# All Questions

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### How do I simulate an astrophysical object with a software?

I am a high school student who seek to find a fun extracurricular thing to do. I am interested in astrophysics and I want to simulate some astrophysical objects with computer software. Can I get some ...
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### Final potential difference between plates of capacitor

If the plates of a parallel plate capacitor are given charges 4Q and -2Q . The capacitor is then connected across an uncharged capacitor of the same capacitance as first one (=C) . Now we have to find ...
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### Validity of the Lyapunov exponent approximation

I was trying to get the Lyapunov exponent for some dynamical nonlinear systems and found that it is not true (as I had expected) that the distance between two trajectories with slightly different ...
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### Error measurement barycenter of the Solar System - NASA data

What are the possible measurement error barycenter of the Solar System in NASA data? In the data JPL's HORIZONS system for NASA (http://ssd.jpl.nasa.gov/?horizons): Target Body: Solar System ...
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### As distance increase why no change in electric field in parallel plate condenser

If the distance between the plates of a parallel condensor is 4mm and the potential difference is 60 volts. Now if we increase the distance between the plates to 12mm, then: Why the electric field ...
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### Degrees of freedom of rolling coin

I gave a mental ability test yesterday in which this question was asked. A rolling coin on a flat surface has how many degrees of freedom? I read about degrees of freedom but I haven't had much ...
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### Type of motion when a long wire carrying current is inserted between two wires carrying current is moved normal to its length

Two long rigid wires separated by a distance d and placed parallel, carry current I in the same direction. Determine the force developed . Now a third wire is placed in between the rigid wires keeping ...
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Yesterday i got a MCQ in exam that a body in projectile motion with initial velocity 20m/s creating an angle of 60 degree with horizontal. What is its velocity at max. Height (A)10m/s Or (B)0m/s ...
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### Equation of distance for two racing cars?

Two cars were racing along a straight track namely CAR A and CAR B. They both started from same starting point with initial velocities $v_1$ and $v_2$ and constant acceleration $a_1$ and $a_2$ ...
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### Radial and angular coordinates of a route?

Certain bug has the route described by the radial coordinate $r(t)=\frac{at²e^{-bt}}{1+t²}$, where $t$ is in minutes, and the angular coordinate $\theta(t)=b+ct²$ in radians. Consider a,b, and c real ...
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### Mechanics Laws of motion

Two Blocks A and B are pushed against the smooth wall with force F. Surfaces of A and B are rough. Which of the following is true for the system of blocks? A) F should be equal to weight of A and B ...
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### why in such a fundamental theory as QFT we learn only two computations?! (cross sections, decay rates)

when i learned Newtonian mechanics i found a wast variety of computations that i could do and that was so interesting. and it was so when i learned Maxwell theory. when i started learning QFT i hoped ...
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### Total Angular Momentum of Hadrons

Hadrons are made of 2 or 3 quarks. Quarks have spin 1/2, so Mesons can have spin S = 1 or spin S = 0, and Baryons can have spin S = 3/2 or spin S = 1/2. Is there orbital angular momentum of the quarks ...
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### Terminal velocity after vertical launch

If an object is launched directly up at it's terminal velocity, will it have enough time/energy to reach it's terminal velocity again before it hits the ground, or will drag prevent this? In this ...
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### Does a degassed magnet weigh less than one that is not?

I learned matter with an electric current weighs more than matter with no current. Does that apply to magnetic material in the same way but with it's magnetic fields instead of electric current? A ...
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### Is the time ordering in Dyson series either 1 or -1?

Because I think to make it a unitary operator, the norm of the unitary operator should be one. But I did not see any claim about the value of time ordering in Dyson series.
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### Density of the universe [on hold]

Why is the universe of the same uniform density at all distance and time scales? Why haven't cosmologists realised this simple fact disproves the big bang? Why do they keep pushing theories as ...
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### Can a magnetic field speed molecules up?

I heard somewhere that If you add a magnetic field to atoms in a closed space you would speed them up. Similarly to heating them up. Is this true is so what the atom consists of for this to work?
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### Meaning of non diagonal terms in decoherence

It is my understanding that the non-diagonal terms in the density matrix of a macroscopic system that it is initially in an entangled state go exponentially fast to zero as the system interacts with ...
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### How do I determine the information needed to design a solenoid electromagnet that can ionize a gas?

I have been trying to answer this question for a long time. I watched a video where a person used a solenoid to heat up aluminum till it became a liquid. I want to apply this, to a gas. I want take ...
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### Correct Definition of Angular Momentum of a Charged Particle in an Electromagnetic Field? (Classical Mechanics) [duplicate]

What is the more correct definition of angular momentum $\vec{\mathbf{M}}$ in three dimensions? (I.e. classically/Lagrangian/Hamiltonian, not necessarily quantum or relativistic) ...
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### “Anti-classical” limit of large Planck's constant

A central theme in quantum physics is the classical limit where $\hbar \rightarrow 0$, and there is lots of interesting structure to this limit (i.e. classical mechanics). Is there anything ...
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### Chapter 6 Relativity [on hold]

I am having trouble visualizing the last sentences in the chapter. "However, the most careful observations have never revealed such anisotropic properties in terrestrial physical space, i.e.a physical ...
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### Finding the resultant electric field intensity? [on hold]

Q: Two charges Q1 = 4×10^-7 and Q2 = -8×10^-7 are placed at the two corners A and B of an equilateral triangle ABP of side 20 cm. Find the resultant intensity at P? I calculated the electric field ...
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### Potential Energy for dipole in Electric Field

Potential Energy is the work done by the external agent in turning the angle of the dipole from the U=0 position to another position against the influence of the electric field applied right? So if ...
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### Is there a way to make atom move faster without heating them?

