# All Questions

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### Time and speed - Theory of relativity - 'felt time'

Assuming time is relativ according to the objects current speed, means that a clock within a spaceshuttle which has 30% of lightspeed is 'ticking' slower than a clock staying on planet earth just ...
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### Probability with expectational value

How can I calculate: $P(T)=T^2 b^2 |<n| \delta (x) |n>|^2$ Where P is the probability.
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### Is it possible to write the Lorentz oscillator model using Green's functions concepts?

Is it possible to write: $$\lim_{\gamma_j\rightarrow0}Im\left(\frac{1}{\omega_j^2 - \omega^2 - i\omega \gamma_j}\right)$$ which occurs, for example, in the Drude-Lorentz oscillator model for ...
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### Expectation value of operators in quantum mechanics

Can the expectation value of an operator be zero?
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### What is the relationship between the Boltzmann Transport Equation and the Navier-Stokes Equation?

What is the relationship between the Boltzmann transport equation and the Navier-Stokes equation? Can the Navier-Stokes equation be derived from a moment of the Boltzmann transport equation?
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### Does a magnetic field decrease or increase entropy?

My question is just the title: Does a magnetic field decrease or increase the entropy of a system? For example if we apply a magnetic filed to a substance, is the entropy decreased or increased?
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### Show that a function takes the following form using the definition for the function of an operator

If $f(z)$ is a function with a Taylor series expansion $f(z)=\sum _{ n=0 }^{ \infty }{c_n z^n }$, then we define $f(M)=\sum _{ n=0 }^{ \infty }{c_n M^n }$ First consider ...
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### Relativity : Consider an object which respond to two different signals A and B

It respond to signal A with blue color and signal B with red color. Also it respond only to signal that reached first and in case they both reach together, there is no observation. Now consider three ...
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### What are the forces acting when we squeeze a ball? Free Body Diagram?

As part of my project, I am trying to figure out the forces acting while squeezing a ball. The ball in question is a foam rubber ball( stress ball). The ball deforms when we squeeze & the mode of ...
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### Relation between Vector space $V$ and its dual $V^{*}$

I asked the same question in Math.SE, but I was suggested to ask it here as well. I am studying relativity, and as you know the theory extensively uses the notion of covariant and contravariant ...
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### Given an initial push, is work done on an object infinite in a hypothetical empty universe?

Consider a hypothetical empty universe containing a single object. Given an initial push, will the work done by the forever moving object be infinite?
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### Entangled Photon [laser pointer]

from a laser pointer emission; 1- is it creating entangled pairs of photon ? 2- is it possible to get more than "pair" entangled, like group of photons all entangled ? Thx
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### Long life energy usage

Im doing a project on school. I want to re-use energy. I know that it will not run forever (but i hope it runs very long). So i wanted to ask if the image below is right and i could use it at school. ...
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### WKB formula and Langer correction

The general WKB approximation formula states that $$\int_a^b\sqrt{E_k-V(x)} = (k+1)\pi \text{ with } x \in [a,b]$$ for a regular Schrödinger equation (without the $\hbar$ and such). However, in the ...
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### Why is entropy in a heat flow process always positive?

Entropy in a quasistatic heat flow process is given by $$\Delta S=C_1\ln(\frac{T_f}{T_{10}})+C_2\ln(\frac{T_f}{T_{20}})$$ Where $C_1, C_2$ are heat capacities at constant volume, $T_{10}<T_{20}$, ...
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### Standard partial differential equation?

Is there any standard equation which looks like this one, $u_{t}(x,t) = \alpha ~ u_{xx}(x,t) - \beta(t) ~ u(x,t)$, where $\beta(t)$ is nonlinear in time, and $\alpha$ is a constant. Or, suggest me a ...
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### Presuure-Velocity relation at a point in a flow

How can we relate pressure and velocity at the same point in a fluid flow? Why does pressure decrease with increase in velocity?
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### Thermal conductivity of oak wood

I have to calculate the thermal conductivity of a natural material (oak wood sample). The heat penetration through a wood sample was evaluated for 4 investigated temperature (55°C, 57.5°C, 60°C and ...
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### Equations for a collision between two particles

Say I have two particles on a 2D plane, they have a x and y coordinate, a x and y velocity, a mass, a coefficient of restitution and a coefficient of friction. What formulae would I need to determine ...
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### Is this fine to think of light as the following?

Is light quantums (increments [photons]) of the electromagnetic waves which are synchronized by oscillations of electromagnetic fields
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### Experiment of plume of smoke

If a burning candle is covered by a transparent glass, the flame extinguishes and a steady upward stream of smoke is produced. Which factors will infulence the figure and properties of the plume of ...
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### Solar CNO neutrino flux

I am new to research on solar neutrino flux. I have been told that the measurement of the CNO neutrino flux needs to be complimented with a measurement of the $^{8}$B neutrino flux but I can't figure ...
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### How water anomalies affects the Mpemba effect?

I understand basic explanation of Mpemba effect like this: Distant molecules are easier to realign into new formations. But if we compared two bottles of water like in Mpemba effect and one of them ...
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### Launching a Spring from a meter stick

In class we are engaging in 'war games'. We receive a random spring and launch it from a meterstick at a target flat on a nearby table. we will have the variables for: ...
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### Influence of a defect on the flow field

I have a long microchannel where flows some water. Within the structure of this microchannel there is a big defect. It looks like a bump of size approximately 20 micrometer and the microchannel's ...
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### Have they really photographed light behaving both as a particle and a wave?

