Wikipedia:Reference desk/Archives/Science/2010 December 30

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December 30

Wormholes

From what I have heard in the past Hawking said that wormholes cannot exist because if matter gets sucked into the blackhole, it gets destroyed. So one cannot "enter" a blackhole and survive it. So what's the latest theory about it?

Also I have read in a newspaper that all blackholes leads to a new universe. Is that true?

Please explain in layman terms without complex equations.

--Tyw7  (☎ Contact me! • Contributions)   Changing the world one edit at a time! 00:04, 30 December 2010 (UTC)

Total non-expert opinion: The only way we have to test such a thing with our current level of technology is through "thought experiments." It may be decades or even centuries before we can actually know the answer to such a question with any degree of certainty. So, Hawking is probably right, but even he doesn't know for sure. Beeblebrox (talk) 00:32, 30 December 2010 (UTC)

The relevant article is Black hole information paradox. AFAIK Hawking capitulated on the point of destruction of information. Vespine (talk) 00:40, 30 December 2010 (UTC)

Yes, and also our Wormhole article says: "There is no observational evidence for wormholes, but on a theoretical level there are valid solutions to the equations of the theory of general relativity which contain wormholes." WikiDao ☯ (talk) 00:43, 30 December 2010 (UTC)

So one cannot use a blackhole (and white hole) as a shortcut because all matter entering a blackhole is destroyed and converted to energy. --Tyw7  (☎ Contact me! • Contributions)   Changing the world one edit at a time! 00:48, 30 December 2010 (UTC)

No, one can not do that because as far as we know they don't exist. There are some thought experiments where they have them, but don't confuse that with actually existing. BTW if you really could convert all matter entering a wormhole to energy that would be tremendously useful, plus you could use them for long distance communication. But in any case the difference between matter and energy is not very clear, so I don't see why a wormhole would allow one and not the other. Ariel. (talk) 01:22, 30 December 2010 (UTC)

How about whether each blackholes lead to a new universe? --Tyw7  (☎ Contact me! • Contributions)   Changing the world one edit at a time! 00:48, 30 December 2010 (UTC)

I haven't heard anything like that. But some people define the inside of a black hole as a different universe since it's isolated from its parent. Ariel. (talk) 01:22, 30 December 2010 (UTC)

So stuffs get sucks in and doesn't escape? --Tyw7  (☎ Contact me! • Contributions)   Changing the world one edit at a time! 18:44, 30 December 2010 (UTC)

Sort of. Its a bit more complex than that. In on definition, the Universe consists of all of the locations which are capable of exchanging information with each other (or places which have overlapping light cones) or something like that. The thing about black holes is that anything which crosses the event horizon is suddenly incapable of exchanging information anymore; such that inside of the event horizon is effectively "outside" of our universe, based on the above definition of The Universe. See cosmic censorship. This does NOT mean that the inside of the event horizon is a universe with galaxies and stars looking like our universe. It just means that, effectively, since it cannot exchange information with anywhere in our universe, it isn't part of our universe. --Jayron32 19:50, 30 December 2010 (UTC)

The wormhole that exists in the Schwarzschild metric (the simplest solution to Einstein's field equations including a black hole) is not an interesting wormhole because a) it disappears when you alter the metric to make it fit reality (for example, making the black hole come into being at a certain time, rather than existing for eternity into the past and future) and b) it doesn't exist for long enough for anything to cross it, even at the speed of light. There are other solutions involving wormholes that would be possible to cross, however they always require exotic matter and there is no evidence that such matter is possible. --Tango (talk) 20:16, 30 December 2010 (UTC)

A rotating black hole has a ring singularity. That would allow for the formation of a parallel universe and anything passing through it would be crushed and streched but would emerge through the white hole relatively intact. ~AH1^(TCU) 17:31, 1 January 2011 (UTC)

Sugar Maple

I recently watched Subway (Homicide: Life on the Street). As Vincent D'Onofrio's character is dying, one of the last things he says is that the leaves of a sugar maple turn upward before a rain to catch the raindrops. Our article doesn't mention this so I'm wondering if anyone knows if it is true or not. Beeblebrox (talk) 00:26, 30 December 2010 (UTC)

I don't know whether or not it is actually true, but a google book search reveals that it is genuine folklore at least. SpinningSpark 01:04, 30 December 2010 (UTC)

