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9 views

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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1answer
46 views

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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0answers
17 views

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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0answers
24 views

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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0answers
24 views

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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0answers
12 views

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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0answers
25 views

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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1answer
66 views

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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0answers
22 views

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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2answers
66 views

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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2answers
57 views

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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2answers
20 views

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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0answers
43 views

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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2answers
23 views

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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0answers
19 views

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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1answer
23 views

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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0answers
18 views

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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0answers
2 views

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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0answers
22 views

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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1answer
22 views

Symmetry of the scattering super-operator

Suppose we have an initial ensemble described by a density matrix $\rho$ and any given member of the ensemble scatters from one of some set of scattering matrices $\{S_g \equiv O_g S O_g^\dagger : g \...
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0answers
18 views

Discretization in pair distribution calculation

I am calculating pair distribution function according to the following equation : which is normalized because of dividing the total number of particles in each shell by the volume of that shell(https:...
-2
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0answers
21 views

Magnetics and magneto statics [on hold]

can you please help me with the question 7 from the link below, I’m having trouble understanding the question, what does “the separation between the plates is 0.1m “ and “so that it grazes the plate ...
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1answer
25 views

Electrical generators: power balance

Usually power generating synchronous generators are rated at around 85-90% efficiency. Curiosity struck me as of how a generator with field coils can ever go to such an high efficiency. My thought ...
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4answers
42 views

Doubt relating pure rolling

As we know, when an object perform pure rolling on a plane having friction the friction acts on the edge in the direction opposite to the direction of its translational motion. There are no other ...
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0answers
10 views

Writing a particular state (spectroscopic notation) as a superposition of n,l,s,ml,ms states

For a hydrogen atom in a particular state, e.g. $|3^2d_{\frac{3}{2}}(m_j=\frac{-1}{2})\rangle$, how would I decompose this as a superposition of $|n,l,s,m_l,m_s\rangle$ states? For example, I ...
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0answers
17 views

Sliding down a spherical ramp [on hold]

A ball of mass M starts at the top of a quarter circle ramp of radius R. The ramp is completely friction-less. What is the height of the ball and x position of the ball as a function of time? My ...
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2answers
43 views

How can a spring contract when magnetic field cannot do work?

When a spring is kept in a magnetic field and current is passed through it, its edges act as parallel conductors and due to the action of Lorentz force, they pull themselves together. A spring ...
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1answer
20 views

Amplitude of EM waves

I'm trying to calculate the Amplitude of electric field in the EM waves using the differential forms from maxwells equations. I've been given frequency ($10^8$ Hz) and displacement current density ($...
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0answers
16 views

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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0answers
24 views

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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1answer
38 views

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 ...
1
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1answer
26 views

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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2answers
45 views

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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1answer
39 views

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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2answers
39 views

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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0answers
28 views

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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2answers
29 views

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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3answers
28 views

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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0answers
12 views

How to derive the $t$-$J$ model from the Hubbard model in the $U \gg t$ limit

Assa Auerbach derives the $t$-$J$ model starting with the zeroth-order Hamiltonian $\mathscr{U} = U \sum n_{i\uparrow} n_{i\downarrow}$ and then includes the hopping term $\mathscr{T}=-\sum t_{ij} c_{...
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2answers
62 views

Confusion re: geodesics, connections, and straightness

In my readings in GR I often come across geodesics characterized as "straightest possible curves." This characterization confuses me. I'd like some clarification as to whether I'm understanding the ...
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0answers
22 views

How do I derive this expression? [on hold]

$w=\frac{1}{\sqrt LC}$ For an LC circuit where L is inductance of inductor and C is capacitance of capacitor
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1answer
20 views

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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0answers
18 views

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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0answers
17 views

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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1answer
16 views

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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5answers
61 views

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 ...
1
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1answer
25 views

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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1answer
36 views

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 ...
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2answers
45 views

Why does earth not follow the same rule around sun as moon follows around earth?

As you all know that only one side of the moon faces earth through the whole of its journey. The reason why it happens can be owed to the fact that the center of gravity of the moon (because of ...
-3
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0answers
29 views

How will time slow down for a body moving at light speed?(assume that if a body moves with speed of light) [duplicate]

How can't time be absolute... using special relativity we will calculate time to be ticking slower for the body...but does it imply that time really slows down for the body...

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