# All Questions

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### Magnetic field strength beyond wire [closed]

If there is a point beyond a semi-infinite wire at a perpendicular distance r from it then what will be the magnetic field strength at the given point and what will be its direction?
10 views

### Mott dengerate semiconductor as absorber in solar cell

Does dengerate semiconductor—which met the Mott criterion—serve any purpose as an absorber for the photovoltaic effect in solar cell applications?
• 121
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### Does a plasma with plasma frequency $\omega_p$ generate photons of the same frequency?

I know that photon emission in plasma results in a change of energy level of the electrons from excited or ionised atoms. However, I saw that photons of 13eV were created in a helium plasma, but this ...
68 views

### How do you determine the electromotive force when the negative plate of the capacitor is connected to the positive terminal?

$\newcommand{\d}{\mathrm{d}}$We have a square wave source with period $T$ and voltage $V_0$ connected to a circuit which is has a resistor of resistance $R$ in series with an uncharged capacitor of ...
• 219
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### How to take the average of a stochastic differential equation?

I am solving a set of stochastic differential equations and I need some feedback about if what I am doing is correct. Given a vector $\boldsymbol{C}(t)=(C_+(t),C_-(t))^T$, we can writte a set of ...
• 13
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### Criticising string theory [closed]

There are a number of pyhsicists claiming string theory has failed. Some facts: String theory did improve our understanding of quantum field theories in various dimensions and their interconnection ...
• 322
1 vote
60 views

### Lagrange multipliers not obeying classical EoMs

I will ask my question about Lagrange multipliers by using an example in string theory, as this question was inspired by my string theory course, but it applies to every theory with Lagrange ...
• 2,975
23 views

### Screening of the electric field by a grounded conductor in the presence of external charge

If we have an incompressible (constantly $\rho=const.$) charged fluid in some parts of space, this will trivially create some electric field. Suppose we surround each of these domains of charged fluid ...
33 views

### Quantum measurement in a strong magnetic field

I have a thought experiment that has been puzzling me regarding a spin-$\frac12$ particle placed in an extremely powerful magnetic field (say 1000 T for the sake of hyperbole) directed along the ...
• 636
1 vote
35 views

### Does frequency affect current in Photoelectric effect? [duplicate]

If frequency of light in a photoelectric effect experiment increases (assuming its already enough to ionize the electrons), apparently the current will remain unaffected. This is contradictory to the ...
1 vote
46 views

### Question in time period of oscillation of a ball in bowl [duplicate]

We know time period of pendulum is $$T=2\pi\sqrt{\frac{L}{g}}$$ While reading through a question on S.E which was based on a ball oscillating on a bowl , I was curious and I thought of its time period ...
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### Why the broadening of coherence peak in superconducting spectrum is described by an imaginary term?

From Phys. Rev. Lett. 41 1509, the density of states of superconductor is where iΓ is the broadening part. Can anyone tell me why the broadening can be decribed by an imaginary part, what is its ...
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• 45.1k
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### Necking stage in bubble detachment

The first image is the bubble dynamics in nucleate boiling, in a) you can see that the bubble is detaching by minimizing contact line with surface until zero, while in b) the bubble is enlongate and ...
20 views

### Magnetic pressure explanation and penetration depths

Can I get an explanation of what magnetic pressure is exactly in the context of MHD? From my simple understand, it's essentially just the force that magnetic field lines exert back onto a plasma that ...
• 25
1 vote
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### Perturbative non-renormalizability and viability?

Does perturbative non-renormalizability indicate the unviability of the theory if we were to define it non-perturbatively (for example through a lattice discretization of the continuum QFT or other ...
• 699
33 views

### Semiconductor conductivity increases but Fermi level decreases

I was going through this question: Why does the Fermi-level decrease with temperature increase? As the temperature increases though the semiconductor becomes intrinsic where number of holes equals ...
• 679
34 views

### Current in a cube resistor [closed]

I am given this cube of resistors, each with the same resistance of 4 Ω. The current that enters at E and leaves B is 6 A. I have found that the equivalent resistance is 3 Ω. However, I am unsure of ...
• 59
23 views

### Understanding the physics of a vertical axis wind turbine

I have a physics background, but not much aerospace. I'm attempting to understand the operating principal of a vertical axis wind turbine. I've found a paper with a free body diagram, which I mostly ...
• 113
1 vote
107 views
+50

### Transformation of basis vector in Kruskal coordinate

For Schwarzschild solution: $\mathrm{d} s^2=\left(1-\frac{2m}{r}\right)dt^2 - \left(1-\frac{2m}{r}\right)^{-1}\mathrm{d} r^2-r^2(\mathrm{d}\theta^2+sin^2\theta \mathrm{d}\phi^2),$ Introduce tortoise ...
• 337
29 views

### Ground states of an Hamiltonian in Statistical Mechanics [closed]

I had a general question in statistical mechanics. If we're given a certain Hamiltonian and we're asked to draw its zero-temperature phase diagram can we equal the energy to free energy. And if we ...
16 views

### Charge on a conducting sphere inside uniform electric field after it is ungrounded [closed]

A grounded conducting sphere of radius R is immersed in a uniform vertical electric field E on the z axis. The electric field induces a distribution of charges on the sphere. What is the net charge Q ...