I doubt it's true. Why would a maple want to catch water on its leafs? Plus how could it do it before the rain? Ariel. (talk) 01:18, 30 December 2010 (UTC)

(edit conflict) Here's an actual link for that: [1]

Speculation: there is often an updraft before a storm – the leaves of many trees will "turn up" in a very distinctive way preceding rain in that case, perhaps sugar maple leaves doing so are particularly distinctive...? WikiDao ☯ (talk) 01:20, 30 December 2010 (UTC)

In the UK there is a common phenomenon during summer whereby the leaves of trees appear to turn up, but in fact are showing there undersides because they are lifted by a southerly or south-westerly wind which often precedes a rain bearing atmospheric depression. Caesar's Daddy (talk) 08:39, 30 December 2010 (UTC)

It wouldn't do the tree much good if it DID have such a capability, since a function of leaves is to lose water and not absorb it. See Transpiration. Alansplodge (talk) 02:03, 31 December 2010 (UTC)

Normal leaves

during a dry period

Where I live there is a lot of Devils club. Normally they have broad, flat leaves the size of a dinner palte. When it is espescially dry these leaves can be seen to distintcly fold upwards. There must be some reason for this. If not to capture water, what would it be? Beeblebrox (talk) 19:57, 31 December 2010 (UTC)

It's possible that the change in pressure or increase in humidity before a rain storm could affect the leaves. Scientific29 (talk) 01:45, 4 January 2011 (UTC)

An unusual problem with viewing a 3D film.

There is, to my knowledge, a certain percentage of people that cannot see stereographic 3D effects - I am not among them. I am somewhat of a 3D enthusiast, I am a master of stereogram viewing (both parallel and cross-eyed) and enjoy viewing anaglyph images and autostereograms. I have seen many 3D movies in a variety of formats, including IMAX 3D and Fusion Camera system - either of which was apparently used to present the 3D in Tron: Legacy, a movie I saw just 20 minutes ago.

So you can understand why I am utterly confused by the fact that at the moment the movie was supposed to change over to 3D, I saw nothing of the sort - the image was flat. I had gone to see the film with a group of friends, and they all saw the 3D effect fine, and they are not the practical joking type. I switched my glasses with one of them during the credits and she said she saw the 3D clear as day, so it wasn't the glasses. All throughout the film I was stupefied, wondering whether we sat down in the wrong theater. I closed one eye and the other to check if the images for each were different for each eye, but they were identical. I took off the glasses and saw slight blurring like the image was focused "behind" the screen (and in fact I could see a slight 3D effect of the image "behind" the screen when I looked at the edges with the glasses on), but not the characteristic difference of blurring between near and far focused objects.

The biggest mystery was the previews, all of which were in 3D. I saw them in all their glory. The 3D effect in some of them took my breath away. And yet during the movie I saw none of that. I was very disappointed by this development.

I decided half-way through that they put the wrong version on and just enjoyed the movie. But when I told my friends it wasn't 3D they looked at me like I was crazy. I thought about it during the drive home, and I came to the conclusion that what happened to me was impossible, but it happened!

What could have caused me, someone who has never had a problem seeing 3D, to have this happen? This is the most bizarre thing that has ever happened to me, and I want to know what caused it so I can keep my sanity. Thanks in advance. Chris16447 (talk) 07:35, 30 December 2010 (UTC)

The only explanation I can think of is that your experience with autostereograms caused you to mentally cancel out the 3-D effect. As you will know, 3-D vision is processed entirely within the brain as an interpretation of what is "seen" by the eyes, so there must have been some discrepancy between what you expected to see and what was actually received by your eyes. I'm surprised that this lasted throughout the whole film. If it ever happens again, try closing your eyes for a while, then persuade yourself that the picture is just 2-D, then open your eyes and be pleasantly surprised. Dbfirs 10:24, 30 December 2010 (UTC)

An alternative (speculative) explanation is that you are colorblind and that your eyes cannot be fooled by any 3D system (there is more than one). Quest09 (talk) 13:43, 30 December 2010 (UTC)

I have not seen the movie, so this doesn't even qualify as good original research, but I was recently told by friends that are big 3D enthusiasts that the 3D effects in the movie were barely noticeable as well. 10draftsdeep (talk) 13:56, 30 December 2010 (UTC)

