# All Questions

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### Launch velocity of point charge in electric field

The question as follows: Consider a long line of charge with linear charge density $\lambda=4\mu C/m$ There is a point charge mass 0.1kg, q= $-2\mu C$ at coordinate (-2,0) at t=0. Point charge is ...
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### How come this is a gravitational plane wave?

In Wikipedia's Gravitational plane wave article a metric for a gravitational plane wave is given by \begin{equation} ds^{2}=\left[a\left(u\right)\left(x^{2}-y^{2}\right)+2b\left(u\right)xy\right]du^{2}...
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### Why is the probability of a microstate independent of its energy in Boltzmann statistics?

**Intuitively, I would think that the bigger the energy, the less probable it is to have a particle in this microstate, but Boltzmann hypothesis is that the probability of all microstates is the same. ...
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### Why we are not using Lagrangian instead of Hamiltonian in non-relativistic quantum mechanics? [duplicate]

Why we are not using Lagrangian instead of Hamiltonian in non-relativistic quantum mechanics?
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### Why do I get a non-zero Coriolis acceleration for a reference frame that moves in a straight line without rotating?

When you have a stationary reference frame $\{O', (\pmb{e}'_1, \pmb{e}'_2, \pmb{e}'_3)\}$ and a moving reference frame $\{O, (\pmb{e}_1, \pmb{e}_2, \pmb{e}_3)\}$, my textbook defines the Coriolis ...
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### Strength of Magnetic Dipole

I know magnetic monopoles doesnt exists .And A magnetic dipole always have equal strength. But what about this magnet This is picture of magnet whose thickness is constantly decreasing Will it have ...
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### Is there a near zone inverse Doppler shift?

Engheta et al. found such an effect in free space in 1980, published as On the Near-Zone Inverse Doppler Effect August 1980 IEEE Transactions on Antennas and Propagation 28(4) Yehuda Ben-...
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### What is exactly rotating in a rotating black hole?

I have read this: https://arxiv.org/abs/gr-qc/9404041 In General Relativity the black hole solutions which have so far been found form a four parameter family called the generalized Kerr-...
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### Power voltage relation

I have a question concerning the relation between power and voltage. We have a lamp with power of 36W when used with 12V. With what power does the lamp work if we connect it to a 6V battery? First,...
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### How to find the constants $a$ and $b$? [on hold]

We consider the motion of a particle without spin submitted by the hamiltonian $H$ defined by the eigen-value equation:$H|n_1,n_2\rangle =(n_1^2+n_2^2)|n_1,n_2\rangle$ the proper kets of $H$ verify ...
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### Poor man's Alcubierre drive?

In general relativity,  the fundamental notions are the curvature (Ricci tensor) and the stress energy tensor. Energy density and curvature are connected .  The Casimir vacuum between parallel plates ...
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### Rotation and potential energy

Please read the question. The solution to this is that since it is a hollow cylinder Ratio of Rotational Kinetic Energy and Translational Kinetic is 1, hence KE (T) = mgh/2 and finally on right ...
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### How to really understand quantum field theory? [on hold]

When I first saw QM I was confused by the formalism and everything. Then I learned about experiments, such as double slit experiment and Stern-Gerlach experiment. From this it was very clear what the ...
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### Change in position of center of mass

A man is climbing a balloon. Will the center of mass change its position as the man climbs up in vertical direction? As there is an external force (weight of ballon and weight of man), then why will ...
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### Black hole surrounded by black holes [duplicate]

Is there any configuration of black holes that surround a central black hole that could lift it out of the singularity due to net effects on space-time? Perhaps a sphere of black holes of equal mass ...
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### Irradiation at high frequency

I read this statement in Feynman Lecture on Physics (see here for more details): In low-frequency circuits the connection is made with wires, but this method doesn’t work very well at high ...
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### Time in the second law of thermodynamics versus relativity [duplicate]

I recently had a debate with someone about time and argued that the most concrete definition of time would be an increase in entropy. The entropy of a localized area of space might reduce, but that of ...
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### Electron spin resonance experiments

Recommend me some good books on ESR. I'm performing an experiment of calculating lande's factor using ESR and I've so many doubts. Please help!
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### How much does science know about lightning? [on hold]

