# All Questions

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### Find the electric field

Let $V=(xyt^3)i+(x^4ta)j$. Find the curl of the magnetic field and the electric field. I've found the curl. I see Maxwell faraday equation links the magnetic and electric fields but how do I apply ...
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### Does expanding space cost energy?

Does the cosmic inflation reduce the energy density proportionally to the volume, or does the inflation "cost" energy? Is space itself "something"?
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### Does this photograph portray double muon impact with nanogold atoms?

1PHOTO 1: Macro-photograph of an NIH/FDA TEM of a nanogold dark stained biological sample projected onto Silver Halide (AgX) photographic gel paper. On June 10 I questioned if PHOTO 1 ...
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### Vectors-a tricky problem

A particle subjected to two equal forces along two different directions. If one of the forces is halved, the angle which the resultant makes with the other is also halved. The angle between the forces ...
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### $m_l=0$ in Hydrogen atom of Scrodinger equation

$m_l=0$ corresponds to s-orbital and the values associated are: $$\lambda=2\pi r/m_l\to\infty$$ It means a wave of of infinite wavelength has a constant height at all values of $\phi$(azimuthal ...
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### Superpositions and expectation values in quantum mechanics

When the wavefunction of a particle is not an eigenfunction of an operator, the property to which the operator corresponds does not have a definite value, Why? Also consider a linear combination of ...
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### Observables in Quantum Mechanics

Studying on own quantum mechanics I came across: Preceeding text: A basic postulate of quantum mechanics tells us how to set up the operator corresponding to a given observable. Observables, ...
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### Determinate the right force intensity given a certain amount of energy to spend

I am using Chipmunk's physics engine to simulate 2D classical mechanics of solid polygons (excellent by the way!). The only way you can alter the spontaneous behaviour of the the simulated objects is ...
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### Sound Interference Practical

ok so we did an experiment where we put speakers 1.5m apart and played a frequency of 330hz. then we had to walk around and find quiet spots and loud spots. the questions we have been given are a bit ...
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### Differences between wave function and set of orthonormal wave functions?

I'm reading a QM book. It first says for wave function: "The state of a physical system (or particle) is completely specified by an entity associated with it called a wave function, Ψ , that in ...
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### An interesting problem on vectors [on hold]

A particle subjected to two equal forces along two different directions. If one of the forces is halved, the angle which the resultant makes with the other is also halved. The angle between the forces ...
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### Double-slit experiment and an experimental laboratory without photons

In order to see interference pattern of an electron, after the shot, an electron must not interact with any photon. So I'm asking how can such an photonless area can be created in the universe? And ...
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### Does yukawa potential of two particles have effect on each other?

Okay,a novice here.Suppose two particle interact with Higgs field.Does The Yukawa potential created by each of them affect each other or the interaction in any way.If so,what is it physical ...
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### Length Contraction in a Particle Accelerator

Consider $N$ particles equally spaced on a circle which are uniformly accelerated to $99\%$ the speed of light. In Newtonian mechanics, the distance between the particles would be $2\pi r/N$ (for ...
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### What is the distribution of energy between the alpha, beta and gamma particles emitted in nuclear fallout per one RAD?

I have been trying to find a relation to be able to convert from RAD to REM. What I found is that I need to know the "quality factor" as some sources call it, which is the effect of different ionizing ...
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Did Feyman suggest even though Q.M. has great predictive power no one will ever really understand it ? Some people have said there may be hidden variables that explain underlying principles of Q.M. ...
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### Why does Pluto's orbit cross Neptune's orbit?

Why does Pluto's orbit cross Neptune's orbit? Is this a fault in Newton's law of gravitation?
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### A question about special relativity theory

We have two sets: set No.1 and Set No.2 as in this picture: The observer is fixed to set No.1 . He sees set No.1 motionless and observes set No. 2 approaching with velocity 100,000 m/s. Each set ...
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### Area covered by particle between it's path and horizontal lines

Question: The maximum range of projectile is R and the maximum height attained by the particle is H. If the area covered by the particle between its path and horizontal line is A, then A = ...
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### Would incense burn at a different rate if oriented differently?

This is motivated by this question in the Puzzling.SE beta about measuring 90 minutes of time using two candles that burn for one hour. (Feel free to read up on that before I spoil the puzzle!) The ...
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### Erosion effect from Coriolis force in a South-to-North water channel?