Colorblindless is definitely a red herring. No modern theater uses the old colored glasses; today's 3D films all employ polarization-based systems. TenOfAllTrades(talk) 14:31, 30 December 2010 (UTC)

Wouldn't that be a gray herring ? :-) StuRat (talk) 18:16, 30 December 2010 (UTC)

Even if they did use the colored 3D glasses, colorblindness wouldn't be an issue. All 3D glasses work by filtering the light that reaches your eyes so that each eye sees an image photographed from a slightly different angle. Whether you perceive those slightly different images in full color or not is irrelevant. —Bkell (talk) 14:42, 30 December 2010 (UTC)

It is just possible that, if you do not already wear spectacles for which you have been properly and recently sight-tested, and if as is probable the 3D system being used utilises directional polarisation, you have slight undiagnosed astigmatism which happens to make the image stream in one eye sufficiently less focussed as to hamper the 3D effect, especially when it is smaller. The everyday effects of mild astigmatism can be unobvious to the sufferer, whose brain compensates for them unconsciously. It might be worth your while to visit an optometrist. 87.81.230.195 (talk) 17:50, 30 December 2010 (UTC)

What I don't get is that the OP claims to have seen the previews in 3D just fine, but then couldn't see the movie in 3D. Did you change seats between the previews and the movie, Chris16447? I think the 3D effect gets worse the further from the center of the theater you are (but I'm not sure about that). WikiDao ☯ (talk) 18:14, 30 December 2010 (UTC)

The previews likely had the most extreme 3D effects, while the movie was more restrained. That's because the same level of 3D, which makes you want to see a movie in the preview, would probably make you sick, if you watched it for an hour or two. StuRat (talk) 18:18, 30 December 2010 (UTC)

They may have even made the effects more extreme in the previews. It might make sense to do so — a preview is a pretty brief encounter, and you'd want it to be eye-popping. But for a multi-hour viewing, eye-popping might turn into eye-strain too easily, at least amongst the non-enthusist population. My understanding is that it is not too hard to adjust the depth of a 3D film at different points in its production; it is not the case that it is simply "filmed in 3D" and that's the depth that it is permanently set to, I don't think. --Mr.98 (talk) 18:20, 30 December 2010 (UTC)

I think that depends on the type of movie. With a CGI movie, it's relatively simple to adjust the camera angles on an existing scene in the computer. With live-action, though, you're limited by the placement of the original cameras. Picture something behind a pole. The two cameras will hide different parts of the scene behind the pole. By moving the depth you also change what is hidden (from each eye) behind the pole. Hiding part that was visible before could probably be done simply enough with a computer, but creating the portion which was formerly hidden is a bit trickier. Your computer program would have to figure out the pattern on the wallpaper and then recreate it there, for example. To simulate this problem, place a vertical finger right in front o\f your nose, then close one eye while moving the finger forward and back, then repeat with the other eye closed. See how the portion of the room which is hidden (behind the finger) changes, in each eye ? StuRat (talk) 18:32, 30 December 2010 (UTC)

My understanding is that even in a "real life" 3D film, you can enhance or decrease the amount of depth perceived. I recall seeing something on this regarding one of the many 3D movies of awhile back; you can magnify or reduce the depth in specific scenes, and the director spends a lot of time trying to figure out what the magic depth should be for any particular scene. Obviously there are limitations to this, but I don't think you have to change it by much to have hugely different qualitative experience. --Mr.98 (talk) 20:58, 2 January 2011 (UTC)

98 may have a point. If the question-asker was sitting somewhere where the 3d effect was weak (or if his own stereo perception is weak) he still would have noticed the 3d during the previews because they're packed with crazy out-of-screen effects that you'd have to be completely stereo-blind to miss. The film, thankfully, had almost no out-of-screen gimmick shots. APL (talk) 20:17, 30 December 2010 (UTC)

Some things which can prevent the eyes from working together are:

1) Alcohol, causing the classic double vision.

2) Head injuries.

3) Obscured vision in one eye, due to dirty glasses or contacts, or "slime" on the eye. I often have this problem when I first wake up.

