# All Questions

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### Are quantum fluctuations completely uncaused events?

I read here that particles/antiparticles appear and annihilate each other spontaneously in empty space. Since particles appear and disappear in empty space, it would seem that empty space has some ...
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### Optical Simulation Tool [duplicate]

I am a student and trying to design an aperture from which a light will pass will project on a sensor. I tried to find some software simulation tool for this purpose where i can draw the aperture ...
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### Capacitor charging and discharging

I have a conceptual question. The circuit is shown below. Let us assume that the capacitor shown in the figure is of 2.2 micro-farads having rated level of 5 volts and we decide to charge it up to 2 ...
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### Basic concepts in quantum theory to start learning semiconductor physics [closed]

What basic concepts in quantum theory one must known to start learning semiconductor physics?
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### Schrödinger's Equation and the depth of a finite potential well

Before I ask my question, I have to stress: I have absolutely no idea what the math is going on. I've read my textbook, several Wikipedia articles, scoured the internet, and don't feel anymore ...
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### Quantum Field Theory and antiparticles vs particles

Does a particle and its antiparticle share the same field in QFT? If an electron is an energized spot in the electron field, is a positron a less energized spot or even a spot of negative energy (if ...
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### Definition of electric charge and proper explanation

Is there a definition of electric charge and proper explanation of it? It is said "Electric charge is the physical property of matter that causes it to experience a force when close to other ...
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### Do all planets have an electric charge?

Do all planets have an electric charge? If yes, is positive or negative? And how much each magnitude? I have read some articles which really confused me. Some of these articles said that all ...
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### group velocity VS probability current

Think about an electron been accelerated from rest in a static electricfield. If we treat the problem classically, in which the electron is just a point charge. The velocity of the electron would ...
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### Origin of electric charge

Baryons have charges that are the result of a polynomial calculation of their building blocks (quarks)'s fractional charges. But what gives these quarks electric charges? What interactions do they ...
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### How does a microscopes optics expose defects in the users vision?

I've got cataracts in both eyes. My vision is correctable to 20/30, so the cataracts are essentially a non-issue in daily living. But when I use a microscope, which I do daily, (binocular, zoom ...
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### Inertial Frames in Special Relativity

According to the postulates of special relativity, all inertial frames are equal in all respects. Then how does it follow from this, that the space is isotropic and homogenous for an inertial frame ...
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### Kaluza Klein theories, dilation field, and dimensional reduction

I am reading something about Kaluza Klein theories and compactification. I have some conceptual question: (1) Why do we call the fifth scalar field $\Phi$ the dilation field? Is there any scaling ...
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### Equation of motion for a falling rod (with one end touching a frictionless surface)

I have a quick question about the equation of motion for a falling rod (with one end touching a frictionless surface). The end touching the surface is not fixed. I am given the moment of inertia about ...
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### Relation between different quantum excitation energy, mass energy and kinetic energy

When a particle enters an excited state, the energy appears in its quantum wavefunction according to $E = h \nu$. Does the $E$ in this equation also include kinetic energy, and rest mass energy? ...
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### How is the width of a slit related to the intemsity of light passing through it?

Here's a question I got in my final exam this morning. "If in a Young's double slit experiment setup, the ratio of intensity of the bright spot to the dark spot is 25:9, what is the ratio of the width ...
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### Why does a solenoid's field look like this?

My book gives the above diagram but doesn't provide an explanation why the field looks like that. It simply says that the fields mostly cancel leaving the field above. Could someone walk me through ...
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### What is electricity?

What is electricity? I know very little physics. I know that there are neutrons, positively charged protons and negatively charged electrons in a particle. I know that electrons have some role in ...
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### Voltage Drop and Charge Flow

I am hoping someone can help me with understanding voltage drop and charge flow. Here is what I think I know. The voltage drop through a circuit must equal the voltage of the battery source, and ...
243 views

### Do gamma matrices form a basis?

Do the four gamma matrices form a basis for the set of matrices $GL(4,\mathcal{C})$? I was actually trying to evaluate a term like $\gamma^0 M^\dagger \gamma^0$ in a representation independent way, ...
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### In how big percentage of gravity core does play role in?

If something would take whole core of earth and done this $(((coreearth)-(restofearth)):coreearth)*100=X$ What would X be? In short, which part of our planet ...
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### How can I prevent being zapped by static electricity every time I touch a doorknob or handle in the office?

I don't know what it is about this office, but it seems everything I touch (doorknob, bathroom faucet, edge of kitchen sink in the break room), I get zapped by static electricity. It's getting old. ...
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### Quantum State Function $\psi$

If I write in QM at an instant, that the quantum state that describes the particle completely at an instant $\psi(x)=\cos(6\pi x)$. Does that mean $|\psi(x)|^2dx$ after normalisation gives me the ...
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### Can Information Travel Faster Than The Speed Of Light? [duplicate]

Many believe that nothing can travel faster than speed of light, not even information. Personally, i think theoretically information can. Consider this following imaginary experiment: Imagine we are ...
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### Velocity dispersion of galaxies

I couldn't find on web how can I get the velocity dispersion and velocity maps of galaxies from the 3D data cube I get from integral field spectrograph.
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### Questions on electron orbits

I have three questions to ask: Why do electrons (in an atom) specifically move in orbits and not some other type of motion? Where does the energy comes from, for the electron to move at much higher ...
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### Capacitance of bodies with different charge [duplicate]

How does one calculate the capacitance of two bodies with different charges? I was looking at coefficients of potential, but they don't seem helpful.
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### Why does a ballerina speed up when she pulls in her arms?

My friend thinks it's because she has less air resistance but I'm not sure.
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The Earth and the Sun has magnetic fields which shields us from cosmic rays, as a charged cosmic ray particle will loose kinetic energy when its direction is perpendicular to the magnetic field. So ...
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### Refraction problem - limiting radius of observation

I solved this problem but I don't know if the solution is correct. Please, correct me if I'm wrong. There are two mediums, 1 and 2, with absolute refraction indexes $n_1$ < $n_2$, and an observer ...
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### What is Conductance?

What is conductance? I am being said that conductance is inverse of resistance?I do know that resistance is the opposition to the flow of current but do not get conductance? I do know that:it is ...
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### Does limit $\hbar \rightarrow 0$ in Quantum Mechanics mean anything?

Assuming that I learn Quantum Mechanics first, and then I approach Classical Mechanics as a special case of Quantum Mechanics, I will definitely find the relationship between Quantum Mechanics and ...