# All Questions

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### High and low pressure area and raining

In the high-pressure area it is mostly likely that there is sun. In low pressure area it is mostly likely that rain will occur. Because of the law that ...
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### Internal energy, and heat transfer in isothermal expansion of a gas [closed]

I have this question. One mole of ideal monatomic gas is confined in a cylinder by a piston and is maintained at constant temperature $T_0$ by thermal contact with a heat reservoir. The gas slowly ...
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### Is this an exact differential or not? [migrated]

I have the 1-form $$dz=2xy\, dx+(x^{2}+2y)\, dy$$ And I want to integrate it from $(x_{1},y_{1})$, to $(x_{2},y_{2})$. If I'm not drunk, checking mixed partials, I find that $dz$ is an exact ...
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### If an area is prone to fog in the mornings, is it less likely to rain?

I live in a city that is very well known for having foggy mornings. Would it be less likely to rain in the morning as a result of this fog?
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### What is the electric field in a parallel plate capacitor?

When we find the electric field between the plates of a parallel plate capacitor we assume that the electric field from both plates is $${\bf E}=\frac{\sigma}{2\epsilon_0}\hat{n.}$$ The factor of two ...
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### Some Dirac notation unclarities

Q1: Ok so i have come to a point where i know that $\Psi(r,t)$ which we denote only by $\Psi$ can be represented in a Hilbert space by a vector which we denote $\left|\Psi\right\rangle$. Does this ...
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### Error bars for pair-correlation function [migrated]

I have obtained some data from neutron diffraction for some material samples. The "rawest" form of the data is the structure function $S(Q)$. We can choose a variety of different Q-maxes when ...
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### Why the magnetic flux is not zero?

According to Maxwell's equations the magnetic flux over a closed surface must be zero, why in this case does not happen? Thanks for your help
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### Image formed by a spherical ball [closed]

There is an object on one end of a sphere and an image is formed on the other end. I am given the index of refraction,radius and the distance of the image from the center ball. How do I find the ...
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### Acceleration due to gravity?

I was looking into orbitals and found something I haven't been able to understand. http://www.math.ubc.ca/~cass/courses/m309-01a/hunter/satelliteOrbits.html There is a part on the page which states ...
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### Hamiltonion in 2-dimensions?

I am trying to construct a Hamiltonian for a system in 2 dimensions using Matlab. I am not sure how this Hamiltonian will look like in matrix form. If somebody can help me visualize this matrix that ...
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### Is the preferred basis problem solved?

Once and for all: Is the preferred basis problem in the Everettian Interpretation of QM considered solved by decoherence or not? THere are a few people who claim that it's not, but it seems the vast ...
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### Is there any case where one would use, snap, crackle or pop?

As we all know, if you differentiate distance with reference to time, you get speed, and likewise, differentiating speed you get acceleration. However, if you keep differentiating, to the rate of ...
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### Symmetry of the stress tensor

When presenting the stress tensor (say in a non-relativistic context), it is shown to be a tensor in the sense that it is a linear vector transformation: it operates on a vector $n$ (the normal to a ...
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### Why is the temperature zero in the ground state?

This is probably a simple question: I see this claims in many books, but I can't figure a reason why this is true. So my question is why this claim is true: "If we know that the system is in the ...
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### Spring damper model does not work very well [migrated]

I'm trying to model a spring damper system from a tutorial that I've found on this site. If I use the exact same parameters as the ones in the tutorial the system is not stable. I've downloaded the ...
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### Polarization of Light

How do materials polarize light? I know that they polarize light in the same plane, but light has two perpendicular directions with the two fiels, so which direction is reflected and why? And if ...
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### Refraction of light and frequency dependence

Why do higher frequency waves refract more, both ocean waves and light waves? Also why is energy stored in the frequency as opposed to the wavelength.
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### Criticism of String Theory by other string theorists [closed]

*EDIT: Due to policy I will edit this into a question: Do you know any string theorist that have criticized string theory and if so please could you give me references? thanks. End of EDIT. ...
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### Pulley system with rope

Two masses $m_1$ and $m_2$ are connected through a weighty, uniform and an unstretchable rope of length $L$. The surface is frictionless. Masses of the objects are $m_1=m$, $m_2=\frac{2}{3}m$, mass ...
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### Potential E alternation

Considering a permanent magnet moving in a trajectory perpendicular to a straight wire of a given lenght, in a way that the magnet expose always the north face towards the wire, no matter the ...
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### Is the fine-structure constant a parameter of the standard model?

According to the wikipedia entry on the fine-structure constant: In fact, α is one of the about 20 empirical parameters in the Standard Model of particle physics, whose value is not determined ...
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### Electric power transmission

If we want to transmit electic current for a long distance, we must minimize a heat that releases because of the resistanse. We cannot make a cable wide because it is expensive and it will be massive. ...
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### Best current bounds on nonconservation of momentum?

It's not straightforward to test conservation of momentum experimentally, and many experiments that seem like tests really aren't. For example, in a Newtonian system of identical particles that ...
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### Superconductivity

What is the correct explanation of why superconductivity occurs in metals when they are cooled to a temperature below $T_c$? My textbook has the following explanation: Superconductivity is the ...
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### Help Understanding Non-conservative Fields

While watching a video lecture I became uncomfortable with the results, which begin around minuite 35. The professor draws an electric circuit with a 1V batter, and two resistors (1ohm and 9 ohms). He ...
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### Do generators belong to the Lie group or the Lie algebra?