Also, you may just may see 3D effects less than others, so that this movie, with minimal use of 3D, was below the threshold you recognized as being 3D. StuRat (talk) 18:26, 30 December 2010 (UTC)

Obvious question : You realize that the film was only 3d 'On the grid', right? Real-world scenes were intentionally flat. (But strangely, not quite at the plane of the screen, so you needed the glasses throughout.) APL (talk) 20:17, 30 December 2010 (UTC)

I saw the movie recently and also particularly at the start and throughout other points in the movie was wondering if I was "getting" the 3d. Vespine (talk) 23:17, 30 December 2010 (UTC)

At the start there is no 3d to get. The movie is entirely 2d until Flynn enters the computer generated world of 'The Grid'. (Sort of like the color in 'The Wizard of Oz'.) APL (talk) 02:34, 31 December 2010 (UTC)

• I am wondering if it's possible that others will develop this same "immunity" to these new 3D films, and it ultimately will end up being just a fad instead of the new way all movies are made. Personally I would find that hilarious, but I magine a lot of people in Hollywood wouldn't see it that way. Beeblebrox (talk) 20:37, 31 December 2010 (UTC)

What I think is that perhaps the movie does not contain such "intense" 3d scene as the demo. In fact, most move does not contain sharks popping out of the screen... those are usually issolated to "science" type shows/imax or short demos. Imagine the strain you would feel if the body tries, reflexively, to jerk out of the way of the oncomming animal/item/etc. Plus, I also noticed that 3d cinema films are not 3d intensive as home cinema films. --Tyw7  (☎ Contact me! • Contributions)   Changing the world one edit at a time! 08:28, 1 January 2011 (UTC)

Amount of Lanthanum Chloride in a solution.

If a solution is 40% Lanthanum chloride and 60% water, how much pure Lanthanum chloride is there in 5mL of the solution? Abbott75 ღ 12:35, 30 December 2010 (UTC)

You are going to have to know the density of this solution, which because it is strong will deviate significantly from 1. Then from your volume calculate the mass and take 40% if it. Graeme Bartlett (talk) 12:47, 30 December 2010 (UTC)

Ok, thank you. If we know that Lanthanum chloride has a density of 3.84g/cm^3 and water 0.997g/cm^3 (@ 25 degrees), is there a formula for calculation the density of the solution from these numbers? Abbott75 ღ 13:24, 30 December 2010 (UTC)

Unfortunately not; since volumes are not additive in mixing two substances, you cannot simply average the densities. The density of the resulting mixture will depend factors which cannot be directly measured, excepting by measuring the density itself. In other words, you cannot calculate or derive the density of such a mixture, you'd have to measure it directly. --Jayron32 14:50, 30 December 2010 (UTC)

I couldn't (quickly) find a figure for lanthanum chloride, but the density of a 40% lanthanum nitrate solution is 1.4477 g/cm³. So 5 ml would weigh 7.2385 g and contain 2.8954 g lanthanum nitrate. Physchim62 (talk) 15:04, 30 December 2010 (UTC)

This typical commercial product has 42% LaCl₃ and a density of 1.46 g/cm³. That gives 3.07 g LaCl₃ in 5 ml. Physchim62 (talk) 15:11, 30 December 2010 (UTC)

Where are the new inventions?

The last two inventions which changed my life are the cell-phone and Internet, and that was long ago. Where is my flying car? My automatic driving car? My maid robot? Quest09 (talk) 13:38, 30 December 2010 (UTC)

See flying car (aircraft), DARPA Grand Challenge, and Roomba. -- kainaw™ 13:46, 30 December 2010 (UTC)

Well, this Roomba is no maid robot. It is expensive, doesn't cook, doesn't clean the bathroom, doesn't make beds... It is a far cry from a maid. Quest09 (talk) 13:49, 30 December 2010 (UTC)

Then look for other domestic robots. -- kainaw™ 14:16, 30 December 2010 (UTC)

I'm more concerned that it's not bristling with weapons.

