's say we are throwing an object from the surface of the earth, this object reaches 70,000km with initial velocity of $10713 \mathrm{m}/\mathrm{s}$ until it reaches the peak high , the g value at ...
1answer
401 views

### What is the refractive index for partially ionized plasma (mixture of electrons, ions and atoms)?

I asked a question earlier, why ions are not included in the refractive index of plasma . What I do not understand is how a refractive index of plasma can be formed mathematically for plasma that is ...
3answers
198 views

### To what extent can one recover plane waves from the Airy eigenfunctions of a linear potential as the field is turned off?

Consider a single massive particle in one dimension under the action of a static linear potential, with the hamiltonian $$\hat H=\frac{\hat p^2}{2}+\hat{x}F_0.$$ The eigenstate at energy $E$ is, ...

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