Imagine we could build a channel (like those cool ones in some countries) but very, very long, parallel to a meridian (ie South-North direction).. The channel would contain water, which would ...
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### Why are magnetic fields so much weaker than electric?

In EM radiation, the magnetic field is $3*10^8$ times smaller than the electric field, but is it valid to say it's "weaker". These fields have different units, so I don't think you can compare them, ...
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### What kind of mirror do i should use for rear projection? [on hold]

i have around 11 inch to make a rear projection for a 94 inch screen. i have tried with a convex mirror (half dome mirror) but the aberration is too blurry on the sides, so i don't know what kind ...
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### Extracting heat energy without a heat engine

Is it possible to extract the molecular kinetic energy from a system directly (without the use of a heat engine / temperature gradient) and convert that to another form of energy, such as electricity, ...
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### calculate force between two magnets [on hold]

I have used a couple of online calculators to estimate the attractive force between two cylindrical bar magnets. Using d=1"; t=1"; x=0.1"; Neo35 (Br=12,300 Gauss): source 1 gives 63.5 lbf source 2 ...
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### How can space be euclidean when light bends?

I have read people arguing that tridimensional space sections of space time continuum (whatever its number of dimensions) appears to be euclidean from empirical evidence. I cannot reconcile it with my ...
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### Maximum curvature in a black hole

If the curvature inside the horizon of a black-hole is not infinite in some quantum gravity theories (as in Loop quantum gravity), then what is the expression of the maximum value of the curvature ...
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### How to simulate rotational instability?

I'm trying to simulate (for an educational game) the well-known effect that rotating objects with three nonequal moments of inertia are unstable when rotated around the middle axis. Some explanations ...
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### Magnetic moment - magnetic field relation without free currents

I'm trying to understand magnetostatics in the presense of ferromagnetic material. But I'm ending up in a contradiction: Lets take a piece of iron: Assuming that we don't care about the hysteresis ...
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### Is this kids experiment a legitimate way to show that air has mass?

Consider the experiment in this link. The experiment includes using a ruler as a lever, with an inflated balloon on one side and a balloon which is not inflated on the other. The aim of the ...
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### Electromagnetic Inductance: Different voltmeter readings from different positions

In the setup below, the voltmeter on the right would read differently than the voltmeter on the left even though they are both connected to point D and point A. This picture is taken from Lecture ...
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### Time of flight for a projectile with stated initial velocity and size at various distances

I've been mooching round the internet looking for an answer to this one and can't find a ready resource, hence the question. In short, I'm trying to discover the flight time of a shotgun pellet at ...
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### Postulate of Quantum Mechanics on Wavefunction collapse [on hold]

There is a postulate in quantum mechanics about wavefunction collapse. Can anyone provide me some intuitive perspective into it along with the concept of projection (I mean mathematical treatment).
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### Has anyone experimentally shown the quantized thermal hall conductivity in Quantum Hall systems?

For background: In a $D=2+1$ state with edge modes described by a chiral $( c_L \neq c_R )$ CFT there is a predicted thermal Hall conductance associated with the gravitational anomaly at the edge. ...
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### Is there a substance that doesn't reflect OR absorb light from the visible light spectrum?

Is there a substance that doesn't reflect or absorb visible light but may reflect light from another spectrum? Is there a theoretical substance that would have these properties? EDIT: Sorry I wasn't ...
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### Lagrangian for FRW metric

For the metric $$ds^2=-dt^2+a^2(t)(dx^2+dy^2+dz^2),$$ $$L= \sqrt{-g_{\alpha\beta}\frac{dx^\alpha}{dt}\frac{dx^\beta}{dt}}$$ How does this become $$L= \sqrt{1-a^2 (\frac{dx}{dt})^2}~?$$ I guess ...
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### Number of Stars vs Value of Omega (Crtitical Density of the Universe)

I may be badly mixing things up here. If I am, please kindly correct me. As I understand it, if the universe was too dense at the start of the big bang, it would have collapsed back in on itself. Too ...
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### Negative energy/mass bounds on de-Sitter spacetime

There exists a Positive Energy theorem for General Relativity in Anti-de Sitter and asymptotically flat spacetimes, but there is no equivalent theorem for de Sitter spacetimes Question: Is there ...
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### how is “ electrostatic discharge of metals” done? Say for example of a sattelite [on hold]

how is " electrostatic discharge of metals" done? Say , for example of a sattelite.