# All Questions

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### Why can an electric field escape from a black hole?

I know this is a duplicate question but the other answers didn't explain clearly my problem. The talkes about no hair theory for explaining the communication and information problem of matter inside ...
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### Flux through a face of a cube for an arbitrary position of a charge

Consider an imaginary cube with edge length a in space. A charge q is placed at the centre of one of the faces of the cube. So, what is the electric flux through the face opposite to the charge? ...
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### Why is the detection of gravitational waves so significant?

Since there is to be an announcement by LIGO about this today (11 Feb. 2016), I was wondering why the detection of gravitational waves was so significant? I know it is another confirmation of ...
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### electric potential and other potentials

We know that without potential difference no electric current can flow.If two conductors carrying positive and negative charge respectively then the first one will have positive and the rest one will ...
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### Relation of conformal symmetry and traceless energy momentum tensor

In usual string theory, or conformal field theory textbook, they states traceless energy momentum tensor $T_{a}^{\phantom{a}a}=0$ implies (Here energy momentum tensor is usual one which is symmetric ...
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### Deriving Boyle's law from only the Gay-Lussac laws

My physics professor during a lecture presumably mathematically derived Boyle's law from the two Gay-Lussac laws for ideal gasses. What he said is also printed in his own textbook. He states that, ...
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### Polka dot beamsplitter. Is it good for gaussian beams

I am doing pump probe and I am looking for beam-splitter which will not affect beam polarization too much, as I intend to measure polarization dependencies. I have heard of polka-dot beam-splitters ...
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### Energy, Power, normalized time-series [on hold]

Given the following (productino of an energy-plant): Total energy production for a year (in Wh) Normalized hourly production ( 0 - 100%): For every hour a value: 100% means full production; 0 % ...
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### Why do we assert Hulse–Taylor binary system's orbital decay to gravitational waves and not radiation?

From https://en.wikipedia.org/wiki/PSR_B1913%2B16#Star_system The Hulse–Taylor system's orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of ...
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### Is Lorentz Invariance necessary for Maxwell Equations?

An example shows that Maxwell Equations do not need Galilean invariance, therefore Lorentz Invariance is not needed for Maxwell Equations. The example: In a train moving at a constant speed relative ...
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### Heat and mass transfer modes inside rapidly rotating cylinder

My question is about simultaneous heat and mass transfer in rotating cylinder system. System can be detailed as: A rotating cylinder contains wet porous substance in a lump shape. Air stream enters ...
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### When is the spin of an electron changing?

An electron can have a half spin up or down. The up spin can become a down spin to lose his weak charge. But when are electrons changing their spin?
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### Basic question about valence/conduction bands

In most introductions to solid state physics that I've read, they explain the origin, basically, of the band gap as follows: By doing a superposition of the standing waves inside a BZ, one can find ...
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### Understanding the CSV data for hysteresis curve

I have performed an experiment to evaluate the slope between H and B. In order to do that, I did the hysteresis experiment in oscilloscope. In the oscilloscope I found a curve like this After I ...
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### Why the quantization of things is “forbidden” by classical physics?

I would like to know why we say that what gave the idea of Quantum Physics was the fact that things appeared to be quantized Why is it impossible to quantize things in classical physics? Why ...
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### How to understand that Higgs does not imply circular reasoning?

From what I understand about Higgs (boson/field) it gives mass to subatomic particles. When it interacts a lot with the fields it gets a great mass (like a top quark) and when it interacts a little it ...
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### Neutron scattering off molecules

From neutron scattering off molecules it is possible to get information about molecules' geometry. Given the size of a particular molecule, what are the criteria for choosing the wavelengh of the ...
51 views

### Can black holes with the same mass evaporate with different speeds?

I am curious about the following observations: (1) For a normal Schwarzschild black hole, it evaporates according to $dm/dt=-1/m^2$; (2) We have eternal black holes which do not evaporate (though ...
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### Meaning of $R=0$, $R_{ab}=0$. $R_{abcd}=0$.

