# All Questions

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### What is the Reason behind restriction imposed by no-cloning theroem on (k,n) quantum threshold scheme (QTS)?

A $(k,n)$ quantum threshold scheme (QTS) is a method to split up an unknown secret quantum state $\lvert S\rangle$ into $n$ pieces (shares) with the restriction that $k > n / 2$ (for if this ...
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### Existence of affine parametrization

This is a question from General Relativity by Wald Chapter 3, problem 5. Given either pseudo-Riemannian or Riemannian metric $g_{ab}$ and manifold $M$. Assume the $\nabla$ is compatible with the ...
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### is copper a non-magnetic?

I'm working on an optics project that I'm using Fresnel Equation for Intensity. but I've got a question, is copper a non-magnetic ? You know because in Fresnel Equation, for non-magnetic materials ...
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### Viewing tube light through small cracks

This question appeared on a test: If you peer through very small cracks between your fringes at a tube light some distance away will you see interference patterns, Fresnel patterns or Fraunhofer ...
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### PROBLEM RELATED TO HARE'S APPARATUS [on hold]

while using hare's apparatus , ratio of specific gravities of two liquids A and B was found to be 1:4 respectively. the differences in the levels of liquids A and B in the tube were found to be 16cm. ...
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### maximum angle of a prism to have an emergent ray

the critical angle of the prism ABC is 40degree. for a ray of light incident on AB , to emerge from the face AB , what should be the maximum value of angle A? please explain how to do this ...
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### For a projectile to cover maximum vertical distance in the least time, what will be the angle of projection?

My first guess was 90° as there is no horizontal component for velocity when the angle is 90°. But I could not prove it mathematically (and also I'm not sure if it is really 90°).
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### What happens if I have a square conducting wire being permeated by a magnetic field and the field suddenly disappears?

Suppose there is a square conducting wire in a magnetic field. The two vertical branches will have the same emf, and the two horizontal branches will have 0 emf, resulting in a net emf of zero and ...
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### How to get image current in magnetostatics? (magnetic slab)

I want to know the image current and its location which satisfies the boundary condition at the interface. This problem was originated from the problem 6-33 in Fields and wave electromagnetics, D. ...
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### Why does sound wave suffer more diffraction than light waves generally?

Why do sound waves suffer more diffraction than light waves generally ? I would like more of a logical explanation rather than mathematical .
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### How is the final velocity in 2 body collision distributed between the 2 bodies?

Suppose 2 sphere of mass 1Kg move with velocity 5m/s and 10m/s in same direction. Let us call the ball moving with 5m/s blue and other one red with blue ahead of red from origin. Initial KE of Blue = ...
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### Zeroth law of thermodynamics and related discrepancy?

Consider the case: Assume molecules to sphere and their |velocity| as an indication of their temperature. Now for head on elastic collision (i.e transfer of heat), assume the momentum is conserved ...
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### Why couldn't a space elvator's cable be tapered?

Why couldn't a space elevator's cable be tapered to solve the weight issue for the cable? After all you don't need a massive amount of tensile strength at the bottom of the cable.
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### where has the energy gone when the test charge turned away?

Consider an insulated ball with some charge $q_1$ inside it.Now we take a small area over that ball uninsulated i.e we had cut a small portion. Now when we bring a test charge from infinity near that ...
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### How can we define energy?

Can we call matter without mass as energy? just a simple defintion to the word energy; massless matter= energy? and I'm not asking about photons.
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### What allows some objects to have a high specific heat capacity?

I know that temperature is a measure of thermal energy associated with the KE of molecules. But when heat enters an object, surely those molecules now start vibrating and translating, so this results ...
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### Confusion about Fock subspace

I'm currently reading Folland's book on quantum field theory and came along some definitions. On p.90 of his book, Folland defines the symmetric Fock space as ...
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### Difference between a tap and a hosepipe

When the flow of water through a tap is blocked by the fingers, the water does not increase in velocity whereas the velocity of water increases when the same is done tp a hosepipe. Both involve the ...
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### Non-inertial frames in Lagrangian mechanics?

Building on this Phys.SE post I am interested in how non-inertial frames can be considered in Lagrangian mechanics. My understanding is that changing the reference frame causes a transformation of the ...
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### Pointwise and uniform convergence. Examples from physics

I am a first-year mathematical student, and from a mathematical perspective I understand the difference between pointwise and uniform convergence of sequences and series of functions. However, I have ...
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### A metal block in a tub of frictionless ball bearings

If you place a metal block in a tub of small frictionless ball bearings of the same metal, would it stay on top or sink?
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### What a physicist can work in after the graduation? [on hold]

What a physicist can work in after the graduation? if you ask : what is the branch in physics he graduated from! i say give me a view in every domain. thanks
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### Basic Thermodynamics: Adiabatic Process

we know that for adiabatic process $W=-\nabla E$. My question is here why do we consider $W=nC_v\nabla T$
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### Reynolds Average Navier Stokes equations and turbulence scale

To obtain the time average of an unsteady term like $\frac{\partial u_{i}}{\partial t}$ by definition we perform the following: \begin{align} \overline{\frac{\partial u_{i}}{\partial t}} &= ...
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### Energy Transfer Equation - Geothermal water energy

I'm a student of Integrated Water Management, so not physics trained, but attempting to solve this question with your help. I have a bore with geothermal water exiting at an average annual ...
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### Given a VEV how can I compute which generators remain unbroken using tensor methods?