In his Lectures, Feynman says the following: So the fundamental origin of lightning is really not thoroughly understood. We know it comes from the thunderstorms. Source: http://www.feynmanlectures....
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### Fluid dynamics resources (physics perspective)

I'm trying to find online resources for fluid dynamics because I'll be taking a course on it and am very interested in the subject. However, most material I came across (especially online lectures) ...
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### Asteroid Deflection

I am looking for various methods to deflect large asteroids.Apart from the direct kinetic impact(i.e.exchange of momentum), what are the other ways for the asteroid deflection?
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### Why coefficient of states for non-positive Hamiltonian matrix are all non-negative?

For a Hamiltonian $H$, if the all elements of matrix is non-positive under a set of basis $\{|\phi\rangle\}$:$$\langle\phi|H|\phi'\rangle\leq0$$ then the ground state of $H$ will be the linear ...
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### How to simulate an explosion in space [on hold]

I have a simulation of some bodies orbiting each other in space, and I would like to add explosions to it to see how the behave, but I don't know how to do it. Sorry if this is has been asked before, ...
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### Is the GW170817 event evidence or counter evidence for Dark Energy?

I've always figured there must be a simpler explanation for the observed extra red shifting that has lead astronomers to hypothesize Dark Energy. Or at least there must be a simpler explanation of ...
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### Gravity creates heat?

There are three sources of heat in the Earth's core, impacts of the planet when it was created (impacts made heat), radioactive decay of elements, and the extreme amounts of pressure and friction ...
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### Error propagation in sine

Having little experience teaching uncertainties and error propagation to high school students I am learning a lot of new things this year. One thing in the textbook we use states that the uncertainty ...
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### Speculation about antigravity (i.e. repulsive gravity) [duplicate]

Can an object with a stress-energy tensor bend space-time in a way that objects will slow down as they approach the object? We know gravity is only attractive, but I don't know, I am just curious.
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### Electric Field inside an ideal conductor

I have some doubts about the electric field inside an ideal conductor (let's call it E). Precisely, I have read two different descriptions 1) On physics books I read that the electric field inside in ...
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### Why does ohms law not work on transformers? [duplicate]

The voltage for transformer is given by $\frac{V_1}{V_2} =\frac{N_2}{N_1}$ if we use ohms law and assume resistance are same for both inductors, $\frac{I_1 R} { I_2 R}=\frac{N_2}{N_1}$ but in my ...
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### In which situation(s), if any, would two balls of differing mass actually hit the ground at the same time? [duplicate]

This is a common example physics teachers use. As far as I know, it never actually holds true. There are point masses: A(light, eg. feather), B(heavy, eg. hammer) and, C(eg. the Earth). They are all ...
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### Could fundamental laws change in Dirac's Large Numbers Hypothesis?

Paul Dirac proposed a hypothesis called "Large Numbers Hypothesis" (https://en.wikipedia.org/wiki/Dirac_large_numbers_hypothesis), where he basically stated that, if he was correct, laws of physics ...
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### Relative speed of sound (relativistic velocities)

This question is about waves speed, not about waves frequency shift (I already know about Doppler's effect). I know that for all the mechanical waves, e.g. sound, the perceived wave speed depends on ...
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### Summing and averaging in Casimir trick

For unpolarized particle scattering we sum over the final particle spins and sum over the initial spins. Why do we do so? Thanks in advance.
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### Which explodes first? Vacuumed tank or pressurized tank?

We have been arguing with a friend and couldn't agree. Here is the question: We have two systems. In both of the systems, we have an identical sphere tank. In the first system, we are vacuuming the ...
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### Should particle-wave duality be understood as a description of light's dual nature or as a description of two observable states of light?

In double slit experiments, light is observed in two distinct conditions (no measurement of trajectory / measurement of trajectory) that bring two different results (no interferences / interferences). ...
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### Unable to follow Feynman Lectures reading on opacity

Feynman is explaining the phenomenon of opacity in terms of classical electrodynamics. Let us first ask: “What is an opaque screen?” Suppose we have a completely opaque screen between a source S ...