# All Questions

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### Displacement current in the Ampere equation

Does it explain the significance of displacement current in the Ampere equation?
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### Is Gauss's useful to determine the electric field strength of a charge distribution? [closed]

Under what conditions is useful Gauss's law to determine the electric field strength of a charge distribution? Can someone help me with this question?
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### Could someone explain why the alpha angle in the chiral angle proof below is 120 degrees?

Here's the question: Nanotube chiral angle as a function of $n$ and $m$ Can someone explain why the alpha angle in the chiral angle proof below is 120 degrees?
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### Fictional teleportation scenario and conservation of energy [closed]

There are many examples in pop culture where someone can teleport (a mutant in X-Men or teleportation as in Star Trek). There are a lot of scenarios where a character is falling from a great height ...
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### Equal mass on either end of a spring

I'm taking physics this term and this is the first time taking physics in 3 years. Here is my homework question (of course those variables all have values but we'll use variables for now): Consider ...
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### Is the mass of the Earth's atmosphere essentially constant?

Per a few questions and comments on this site such as Huge buildings affect earth's rotation? I wonder, is the mass of the Earth's atmosphere roughly constant? We're burning an incredible amount ...
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### Solving a light ray worldline with the geodesic equation

I'm having trouble solving the geodesic equation for a light ray. $${d^2 x^\mu \over d\tau^2} + \Gamma^\mu_{\alpha\beta} {dx^\alpha \over d\tau} {dx^\beta \over d\tau} = 0$$ I apologise, but I'm a ...
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### What if EM or QCD was spontaneously broken?

Suppose that Standard Model Higgs mechanism broke electromagnetism, by e.g. veving the charged component of the doublet, so that the photon was massive with $m_\gamma\sim v$. Could such a Universe ...
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### How to move an object to follow moving object?

Say you have an object moving increasing on the y axis, lets say 10 points per second to keep it simple. Then you want to have another object on x axis move in from the right, so decreasing x axis, ...
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### Clarification of Landauer approach

I am trying to understand the Landauer approach. Consider the setup: (left contact)-(conductor)-(right contact). For simplicity, the conductor is a 1d wire (the transverse part is not relevant for ...
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### What is the optimal weight ratio of a two-stage rocket?

I've been researching this for some time now and I got stuck. The best resource I've found is this book. The "optimising a multistage rocket" part talks about a three stage rocket but it seems ...
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### What force is responsible for anti-gravity?

I've seen several video which claims that is anti-gravity. I am sure at least one of them, use a kind of electricity to lift an object! (triangle lifter), I would guess electricity lift that object by ...
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### The quickest 6-3 play in baseball: to bounce or not to bounce?

What's the quickest way the get the ball (say from shortstop) into the first-baseman's glove, given some fixed initial (throwing) speed? Directly or with one bounce? I'm fairly sure that the answer ...
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### Limits on stable charged particles

Are there generic model-independent limits on massive stable charged particles (say 10-500GeV)? I mean SU(2)/color singlets with just a hypercharge. For example the LEP search (CERN-EP/99-075) was ...
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### What happens when a ball stops bouncing?

If I were to drop a bouncy ball onto a surface, each successive bounce will be lower in height as energy is dissipated. Eventually, however, the ball will cease to bounce and will remain in contact ...
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### What gives atoms their chemical properties [migrated]

What makes Hydrogen flammable? What makes Oxygen support burning? What makes water behave unlike either components? What gives an element its chemical properties and what makes the compounds behave ...
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### In structural vibration, does energy get transferred between different types of waves in the same body?

I'm beginning to study structural vibration (and statistical energy analysis). While writing out all coupling loss factors (usually denoted by eta) for parts of a built-up structure, this question ...
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### electrostatic repulsion that is troubling me [closed]

Consider a homogeneous ring of radius $R$ made of a thin wire of cross section $A (R^2\gg A)$. A Charge $Q_1=10\mu \mathrm{C}$, uniformly distributed over the ring, broke it apart due to electrostatic ...
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### What really are exotic supersymmetric black holes?

I have just read (in the black holes chapter 14 on p244 of this book Ref.1) that in string theory, when one adds an (electric?) charge $Q$ to a static black hole, one can arrive at an exotic ...
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### Why we call the ground state of Kitaev model a Spin Liquid?

Now we always talk about the so-called Kitaev spin liquid. One important property of spin liquid is global spin rotation symmetry. Let $\Psi$ represents a spin ground state, if $\Psi$ has global spin ...
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### Fitting a circuit scheme to a simpler model

I have to simulate the electric field within a gas filled discharge gap generated by a radio frequency voltage generator. The circuit, provided to me by the experimenters somewhat far away, is given ...
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### Type I' String theory as M-theory compactified on a line segment?

I was considering the S-dual of the Type I' String theory (the solitonic Type I string theory). That is the same as the S-dual of the T-Dual of Type I String theory. Then, that means both length ...
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With reference to these 3 questions . Kindly read all the questions,answers and comments in these 3 links . I wish to get a more detailed and canonical answer that addresses every issue discussed . ...
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### Huge buildings affect earth's rotation?

