Wikipedia:Reference desk/Archives/Science/2017 May 14

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May 14

Is Faraday's law of inductance properly applied to Wiki's article on LC circuits?

The article uses Faraday's law, to explain why a decrease in magnetic field causes and increase in EMF.

"... Eventually all the charge on the capacitor will be gone and the voltage across it will reach zero. However, the current will continue, because inductors resist changes in current. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday's law, the EMF which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field." LC circuit

The correct way of dealing with floating references is to use the template {{Reflist-talk}}. This puts the refs in a neat box and keeps them with the original posting. For example, DrChrissy ^(talk) 15:19, 14 May 2017 (UTC)

DrChrissy, You just placed "This is a bogus ref to illustrate the template that prevents floating refs" at the bottom of this page, in the wrong section. Was that your intent? --Guy Macon (talk) 16:52, 15 May 2017 (UTC)

@Guy Macon: Hi. Another editor has already raised this on my Talk page - I suggest you read that thread to put this into perspective. DrChrissy ^(talk) 16:59, 15 May 2017 (UTC)

Correct way to deal with floating refs on Talk pages
Floating references The correct way of dealing with floating references is to use the template {{Reflist-talk}}. This puts the refs in a neat box and keeps them with the original posting. For example, This posting contains 3 bogus refs to illustrate the use. References References

Faraday's law of induction applies to magnetic INDUCTION. Magnetic induction occurs when a magnetic FIELD produces magnetic energy within a superconductor, or both magnetic energy and EMF within a non-superconductor.

In an LC circuit, the capacitor does not contain a magnetic field. The capacitor gains its EMF when magnetic energy directly converts into electrostatic energy.

Note: The article uses an inductor's resistance to change in current to explain why current begins to flow to a capacitor after a polarity change.

However, the inductor does not resist a polarity change. Current INSTANTLY reverses direction during the two polarity changes that occur within each cycle.

In my opinion, a better explanation of current flow to the capacitor after a polarity change is the fact that:

WITHIN AN LC CIRCUIT, RELATIVE POLARITY DETERMINES THE DIRECTION OF CONVERSION OF ENERGY.

For example, electrostatic energy cannot convert into magnetic energy without proper magnetic versus electrostatic polarity. Exhaustion of electrostatic energy results in the instability of having an inductor with the entire circuit's stored energy. A polarity reversal makes it possible for magnetic energy to convert into electrostatic energy.

Overall, relative polarity drives the direction of energy conversions. Capacitance and inductance determine the rate of energy conversion. Current and volts are the result of the energy conversions within an LC circuit. Vze2wgsm1 (talk) 01:15, 14 May 2017 (UTC)

You're referring to the article LC circuit. You linked to it in an obscure way, so I hope this helps. Akld guy (talk) 02:06, 14 May 2017 (UTC)

You state that the inductor does not resist a polarity change, and you refer to "the two polarity changes that occur within each cycle". The only way to read that is that you're referring to an LC circuit connected to an external signal source, but the part of the article that you're dissatisfied with is discussing only a capacitor and inductor connected together and to nothing else. It explains what happens when the capacitor, which is charged, begins discharging through the inductor. There is no signal from an external source involved at this part of the article. Akld guy (talk) 02:44, 14 May 2017 (UTC)

An example of capacitor charge and discharge without polarity reversal within a capacitor is when a discharging battery adds electrostatic energy to a capacitor. Afterwards, (after adding extra charge) the capacitor could charge the battery, without changing the polarity of the battery or the capacitor.

Let a battery substitute for a capacitor within an LC circuit. After the battery completely discharges into the inductor, the energy within the inductor would begin trying to charge the discharged battery, in a direction that would make the anode negative, and the cathode positive.

The inductor's attempt to reverse the polarity of the battery requires a reversal of polarity of the energy within the inductor.