First let me state some definition The Einstein tensor is given by \begin{align} G_{\mu\nu} = R_{\mu\nu} - \frac{1}{2} g_{\mu\nu} R \end{align} and note that \begin{align} G^{\mu}_{\phantom{\mu} ...
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How will we derive the component of electromagnetic field tensor by using the electromagnetic field tensor formula; what is the procedure? Can anyone tell me about how I would derive $F_{00}, ... 4answers 112 views ### How do they find the energy of a photon? Is the actual energy of a photon ever measured? How is it done? I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ... 0answers 15 views ### What is the mass defect of stable nucleus? [on hold] What is mass defect of stable nucleus? A-positive B-zero C-negative D-less than unstable nucleus 0answers 20 views ### Converting a Bell state to a less entangled state by LOCC [on hold] How can I convert a maximally entangled state,$ \frac {1} {\sqrt2} (|00\rangle +|11\rangle) $, to a less entangled state like, $$cos(\theta)|u_0 v_0\rangle + sin(\theta)|u_1 v_1\rangle$$, by using ... 2answers 111 views ### A classical explanation of why there is a speed limit in the universe The question is - is there any flaw in this explanation, or it is the right explanation in general language? Let me break the explanation into two parts - (1) Why there is a certain speed of ... 2answers 28 views ### Confusion in understanding the derivation of wave speed from Newton's Second Law In the book 'Principles of Physics' by Resnick,Halliday and Jearl Walker,the opening para of derivation of wave speed from Newton's Second Law is such: Let us consider a symmetrical pulse moving ... 2answers 16 views ### How to determine the friction constants We know that the friction is formulated in this form $$F=av+bv^2+Nμ$$ I'm working with an object and surface and I want to find$ a, b, μ $for them. Can you please give me an experimental method ? 0answers 47 views ### Why do you believe in [on hold] Is it possible that gravity doesn't exist? 0answers 63 views ### What can be the way of the light [on hold] All we know that from the Sun to the Earth is comming light. But what can be the motion of the one particle of the light? Its have the source of the light Sun and opened eye on the finish of this ... 1answer 23 views ### Wave optics physics When does monochromatic beam of light incident on a reflective surface get completely transmitted.according to the question what exactly the word transmitted means? I'm little bit confused .could you ... 0answers 10 views ### circular motion pf hc verma [on hold] a particle of mass m rotates with a uniform angular speed 'w' . It is viewed from a frame rotating about the Z-axis with a uniform angular speed 'z' the centrifugal force on the particle is 1answer 19 views ### How to apply torque impulse In the below question, can we apply conservation of Angular Momentum? If not, why? Moreover how do we apply Torque impulse to the system ? The contact force between the cylinders will be normal to ... 0answers 11 views ### damage a size D tourch battery will do when thrown forward out a moving vehilce doing 80 kmh What damage would a size D tourch battery do when thrown hard in a forward direction out a moving vehilce doing 80 km at another vehicle in front of it doing the same speed and would the battery ... 1answer 39 views ### Physical Nature of the electric field of the current in a circuit [on hold] As most of us know that the electric current in a conductor is due to free electrons moving in the conduction band of metallic conductors. What makes them move ? An electric field of course. Today my ... 2answers 79 views ### Successor to Copenhagen Interpretation as Orthodox Interpreation of Quantum Mechanics First, I read the questions FAQ for this and I hope this does not violate the rules. I am not asking for personal opinion, but for observations of hard evidence of trends on this subject. When I ... 1answer 24 views ### Question about the Blandford–Znajek process I've been trying to understand the Blandford–Znajek process which explains how Gamma Ray Bursts form, but it's still not clear to me how it works. In this article, several theories about the formation ... 2answers 55 views ### What is the Benefit of Plotting a Log of Net Force vs. Log of Acceleration Graph? In preparation for a quiz, I've been going over a set of sample questions. One question in particular asks that if I am to graph the logarithm of the horizontal net force of a system vs the logarithm ... 0answers 14 views ### event horizon vs apparent horizon ramifications If the event horizon doesn’t exist in the 2-dimension or 3-dimension time-space - and it doesn’t exist if it can’t be measured or observed - then an apparent horizon would be necessary to reconstruct ... 1answer 21 views ### How do buoyancy control devices (BCD) work? I get that having more air decreases density and increases buoyancy. However, we can take the diver-BCD-oxygen-tank to be a single system. How can the pumping of air from the tank into a vest around ... 3answers 38 views ### How do we determine the pressure at the surface of a star? Is there any means to do so? I know there are some means to determine the surface temperature. 2answers 31 views ### Free falling object with air resistance, what's the velocity as a function of time? So, I'm looking into how velocity can be represented as a function of time when the air resistance is also function of velocity. The force of drag is $$F_d = C||\vec{v}||\vec{v}$$ where$C$is an ... 0answers 59 views ### Are there any open questions in physics that a layman can analyze? [on hold] In math, there are questions like "What is the minimum number of crosses that this knot has?" which can't fundamentally be solved and simply take a lot of trial and error for an answer. This means ... 1answer 24 views ### Can we determine the surface temperature of stars other than the sun by using the black body radiation theory? It is well known that the surface temperature of the sun can be determined by fitting the solar spectrum to the black body radiation spectrum. Is this scheme feasible for other stars? Possibly the ... 1answer 26 views ### Why does a dynamical gauge field accompany fractionalisation? I'm trying to understand fractionalisation, of which spin-charge separation is an example. I've read that this is accomplished by introducing a Lagrange multiplier field, which becomes a dynamical ... 1answer 27 views ### Calculating stopping distance of a car on a slope I'm having trouble setting up a homework problem properly. We are given the following: A given car can brake to a stop from a speed of 60.0 mi/h in a distance of 123 ft on a level roadway. What ... 1answer 80 views ### Can a particle have an imaginary mass? Now, I'm not very involved in the physical sciences, beyond some high-school classes - though I did listen to some college lectures for physics. I was reading "Do Tachyons Exist?" by John Baez, which ... 0answers 24 views ### Scattering in Black Holes Let's take your favorite Black Hole and consider the scattering problem for a scalar field around it. Suppose that the Klein-Gordon equation can be separated in the radial and the angular part. Which ... 1answer 26 views ### Degenerate perturbation theory I don't understand the part about turning off the perturbation. What is meant by or what is he referring to when he says "upper" and "lower" states. Why must the "upper" state reduce to a ... 1answer 20 views ### What do I need to calculate UV intensity? I have a mineralogical UV lamp that I want to use for some research, I only know it's wavelengths. To calculate the µJ/cm3, what else is needed? Distance, time, wattage? Is the value I'm looking for, ... 1answer 92 views ### Which non-Copenhagen interpretations of Quantum Mechanics have actually produced something useful? The question has most of it in the name. "Useful" may be interpreted as: measurably different from Copenhagen interpretation and true potentially measurably different and potentially true (i.e. not ... 1answer 16 views ### Dependance of diffusion coefficient on size? What's the dependance of the diffusion coefficient on size? More explicitly, suppose I have a particles of characteristic length$l$, dissolved in a liquid. How does$D\$, the diffusion coefficient of ...

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