# All Questions

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### Dark matter or Misunderstanding

Is it possible that the dark matter is simply missed variables in the math? I am not a physicist but examples might include: effects of planetary and galaxy rotation, electromagnetic fields, ...
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### Phase lag between current and magnetic field due to a wire

I am running an experiment in which an AC source generating current at 50 Hz is in series with a resistor and am measuring the current and induced magnetic field in air. Should I expect there to be a ...
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### Linear momentum based question [on hold]

The actual answer is 15km/s. So i think that taking astronauts in the system is incorrect as the astronauts and the spaceship have no common acceleration. So their reduction in weight would have no ...
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### Proving electric field constant between two charged infinite parallel plates

It is known that the electric field intensity between two infinitely long charged parallel plates is constant. I had read that one explanation is that if a test charge is placed between the plates, ...
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### Trajectory Problem On Kinematics [on hold]

A ball is thrown vertically upwards in the air by a passenger(relative to himself) from a train that is moving with constant acceleration on a slope of inclination $\theta$. What will be the ...
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### How is water a worse insulator than air?

I know I must be missing something here. Water has a much higher permittivity than air, which means it has higher (distributed) capitance. That means it can more effectively convert an electric field ...
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### Equation describing Raman gain in stimulated Raman scattering

I am looking for an equation for the Raman gain coefficient gR as used in these following equations describing stimulated Raman scattering. adopted from here. The article mentions that when pump and ...
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### Can electrons jump between levels in same shell with constant $L$?

I see many cases where electrons jump from various energy levels of some $L$ value to various levels of other $L$ value. But is there any transition in same $L$ level between its different ...
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### Why does the merger of 2 identical black holes into mass and volume, generate a black hole with a volume 4 times larger?

I know that the radius is directly porportional to mass, but this result seams crazy. Would be this effect responsible for the universe accelerated expansion? May I say that this effect is black ...
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### Calculating the specific heat capacity of water

So for a thermodynamics assignment I'm doing, I need to build a solar oven and then use that to gather data. That bit's fine. The problem I'm having is that I need to use this data to calculate the ...
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### Example calculation of increase in accessible states upon reimposing constraints in an isolated system?

Can you show me some example calculations of where the accessible states of a system increase upon reimposing the constraints of an isolated system (like moving the piston in a cylinder back to its ...
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### Solving vector equations using matrix

From "Classical Electrodynamics" by Jackson (3$^{\text{rd}}$ edition): \begin{align} \frac{\partial \mathbf{E}_t}{\partial z} + i \omega \mathbf{\hat{z}} \mathbf{\times} \mathbf{B}_t &= \mathbf{...
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### Can the black hole singularity, the point at which the space-time curvature becomes infinite, actually exist in nature?

(1) Can the black hole singularity, the point at which the space-time curvature becomes infinite, actually exist in nature? (2) Please explain in detail about the difference between timelike and ...
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### Error in Fluid Mechanics (2nd ed.) by Landau and Lifshitz [on hold]

In equation (26.11) on page 97 (2nd ed.) the absolute value of alpha should be replaced by 1.
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### When I am on a moving bus and the bus stops abruptly how to cancel the extra motion due to Newtonian Law without holding steel bars in the bus?

Today I was on a City bus. And Newton's first Law hit me hard. I was standing. And the bus stopped suddenly. I fell down. Because of Newton's Law of Inertia, which states: An object at rest stays ...
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### Uniform Acceleration: Pulley Problem

This situation came up in my physics lab. Assume there's 0 friction between mass m and the ground. Given some constant mass M, and you are to vary the mass m, will the acceleration of the block with ...
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### Relation between topological insulators and breaking of time reversal symmetry

Whenever one talks about topological insulators, the breaking of time reversal symmetry is always mentioned. Is there an intuitive reason as to why one need time reversal symmetry to be broken in ...
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### Are twisted versions of supersymmetric field theories supersymmetric on any general four manifold?

Witten in his famous paper (Topological Quantum Field Theory) writes -- " I do not know whether twisted versions of other $\mathcal{N} \ge 2$ supersymmetric field theories will similarly be ...
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### What is the point to ask a question that everyone knows the answers? [migrated]

I've asked the question twice, How central forces work? I gives examples of bodies that have determined position and a defined angular velocity. But these are questions from forbidden knowledge, no ...
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### Electric field due to a line charge in cylindrical coordinates

We have a straight line charge along the $z$-axis from $-\infty$ to $\infty.$ Now, I understand that by keeping $\rho$ and $z$ constant, we have azimuthal symmetry; and, by keeping $\rho$ and $\theta$...
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### Is it possible to create a constant acceleration with a series permanent magnets?