Vze2wgsm1 (talk) 22:50, 14 May 2017 (UTC)

• @Vze2wgsm1: Just a sidenote, "Wiki" is not a correct way to refer to Wikipedia.--Jasper Deng (talk) 22:58, 14 May 2017 (UTC)

ceramic capacitor vs tantalum capacitor

Between a ceramic capacitor and a tantalum capacitor of the identical capacitance and rated voltage, let's say 100 µF and 10 V, which one would have a smaller leakage current? ECS LIVA Z (talk) 03:06, 14 May 2017 (UTC)

The leakage of the ceramic is typically a thousand times lower. Typical leakage for a 100 uF, 6.3 VDC rated tantalum-polymer capacitor is 60 uA. A ceramic capacitor of the same capacitance and voltage would have an equivalent leakage of 6.0 nA. Source: Technical Update – Comparison of Ceramic and Tantalum Capacitors --Guy Macon (talk) 03:54, 14 May 2017 (UTC)

Holy crap that's a big difference. Thanks a lot! ECS LIVA Z (talk) 04:08, 14 May 2017 (UTC)

It's an unrealistic comparison though. Tantalums are electrolytics, where many drawbacks (polarisation, leakage, low voltage rating, sometimes accuracy of their value) are sacrificed in order to achieve a high capacity or a small physical size. 100μF is a typical value for tantalum, but would be exceptional for a ceramic. 0.1μF is a more practical upper limit for an off-the-shelf commodity disc ceramic capacitor, 1μF for newer MLCC devices. You can go higher with recent devices (my usual suppliers peak at 22μF] in similar packages to tantalum but the price gets steep (although the voltage rating is high enough to be board-design limited).

Specialist HV ceramics have always been around in large capacities, but those get expensive and obscure. They're more usually made these days from polypropylene capacitors (look at the Tesla coil people and 'MMC' banks). This highlights another issue - at higher frequencies it might not be a simple leakage current that is the problem, but losses within the dielectric. Andy Dingley (talk) 12:22, 14 May 2017 (UTC)

On Digikey I'm finding ceramic capacitors significantly cheaper than tantalums at 0.1 μF, 1 μF, and even 10 μF. The two only reach price parity (with tantalum still trailing badly in performance) at 100 μF, but I don't use anything that big (nor do most hand-held consumer electronics). Seems like the latest technology advances and price drops in MLCC have made tantalum virtually obsolete.ECS LIVA Z (talk) 21:10, 14 May 2017 (UTC)

Here's a ceramic capacitor at 100 μF[1] that's actually cost-competitive against the tantalum equivalent. ECS LIVA Z (talk) 21:18, 14 May 2017 (UTC)

Thanks, those haven't reached my end of the workshop yet. Note the low voltage ratings, which are characteristic of MLCC and indicative of the thin layer trick that allows them to get such a high capacity into a small package. Andy Dingley (talk) 08:45, 15 May 2017 (UTC)

Capacitors can be wired in parallel to increase the total. For example, three ceramic 10 μF units in parallel result in 30 μF, with the same voltage rating as the lowest rated one. Akld guy (talk) 02:33, 15 May 2017 (UTC)

Also take a look on the ESR. You can get capacitors in an identical package and technology and rating, differing in half/double impedance. --Hans Haase (有问题吗) 18:16, 19 May 2017 (UTC)

Resolved

Data and maths of man-made climate warming

If a non-climate scientist got basic climate and weather data (like temperature, CO2 concentrations, floods and hurricanes) and he wanted to know whether it's man-made or not, what maths would he need? What steps would he need to take? That is, without appealing to authorities or experts, how could he come to this conclusion? --Clipname (talk) 11:50, 14 May 2017 (UTC)

From an inhuman point of view, the best test would be to get rid of all the men (inclusive) and observe subsequent weather data. Apologies for that answer. Dbfirs 11:56, 14 May 2017 (UTC)

• Attribution of recent climate change and the sources therein may help. Loraof (talk) 14:03, 14 May 2017 (UTC)

First you need to determine whether the CO2 increase was man made. There are multiple lines of evidence that show this is indeed the case, but perhaps the most straightforward is the change in relative concentrations of carbon isotopes in atmospheric CO2. See Seuss effect.

