# All Questions

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### Where does the polarity of particles come from?

Going though current lessons, I can clearly see that some particles, electrons, are charged negatively and other, protons, are charged positively. Where does this polarity come from? Knowing that ...
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### How to model the impedance of a coil with a dielectric slab on the top

I have sketched what I meant in the image below. Were there no dielectric slab, the coil could have been simply modeled as an inductor. But I am not sure what the impedance can be if there is a ...
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### Representations of Galilei group

Show that the operator $U(\alpha, \beta) = e^{i(\alpha \hat{x}^2 + \beta \hat{p}_{x}^2)}$ can represent the space reflection of the 1D Galilei group: $x \to -x; t \to t$. I don't really know ...
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### Voltage changes under load across parallel pack

I have 97 LiFePO cells in parallel. They've been sitting for days so the voltage is equal at 3.19v. I put a 5A load on the pack, connecting + at the near end, - at the far end. I measure V across ...
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A question about memristors: These semiconductor entities have been defined in terms of magnetic flux leakage, and a non-linear relationship to the electric charge that has flowed. In essence, the ...
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### How does matter interact with spacetime? [on hold]

It's easy to see how matter interacts with itself but how does it interact with spacetime which is "not" matter? Einstein showed us that mass and energy cause a curvature in spacetime, which intern ...
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### What is the symbol for the moment of force (torque): $N$, $M$ or $\tau$? [on hold]

Classical Mechanics (Goldstein, Poole and Safko) calls it $N$. Principles of Dynamics (Donald T. Greenwood) calls it $M$. Google calls it $\tau$. So... which is it?
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### Parallel Resistors (special cases formula)

Problem: A car's rear window defroster uses 15 strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged the ...
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### Ray tracing in General Relativity

I would like to find out what one would see at the Schwarzschild radius of a massive non-rotating black hole, if the black hole is surrounded by a bright ring. For that, I would place the observer at ...
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### Force-carrying particles instead of forces

In which physical theories do we have such mathematical models, in which only a notion of particle is used (and e.g. the concept of force is not present in the model)? I know about e.g. gauge ...
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### Negative pressure experiments

One method of understanding the physics of materials is to study their properties under the effect of pressure. Under high pressure, new phases can arise. Experimentally, high pressure can be obtained ...
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