Say you achieve levitation of an object on a track through any means such as superconductivity, electromagnetism, or permanent magnets. Assume for this problem that there are zero frictional forces ...
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### Electromagnetic wave inside a conductor

When considering a coaxial cable it is said that the EM-Wave propagates only in the dielectric between the inner and the outer conductor. But does not also exists a wave inside the inner conductor due ...
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### What does the time reversal of stimulated emission look like?

The lay-person level explanation that we give for stimulated emission goes something like this: because photons are Bosons, they "like" to be in the same state, therefore when a photon is passing by ...
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### “The value of a quantum field at a point in spacetime is not precisely determined” explained in layman’s term

The value of a quantum field at a point in spacetime is not precisely determined. I haven’t studied quantum physics but came across this. Please explain it to me in simple term what it physically ...
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### Why doesn't gravity make the universe have positive curvature?

If mass/energy causes positive curvature in spacetime, and measurements of the curvature of the universe show that it is flat (or very close to flat), then is there something causing negative ...
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### Does an object falling into a black hole appear to become flat for an outside observer?

In special relativity when an object moves close to the speed of light it will appear redshifted due to time dilation. In addition the object will also appear to be length contracted. But what about ...
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### Is there any coincidence that Giza's pyramid coordinate is exactly like the speed of light… i.e 299,792,458 [on hold]

Is there any coincidence that Giza's pyramid coordinate is exactly like the speed of light... i.e 299,792,458 And this bullshit saying that is doesn't meet our standard so i have to extend it soory
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### Magnetic torque

Consider the loop of wire in Figure 29.25a. Imagine it is pivoted along side 4, which is parallel to the z axis and fastened so that side 4 remains fixed and the rest of the loop hangs vertically in ...
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### Box counting dimension of a 2d surface

The box counting dimension of a 2d object say a lake, when calculated by taking the boundary only is a descriptor of the fractal dimension of the 3d surface (here mountain or local topography). ...
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### Can you connect a battery to metal and make it electrical?

I'm writing a book and I need to know if a "defense mechanism" in it would actually work. There is a fire escape ladder (made of metal) leading from a window. The house is completely barred on the ...
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### What set of experiments can I make to derive Newton's laws myself?

I have read this great answer (first one) by joshphysics: Are Newton's "laws" of motion laws or definitions of force and mass? It cleared all my confusion regarding what mass actually ...
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### The minimum value of accelerating potential required to produce the characteristic Kα and Kβ lines [on hold]

can you help me for this exercise ? For an x-ray apparatus containing a molybdenum target of atomic number, z = 42. (1) Determine and explain the minimum value of accelerating potential required to ...
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### Can a solid have a different melting point depending on the orientation of its surface with respect to its crystal lattice?

If we assume the second law of thermodynamics, then it's easy to derive the zeroth law of thermodynamics and then show that since the second law of thermodynamics and zeroth law of thermodynamics are ...
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### What Exactly is a “Supersymmetric Cycle” in String Theory?

In a lot of physics papers I hear talk of "wrapping a stack of D-branes on a supersymmetric cycle in a Calabi-Yau threefold $X$" and I'm wondering if I understand this correctly from a mathematical ...
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### Does aerodynamic heatings at the wall depend on the material of the wall itself?

I am reading "Fundamentals of Aerodynamics" 5th edition, J.D.Anderson. He said: "The slope of the temperature profile at the wall is very important; it dictates the aerodynamic heating to or from ...
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### Does a Helix shaped object floating in water stream rotate?

A Helix shaped light weight object is placed a water stream. Does it rotate? It is pushed by water body, will it also experience turning force and thus rotate?
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### Is it possible to calculate natural gas (i.e. methane) flow in pipe based on temperature and pressure?

Given a known pipe diameter, pressure, and temperature, is it possible to calculate the flow rate of natural gas (i.e. methane et al) in the pipe? To me, this doesn't seem possible without some sort ...
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### Real space chern number for two orbital system

The real space Chern number is given by $C = 12\pi i \sum_{j \in A}\sum_{k \in B}\sum_{l \in C} (P_{jk}P_{kl}P_{lj}-P_{jl}P_{lk}P_{kj})$, where $A, B,C$ are three regions arranged anticlockwise, ...
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It is a geometrical problem which I find difficult to solve reading the Fresnel's paper "Memoir on the diffraction of Light". According to the figure Fresnel sets $z$ as the distance of the element $... 0answers 17 views ### Reflection and Transmission question I have a situation, where I have an expression like$R^2+R_0^2+2RR_0cos2k$,$k$is the wave vector, R is the reflected amplitude,$R_0$, the incident amplitude. So I can write my expression as$(R+R_0)...

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