From this point onward you can choose between approaches that run from the simple to the very complex. Possibly the easiest would be to use one of the simplified formulas for radiative forcing as a function of CO2 concentrations. You could then take this answer and use a reasonable value for climate sensitivity to get the resulting temperature change. For this calculation it would be more appropriate to use a value for transient climate response rather than equilibrium climate sensitivity.

You have to also keep in mind that the observed warming is not solely due to CO2. Radiative forcing due to methane is also substantial (a bit more than half as large as the forcing due to CO2).

There's a whole range of approaches beyond this, from fairly simple radiative-convective equilibrium models to full-blown climate system models such as the CCSM. Shock Brigade Harvester Boris (talk) 15:17, 14 May 2017 (UTC)

The thing is, while quantifying the exact amount of past and future global warming takes a lot of effort and calculation, the simple fact that manmade greenhouse gases are warming the planet really doesn't. The greenhouse effect of gases like CO₂ and methane can be demonstrated in a laboratory. We know human activities like intensive agriculture and burning fossil fuels releases these gases into the atmosphere (again, demonstrable in a laboratory). So either the planet should be warming, because we're dumping these greenhouse gases into the atmosphere, or some unknown process is precisely compensating for these manmade alterations to the atmosphere. Occam's razor suggests the former. --47.138.161.183 (talk) 07:43, 15 May 2017 (UTC)

That is a poor argument. If the effect is small, say 1 deg C per doubling (about what you get in the lab) then it will be hundreds of years before we see another 1 deg C, other than short term spikes due to El Nino etc. Who knows what will happen in several centuries? Maybe some actual science as opposed to guessing games and alarmism. Greglocock (talk) 12:10, 15 May 2017 (UTC)

If you mean 1 deg C per doubling of CO2 it won't take centuries to happen. Since the 50s it has not only doubled, but went up by a factors of 8. And that's discounting other greenhouse gases, a chain effect (more heat -> more water vapor in the atmosphere -> even more heat) and other side effects like increased acidity of oceans, disturbing ocean currents, triggering the release of methane crystals. Hofhof (talk) 13:12, 15 May 2017 (UTC)

What has gone up by a factor of 8 since 1950? Not CO2 concentration. On another note, Greglocock's value of 1 deg C per doubling is roughly the effect solely of CO2 in an isolated, static system; it is not plausible to apply such a value to the Earth. Shock Brigade Harvester Boris (talk) 13:47, 15 May 2017 (UTC)

I meant the emissions of CO2. A part of it is absorbed, mainly by the oceans. And it's somehow below 8, but not much. Hofhof (talk) 19:32, 15 May 2017 (UTC)

Exactly. Technology seems to find ways to do things like increase the depth of rock or water fossil fuels can be economically extracted at to amounts that would've been Jules Verne-like fantasy only generations before. Wait, we've done that only a few generations after too (walk on the Moon) Sagittarian Milky Way (talk) 19:45, 15 May 2017 (UTC)

Since 1880 CO2 has increased from 280 ppm to about 400 ppm. So in logarithmic terms that is log(400/280)/log(2), or about 0.5. That is, roughly half a doubling. In the same timeframe global temps have increased by perhaps 0.8 deg C, so a simple estimate of CO2 sensitivity is 0.8/0.5, ie 1.6 deg C per doubling of CO2. That is at the lower end of IPCC estimates, and somewhat more than the direct effect measurable in the lab. The latter is confounded by positive and negative feedbacks when translated to the real world, the sizes and balance of which are very much up in the air. I don't know where any factor of 8 appears in the above numbers, looks like hysterical exaggeration to me. Greglocock (talk) 12:19, 16 May 2017 (UTC)

In your analysis of temperature change you've compared the observed change to equilibrium climate sensitivity, which includes "slow" feedbacks that continue to unfold for a few centuries after CO2 doubling. A better comparison would be to transient climate response, which is the temperature change at the time of CO2 doubling (i.e., before the slow feedbacks have evolved). The ratio of TCR to equilibrium climate sensitivity is around 0.5-0.6. Applying the inverse of this ratio to your computed value of TCR gives us an equilibrium climate sensitivity of 2.7 to 3.2 for a doubling of CO2. That's squarely within the middle of the accepted range from both models and paleoclimate estimates. So, your analysis shows that the models correspond rather well with current observations.