In Physics papers, would it be correct to say that when there is mention of generators, they really mean the generators of the Lie algebra rather than generators of the Lie group? For example I've ...
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### Why is planar geometry preferred to observe ordinary Hall effect?

In the Physics Today article by Avron et.al. "A Topological Look at the Quantum Hall Effect" Physics Today (2003) it is suggested that to observe ordinary Hall effect, planar geometry is preferred to ...
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### Why are some jenga pieces easier to remove than others?

Jenga is a game place with wooden blocks stacked on top of one another in an alternating pattern. Players take turns removing blocks from any layer and placing them on top. As the game progresses ...
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### Solution of multiple materials

Introduction I'm trying to make some strawberry liqueur. The recipe I got says I should put alcohol, strawberries and sugar in a bowl and leave it soaking for 4-5 weeks. I read that making liqueur is ...
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### What is the result of applying a fourier transform n times to a distribution?

For a function applying the fourier transform twice is equivalent to the parity transformation, applying it three times is the same as applying the inverse of the fourier transform, and applying four ...
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I have a cylindrical container say of some base area $A$. The atmospheric pressure is $P_0$. The cylinder is moved at an acceleration $a$ horizontally right. I need to find which base would have to ...
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### Calculate the electric current in the given circuit when (a) Key K is open [closed]

Calculate the electric current in the given circuit when (a) Key K is open. (b) Key K is closed. !]each resistors of 6 ohm 1
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### The Hartree solution of two harmonic oscillator coupled by potential $V \propto ({\bf r}_1-{\bf r}_2)^2$ [closed]

$H={\bf p}_1^2+{\bf p}_2^2+{\bf r}_1^2+{\bf r}_2^2+x({\bf r}_1-{\bf r}_2)^2$. $x$ is the coupling factor.
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### can be exist the negative mass? [duplicate]

I'm not sure about this but I guess there must be negative masses in the universe because of the symmetry. If the gravity is one of the main forces in nature it must has negatives mass to be able to ...
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### What is the effect of humidity in temperature?

Suppose we have a building in an area with weather conditions $W_t$ at time $t$, and suppose we could change the relative humidity $\phi_t \in W_t$. Would the change in relative humidity $\phi_t$ have ...
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### Counting the modes of the vector potential in a coulomb gauge

With a view to quantising the EM field, consider a classical free field in the absence of charge and currents, we can take a coulomb gauge, $\phi=0, \partial_kA_k=0$. The physical fields in terms of ...
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### Is it possible to determine the state or values of something without measuring it

To give context to this question, I am currently looking into non-locality / hidden variables / Bell's Theorem, EPR / etc. I've noticed the assertion that the values / state of something when ...
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### if a simple pendulum is dropped in a elevator with a acceleration greater than acceleration due to gravity then what will be its frequency

if a simple pendulum is dropped in a elevator with a acceleration greater than acceleration due to gravity then what will be its frequency ? We know time period depends on frequency.
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### Resistance of a copper wire [closed]

Resistance of a copper wire is 20ohm. If the diameter of the wire is 5mm and length 1ohm. Find the resistivity of the copper.
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### Easy to do experiments that clearly show outstanding properties of graphene

By chance we received for free some monolayer graphene sheets (20 cm x 20 cm) and mixed coper-graphene wires at our University. I would like to prepare some very easy to do experiments for the ...
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### Derivation of Dirac equation using the Lagrangian density for Dirac field

How can I find Dirac equation using the Lagrangian density for Dirac field?
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### Software for electric schemes [migrated]

I am looking for an open source software for creating electric schemes. Could you, please, recommend your favorite programs? Also, it will be better if your programm can do other schemes (for ...
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### Why is the Heisenberg Uncertainty Principle not obvious give the conservation of mass- energy?

A photons energy is given by $E=h *f$ and momentum $p=E/c$ (spin?) but the photon has no (rest) mass! Therefore it is the ultimate probing tool for looking at any mass position and velocity because ...
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### T-Duality between Type HE String theory and Type HO string theory

My question is regarding T-Duality between the 2 Type H string theories. I know that the Type II String theories are T-dual to each other because T-Duality changes the sign of the Gamma Matrix so ...
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### Momentum, Impulse and Newton's Second Law of Motion

Newton formulated his Second Law as such: $$\sum{\vec{F}} = \frac{\delta \vec{p}}{\delta t}$$ and of course, $\vec{p} = m \vec{v}$. Why is it that if the net force $\sum \vec{F}$ is constant (which ...
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### In coordinate-free relativity, how do we define a vector?

Relativity can be developed without coordinates: Laurent 1994 (SR), Winitzski 2007 (GR). I would normally define a vector by its transformation properties: it's something whose components change ...
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### Photo of reflection in magnifying mirror shows normal magnification. Why?

I just took a picture of myself in one of those magnifying shaving mirrors and in the photo I am unmagnified! Why is this?