# All Questions

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### Light absorbs and Color [closed]

I'm curious about how the material absorb the light and reflect the light back as colors in a sense of Quantum Mechanics (Quantum Electro Dynamics) Does Hadron related to the absorbs of photon ? or ...
1k views

### Upthrust vs Drag

24: A ball is falling at terminal speed in still air. The forces acting on it are upthrust, viscous drag and weight. What is the order of increasing magnitude of these 3 forces? ...
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### How do you know which way to choose the limits of an integral?

I am reading http://www.feynmanlectures.caltech.edu/I_13.html#Ch13-S4 In the beginning of equation 13.18, in which Mr. Feynman calculates the potential energy of an object outside a spherical shell, ...
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### How do substances with like charges repel each other?

I have read in a number of places how substances with opposite charges attract each other: The excess electrons in the one substance repels the electrons in the other substance so that they move away ...
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### E and B field from Time Varying Current

How would I go about calculating the B field and E field from a time varying current charging a capacitor. Theoretically I feel like a solution should exist, but there seems to be a dependence between ...
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### Is space-time a special form of energy?

I know space-time can be influenced by matter and energy, so it must be somehow mingled in with the mix of it all, but does space-time have a fundamental particle? Can we make a little bit of ...
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### Quantized coefficients of Chern-Simons action and F $\wedge$ F $\wedge \dots$

We know that for U(1) gauge field Chern-Simons action in 2+1 Dim(ension), we have an action $$S=\alpha \int A \wedge dA$$ with $\alpha=k/(4\pi)$ for a proper level quantization. Here $k$ is the ...
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### Find values of $x$ such that the probability density $|\Psi(x)|^2$ of a wave function is maximized

How do I find the values of $x$ for a given wave function $\Psi(x)$ such that it's probability density function $|\Psi(x)|^2$ will be maximized? My guess is to to constrain the derivative by the ...
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### Topological phase in Laguerre-Gaussian transverse mode

Why is the topological phase in a Laguerre-Gaussian transverse mode is the sum of orbital angular momenta per photon, and why is it quantized?
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### Space-time Topologies?

When it comes to questions of existence of bounds for PDE's and such, one must often make some assumptions regarding the topology of the space-time to use well known theorems. My question is ...
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### What is the cause of Special Relativity [closed]

Why does special relativity exist? Via studying the outcome(s) of such relativity, one can end up with all the equations involved in special relativity. Thus one runs into things such as contraction, ...
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### Does the wave function of a particle completely describe the state of the particle?

In classical mechanics, if you know the position and momentum of a particle at time $t$ and the Hamiltonian, you can predict the particle's position and momentum at any time. In quantum mechanics, if ...
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### Why can't microwaves use molecules' dipole moments to cool?

My understanding is that microwaves use the dipole moments of water molecules to heat things. The microwaves resonate with the dipole moment, and add energy to the system. How exactly does the ...
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### What is happening to the electrons, and E & H fields, in an antenna with a standing wave inside?

Diagrams like the one shown below are often shown to explain antenna theory, but I have always had problem with the concept of voltage being a wave, and because of this the diagrams never make any ...
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### What does $\left|x,t\right>$ actually mean (Heisenberg picture)?

I am pretty much confused with this notation I believe. The Heisenberg states are denoted by $\left|x,t\right>$ and the Schrodinger states are given by $\left|x(t)\right>$. It seems like both of ...
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### Can I measure a journey time < 100 years on a 100 light year voyage? [duplicate]

So, I'm traveling to another star 100 light years away in my spaceship. This ship has a solar sail pushed by a laser beamed from my home star system, so can achieve a velocity close to c. It's also ...
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### Differences between strong, weak, and micro lensing distinct or subtle?

In gravitational lensing, there are three categories of lensing: strong, weak, and micro. As I understand it, strong lensing (just as the name implies) occurs when a source and a gravitational lens ...
9k views

### How does a spinning electron produce a magnetic field?

I learned in my undergraduate physics class that atoms have magnetic fields produced by the orbit of electrons and the spin of electrons. I understand how an orbit can induce a magnetic field because ...
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### What would the gravity be like if Earth and the moon were touching?

What would the gravity be like if Earth and the moon were touching? Assuming the moon keeps its form and doesn't collapse on its own weight, would the area between it and the Earth (point B) have ...
2k views

### Thermal physics question, final temperature of ice and water

Here is the question from my textbook: "In an insulated vessel, 250g of ice at $0^{\circ}$C is added to 600g of water at $18^{\circ}$C. What is the final temperature of the system?" The solution ...
1k views

### Would atmosphere of Jupiter blow up if I launched a atomic bomb there? [duplicate]

This is based upon an question I had, since in Jupiter there is no oxygen a simple fire cannot be started let alone even happen due to its temperature. Anyway that being said, If I somehow used a ...
242 views

### Terminal velocity?

I am having a problem with a particular concept. Here is where I have gotten, since the ball never loses contact with the stair, it will rotate around through the edges, the edges being the pivot, ...
109 views

### Direct rocky planet formation without protostellar disk?

Inspired by this question, which sort of asked what I'm asking, but emphasized a different point (and the answers accordingly addressed that). Can a rocky planet form directly from the collapse of ...
3k views

### Temperature of ideal gas after volume increases in piston

A three part question, all related Part 1. My question is about an ideal gas in a rigid container with two (equal volume) compartments separated by a rigid wall. One compartment has an ideal gas at ...
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### Quantum Temperature?