Follow-up: if we had a very efficient battery, which would weigh just a couple of pounds and hold lots of energy, would a (Blade Runner like) flying car be feasible? Or does the problem lies elsewhere? Quest09 (talk) 14:04, 30 December 2010 (UTC)

If that was possible, then yes, but I don't think it is, due to inherent limits on how much energy a chemical battery can store. Batteries only store a few extra electrons on atoms, and electrons weigh around 1/1836 of the weight of a proton (a little more for a neutron). So, if you use an ion engine, you propel only a tiny portion of the mass of the battery out the rear of the plane, whereas a jet fuel engine can propel 100% of the mass of the fuel out the back. Plus, the battery powered plane would have the weight of the battery to carry the whole trip, while a conventional jet plane is much lighter when it lands, having much less fuel on board. (I suppose you could arrange for a system where spent batteries are ejected with parachutes, then returned to the base and recharged, but that doesn't sound very practical, either). StuRat (talk) 20:24, 30 December 2010 (UTC)

The problem is the definition of an "invention." Historians like to say the "printing press" was one invention; but it relied on several abstract concepts (like written language), several constituent technologies (like reflowable lead metallurgy), and several "sub-inventions" (like the hinge on the lever that operated the paper-press). So, you have listed "the internet" as an invention; but in fact that "invention" really depends on many thousands of abstract concepts (like Turing completeness), constituent technologies (like low-noise radio frequency modulation), and specific sub-inventions (like ARP/RARP). Yet, you and many others consider "The Internet" a single "invention" worthy of listing next to "The Transistor" and "Fire." My point is, it's up to historians to decide which abstractions and implementations count as An Invention, and which are merely Contributing Knowledge.

Personally, I consider the Wikipedia to be an important invention. Sure, it didn't pioneer any new physics equations and it suffers from a dismal lack of flashing lightbulbs that blink; but it is an accomplishment of technology. It is a simple synthesis of pre-existing technologies to address an actual social need (the need for free, free information). I would place the accomplishment of "invention of Wiki" on the same tier as "invention of packetized data routing" (another critical technology step towards making free information possible). Futurists have dreamed about a free encyclopedia for nearly a century. Some of the greatest minds of the 20th Century predicted such a device. (H.G. Wells predicted it in 1937, Vannevar Bush predicted it in 1945, Doug Engelbart demonstrated a very simple prototype in 1968). But until very recently, these geniuses lacked several critical pieces of technology necessary to implement their technology: they did not have digital computers; cost-effective display screens; packetized information transfer; and a few specific computer programming languages (in specific, free implementations of HTTP, PHP, and SQL that make it plausible to design a machine that bidirectionally communicates encyclopedic data to and from humans). While the Wikipedia is not a new ASIC technology, nor a new computer algorithm, nor a new energy source or material, it is an invention: it is the synthesis of present technologies to address a need. Other inventions - flying-cars, laser-ignition hydrogen bombs, smart-phones - all do exist; but they fail to address an actual need for the human species. We have finally invented the Wikipedia; at present, it takes the form of an Organization with semi-centralized repositories of huge digital electronic computers that are programmed in PHP and SQL, and relaying their information bidirectionally over wired and wireless electromagnetic signals to billions of small digital computers across the planet. Since the invention of the Printing Press, I am not sure that our species has made such an important contribution toward free, free information. Nimur (talk) 14:51, 30 December 2010 (UTC)

Nimur, thank you for bringing attention to the lack of flashing lightbulbs that blink on Wikipedia. Hopefully this will help the problem a bit: —Bkell (talk) 15:01, 30 December 2010 (UTC)

Do you think you could design a wikipedia-bot to make those blink every time vandalism is added to the project? Just monitor the recent-changes RSS feed and filter by evil bit. Nimur (talk) 15:31, 30 December 2010 (UTC)

Timeline of historic inventions (permanent link here) has inventions from the 21st century.

—Wavelength (talk) 15:55, 30 December 2010 (UTC)

Some other inventions in the "change your life" category might be GPS, Virtual Reality, flat screen (and now 3D) TVs, etc. While not all of these technologies are yet fully implemented, at some point we may instantly always know where we are relative to our destination (thanks to GPS) and be able to do many activities (games, shopping, exercise, gatherings with friends & family, business meetings, etc.) without leaving our living rooms (thanks to VR and high tech TVs). StuRat (talk) 18:07, 30 December 2010 (UTC)

It seems a little counter-productive that half our inventions are about finding your way around outside easier and the other half are designed to keep you from wanting to leave your house. Matt Deres (talk) 19:35, 30 December 2010 (UTC)

