# All Questions

295 views

### Do Cooper pairs act like Cheshire cats?

Could the pairing up of electrons be explained by their spin being in a different position? What would separating the spin from an electron in matter do in theory?
164 views

### How would you explain the cause of earths magnetism to an 8th grade student

What would happen if I freely suspend a bar magnet at north pole, will it become vertical? I am the 8th grade kid.What would happen if earth brakes into two pieces,will there be new north and south ...
17k views

### Is the Earth negatively or positively charged?

The Earth carries a negative electric charge of roughly 500 thousand Coulombs. Does that mean the Earth is negatively charged?
275 views

### Do electromagnetic waves have endpoints?

When learning about electromagnetic waves at school we never talked about any endpoints as we did with standing waves, so I assumed that light has an endless length, but that doesn't make sense. So my ...
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### Transport theorem derivation question

I am trying to rigorously go through some fluid mechanics proofs and theorems. I am currently going through a proof related to the transport theorem and I am having trouble with a step. The steps in ...
178 views

### What software do publishing companies use to create drawings for text books?

What software is used to create free body diagrams, inclines, springs and so on in the introductory physics textbooks ? I know Adobe, Luxology, and many others could, but I am more interested in ...
34 views

### Are “phase-specific” masks ever used in the context of double exposure lithography? Can these sorts of things exist?

I was recently reading an 08' paper on double exposure lithography: and I was wondering if there existed some material that could be used to create a mask for e.g. a 193 nm light source that was only ...
155 views

### What is the interstellar density of mm sized “dust” particles?

If you assume an interstellar spacecraft of 100 m in diameter traveling to the nearest star - that ship would plow through 3 x 10^20 m^3 of interstellar space. At 0.5 c the energy release of such a ...
388 views

### CP violation from the Electroweak SU(2)$_{weak,flavor}$ by $\int \theta F \wedge F$

Question: Why there is NO Charge-Parity (CP) violation from a potential Theta term in the electroweak SU(2)$_{weak,flavor}$ sector by $\theta_{electroweak} \int F \wedge F$? (ps. an explicit ...
38 views

### Placatory motion of more than two bodies

Recently in a documentary I heard that Newton's law of gravitation very well explains motion of two bodies such as sun and earth. And when applied to three bodies the answer is chaotic and not stable. ...
835 views

### Is Conformal Symmetry Local or Global?

I'm just brushing up on a bit of CFT, and I'm trying to understand whether conformal symmetry is local or global in the physics sense. Obviously when the metric is viewed as dynamical then the ...
211 views

### Is it feasible to transfer energy from power stations to communities via photons instead of electrons?

Electrical wires are relatively inefficient in transferring energy--especially when the place of production is quite far from communities. Would it be possible to transfer that energy via photons? I ...
118 views

### Holographic Image

In a holography set-up, as shown in the figure below, Illumination beam and reference beam both are in phase. The interference pattern generated at the detector contains the whole information about ...
299 views

### Derivation of normal shear stress

I am self-studying this note and I am stuck in the derivation of the normal shear stress. Specifically I can't see how the relations (23) and (24) come about. Specifically, what I don't understand is ...
99 views

### Why don't fogbows appear on clouds?

As far as I know clouds are lot of small droplets condensed in air. If droplets are large enough we see a rainbow. If they are small we see a fogbow. Although the size of the droplets are big enough ...
326 views

### Distributions (e.g., Dirac Delta): confused and unhappy [closed]

I am sorry that the following set of questions is very fuzzy and ill informed. I am a trained mathematician and now studying an undergraduate theoretical physics course. We use distributions. I have ...
121 views

### Do we have a fundamental Hamiltonian for the system of H$_2$O molecules?

From the quantum mechanics(QM) viewpoint, does there exist a Hamiltonian $H$ for the system of H$_2$O molecules? Assume that the number of H$_2$O molecules is fixed. Imagine that by calculating the ...
76 views

### Does thermal energy change within a chamber depending on what's in it, where it is, what it is?

I have noticed that some people will say that, when you put more mass in an oven, it takes longer for both to cook than if just were one. Some others will say that timings are the same. Assume we ...
7k views

### Force applied to wheel in pure rolling motion at contact point with road [closed]

Suppose a wheel with radius $R$ is resting on a non-inclined surface. A torque $\tau$ is applied to the wheel center. In an attempt to prevent wheel from spinning, the ground applies a static friction ...
806 views

### Pendulum water pump - apparent free energy

I've seen plans for a pendulum oscillator water pump that is claimed to pump a large volume of water (100 gallons) from a well of 100 feet deep. The pendulum consists of a 100 pound weight raised 6 ...
684 views

### Is there any optical component that uniformizes the incoming light?

Is there any optical component in existence that uniformizes randomly pointing rays?
3k views

### What keeps mass from turning into energy?

I understand the energy and mass can change back and forth according to Einstein. It is fluid; it can go from one to the other. So, what keeps mass from just turning into energy? Is there some force ...
1k views

### What are mass eigenstates?

According to Wikipedia Neutrino oscillation arises from a mixture between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in ...
78 views

### How to prove the equivalence of two definitions of the scattering cross section

I have noticed that there are two definitions of differential scattering cross section in non-relativistic quantum mechanics. One of them is the most popular, particularly it is used in the book of ...
127 views

### Optical coherence tomography

In Optical Coherence Tomography, Broader bandwidth/low coherence light sources are used. Is it only because to increase the resolution or are there any other reasons? What will happen if we use a high ...
116 views

### With respect to what quantities do I vary Lagrangians in field theory?

I have recently been wondering, with respect to which quantities (covariant or contravariant) one should vary QFT Lagrangians and whether there is some rule regarding this. Let me give an example ...
215 views

### Confocal Microscopy

In the context of Confocal Microscopy literature state, "spatial rejection of out of phase light".Is that mean only light which is pass through the pinhole is used and the rest is blocked ?
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### Why isn't ray optics applicable for marginal rays?