Also, as Hofhof clarified just above, the factor of 8 applies to CO2 emissions. Data from CDIAC show that CO2 emissions from fossil fuels and cement production increased from 5977 million metric tons in 1950 to 35,849 million metric tons in 2013. That's a factor of 6 than a factor of 8. (Note these figures do not include non-fossil fuel based CO2 emissions such as biomass burning.) Whether 6 versus 8 is a "hysterical exaggeration" as you say or "below 8, but not much" as Hofhof says is up to the reader's judgment. Shock Brigade Harvester Boris (talk) 14:08, 16 May 2017 (UTC)

Not a proof, but the "hockey stick curve" is dramatic enough that, if you see it graphed out, you don't have to be an expert to see that something unusual has happened to our weather in the last century. (example)

The caveat there is that all the temperature data older than the late 1600s is based on pretty intense research that could only be done by experts.

... but that's going to be true no matter what. There's no way something as big as this could be deduced entirely from personal knowledge and personal calculations. At some point, you're going to have to use someone else's data. It's just a question of which data you use or don't. ApLundell (talk) 13:51, 15 May 2017 (UTC)

There's also the problem that science is collaborative and cumulative. Scientists are not hermits collecting data and creating theories from it in isolation. There are literally thousands of climatologists around the world that have been working together on this subject, and one person is unlikely to have the time or resources to recreate it all on their own from scratch. --Jayron32 14:43, 15 May 2017 (UTC)

Agreed. Even very basic science is difficult to work out from first principals all by yourself.

Something as basic as personally proving that the world is spherical would involve quite a bit of travel and careful observation of the sun and stars.

It's just not reasonable to expect to be able to personally work out something as complex as global climatology. It'd be like trying to build a battleship all by yourself. ApLundell (talk) 15:19, 16 May 2017 (UTC)

• I will just leave this here --Guy Macon (talk) 17:03, 15 May 2017 (UTC)

I didn't know the Dilbert cartoonist was denialish. Sagittarian Milky Way (talk) 18:54, 15 May 2017 (UTC)

I believe he's also wrong about climate scientists using economic models that have never been right. Economy has used/tried to use physical models to transform their discipline into a real science, but not the other way round (AFAIK). Hofhof (talk) 19:36, 15 May 2017 (UTC)

He does NOT use economic models to address the scientific question. He separates the issue into the scientific questions and then the economic theories behind certain proposed responses to assumed scientific results. He harps on this theme so often its impossible to miss; I've only been looking at his blog since February. μηδείς (talk) 00:19, 16 May 2017 (UTC)

Thanks μηδείς. Now I notice that my answer was poorly formulated. Yes, I meant he bashes climate scientist for supposedly using economic models, which they don't.

I have never read his blog, but in the cartoons, which I read often, this is the first time I see something about his denialism.Hofhof (talk) 00:46, 16 May 2017 (UTC)

Adams is an interesting fellow. Shock Brigade Harvester Boris (talk) 01:17, 16 May 2017 (UTC)

In my personal opinion, Adams is more of a provocateur and self-promoter than anything else. I started reading his cartoons on line in January, then started reading his blogs. His basic premise is Skepticism, and that people are easily manipulated. Whether he applies those premises to his own theories is an open question. μηδείς (talk) 00:48, 17 May 2017 (UTC)

• Bloomberg published a really great graphic that shows the relative contributions of various warming factors since 1880. Answer: it's CO₂. the really scary part is not emphasized in the text, but is very clear from the chart: Warming would be much worse if not for aerosols caused by man-made sulfur dioxide emissions. But these emissions fall out of the atmosphere in 20 years, while the CO₂ does not. This means that we will see an abrupt temperature increase when the Chinese quit burning high-sulfur coal. -Arch dude (talk) 05:20, 16 May 2017 (UTC)

