# All Questions

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### Time variable double slit single photon interference

Has the double slit, single photon interference experiment ever been performed where time is a variable, ie. one photon emitted per day? Would the interference pattern emerge?
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### Is diffuse reflection elastic or inelastic scattering of light and how about with spectral?

If images are lost in diffuse reflection does this mean the light will only scatter inelastically or can it be elastic as well?
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### Torque, need help understanding a solution

https://www.scribd.com/doc/100022472/Monbukagakusho-Physics-2010-Solution Problem B. This guy's answer just doesn't make any sense at all to me but he did arrive somehow at the correct solution. If ...
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### How does Einstein's curved space time produce acceleration in a free falling object?

I never really thought much about all of this before so I'm definitely a newbie. Please excuse my ignorance. If I understand what I have read so far: if spacetime is curved time would click by at a ...
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### Work done on an object by the internal forces

How is the work done by the internal forces acting in a rigid body zero? Actually I read in a book an example for the same. Let me present that example here. Consider a rigid body having two ...
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### Do electrons in a CRT emit radiation?

According to electrodynamics, accelerating charged particles would emit electromagnetic energy as radiation. Isn't it applicable to the accelerated electrons within a cathode ray tube? Do they give ...
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### How can there be an infinite number of universes? [on hold]

Many proponents of the multiverse (Greene, Krauss, perhaps Hawking) have posited that there may be an infinite number of alternative universes. How could this be possible, or even understood? ...
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### Ampere's law and Stokes' Theorem for current density

In both Griffiths and Jackson, Ampere's Law (or conversely the curl of the magnetic field) is derived by applying Stokes' Theorem to the surface integral of the current density J. The argument relies ...
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### An example of a theory that respects the Weak Equivalence Principle but violates the Einstein Equivalence Principle

The Weak Equivalence Principle has any one of the following forms: the inertial mass is equal to the gravitational mass there exists a preferred class of trajectories through spacetime, known as ...
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### Particle in a box, quantization of energy

I'm learning about how the energy of matter is quantized like how the energy of light is. My textbook illustrates the concept of quantization with the particle in a box: "A particle of mass $m$ ...
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### How many pieces of paper to the length of the observable universe?

Correct me if I'm wrong, but if you fold a piece of paper to the point where it's a long stain of atoms, you would need 601 pieces of paper to get to a light-year. That would mean that you would need ...
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### A problem on Doppler's Effect [on hold]

A source of sound emitting a frequency of 660 Hz is moving counter-clockwise in a circular path of radius 2 m with an angular velocity 15 rad/s. A recorder at a distance from the source is moving ...
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### how to apply capstan law? [duplicate]

I am having trouble to apply Capstan Law. I don't know which side is supposed to be the large force and which the small. If you have a capstan that doesn't rotate, and you have a mass 1kg from one ...
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### Is magnetism just electricity in a different FoR?

I am trying to understand magnetism and its relation to electricity: Suppose there are two electrons travelling side by side in deep space at 1 cm distance at .99 c In this article it is said that ...
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### Relation between Canonical and Grand Canonical Ensemble for a two levels system

For a two-level system of classical non interacting distinguishable paricles, labelling energy levels as $+\epsilon, -\epsilon$, in the canonical ensemble I found for the partition function ...
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### EM: invariant property in electromagnetic relativity

I have problems answering the following question: "What is an invariant property in electromagnetic relativity? Which of the following is an invariant quantity for the electromagnetic waves?: ...
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### Expectation value [on hold]

Which of the following equations is correct? why?
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I have an AdS space written in Poincare' coordinates and in global coordinates. The transformation that brings one set in the other is a conformal transformation?
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### Are alpha and beta rays also generating electromagnetic rays?