I have been studying light and going a little bit ahead I studied about ray optics and one thing each book had in notes is ray optics is applicable only for paraxial rays not marginals rays, I was ...
416 views

### Is the spin 1/2 rotation matrix taken to be counterclockwise?

The spin 1/2 rotation matrix around the $z$-axis I worked out to be $$e^{i\theta S_z}=\begin{pmatrix} \exp\frac{i\theta}{2}&0\\ 0&\exp\frac{-i\theta}{2}\\ \end{pmatrix}$$ Is this taken to ...
112 views

### Stacking Shelves with Overhang

I want to stack some boxes which are 14" x 10" with some 12" records inside. This means that there will be a 2" overhang outside of each box. I know that to have an item to balance on a edge 50% of ...
235 views

### Is it possible to determine the universality class of phase transitions by just analysing symmetry?

Since phase transition is closely connected with symmetry, I am wondering whether it is possible to determine the universality class of phase transitions just by symmetry? Actually, I found it is ...
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There is something I don't fully understand. When I have a problem like this: Let's look at a system with $j_1=1$ and $j_2=2$ spins. Let our system be in the state in which the total spin is $2$ and ...
6k views

### Unbalanced wheatstone bridge

Suppose I have an unbalanced Wheatstone bridge (resistances $R_1, R_2, R_3, R_4, R_g$), to which I apply some voltage $V$. I need to find the voltage across the the galvanometer. Solving the system of ...
139 views

### Can the electric field — always — be derived from the potential?

After studying the definition (& derivation) of the potential to an electric field and the Poisson equation I'm currently wondering whether the following is possible: Can one give an example of ...
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I am having difficulty of finding more basic information on warped geometries. All the standard textbooks are not covering it. In the wiki article it's only said that warped geometry is the one which ...
90 views

### How does a transverse wave propogate in a medium?

I have been told that trasverse wave propogates by the oscillation of medium particles in direction perpendicular to propogation. Consider a wave on a taught string (x-y plane). What is the ...
70 views

### Find out ground sates for large 2D classical spin model

Reaching the ground state of a large 2D classical spin model (e.g. classical Heisenberg model) might be a relatively difficult task while using conventional "flip/reject" Monte Carlo method. The ...
2k views

### Is a real life electric shield possible? [closed]

I got this question from playing games like Halo and Borderlands (I know kinda dumb but raised a good question) in which the primary protection is an electric shield. Now I'm wondering if it would be ...
232 views

### How is Momenergy frame independent?

momenergy = mass * spacetime displacement/proper time for that displacement What I dont understand is how can the momenergy be frame independent? The unit-4 vector always points in the direction of ...
193 views

### Does electromagnetic radiation make sense in one dimension?

I'm trying to do a simple simulation of a 1D charged quantum particle, which gets irradiated by an electromagnetic wave — in context of non-relativistic QM. The Schrödinger equation for such a ...
2k views

### Why does light travel at finite speed? [duplicate]

We have known for quite some time now that light travels at a finite speed of 3x10^8m/s (approx) through vacuum. But why is that? Why can't the speed be infinite? Or at least higher than the current ...
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### Do these steps demonstrate that acceleration of charged particle is proportional to current?

One formulation of Maxwell's Gauss Law for electric field is: $$\bigtriangledown E = 4 \pi k \rho$$ This can be worked into the Divergence Theorem as follows: \int\int_{A} F_\perp \:dA= 4\pi k ...
184 views

### In Jackson's expression for the electrostatic Green function, why is the Laplacian taken with respect to the primed coordinates?

Jackson writes, The function $1/|\mathbf{x} - \mathbf{x}'|$ is only one of a class of functions depending on the variables $\mathbf{x}$ and $\mathbf{x}'$, and called Green functions, which satisfy ...
641 views

### Is energy released during change of state?

When a substance changes state from solid to liquid, the temperature of the substance remains the same and the heat energy from the external source is converted to potential energy within the ...
3k views

### Exactly how much lift is needed to overcome the weight of an average person?

I am designing a "glider" of sorts, and I have some basic questions about the physics involved to get me started. How much lift is required to overcome the weight of an average person, say 150 pounds? ...
217 views

### Quantising the Electromagnetic Field in QED

How exactly do you derive this result?
433 views

### Block Sliding Down a Plane (Perpendicular Velocity)

I'm having trouble understand the concepts for this problem. Here's the problem: A block is placed on a plane inclined at angle $\theta$. The coefficient of friction between the block and the ...
275 views

### Did the Goudsmit-Uhlenbeck analysis of spin consider relativity?

It's frequently mentioned in introductory quantum mechanics texts that Goudsmit and Uhlenbeck conjectured that the magnetic moment of an electron was due to angular momentum arising from the electron ...
Imagine three different worlds describe by three theories (I), (II), (III). Theory (I) - compact U(1) Chern-Simons: A compact U(1) Chern-Simons theory with magnetic monopole charges $m_1$. ...
The electromagnetic tensor is given as: $$F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu A_\mu$$ How do you derive this? And how come there is a partial derivative in ...