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2h
comment Non-uniform circular motion, computing the angle
Since $\theta = \theta_0 \sin(kt+\phi)$ I think you are ok.
3h
comment Non-uniform circular motion, computing the angle
You face a standard differential equation, which is $y'' +\omega^2 y =0$. If $\omega \in \mathbb{R}$ then one way to write the general solution of this equation is $y(t) = \lambda \sin(\omega t + \phi)$ where $\lambda$ and $\phi$ are two constants that depends on initial conditions. You can check it yourself since you only need to derive $y(t)$ two times. But the way you started seems a bit complicated to me, the equation you're resolving is to simple to do that.
1d
comment The momentum of a hole
The answer you gave seems correct to me.
1d
awarded  Commentator
1d
comment The momentum of a hole
No, I'm not going to say the book is wrong, not before I've seen it. If you apply $-i \nabla$ on $\phi_k$ then you get $\vec k$, so I agree with you, the book seems to use another operator for the momentum. I don't know why. If it's not said in your book that the electron had a momentum equal to $- \vec k$, then I can't answer your question.
1d
comment The momentum of a hole
It is said that $\phi_k = \frac{1}{\sqrt V} e^{i \vec k \cdot \vec r}$ is the wavefunction of the hole, but is it specified somewhere what is the wavefunction of the electron that leads to the creation of this hole? As I see it, the momentum operator is intrinsic. I don't see any physical reason for the redefinition of the momentum operator.
1d
answered The momentum of a hole
Apr
11
awarded  Nice Answer
Apr
11
awarded  Yearling
Apr
11
answered Why can lights(photons) bends in a curve through space without mass?
Apr
11
comment Restrained double pendulum
You took the EOMs of the double pendulum, expressed both of them with $\Delta(t)$ ? Can you check if the two obtained equations give the same solutions ? I'd guess that the two equations (in $\Delta$) are equivalent.
Apr
11
comment Restrained double pendulum
Are you looking for the constraint? It seems to me that in your example $\theta_1 (t) = \theta_2 (t)$ (only if the two pendulum have the same length). Have you tried to put that constraint in the double pendulum's equations of motion?
Apr
8
revised Calculating the most probable radius for an electron of a hydrogen atom in the ground state
I switched the formulas to LaTeX.
Apr
8
suggested suggested edit on Calculating the most probable radius for an electron of a hydrogen atom in the ground state
Apr
7
answered Calculating the most probable radius for an electron of a hydrogen atom in the ground state
Apr
2
answered Is this two forms of Hubbard model equivalent?
Mar
27
comment NMR Analysis of Ethylene glycol
I studied NMR recently, it seems like physics to me. Maybe nulcear physics isn't the best tag ever, but Experimental-physics might be a good one. The physical understanding of the NMR spectrum is quite interesting.
Mar
27
answered NMR Analysis of Ethylene glycol
Mar
27
comment Why is titanium dioxide transparent for visible light but not for UV?
I once visited a lab where they were showing a little experiment. They gave us a silicon wafer (monocrystalline) and a piece of glass. They had set a UV camera connected to a screen. When I put the glass between me and the camera my face didn't appear on the screen (even though I was able to see it with my eyes). When I tried the same with the silicon wafer I didn't see with my eyes but my face appeared on the screen. Silicon is also transparent for UVs and not for visible light.
Mar
20
answered Why does $c_{-k,-\sigma}$ create a particle with momentum $k$?