I just came across this article where they are claiming that they have photographed light behaving both as a wave and a particle! The paper has been published in Nature and I read the abstract which ...
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### How does Einstein's gravity work? [duplicate]

I'm a chemistry student interested in physics. Hope the question doesn't sound funny. As opposed to Newton's gravity, which doesn't explain how gravity works, Einstein explained gravity as a result ...
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### Fundamentals of Quantum Mechanics

I am currently midway through the undergraduate quantum mechanics series at my university, and I am beginning to feel somewhat troubled by the some of the implications of the subject. We accepted some ...
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### Can a fluorophore emit a higher energy photon than it absorbed

It is unclear for me what processes are exactly in place during the absorption-reemission process of a fluorescing photon. I am thinking about the case when the absorption and emission spectrum ...
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### Why renormalizable theory is useful?

Why renormalizable theory is useful? I want to know detail reason for above question. At a glance, I know following things. In quantum field theory, $i.e$ computing self-energy(or self-interaction) ...
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### Need a Suggestion regarding to final year Project in Computational Phy [on hold]

I need a suggestion regarding to my final year project. I am in 8th semester of BS(Hons) Computational Physics offered by Center For High Energy Physics Punjab University. I want to design a ...
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### Work done against a physical field: positive or negative?

My understanding of signing conventions contextual to physical fields: With frame of reference as object: Work done by an object against a physical field is positive. Work done by a physical field ...
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### What are the recent development on theoretical physics and how to move furthermore? [on hold]

I am searching for theoretical physics related queries.what are the recent development on theoretical physics.what are the impacts by those developments in physics.please explain me.and furthermore ...
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### White, is it a colour or absence of colours?

Our chemistry sir and we had an argument today at the lab, he says that white actually is not a colour, it is the abscence of colour, but we say that it is a colour and we gave the following point to ...
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### Fine Structure Correction

The fine structure correction is composed of the relativistic correction and spin-orbit coupling. The lowest-order relativistic correction to the Hamiltonian is $$H_r' = -\frac{p^4}{8m^3c^2}$$ ...
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### Given the quadrupole moment of the nucleus as Q, is it possible to find the order of magnitude of the dimensions of the nucleus?

Given the quadrupole moment of the nucleus as Q, is it possible to find the order of magnitude of the dimensions of the nucleus? ( order of magnitude means approximate value to the powers of ten)
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### Solving Schrodinger Equation with Anisotropic Effective Mass

How can I discretize a time-independent Schrodinger equation using the mass tensor and considering the valley degeneracy for the specific material at hand? I intend to investigate the confinement ...
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### How can heaters using the same type of fuel be more or less efficient than each other?

I can understand there being a cost difference if you used gas vs electricity to heat your home. But for heaters using the same energy source, how can they be more or less efficient than each other? ...
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### Definition of generalised coordinates?

I think the definition of generalised coordinates is something along the following lines: A set of parameters that discribe the configuration of a system with respect to some refrence ...
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### Why does the nuclear volume scale (roughly) linearly with number of nucleons?

As far as I know, it is the fermi repulsion that gives a collection of protons or neutrons its finite size. But this only acts on indistinguishable fermions. If the protons and neutrons do not repel ...
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### Puzzling : Relative motion of two points on a rotating disc

Consider two points on a radial line for a rotating disc. One point, $A$, is at the circumference and the other, $B$, is at distance $R/2$ from disc's centre. Relative velocity of $B$ w.r.t. $A$ ...
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### The delta function as an eigenfunction of the position operator explanation

$\delta (\textbf{r})$ can be interpreted as a wavefunction. [...] It is non-vanishing only for $\textbf{r}=0$. [...] $\delta(\textbf{r})$ is an eigenfunction of the position operator with ...
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### Decomposition into symmetric and antisymmetric form [on hold]

(a) Given a second-rank tensor Tμν, often viewed as an $N \times N$ matrix (for a space of dimension $N$), show by explicit construction that one can always decompose $T_{\mu\nu}$ into a symmetric ...
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### Computing And Finding The Trajectory From The Lagrangian [on hold]

The Euler–Lagrange equations come from extremization of the action. So we expect the "true", dynamical trajectory to minimize (in this case) the value of $S=\int L \,dt$ For free particle motion, the ...
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### Generate the equations of motion for the one-dimensional Lagrangian [on hold]

Generate the equations of motion for the one-dimensional Lagrangian: $$L=\frac {1}{2}m\dot{x}^2-(Ax+B)$$ From the equations of motion (and the implicit definition of the potential), provide a physical ...
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### What are the contribution of Greek in modern physics? [on hold]

modern physics which had their origin in Greek
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### What is the smallest engine theoretically possible?

Is there some law of physic forbiding small engines that use say petrol? I would like to know of some analogy between electric motors and heat engines. In the latter we can make a motor so small that ...
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### Perturbation theory of states [on hold]

A particle in 1 dimension with mass $m$ is in potential well with $V = 0$ for $–a/2 < x < a/2$ and infinite potential elsewhere. The particle is initially in the state $n = 10^9 + 1$, with the ...