Well, they both seem designed to keep us from getting lost outside. It would have made for a different ending to The Shining, although perhaps Jack never would have gone nuts in the first place, if he had a Wii to play with, instead of talking with ghosts. :-) StuRat (talk) 20:08, 30 December 2010 (UTC)

Should someone come up with a cheap flying car, I would be first in line to vote to have its use heavily restricted. It's bad enough dealing with the hazards of regular automobiles, even though we've had hundreds of years to develop rules, regulations, and infrastructure to support them. The last thing I want is everyone and everybody flying a plane over my house! --Mr.98 (talk) 18:12, 30 December 2010 (UTC)

Here are some answers to specific inventions you asked about:

Flying car ? These have been made, but aren't very practical. Cars need to be tough, which means heavy, since we want to be able to survive a fender-bender, and they can't have big wings on them. The wings can be removed, but then must be stored somewhere, which is almost as inconvenient as just storing a whole plane. Thus, this may never be practical.

My automatic driving car ? This is a possibility, and work is being done on this now. The problem is safety, as a car that crashes only 1/1000th of the time would still be completely unacceptable. In the meantime, we could maybe have a car supplement your own driving, like warning you of hazards and pulling off the road and bringing the car to a safe stop if you slump over the wheel.

My maid robot ? This is probably the most practical invention in the short run. If it's small and light enough, and doesn't have sharp parts, it shouldn't be particularly dangerous, so we could handle ones that make occasional mistakes. They likely will be given one task at a time, until eventually they do most of the things a maid would do. We have vacuuming handled by the Roomba, and there are others that can deliver drinks, control the lights and temperature of a house, order food from the grocery store, etc. Whether it's best to leave all these as separate devices or combine them into one is an open question. A big improvement in artificial intelligence is needed to allow for a general purpose robot that you can tell to do something new, like "kill that hairy spider in the tub", so it can figure out all the steps to do it. StuRat (talk) 20:49, 30 December 2010 (UTC)

Regarding the car, I ask myself if it would crash very often in a specially adapted route. Imagine that you put some sort of sign for the robo-car to orient itself. In a road, it might be easier, mostly, you get a straight line, if something is in front of you, you brake. Quest09 (talk) 21:11, 30 December 2010 (UTC)

Well, that much is already being done. Cars in the higher price range have systems that, if the car strays too close to the middle line in the road (and the sideline, where applicable), will start shaking the steering wheel and even adjust the course - this is to (to an extent) prevent people from dozing off at the wheel and crashing. And while navigation systems are a far cry from autopilot for cars, you could argue that to an extent they do perform that role - the driver still has to do the actual driving, but now the car or a mounted device in the car takes care of the directions. TomorrowTime (talk) 21:32, 30 December 2010 (UTC)

The automatic driving car is already reality, it will just need 10 years of technological development and legislation to make it production ready. Both BMW and Audi have demonstrated it. BMW's autonomous 330i did a full-on flying lap of the Top Gear test track (with an extremely frightened Jeremy Clarkson at the wheel just in case he needed to take over the controls). Audi's autonomous TTS did a hill climb at Pike's Peak at a very respectable average speed. The technology is already there: military grade GPS, radar guided cruise control, lane detection systems, automatic road sign recognition, pedestrian and animal recognition, autonomous parking. All it needs is a standardised car-to-car communication protocol (which the manufacturers are already working on). The technology is basically ready, all we need is for it to mature and also for legislation to catch up. Zunaid 08:38, 31 December 2010 (UTC)

Is there any way of predicting the next killer application like Facebook? If anyone could do that, then their fortune is made. 92.24.176.169 (talk) 19:20, 31 December 2010 (UTC)

• Flying car: [2]. It's not cheap, and it it's not like The Jetsons flying car, but it's a start. Beeblebrox (talk) 20:41, 31 December 2010 (UTC)

Don't forget Roxxxy. ~AH1^(TCU) 17:27, 1 January 2011 (UTC)

You should know by now that we would have an article on the flying car: Terrafugia Transition. SmartSE (talk) 23:22, 2 January 2011 (UTC)

Dry cleaning chemical

We use the chemical called Tetrachloroethylene for dry cleaning . However, this chemical has become very expensive due to its increasing scarcity.Kindly recommend either a more easily available and safe to use alternative chemical or a combination of chemicals with their respective proportions. —Preceding unsigned comment added by 41.205.179.120 (talk) 14:12, 30 December 2010 (UTC)