@Arch dude: Their plot for aerosols shows a strong decline, actually. And I'm not sure how they defined "aerosols". And I'm skeptical that sulfur dioxide would affect climate that long - I remember Mount Pinatubo caused colder temperatures, but the next year was pretty OK (according to a greenhouse-acclimated baseline). The article I trot out in this context is this one -- it shows that the infamous "chemtrails" or "geoengineering" conspiracy theory is true, and the conspiracy was killing 1000-4000 people yearly; however, contrary to various disinformation, the source of the chemicals is, of course, the airplane's fuel tank, and the geoengineering occurs in the context of executives trying to talk the government out of raising their fuel costs in the name of safety. Anyway, that was said to hold back global warming by six months, and there are other sources of SO2, so you're not tremendously off, but I think by an order of magnitude or so. Wnt (talk) 14:01, 16 May 2017 (UTC)

"Aerosols" in this context refers to tropospheric aerosols, not stratospheric aerosols from volcanoes. The Bloomberg graphic has a separate line "Volcanic" (which indeed shows a sharp but short-lived cooling effect from Pinatubo). Shock Brigade Harvester Boris (talk) 14:13, 16 May 2017 (UTC)

Yes, the aerosols are currently contributing a strong net cooling, which somewhat offsets the CO₂ warming. That was my point. When China quits burning high-sulfur coal, there will be a sharp increase in temperature. But if they continue to burn coal, with or without sulfur, warming will continue anyway. The sulfur just lagged the effect of the previous decade's CO₂, which will still be there when the sulfur precipitates out. -Arch dude (talk) 15:13, 16 May 2017 (UTC)

@Wnt: Yes, I was imprecise about the atmospheric lifetime of SO₂. Your figure may be correct. I knew it was short but not that short. The increase in net aerosol cooling in the chart comes from increases in net annual generation, which keeps the total up even though it drops out in a few years. But the very same coal plants that add that SO₂ are also adding CO₂, which will keep warming the earth long after we are all dead. -Arch dude (talk) 15:24, 16 May 2017 (UTC)

• Let me just give a pointer to a Scientific American guest blog I wrote on this general issue: https://blogs.scientificamerican.com/guest-blog/global-warming-the-folly-of-certainty/. — Preceding unsigned comment added by Looie496 (talk • contribs)

Thanks for the OR self plug. Given there is a non-zero probability that one of the aliens from Signs is hiding in your house, do you hose it down before bed every night? μηδείς (talk) 19:43, 16 May 2017 (UTC)

Come on Medeis, I've seen you around and know that you're smarter than this. There's a huge space between "non-zero probability" and absolute certainty. The issue is where any specific risk lies along that continuum, together with the costs involved with that risk. Shock Brigade Harvester Boris (talk) 00:22, 17 May 2017 (UTC)

Obviously I am using an extreme example for rhetorical effect, kind of like Al Gore having a dam opened so he can film a clip about water conservation. But there is no such thing as absolute risk, only comparative risk. One really can't argue from "humans burn hydrocarbons" to "Al Gore needs 17 trillion dollars" without a whole lot of assumptions in between. Climate alarmism is really no different from new-Earth creationism when you look at it. It ignores almost the entirety of the planet's history, all the scientific evidence for solar variation, interstellar clouds, orbital fluctuations, volcanism, etc., and rushes to passing the collection plate. The bridge out analogy may be more realistic than the Signs aliens analogy, but it's not much more sophisticated. μηδείς (talk) 00:41, 17 May 2017 (UTC)

Yeah, as someone who studies this stuff I sometimes think the "alarmists" may do even more damage than the "skeptics." I cringe whenever I read things like global warming will mean the end of humanity within a decade. As for the phenomena you mention we know and account for all that, except maybe interstellar clouds (by which I assume you mean things like this) which are on a time scale way too long to be relevant to recent climate change. Shock Brigade Harvester Boris (talk) 13:46, 17 May 2017 (UTC)

