# All Questions

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### Given state cannot be written as a linear combination of pure states

Ok. This is just a numerical example to be better understood. If I am given a state let's say (1,1,0) of a H matrix let say ((3.2.0),(2,0,0),(0,0,1)), since the initial state cannot be written as a ...
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### Kinematics - Projectile Motion problem, projectile lands at an angle

Question: You are watching an archery tournament when you start wondering how fast an arrow is shot from the bow. Remembering your physics, you ask one of the archers to shoot an arrow parallel to the ...
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### Kähler Potential of Calabi-Yau volume

At tree level, the Kähler potential is given by (neglecting complex structure) $K = -\ln(-\mathrm{i}(\tau - \bar{\tau})) - 2\ln(V_{CY})$ where $V_{CY} = \frac{1}{6} \kappa_{abc}t^at^bt^c$ ia the the ...
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### Can the mass of a body change under any condition or not?

We know that mass can neither be changed nor be destroyed, but I want to know if there is any circumstance under which the mass of a body can be changed?
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### From what time does we humans are knowing about charge?

We know that the electron is discovered in 1897 by JJ Thomson. So the knowledge about charge, current, electricity and all those terms related to it which we study today are discovered after it or the ...
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### Movement of accelerating points with maximum speed (i.e. running away from tiger)

I'm walking through forrest and suddenly I see a tiger. And now I have a problem. I want to know how much time I have left but I don't know how to calculate it. Or more fomally: Let's say there are ...
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### How do we know that the cesium-beam frequency used in atomic clocks is always the same?

Atomic clocks use cesium-beam frequency to determine the length of a second. This has shown that the period of orbit of the earth is decreasing. But what experiment showed that cesium-beam's period ...
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### Work and energy

when a ball of mass m is brought with uniform velocity from infinity into the g field of the earth at a distance r from it, the potential energy of the ball earth system decreases from 0 to -GMm/r. ...
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### How to calculate Electric Field near a charged conducting surface without Gauss' law?

I have two problems : In every textbook I find the use of Gauss' law in calculation of Electric Field near a charged conducting surface. Can it be calculated without Gauss' law? Suppose while using ...
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### Unitary evolution operator

Assume we have a system in a state $\psi$ that is a superposition of eigenvectors of some observable $A$. Now we make a measurement of the observable $A$; the state after the measurement $\phi$ is a ...
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### The general equation for a wave packet derivation?

On Wikipedia it gives the general equation for a wave packet (and therefore for a wave?) to be: $$u(x,t)=\frac{1}{\sqrt{2\pi}}\int^{\infty}_{-\infty}A(k)e^{i(kx-\omega t)} dk$$ I have been trying to ...
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### Calculating Time to reach a given velocity knowing force of thrust

so I am working on a physics problem for a class I am taking. The problem is as follows: -A rocket, weighing $4.36\times10^4 N$ has an engine that provides an upward force of $8.90*10^5 N$. It reaches ...
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### Time dependent Hamiltonian and Gauge invariance

In general, in quantum mechanics we can prove probability current or the Schrodinger equation and other quantities are gauge invariant. However, the Hamiltonian isn't gauge invariant. Under a gauge ...
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### Angular momentum of light in classical electrodynamis [on hold]

I' reading at this time electrodynamics from Griffith's Introduction to electrodynamics. As i see, to have the conservation laws in field theory we have to consider the fields as carrying energy, ...
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### Object moving in a circular path without accelerating

A train is moving with a constant speed on a straight portion of track. Then, it encounters a curve in the tracks, and goes along the curve. However, it does not accelerate during its time on the ...
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### Does elementary particle emit photon?

Charged particles are accelerated by the magnetic field in a particle collider before allowed to smash together at specific location where the detectors are housed. My question is do the ...
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### Construction of free energy based on Landau theory

Consider an Ising model system where the total energy is $E = −J \sum_{<ij>} S_iS_j$, $S_i = \pm 1$ and $< ij >$ implies sum over nearest neighbours. For $J < 0$ the ground state of ...
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### Jee Main 2015 Question. Inter-molecular Interaction [on hold]

The Intermolecular interaction that is dependent on the inverse cube of distance between the molecules is: Hydrogen Bond? ion-ion interaction? ion-dipole interaction? London Force?
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### Number of microstates compatible with two boxes

From my notes I have: From one point of view there are many more microstates compatible with the LHS than the RHS, in fact the relation between the number of microstates is ...
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### JEE MAIN 2015 Question. Electromagnetism [on hold]

Two coaxial solenoids of different radii carry current I in the same direction. Let F1 be the magnetic force on the inner solenoid due to the outer one and F2 be the magnetic force on the outer ...
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### Understanding the behavior of light/photons inside a Laser

I am trying to establish a model inside my head of how light behaves but find it hard with all the seemingly contradicting information. For example, electrons inside a Laser are raised to a higher ...
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### Neutron star: free fall acceleration

The textbook from which I teach physics at the end of secondary school, has a question about a neutron star: $M_{star}=1.4\cdot M_{sun}$, radius 15km. "Calculate the free fall acceleration at the ...
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### Is $SU(2)$ really broken by the Higgs VEV or just hidden?

It's generally stated in the textbooks that whent the Higgs field acquires a certain vev the corresponding symmetry is spontaneously broken. For example in A. Zee - QFT in a Nutshell: But none of ...
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### How to calculate earth's magnetic field by time period of suspended magnet?

Assuming that torsion of the suspension wire small enough to be neglected, how can we derive earth's magnetic field by measuring time period of an oscillating magnet suspended on a string?
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### Ice at zero gravity

I wish to know the behavior of ice at zero gravity, sound at zero gravity. How ice will behave when melted and how sound will break a closed glass at zero gravity vs g on earth? Thanks
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### Infinite force between two point charges as $r$ approaches 0 [duplicate]

According to coulombs law the Force experienced by two point charges increases with the inverse square of their separation. This would imply that at distances approaching 0, the Force approaches ...
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### Energy conversion (conceptual) question

Suppose I have a electronic car. It runs by electrical energy. So when wheels rotate, mechanical energy is produced. Then why can't we convert it back to electric energy and produce somewhat unlimited ...
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### Why do termite pellets fall in a perfect circle?

I was just wondering why termite pellets fall down from my bed in a perfect circle. You can see from the images that the follow down on the floor making a perfect geometric figure which is void in ...
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### Could there be a function or property having non-linear mass dependence? [on hold]

I'd like to know some properties or functions that possess a *non-*linear relationship with mass. For example: a property like $x = T m^n$ I am interested particularly in classical newtonian ...
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### Does gravity exist in a vacuum?

My understanding has always been that it does from conventional science courses, but really thinking about it, I was wondering if this is really the case. To my limited understanding there is a ...
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### Whether phase congruency and phase coherence terms are same or different?

I am studying the importance of phase in signal.Can anybody explain what is phase congruency ? Also,I am confused between terms i.e. phase congruency and phase coherence. Whether phase congruency and ...
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### Ohmic and non-ohmic conductors

What sort of materials are ohmic and what sort of materials are non-ohmic? I have tried looking around on the internet and have not found any clear way to differentiate between ohmic and non-ohmic ...