# All Questions

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### Can magnets induce magnetism stronger then their own magnetism?

This might sound foolish but bear with me for the explanation. I came across a weird magnetic behaviour playing with coins on a mac. There are magnets in mac, two on the top corners of the screen and ...
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### Fresnel diffraction approximation (parabolic waves)

The Huygens-Fresnel principle (Introduction to Fourier Optics, Goodman), $$U(x,y)=\frac{z}{i\lambda}\int_\Sigma U(\xi,\eta)\frac{e^{ikr}}{r}d\xi d\eta\,,$$ where $\cos \theta=\frac{z}{r}$, shows ...
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### Ask for Frank Wilczek's notes on entropy and entanglement

I know that I am not asking a question on physics. My question is just about learning physics. I am studying entanglement entropy and find some lecture notes by Frank Wilczek But I can only find the ...
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### How dopant enhances the superconductivity of BSCCO

i really need your help, I want to know the effect of Dopant (for Example Manganese) in BSCCO (for example Bi-2212) in Resistivity? i read some articles saying it increases the critical temperature ...
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### Helical killing vector

A killing vector X is defined as a vector field that satisfies the relation $$\mathcal{L}_X g_{\mu\nu}=0.$$ which basically means that if one were to transport the metric along this vector, there ...
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### Geometric and radiometric distribution of light

I'm studying the behavior of the light in a scene, to know how much light arrives at a specific point of a surface and how much of it leaves from the point. From the documentation I'm reading, it says ...
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### Average energy of a damped-forced harmonic oscillator during a period t

In my textbook, it's stated without proving the following identity for a classical damped-forced harmonic oscillator: $$\bar{E}^t = \bar{T}^t + \bar{V}^t = 2 \bar{T}^t \, ,$$ which states that ...