This has been done, see this article. So, you can consider only the climate data and analyze the data in a way that doesn't invoke any detailed atmospheric physics and that's then enough to verify that human CO2 and aerosol emissions are the main driving force of climate change. Count Iblis (talk) 20:39, 16 May 2017 (UTC)

My point is not that interstellar gas clouds will be here tomorrow, but that on the long scale they and innumerable other factors affect the climate, but are not taken into account on climate models. Sea levels have been hundreds of feet lower than they are now in the past, and hundreds of feet higher. We have nothing at all like a comprehensive controlled and uniform surface temperature database now; most areas of the earth are not measured with the accuracy at Greenwich, and that record doesn't go back before the 1800's.

We simply haven't got the knowledge or the data to predict anything with the often quoted 97% consensus. (In the 70's, the consensus was that SO2 was driving a new ice age, and acid rain that would ruin the world's ecosystems. That should be the prologue to any climate discussion.) And if we did, simply fertilizing the pacific with iron might cause sufficient algae blooms to address any real problem.

For an unbiased approach on climate change, I recommend Canadian scientist E. M. Pielou's After the Ice Age. She argues that we have actually entered the next cooling phase, although since it is still warmer now than it was during the last ice age, some local warming can make us think the trend is toward warming. μηδείς (talk) 15:27, 17 May 2017 (UTC)

A scientific consensus of a global cooling in the 70s? No. --Modocc (talk) 04:54, 18 May 2017 (UTC)

That is a subscription article, plus time series based articles are at best just for checking that things are okay with the calculations rather than really showing the basics. Plus people can delude themselves by sticking in all sorts of cycles into time series and prove to themselves the opposite of what is evident, that is a common problem with climate change skeptics. I think it would be nice if there was a good illustrated model which showed the main effects for people, one can't expect the general public to trudge through the figures. It is after all a complex second order effect as far as the change in absolute temperature of the earth from about 290 Kelvin is concerned, where the first order effect of the atmosphere has already heated the earth up by about 35K. Sticking in extra CO2 should obviously heat it up more but a good interactive illustration would help elucidate the main actors in the process and their effects and possible future problems like increased methane emissions or the effects of possible mitigations. After all it isn't immediately obvious to people who haven't looked into it why increased CO2 might lead to a cooler stratosphere or why the melting of Antarctica leads to there being more sea ice there.

The talk about climate alarmism and comparing to creatonism is just silly though. It assumes thousands of climate scientists are in some conspiracy. Ignoring scientists is like ignoring a doctor who tells you that you have a tumor, yes they are sometimes wrong but I think a person going and chanting some healing chant instead of going to a medical specialist shows more sense than these 'skeptics'. If they want to do nothing let them dispute any action on economic grounds. Dmcq (talk) 08:32, 17 May 2017 (UTC)

---

This being Wikipedia, I think it only fair to point out Scott Adam's actual views on climate science do not match what some here claim his views are.

Besides the cartoon at http://assets.amuniversal.com/97ed9410fd89013486fb005056a9545d we have his blog post at http://blog.dilbert.com/post/158778029326/how-to-change-my-biases-on-climate-science

I am not saying that I agree or disagree with him, but at least we should have the decency to address his actual, views instead of a straw man. --Guy Macon (talk) 09:27, 18 May 2017 (UTC)

Thanks for that blog post. It's clear that Adams doesn't have the slightest idea how climate models work. That's OK, because few people do. Shock Brigade Harvester Boris (talk) 13:15, 19 May 2017 (UTC)

How is a workplace humor comic strip relevant anyway? I learn all my science from cartoonists. Roadrunner cartoons taught me that you can fall off a cliff and it's no big deal. A cartoon showed it so it's reality by definition. Sagittarian Milky Way (talk) 13:28, 18 May 2017 (UTC)

Might I provide another Dilbert cartoon to show what I think of Scott Adam's views and abilities in this mattter [2]. Dmcq (talk) 13:49, 18 May 2017 (UTC)