I was thinking if temperature is proportional to the rate at which energy is transferred then does it exist on a quantum as well as a classical scale? If so what is it proportional to exactly?
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### Rocky Planet in the center of System [duplicate]

We all know that mostly stars are at the center of planetary systems, but is it possible that instead of a star there was a rocky planet in the center with stars (and other planets and moons) orbiting ...
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### Reference frames and speed of light

If the speed of light is a constant, and the universe is expanding, wouldn't shining a light in the direction of the center of the universe have a different color (frequency and wave length) than ...
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### Kinetic energy of a gas molecule

I am working through the derivation of the equation $$pV=\frac13mNC_{rms}^2,$$ but relating to this formula my textbook states that the kinetic energy of an average molecule of gas is given by ...
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### Relative error of equivalent resistance of resistors in parallel

I just saw a formula in my book for relative error in equivalent resistance of two resistors connected in parallel. $\frac{\Delta R}{R^2} = \frac{\Delta R_1}{R_1^2}+\frac{\Delta R_2}{R_2^2}$ ...
169 views

### Electron in the proximity of a magnetic monopole

I am puzzling about an exercise in the book "Electromagnetic Theory" by Ferraro (p.543). An electron (mass $m$, charge $-e$) in a monopole magnetic field ...
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### Why do we need an old perturbation theory?

There are two types of perturbation theory corresponding to explicit lorentz-covariance of amplitudes. The first one is called Rayleigh-Schrodinger perturbation theory. It is based on following ...
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### If I had a 1cm iron sphere that I could vibrate at an rate, how fast would it have to be vibrating before it could not perceived by sense of touch?

Is there a vibratory rate at which my hand would just pass right through the object and it could not be perceived by touch anymore?
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### Earphones and electric guitars

I remember being in my college dorm, watching a film with a friend. His computer wasn't loud enough and we couldn't hear properly. So he took his earphones and put them on a electric guitar coil. He ...
451 views

### Euler-Lagrange equation for continuous systems

I'm having a little trouble with wrapping my head around a part of a method which is fairly 'new' in some fashions to me. I imagine it should be fairly obvious, but I am not seeing something at the ...
630 views

### Chemical potential in Thermodynamics

In many scenarios, on computing the partial derivative of the internal energy (U) with respect to mole number (N) is negative. This implies that adding more moles of the substance decreases the U of ...
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### $D$-brane and 5th dimensions

While I was looking up the 5th dimension of the Randall-Sandram model, I have wondered whether Kaluza Klein theory can be applied to the $D$-brane or $p$-brane. Can the $D$-brane and $p$-brane ...
343 views

### Non Adiabatic Coupling Term in Born Oppenheimer Approximation

I am attaching a section from a text book (Conical Intersections Electronic Structure, dynamics and spectroscopy: David R Yarkony & Horst Koppel). Here I am not understanding the so called 'Non ...
131 views

### Does squeezing a vacuum state produces photons?

A squeezed vacuum state is produced by applying a squeezing operator $S$ on the vacuum state $|0 \rangle$: \begin{eqnarray} S | 0 \rangle = \sum_n C_n |n \rangle \end{eqnarray} My question is, from ...
129 views

### Duality behavior of light and effect of system scale on its behavior [closed]

Does an electromagnetic wave that makes by antenna behaves purely as wave for all the times? or it can change its behavior as photon? and does the scale of system effect on behaving as EM wave or ...
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### does space-time expansion affect on fundamental particle? [duplicate]

does space-time expansion affect on fundamental particle or point particle?
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### Chasing a photon [duplicate]

According to this article, the Theory of Special Relativity holds that if you were chasing a stream of light at half the speed of light, $c/2$, the light's speed relative to you would still be $c$. ...
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### Stopping an isolated metal ion

If we obtain something like a single isolated hydrogen atom I.e. $H^+$ is it possible by keeping it in a system of charged rings to contain and stop it at the centre of the system? Any positively ...
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### modern physics :emission spectrum [closed]

If in a hydrogen atom all possible transactions take place. The ratio of maximum frequency to minimum frequency is 135/7.what is the principal quantum number of excited state. The max frequency case ...
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### Lattice Gauge and Spin Network

I see the similarity between the Lattice Gauge and Spin Network . (For example , the both theories depict the node part as quantum (the latter is explained as spin)) Are there any other ...
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### When can we take the Brillouin zone to be a sphere?

When reading some literatures on topological insulators, I've seen authors taking Brillouin zone(BZ) to be a sphere sometimes, especially when it comes to strong topological insulators. Also I've seen ...
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### Trying to understand explosions

I’m trying to understand the nature and amount of energy/force generated in an explosion. Take, for example, the explosion that results from the complete annihilation of one gram of matter, releasing ...