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17h
comment what could generate a high-pitched whine in electronics where the frequency depends on the current?
@user6972, I concur about power supply switching frequencies in general; it all depends on the supply. However, high voltage supplies tend to run at lower frequencies because of the high effective capacitances presented by the high voltage transformer. Moreover: 1) I claim magnetostriction as part of the power supply, since the transformer is an element in it. 2) a steady sound usually requires a driving signal at the same or a related frequency, so just saying "magnetostriction" without identifying an underlying frequency source is not an answer, imho.
17h
comment Physical explanation for capacitive circuit
@IncnisMrsi, I take your point that my answer could be elaborated. Would you care to add an answer that does so?
23h
comment How does current flow from the emitter, through the base and to the collector in a NPN transistor?
@IncnisMrsi, updated per your recommendation. Thanks!
1d
comment Reading the Feynman lectures in 2012
The potential-based approach to EM you mention may be "Collective Electrodynamics" by Feynman's student Carver Mead: en.wikipedia.org/wiki/Carver_Mead . PS: I recall you writing favorably of Steven Frautschi's S-Matrix book. I saw him recently; in retirement, now 80, he has re-invented himself as a teaching assistant, and won Caltech's Feynman Prize for Excellence in Teaching this year. When I mentioned his S-Matrix work being cited here, he ducked his head and said, "Well, that was a long time ago..."
1d
comment Reverse bias P-N junction
@IncnisMrsi, 1) Thanks, my wording was poor; I've attempted to improve it. (I meant excess in comparison with the unbiased junction.) 2) I concur. Apparently this ideal diode characteristic works fairly well in germanium diodes (because $I_0$ is larger than for silicon?), but in Si, other mechanisms, like carrier generation in the transition region, cause the reverse-bias current to vary with voltage.
2d
comment Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?
After way too much time, I see that my criticism was incorrect. Apologies for my confusion...
2d
comment Reverse bias P-N junction
@IncnisMrsi, I've added a sketch of stored-charge analysis, plus a link to reference with figures (which are always helpful).
2d
comment Reverse bias P-N junction
@IncnisMrsi, yes, the depletion region is formed by depleted majority carriers. However, if you want to understand how much current flows in a reverse-biased diode (the question I'm addressing) you must focus on the minority carriers (the ones the applied field can sweep across the junction), and minority carrier concentrations are in fact depleted by a reverse bias. It's not an exclusive-or situation.
Oct
7
comment Why is Earth's climate so stable?
A leading (maybe the only?) explanation for the escape from snowball earth is by Kirschvink: the build-up of atmospheric carbon dioxide (and resultant surface heating) emitted by volcanoes, since the usual scrubbing mechanisms are ineffective in snow-land. Reference: web.gps.caltech.edu/~jkirschvink/pdfs/laRechercheEnglish.pdf
Sep
2
comment Cyclist's electrical tingling under power lines
@Dmytry, on the other hand, your identification of field intensification effects is very relevant; I have edited my answer with credit to you. Thanks!
Sep
2
comment Cyclist's electrical tingling under power lines
@Dmytry, as I stated in my 4th paragraph (which starts with "1)" ), I did in fact use the method of images, so no additional doubling is required.
Jun
15
comment What does the work on a current carrying wire in a Magnetic Field?
Related: physics.stackexchange.com/questions/89398/… and links therein.
Jun
6
comment What's the relationship between glow and arc discharge?
Your perceptive question caused me to completely revise my answer (after considering deleting it). Thank you! I think I've got a better handle on things now.
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: Good luck with your lecture!
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: I agree that BICEP2's result including foreground model DDM2 is (just) consistent with Planck's upper bound, although BICEP2 still considers it to be in tension with Planck (section 12). The recent criticism of the BICEP2's result is that the DDM2 foreground model's B-mode levels are too low, so the r-range should move lower (improving agreement with Planck), and the 5.9 confidence should drop. (See the link in my previous comment.) In fact, BICEP2 is now waiting for a measured dust map from Planck (due this fall) to replace the DDM2 model. The message is "patience".
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: BICEP2 claimed $5.9 \sigma$ for a cosmological signal, i.e. after subtracting out the dust. That number is under pressure. All reviewers I have read agree with you that BICEP2 has seen a B-mode signal "in the sky". The question is whether they understand the foreground contributions. (In fact, they have no error bars on their foregrounds!) Again, BICEP2 themselves acknowledge the tension.
May
22
comment What experiments compete with BICEP 2, and when are their results expected?
@annav: As I excerpted above in comments 3-5, the BICEP2 paper itself acknowledges the tension. (After all, it claims a signal at $5.9 \sigma$ confidence, while Planck sees nothing.) By the way, BICEP2's handling of the dust foreground is under intense pressure; see here: pcts.princeton.edu/PCTS/SpecialEventSimplicity2014/…
May
14
comment Child-Langmuir Space Charge Law for Non-Zero Cathode Potential (Non-Zero Initial Electron Velocity)
These formulas might be attempts to combine two effects: 1) the actual anode-to-cathode accelerating voltage potential $V_{AK}$, which can only depend on the difference between the two potentials, 2) an "effective" (e.g. fake) cathode potential $V_{eff}$ that models the initial velocity of the electrons that are "boiling" out of the heated cathode.
May
10
comment What is $vdp$ work and when do I use it?
Nice, thanks. I think the point of the answer by Bryson S. is that $H_{exit}=H_{entry}-W$ for an adiabatic process, where $W$ is the (positive) work output of the shaft, so $H$ decreases as shaft work is performed.
May
7
comment Is there a compound denser than the densest element?
As a rejected edit noted, osmium forms toxic osmium tetroxide when exposed to the oxygen in air (ref wikipedia). Do not suggest it!!!