# All Questions

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### Lorentz Transformations in Minkowski space

If $\Lambda$ represents the Lorentz transformation matrix, then the transformation of contravariant components $x^\mu$ is given by $$x'^\mu=\Lambda^{\mu}{}_{\nu} x^\nu$$ and that of the covariant ...
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### Hidden momentum

I'm trying to learn about hidden momentum. After reading what I could find with a google search, I understand that it is equal to the momentum carried by radiation, calculated with the Poynting vector....
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### Why we do calculus of variation instead of finding maxima or miniama of function? [on hold]

Why we do calculus of variation instead of finding maxima or minima of function? What is the difference between finding maxima or mimima i.e. critical point of a function and calculus of variation?
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### “Simple” air resistance question

Two balls with exactly the same size and shape, but different mass, are launched at the same velocity 90 degrees to a flat plane. When air resistance is considered, the object with the larger mass ...
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### Two qubits system in polar co-ordinates

I know that I can write a single qubit state in terms of polar co-ordinates $(r,\theta,\phi)$ on a Bloch sphere. \rho = \begin{pmatrix} \frac{1+r \cos\theta}{2} &\frac{r \exp(-i\...
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### Tight binding Hamiltonian for 2D finite dimensional lattice and nanowire

The Hamiltonian of a 1D lattice having finite $N$ atoms, (if we consider one basis per atom) is given by the following $N\times N$ matrix- Here $E$ is the onsite energy and $t$ is the hopping ...
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### What is the significance of the Inverse-square law? [duplicate]

Considering its occurrences in various fields like Electrostatics, Gravitation, Acoustics etc. how does the law bind these topics together?
Two bodies of mass $M_1$ and $M_2$ are connected by a spring but are otherwise free to move along a horizontal line. A periodic force $F\cos\omega t$ is exerted on the body of mass $M_1$ along the ...