To discover radio waves in 1886, Hertz used electric sparks between two iron balls. These sparks caused radio waves which generated a current between other balls. The oscillating charges caused a ...
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### problem in making hologram (3 sided) [on hold]

why the image become illusion in transparent glass ? (in making hologram).
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### Pauli matrices and $SU(4)$ [on hold]

together with the 2-dim identity matrix, the pauli matrices build a basis of the vector space of the 2x2 hermitian matrices. The set of i*pauli matrices build a basis for the SU(2). Assuming, we ...
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### Can a theoretical object exist as such that its mass overcomes gravitational collapse

A daydream the other day led me to the question if "a universe filled with water (or any other substance for that matter), instead of being mostly void" could exist within the rules of our current ...
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### Electrical and magnetic energy [on hold]

I have problems answering the following question: What is the ratio of the electrical energy to the magnetic energy stored in a unit volume of the atmosphere just above the Earth's surface, where ...
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### Derivation of Euler-Lagrange equation from principle of least action

When deriving the Euler-Lagrange equation for a field $\phi$ the term $$\int\textrm{d}x^{\mu}~\partial_{\mu}\left( \dfrac{\partial \mathcal{L} }{\partial(\partial_{\mu}\phi)}\right)\delta\phi$$ is ...
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### Tidal heating of body

I am trying to make a plausible, though not necessarily accurate model of tidal heating of a body moving close by a gravitational attractor, not necessarily in orbit and not considering the spin of ...
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### Infrared Camera spectral filtering with an uncooled camera? [on hold]

I have been doing experiments with thermal cameras and stumbled upon CO2 detection. Having ordered a filter I was full of joy and immediately tried it out - nothing happened. So I talked to the ...
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### EM waves: Circularly polarized light incident at Brewster angle

I am having problems in answering the following question: " Circularly polarized light is incident at the Brewster angle on a dielectric surface. With explanation, describe the polarization of the ...
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### Thermodynamics : Heat transfer : Conduction or convection?

I have an hot object, that is place in a room of 20°C. My goal is to be able to estimate how warm the object will be in T seconds. To be able to do that, I must first understand what is really ...
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### Simple harmonic motion angular frequency

I'm struggling with this physics question. "A simple harmonic wave of wavelength 16 cm and amplitude 2.5 cm is propagating along a string in the negative x-direction at 35 cm/s." a) Find its angular ...
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### What kind of other light sources can disturb the detection of LASER

My project objective is to detect different lasers , for example Laser Range Finder: pulse width 10ns and repetition rate is ...
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### Torsion-free, symmetric connection and non-coordinate basis

The torsion tensor is defined as (Hawking p.34) \mathbf{T}(\mathbf{X},\mathbf{Y}) = \nabla_{\mathbf{X}}\mathbf{Y} - \nabla_{\mathbf{Y}}\mathbf{X} - [\mathbf{X},\mathbf{Y}]. ...
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### Under what conditions does a beam splitter entangle two input photons?

There is a dispute on PhysicsForums related to what are the conditions necessary for two photons to be entangled by a beam splitter. Lots of references given by the forum users but they never arrive ...
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### How to Calculate Engine Torque from Drive Torque @ The Wheels for All wheel drive and Front wheel drive? [duplicate]

Would it be possible for someone to explain how engine torque is calculated from drive torque at the wheels and how this differs between AWD and FWD. Thanks.
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### How would one attach black hole to starship in the Black hole Starship model? [on hold]

A black hole starship is a theoretical idea for enabling interstellar travel by propelling a starship by creating an artificial black hole and using a parabolic reflector to reflect its Hawking ...
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### Majorara zero mode in Ising chain, not exactly zero subtlety

We know the transverse field Ising model with N sites(open boundary), can be mapped into N free fermions(there are 2N modes if including the negative energy counterparts) With property: ...
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### Intuitive understanding of vector spaces [on hold]

I want to understand the intuitive meaning of vector spaces (Hilbert, Banach, metric, normed). I have read a lot of texts and understand the mathematical formalism given but how does it correspond to ...
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### How do I find the relation between the accelerations of the ring and the disc (see image)? [on hold]

What is the relation between the accelerations of the ring and the disc (see image)? Both the ring and the disc have mass $M$. The ring has a radius $R$ and disc has radius $2R$. They are connected ...