Dry_cleaning#Solvents_used has some ideas. --Jayron32 14:48, 30 December 2010 (UTC)

Measuring my PC's power consumption with an oscilloscope

How could I do it? I'd appreciate if someone provided an "equivalent circuit", so that the setup is easier to understand. --Belchman (talk) 22:33, 30 December 2010 (UTC)

Apologies for not answering your question, but why not use a Wattmeter#Electronic_wattmeter? Are integrating oscilloscopes common? Dbfirs 22:44, 30 December 2010 (UTC)

You put a low-resistance precision resistor in series with the power flow, then measure the voltage (drop) across the resistor, for example http://www.rcgroups.com/forums/showthread.php?t=393591 You can also build a Current transformer which magnetically couples with the source to provide a fraction of the original current. Ariel. (talk) 22:56, 30 December 2010 (UTC)

If I understand correctly, by measuring the voltage drop across the low-resistance precision resistor I'll get the current drawn by my PC, right? But what about the voltage? How would I measure it? I'm afraid I can't connect my oscilloscope directly into the mains without getting something burnt. --Belchman (talk) 23:21, 30 December 2010 (UTC)

I think you can just assume the voltage is correct for where you live (110, 115, 120, 210, 220, etc.). If you want, you can measure voltage separately by running it through a very very high resistance precision resistor, then measuring through (NOT across) that resistor. It's A/C though, so the voltage is a bit complicated. If you are willing to assume it's a sine wave, then you can filter it slightly and then apply a correction factor (I don't remember how much). You'll need to do the same correction for the current as well since it's A/C current. Or you can leave it unfiltered and watch the waveform as is (see power factor to learn a bit more about what it will look like). Ariel. (talk) 23:39, 30 December 2010 (UTC)

This may sound really dumb, but what's the difference between "measuring through" and "across" the resistor? Probably I'm more than familiar with the concept, it's just the wording (I'm not a native speaker of AmE). --Belchman (talk) 23:52, 30 December 2010 (UTC)

Through:
----/\/\/\/\/\/\/\----(measure)-----

Across:
----/\/\/\/\/\/\/\------
    |             |
    |             |
    \--(measure)--/

Ariel. (talk) 00:13, 31 December 2010 (UTC)

Okay, that's what I thought. Anyway, it's a bit weird to my understanding to be measuring voltage "through" since there's no such thing as "absolute" voltage. I guess the "through" measure is the voltage between that point in your chart and the ground, right? --Belchman (talk) 00:31, 31 December 2010 (UTC)

In my chart the voltage source and sink is on the left and right (the open lines). When I say "through" it means the voltage passes through the resistor before being measured. Ariel. (talk) 01:25, 31 December 2010 (UTC)

BTW, I'm answering because you asked. But I'm a bit worried about you building/measuring this without really understanding it. At the very minimum please run all your tests via a GFCI outlet. Ariel. (talk) 23:41, 30 December 2010 (UTC)

(After Edit Conflict)

I'm not sure than an oscilloscope is the right tool for this job. Scopes are very versatile, so I'm sure some clever person could devise some way of making it work with enough extra components, but wouldn't you be happier with a watt meter like a Kill A Watt? APL (talk) 23:42, 30 December 2010 (UTC)

I'm an electrical engineering student and I have this cheap oscilloscope. I'm just 'playing' with it a little in order to understand it better. --Belchman (talk) 23:46, 30 December 2010 (UTC)

"Playing" with mains electricity isn't to be recommended... perhaps you should wait until you are further on in your studies when you'll be able to answer questions like this yourself. Then you should be able to experiment in a safe manner. --Tango (talk) 23:56, 30 December 2010 (UTC)

I should have said that I'm a graduate student, not an undergrad. And believe me it's surprisingly difficult to gather information about such a simple thing like this one... --Belchman (talk) 00:07, 31 December 2010 (UTC)

The reason you're finding it hard is that an oscilloscope is not the usual tool for the job. Most people who want to measure power consumption do it either directly with a wattmeter or indirectly with a voltmeter. --Carnildo (talk) 01:03, 31 December 2010 (UTC)

