Art Brown

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	1,682 reputation	bio	website		visits	member for	1 year, 1 month
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45m	comment	Why doesn't this equation for orbital motion change with position in the orbit? Nice explanation. To be cheeky, the pair of equations will indeed yield precisely two solutions: apapsis and periapsis.
3h	comment	Doubt on the analysis of $RC$ circuit @user1620696: You're welcome. Unfortunately, life is usually not so simple. Most circuits do not split up nicely like this one, and other techniques are required.
2d	comment	Electric power transmission @User58220: Why don't you write up your comment as an answer (since it is)?
2d	comment	Questions concerning some parts of the section on one-particle states in Weinberg's first volume on QFT @LakshyaBhardwaj: Ah, now I see. Ouch, I did not recognize that interpretation of my words. The "slow student" in question is I, not you. Sorry for any offense; none was intended. I'll edit the post.
2d	comment	Questions concerning some parts of the section on one-particle states in Weinberg's first volume on QFT @LakshyaBhardwaj: You're welcome (but no professors here).
May 13	comment	Displacement Current - How to think of it? @BenCrowell: Yes, it's an awkward description. See the 2nd figure in the Wikipedia article for displacement current: en.wikipedia.org/wiki/Displacement_current , where S1 and S2 are the 2 surfaces.
May 6	comment	Definition of Casimir operator and its properties No problem, I was not expecting a proof, intuitive or otherwise. Your edit more than answered the mail and is much appreciated.
May 5	comment	Definition of Casimir operator and its properties @Vibert, thanks, but we are talking about "exact definitions".
May 5	comment	Definition of Casimir operator and its properties Nice, concise answer, as usual. (Personally, I'd like more explanation, but...) My venerable Schiff asserts that the number of Casimir invariants is equal to the maximum number of mutually commuting generators, which seems like a useful fact. Can you say how it emerges from your analysis (assuming it's true)?
May 5	comment	Definition of Casimir operator and its properties Since, as Qmechanic notes, Casimir operators need not be quadratic, it appears that the two definitions in the question are not in fact equivalent.
May 5	comment	Phasor representation of voltage in frequency domain @user1285419: You're welcome. Yes, $\beta x$ gives the phase characteristic of the wave as a function of position, but it has a fixed value of 0 at $x=0$. A complex amplitude permits that value to be different.
Apr 21	comment	Gravitational potential outside Lagrangian points or Lagrange points @AlanSE: just like the vector potential in electrodynamics, it turns out. See my answer to the question referenced in this question.
Apr 9	comment	Why isn't this capacitor charging? @Ovi, you're welcome.
Apr 8	comment	Runge-Lenz vector and Keplerian Orbits @BenCrowell: "Simple" appears to be something Professor Goldstein knows when he sees it: "Only where the orbits are closed ... can we expect the additional conserved quantity to be a simple algebraic function of r and p such as the Laplace-Runge-Lenz vector." Goldstein 2nd ed, Section 3-9, pp. 104-105 (and section 9-7 for the isotropic harmonic oscillator).
Mar 24	comment	continuity of the electric potential due to a surface charge possibly related: physics.stackexchange.com/questions/40919/…
Mar 14	comment	Is equivalent resistance always lower if we add a resistor to a passive electronic circuit? @EmilioPisanty: yes that's a good one.
Mar 11	comment	Capacitor circuits with light bulb Sorry, I'm not getting it. My mental model is: I connect a resistor to a charged capacitor, with the wires and cap plates modeled as perfect conductors. Current steps up in the resistor, wire, and cap (ohm's law and kcl), and that current is exactly balanced by the displacement current between the cap plates. Where does the fringe field enter? Thx again.
Mar 11	comment	Capacitor circuits with light bulb Why is the fringe field required to understand charging a capacitor? Or maybe, what do you mean by a "fringe field in the wire just outside the plates? It seems to me that considering the "standard" E-field between the plates is sufficient to comprehend the displacement current. Thanks.
Mar 6	comment	When should I take wine out of the fridge - transient heat transfer problem 1) I address emissivity in my edit. 2) I think a bottle standing upright has a good view of its surroundings.
Mar 2	comment	When should I take wine out of the fridge - transient heat transfer problem I thought radiation would be negligible and was only making an estimate to justify ignoring it, per Chris White's comment to your question. I was surprised to see it had an effect.