# All Questions

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### Why does a sheet of paper fall slower than the same when rolled into a ball?

It depends on volume but both the sheet and the sphere have the same volume.Does surface area play any role here?
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### Photon energies and attenuation

I hope you can help. I am trying to understand which attenuation effect (photoelectric, compton scatter and pair production) is dominant at which level of photon energy and why. The levels are 10keV, ...
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### One stupid question about Dirac mass term and grassmannian numbers

Let's have Dirac mass term in lagrangian: $$L_{M} = \bar{\Psi}\Psi$$ Lagrangian must be real-valued, i.e., its hermitian conjugation doesn't change it. But due to grassmannian nature of spinor ...
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### Show that the boundary layers diffuse out from the plate with speed $\sqrt{\frac{\nu}{t}}$

I was wondering if somebody would be able to help me with this problem. I know how to solve it using dimension arguments but I'm unsure what is meant by transformation techniques. Any help would be ...
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### What justifies adding phasors' vertical components

I learned that, when superimposing two waves on top of each other to calculate the resulting wave's amplitude, it's helpful to use phasors. From what I gathered, phasors are vectors originating at the ...
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### How does rainbow stay for such long time even it is caused due to raindrops?

Rainbow forms when light rays pass through a raindrop (usually, it can be a watet droplet also) and it undergoes several phenomenon like refraction , reflection , dispersion , But after the rainbow is ...
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### Can an electron go along different paths at once in a circuit

A single electron moves along a circuit and comes to a fork in the wires. The wires separate but come back together near the end of the circuit. From what I know, the electron will travel along all ...
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### Could the Big Bang have simply been two black holes hitting each other at 99% of the speed of light? [on hold]

Given two equally massive black holes moving at 99% of light speed, it seems there would clearly be enough energy for most (99%?) of the mass of both to be ejected and / or radiated well beyond the ...
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### Can one detect a single photon through measuring its impulse/momentum on a mirror?

Can one detect a single photon through measuring its impulse/momentum on a mirror? If the answer if YES or theoretically possible, photon path and interference fringes can be detected simultaneously ...
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### Why does electrostatic energy not obey superposition principle? What does the extra energy term account for?

Energy stored in an electrostatic field is given by $\frac{\epsilon_0}{2}\int\text{E}^2\text{d}\tau$ where the integration is over all space.If $\vec{\text{E}_0}=\vec{\text{E}_1}+\vec{\text{E}_2}$ and ...
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### why we can't see light emitted from tv remote while a camera can?

If we try to see light emitted from tv remote we can see this.while if we try same in camera we are able to see this. Why
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### What is the pressure equation of an ionized gas?

I have $N$ ${\rm H}^+$ gas molecules in a sealed, electrically insulated container. What equation can I use to accurately calculate the pressure of the gas? It seems to me that $PV = nRT$ will not ...
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### How M theory or String theory explains fundamental forces and Quantum mechanical phenomena? [on hold]

How M theory explains fundamental forces gravity,strong,weak and electromagnetic? And how does M theory explains phenomena of light like reflection,refraction,diffraction,interference etc?
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### Question related to charged concentric conducting shells

There is a charged conducting spherical shell given a certain positive charge.Another larger spherical shell is given the same negative charge.The first shell is now placed inside the second shell so ...
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### How to approach proofs in Electricity and Magnitism that involve integrals?

I have read through both Franklin and Jackson's Electromagnetism books and I am able to understand the different proofs involving integrals but when I try to re-derive them on my own later I am always ...
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### Rigourous Treatment of Antenna Theory/Physics

As a rising senior who has finished his QM sequence but not yet done an E&M/optics sequence, but is about to start a research project that will be a large part antenna design and optimization, ...
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### What ice pack formula can hold the largest energy difference?

I recently bought some Freez Pak brand ice packs. The label advertises: "Colder Than Ice". I realize now that it's just a stupid marketing claim, but at first, it got me wondering if they had some ...
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### How to deal with eigenvectors which are not square integrable?

In Quantum Mechanics there is one type of situation I'm still unsure on how to deal with. First of all, I want to make clear I'm trying to understand how to deal with this rigorously. What I'm talking ...
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### Why should physical theories always have a Lagrangian formalism? [duplicate]

I've often heard that every physical theory has some kind of Lagrangian formalism, or a formalism in terms of a principle of stationary action. The Standard Model has one, General Relativity has one, ...
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### Klein-Gordon Field Angular Momentum Operator in Terms of Creation and Annihilation Operators

I am computing the angular momentum operator for real Klein-Gordon field (essentially question six of here (though please note this is not a homework question, I am following through Tong's course via ...
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### Quantum entanglement thought experiment

One can "filter" a collection of electron pairs generated in an entangled (fixed-direction) spin state (e.g. singlet $\left|\uparrow \downarrow \right\rangle - \left|\downarrow \uparrow\right\rangle$) ...
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### Misbehaving singular isothermal sphere potential

The singular isothermal sphere (SIS) is a useful simple model often used in astrophysics. It has density profile: $$\rho(r) = \frac{\rho_0 r_0^2}{r^2}$$ This is well known to have some quirks ...
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### How to produce a given entangled state of two quantum bits?

I was watching Leonard Susskind's video series on quantum entanglement, where he looks at the spins of two electrons. In particular, there are entangled states of the form \alpha\left|\uparrow ...
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### Gravitational waves in general relativity

After reading some concepts of general relativity,is it true that the universe communicate with its different constituents (stars, galaxies, etc...) via gravitational wave? If so, how is that? Do ...
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### Can a fruit fly move through a large bubble without popping it?

Assume what logistics you need to in order for something like this to be possible. Can a fruit fly move through a large bubble without popping it?
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### Field outside of conducting surface held at potential

Problem 1.17 in Jackson (3rd ed). A volume $V$ in vacuum is bounded by a surface $S$ consisting of several separate conducting surfaces $S_i$. One conductor is held at unit potential and all the ...