The more heat you add the faster the atom will move. This is something that is common knowledge. My question is it possible to make the atoms in let's say a gas move faster without adding heat of a ...
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### Absorption spectra of molecules library

do you know where I can find a library with absorption spectra? I would like it if then I could input a wavelength and get back a specific value. More specifically I would like to see the absorption ...
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### On the expansion of space on small distances

After reading this post :Why does space expansion not expand matter? and after posting some comments to Peter Diehr, I was invited to make my argument to a question. The main things one needs from the ...
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### Equilibrium states for the Curie-Weiss-Potts model and large deviations

I am doing a project in Large deviation theory applied to statistical mechanics and I was reading this paper http://arxiv.org/abs/cond-mat/0410744. For the general setting we start with a finite ...
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### Prove energy conservation using Noether's theorem

I wonder how you prove that energy is conserved under a time translation using Noether's theorem. I've tried myself but without success. What I've come up with so far is that I start by inducing the ...
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### CP-Symmetry of the axion field and decay constant

In the $U(1)$-Peccei-Quinn-Symmetry an axion field $a$ is introduced in order to solve the strong CP-Problem. It is said, that below a certain scale $f_{a}$ this symmetry is broken and you are able to ...
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### Average speed of a molecule in a fermion gas

Starting from Fermi-Dirac statistics, how can be calculated the average speed on the x-axis, $\langle v_{x} \rangle$, of a molecule in a fermion gas a $T= 0\ \mathrm K$?
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### What moves the charges between capacitors?

Suppose I charged two capacitors to charges Q1 and Q2. By charging a capacitor to charge +Q , i mean that one plate acquires net charge +Q and another plate acquires net charge -Q.The capacitors were ...
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### What is the shape of a band electron in momentum space?

Band electrons occupy adjacent sharply defined momentum states that in xyz space take the form of a spectrum of wave functions. These wave functions span the entire xyz volume of any compact unit of ...
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### Why we have to sum in all final states of hadrons

Correct if i am wrong. In deep inelastic scattering have to sum in all final sates hadrons because we do not want to detect the hadrons. all we want to detect is the electron. Am i right?
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### Pressure exerted by a gas and the ideal gas equation

While determining the pressure exerted by any gas at a temperature why do we not consider the surface area of the container in which it is kept? We say that : P=nRT/V, where, n is the no. of moles, R ...
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### deriving Bio-Savart law in QFT

It's so important and meaningful that a new theory of physics contains main equations and results of previous related ones. Maxwell theory and QFT both have explanations on electromagnetic phenomenon ...
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### Which timestep should I use for a $N$-body simulation of the Solar system?

I am trying to implement a $N$-body simulation of the Solar system and I am stuck on the issue of the simulation timestep size. At first I would like to use a simple Euler stepping scheme. Knowing ...
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### Usage of tensors in physics

As I understand it, tensors are multi-linear maps that map vectors (and dual vectors) to real (or complex) numbers, but I'm hoping to gain some intuition as to why they are useful in physics. Is it ...
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### Why does time-independent Hamiltonian not depend on angle variable?

In Landau and Lifshitz Mechanics, $\S50$ Canonical variables a time-independent Hamiltonian is considered, and a canonical transformation is done such that adiabatic invariant $I$ becomes the new ...
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### A Formula for the Phase Difference Between the Electric and Magnetic Wave Oscillations?

A) Is there a formula for the phase difference between the electric and magnetic field oscillations, in vacuum, in an electromagnetic wave emitted from an antenna, as a function of the frequency the ...
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### Why would two inertial frames be distinguishable, if the coordinate of an evenet perpendicular to the motion would be different?

This question arises from the classical example: imagine a laboratory frame, and a space shuttle frame, the space shuttle moving in the laboratory frame with a constant velocity, let's say in the $x$ ...
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### Conserved quantity in a spacetime with Killing vector

I am trying to prove that that the expression $Q=-\frac{1}{\kappa}\int_{S_\infty} \nabla^i \xi^k \mathrm{d}\sigma_{ik}$ is a conserved quantity for a spacetime with Killing vector $\xi^i$ where ...
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### Can/will a proton escape the nucleus when a force is applied?

Protons are contained within the nucleus of an atom. Protons carry a positive charge. With an electric field, we can exert a force on the proton. Is it possible for the proton to escape the nucleus? ...
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### normal force on a physical pendulum

I have read and understood that a normal force has got nothing to do with torque on a physical pendulum. But I can't understand in which direction the normal force points to. Can someone help? This ...