I strongly recommend that you do not attempt any of the suggestions above. Measuring directly at the mains cables is only something to be done if you are sure you know exactly what you are doing. I am fairly convinced that not even the people making the suggestions know what they are doing here. For instance, no one has mentioned that the scope needs to be earth free if the measurement is not to end with a loud bang and tripped breakers. Taking the earth off equipment is something that is done in a controlled lab environment but is in no way suitable for use in a home - especially one with children and pets present. In short - don't do it. SpinningSpark 16:32, 31 December 2010 (UTC)

If your house has an mechanical electric power meter with a spinning disk then you need only a stopwatch to calculate the power consumption of your PC, see Electricity meter#Electromechanical meters. Cuddlyable3 (talk) 00:59, 31 December 2010 (UTC)

Not a bad idea. Years ago I had one of these mounted above my workbench, with one side set to plug into the wall, and another with a socket for the device under test. Worked fine, though it was a little slow. No idea how to get one, and no memory of how I got mine. PhGustaf (talk) 01:11, 31 December 2010 (UTC)

Belchman, why do you think that you, "can't connect my oscilloscope directly into the mains without getting something burnt"? What is the voltage range of your 'scope? Do you have a 10:1 probe? If not, do you know the input impedance of your 'scope, and using that information, can you construct one using some appropriate resistors? Earlier replies told you how to measure the current waveform, so that, with a measurement of voltage, will give your the volt-amps. Are you satisfied with the apparent power or do you want to know the real power dissipated by you appliance? Is your 'scope dual channel, allowing you to measure the phase difference between the current and voltage? -- 119.31.126.66 (talk) 01:56, 31 December 2010 (UTC)

The current drawn by a PC is far from sinusoidal so a simple phase comparison with the supply voltage is not possible. One would need to measure the voltageXcurrent products at many points on the waveform and integrate. This would be practical only on a dual-channel digital recording oscilloscope. Cuddlyable3 (talk) 03:03, 31 December 2010 (UTC)

We are not allowed to give medical or legal advice, but dangerous electrical advice is perfectly ok? Apparently. I suggest that the OP buys something like this. Cheaper than an oscilloscope and perfectly safe to use. SpinningSpark 15:57, 31 December 2010 (UTC)

Here's another one SpinningSpark 16:00, 31 December 2010 (UTC) Marked "Out of stock. Discontinued." Cuddlyable3 (talk) 20:42, 1 January 2011 (UTC)

Surely a graduate electric engineering student, as you say you are Belchman, would know how to do all this already? Including how to measure through or across a resistor. Unless American degrees are like British A-levels. 92.24.185.225 (talk) 12:35, 2 January 2011 (UTC)

Molybdenum#Compounds_and_chemistry

Elevated temperatures makes Molybdenum react with oxygen to make tetraoxide. What is the threashold, in other words, which is the temperature point that makes Molybdenum form Molybdenum Tetraoxide with certainty?199.126.224.245 (talk) 23:51, 30 December 2010 (UTC)

No, the article says that it forms molybdenum trioxide with oxygen at high temperatures. The molybdenum trioxide article also gives values for standard enthalpy of formation and standard entropy. If you could locate a value for standard free energy of formation, you could get a fairly close answer to your question using the equation ΔG = ΔH - T * ΔS, where ΔG is free energy, ΔH is enthalpy, ΔS is entropy, and T is the temperature you are looking for. --Jayron32 00:53, 31 December 2010 (UTC)

Here. Will update the article shortly (you certainly mean trioxide - tetraoxide is not known). Materialscientist (talk) 02:07, 31 December 2010 (UTC)

It says molybdenum suffers from catastrophic oxidation above 790°C.--Stone (talk) 08:39, 31 December 2010 (UTC)

There is a problem with the question. Molybdenum trioxide becomes less stable with increasing temperature, not more stable. The same is true for any metal oxide. If you solve for ΔG = 0 (equilibrium), then ΔH = TΔS at T = 2208 K for MoO₃ ⇌ MoO₂ + ½O₂. But the reaction of oxygen with molybdenum is slow at room temperature, not least because you get a protective oxide layer on the metal surface. If you heat the molybdenum in air, the oxidation becomes faster, especially above 795 °C when the layer of MoO₃ on the metal surface melts. Physchim62 (talk) 11:32, 31 December 2010 (UTC)