Does constructing huge buildings affect the rotation of the earth, similar to skater whose angular rotation increases when her arms are closed comparatively than open.
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### If time stops at the speed of light is a photon 'everywhere' at once? [duplicate]

I am not a physicist so excuse my question if it's paticularly stupid. As a particle gets closer to the speed of light time slows down as for that particle as compared to a reference from the ...
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### Why does heat solidify cake batter? [migrated]

Increased vibration causes the atoms in an object to spread out farther away. Thus, with added heat, and object goes form a solid to a liquid to a gas (and then to plasma, with enough heat). Why is it ...
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### Diagonalizing/eigenvalues of the infinite dimensional matrix of N harmonic oscillators on a ring

I have trying to show that the continuum limit of N quantum harmonic oscillators gives rise the the klein-gordon field. However, instead of a usual finite string, I want to do it on a ring. Hence, my ...
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### Question on friction [closed]

Please look at the figure carefully. The question is written, and one has to match the two columns 1 and 2 given under "choices and explanation". Please tell me if I am really wrong, i.e. would you ...
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### Why is a degree Celsius exactly the same as a Kelvin?

How on earth is it possible that the difference between two temperatures in Celsius and Kelvin is exactly the same. Given the historical definition of Celsius, I find it hard to believe that this is ...
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### How (why!?) does one introduce an UV cut-off in dimensional regularization?

This question is in reference to the confusing equation 3.7 (page 14) of this paper. One sees the 1-loop answers in their theory as given in their A.7 and A.8 on page 20. Each of the terms is a ...
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### Was TP Singh right to say that a theory of quantum gravity necessitates the Copenhagen Interpretation?

http://iopscience.iop.org/1742-6596/174/1/012024 In the above link we see TP Singh arguing that only Copenhagen will work for a theory of quantum gravity. Some of his key points are "quantum theory ...
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### Quantization as a functor

Can anyone give an mathematical elaboration of the following statement: Quantization is a functor carrying the category of Hilbert space and linear maps to that of Symplectic manifolds satisfying ...
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### How to draw a ray diagram from focal length, object and image heights?

Q. An object of height 8 cm is placed in front of a lens. It's inverted image of height 4.8 cm is formed on the screen. If the focal length of the lens is 12 cm then by drawing at scale calculate the ...
I am reading the Section 15.9 of Weinberg's book "The Quantum Theory of Fields, vol. 2". Under a shift $\delta\Psi[\chi]$ in $\Psi[\chi]$, we have $$\begin{split} \delta ... 1answer 42 views ### Why do single particle states furnish a rep. of the inhomogeneous Lorentz group? Following up on this question: Weinberg says In general, it may be possible by using suitable linear combinations of the \psi_{p,\sigma} to choose the \sigma labels in such a way that ... 0answers 34 views ### Physical Interpretation of Lorentz-transformed Single Particle states being linear As in this question, let \psi_{p,\sigma} be a single-particle 4-momentum eigenstate, with \sigma being a discrete label of other degrees of freedom. Weinberg discusses the effect of a homogenous ... 0answers 20 views ### Why are non-momentum DoFs of single-particle states discretely labeled? Following the treatment of Weinberg, chapter 2, we consider \psi_{p,\sigma} as single-particle eigenstates of the 4-momentum. Weinberg says that \sigma labels all other degrees of freedom and we ... 0answers 30 views ### What is energy in z \neq 1  theories? In a critical theory with dynamical critical exponent z \neq 1 , which amongst frequency, \omega, and dispersion, E(\vec{k}), may be referred to as ''energy''? I'm confused about this since in ... 1answer 23 views ### Is there a term for the argument of the sine function outside of geometry? Are there similar terms in other areas for the idea the "angle" conveys in geometry? I find that functions for abstract things such as pressure, electrical currents (nothing geometric there) on AC ... 1answer 42 views ### How far to the 'edge' of the galaxy? Wikipedia lists the average thickness of the milky-way to be about 1,000 LY - but where (roughly) within that is the sun currently? In asking this, I'm fully aware that there's no well-defined edge - ... 1answer 41 views ### Why are the magnetic moment and the angular moment related? I've always read everywhere that they are related but found nowhere a satisfactory explanation of the cause 0answers 63 views ### What goes wrong when one tries to quantize a scalar field with Fermi statistics? At the end of section 9 on page 49 of Dirac's 1966 "Lectures on Quantum Field Theory" he says that if we quantize a real scalar field according to Fermi statistics, the quantum Hamiltonian is no ... 1answer 24 views ### Comparison search with repeated elements I am study the Grover algorithm. I want know what's the computational complexity of the best classical algorithm that finds an element in set M with probability p\geq 1/2?. I know in the quantum ... 2answers 72 views ### Conceptually, what is negative work? I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ... 3answers 95 views ### Why do prisms work (why is refraction frequency dependent)? It is well known that a prism can "split light" by separating different frequencies of light: Many sources state that the reason this happens is that the index of refraction is different for ... 1answer 44 views ### Can convection cells evolve in stably stratified fluid? Assume stably stratified fluid but not in equilibrium, e.g. with non-constant temperature gradient for example. Can convection cells be present? Typical example of convection cells is Rayleigh–Bénard ... 1answer 26 views ### How to calculate air resistance of penny dropped from Empire State Building? If a penny is dropped from the Empire State Building, then its speed, without taking air resistance into consideration, is \sqrt{\left(32\frac{\textrm{ft}}{\textrm{s}^2}\right)(1454\textrm{ ... 1answer 52 views ### Does a lightning rod prevent lightning strikes? I was always under the impression that a Lightning rod worked to protect a building by being the tallest part of the building and having a low path of resistance to the ground, thus being a good ... 1answer 67 views ### Explicit form of \gamma^\mu \partial_\mu in the Dirac equation I'm in an introductory particle physics class, and in performing manipulations on the Dirac equation, my instructor expands the \gamma^\mu \partial_\mu term as:$$\gamma^\mu \partial_\mu = \gamma^0 ...
From the above picture we can prove easily $CF = XF$ because CFX is a isosceles triangle. Now if we move the point X more near near P, it will give the same results(I mean we will get again \$ CF = ...