This is a follow up to this question. A generator $T_a$ of a given gauge group $G$ remains unbroken after some Higgs field $\Phi$ gets a vev if $$T_a \langle\Phi\rangle =0$$ I'm trying to ...
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### Why two bodies won't attract each other? [on hold]

Two bodies cannot attract each other as a body contains mass and mass is a constituent of atoms and molecules,held by electrical force.The electrical force is too weak to attract other objects. And ...
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### How does a bulb light up when it's connected in a circuit with an uncharged capacitor and a cell?

Since there is a capacitor, isn't it an incomplete circuit? How does the current flow across the dielectric medium? If a bulb was connected to a cell alone and if there was a break in the wires of the ...
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### Dark matter configuration

We live in a 3D world comprised of 4 dimensions, if you include time. The unit of spacetime as we "see" it is the proton, comprising of 6 quarks, fermions. Hence since these quarks cannot occupy the ...
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### Origin of pressure gradient in Navier-Stokes integral

I am not understanding the origin of the second term on RHS of momentum conservation equation (cf. the Wiki page),  \frac{\partial}{\partial t}\int_V\rho\mathbf u\,dV=-\oint_S\left(\rho\mathbf ...
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### Can electromagnets repel?

So I saw a video here https://www.youtube.com/watch?v=wzXRFp0DDrU (See the full video first) I don't understand that how is the electromagnet repelling things in the second half of the video? Also ...
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### What's the difference between two types of diaphragms?

What's the principal difference between aperture iris diaphragm and field iris diaphragm?
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### Two long straight wires carrying current in same directions attract each other as electrons attract. Does this violate basic electrostatics?

I think question is silly. Please give simple answer
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### How are smoke cells an example of Brownian motion?

I don't get how smoke cells are an example of Brownian motion.
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### Stern-Gerlach: Why is it probability 1/2 for cooked up silver atoms?

Why does cooking up silver atoms in an oven give them equal probability spin up and spin down?
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### Moving coil through space

Programmer here, I have simple question about existence of magnetic field relative to the coil, when moving in space. Imagine we have coil L, that is connected to battery / power supply and coil is ...
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### Einstein's principle of equivalence; Standing on earth vs sitting in accelerated car

When I am seated in a car that is accelerating in a particular direction I could, for example, throw a ball and it would appear to be flying the opposite way. With the windows covered etc. An ...
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### Is there a phase transition for degenerate matter?

Does electron or neutron degenerate matter undergo a phase transition? Are there any thermodynamic quantities that are discontinuous?
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### Drag force acting on a disk in a 2D system

I have a 2-dimensional system with behavior governed by Langevin dynamics in which disks (circles) move through a fluid. In the Langevin equation, there is a velocity-dependent term that accounts for ...
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### Why is this method valid in special relativity

Here is the question Two clocks are positioned at the ends of train of proper length $L$. They are synchronised in the train frame. The train travels past you at speed $v$. It turns out that if ...
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### Is there a resonance within the earth, separate from the Schuman resonance?

In a very recent biography of Nikola Tesla by Bernard Carlson, the author explains that Tesla measured the resonant frequency of the earth using his invention - the amplifying oscillator. Tesla came ...
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### Why do different phases of matter coexist?

Say at a critical temperature $T_c$ there is a phase transition. If we had water, $T_c$ for the liquid-solid transition is $0 ^\circ$C. If we left a block of ice at $1 ^\circ$C for a bit, it will ...
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### What is causing the Trumpet Sounds that are emited from the sky?

In these last years, a phenomenon have appeared in several countries (US, Canada, Australia, Russia, Germany, and others). It consists of sounds like a trumpet coming from our own planet's sky. ...
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### Show that the electric dipole term vanishes for a particular current

I'm interested to show that given a ring with radius a where there's a current $I_0 \cos \omega t$ ($I_0$ is a constant) there is no radiation due to the electric dipole term (appearing in the ...
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### Thermal efficiency of a compressed air engine

I am doing some personal research on the thermal efficiency of compressed air cars. I am currently trying to come up with an 'ideal' cycle to use as a reference for efficiency (c.f. Otto Cycle for ...
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### How does a world line of an Alcubierre drive look like?

In my recent question ”Speed of light and warp drives in general relativity” I asked exactly how an Alcubierre drive worked and exactly what "FTL travel" meant. One of the comments I got stated that: ...
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### Does RF have any non-orthagonal properties?

Quantum Key Exchange takes advantage of the fact that observing a photons polarization will alter it's polarization. This, along with some tricky back and forth, allows two people to exchange data ...
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### Car sliding down a frictionless banked curve

A car enters a frictionless banked curve with speed $v$. This speed happens to be too great to execute uniform circular motion at the angle $\theta$ the curve is banked at. What will the equations ...