May 14

Suppose you have 12 volt batteries, plenty of wire, and a piece of metal you need to pass an arbitrary voltage through, greater than 12. Is there any way to arrange the batteries and wires to do this? I don't know much (anything) about how electricity works, but it seems to me that if you put the batteries so that the negative end matches with the positive end of the next this should be possible. 24.215.229.69 (talk) 01:18, 14 May 2011 (UTC)[reply]

Yes, if you wire the batteries in series (which is what you're describing), you'll get a voltage equal to the individual battery voltage times the number of batteries. Two 12 volt batteries in series will yield (nominally) 24 volts. Acroterion (talk) 01:29, 14 May 2011 (UTC)[reply]

Batteries connected in series produce a voltage equal to the sum of the individual voltages. Batteries connected in parallel produce a voltage equal to the individual voltage. (Batteries connected in parallel should all have the same voltage.) See Series and parallel circuits. Dolphin (t) 05:34, 14 May 2011 (UTC)[reply]

Connecting batteries in parallel is inadvisable in practice. On the other hand, many bottery-powered electronic devices actually have up to six 1.5 volt batteries connected in series, so what OP asks for is actually done quite often. Just look at the battery holder of a remote control or wallclock etc you have, and you'll likely find an example for this. Further, some batteries you buy as a whole are internally composed of multiple batteries connected in series: for example the rechargable lead battery in your car is like this. – b_jonas 16:54, 14 May 2011 (UTC)[reply]

Using a large amount of wire to make an inductor, you can with an electronically controlled switch make a DC-DC converter that can increase the voltage considerably. Graeme Bartlett (talk) 10:58, 15 May 2011 (UTC)[reply]

...and without making an inductor you can also make a Charge pump DC-DC converter. Cuddlyable3 (talk) 20:01, 15 May 2011 (UTC)[reply]

Standard (North American) 9 V batteries are convenient for this, since the negative and positive terminals can be snapped together. I used to make ~50 V battery packs for lab use by snapping together 9 V batteries. I soldered a wire to the final + and – terminals (before snapping the batteries together), and then wrapped the whole assembly in electrical tape. This gives a nice sturdy higher-voltage battery.

Caution: connecting batteries in this way can produce voltages high enough to give you a painful shock. In principle, once you get over 50 V this could potentially be a lethal shock.--Srleffler (talk) 23:46, 16 May 2011 (UTC)[reply]

I guess this is loosely a "technology" question... My Leatherman multi-tool has a little nub on the screwdriver, as seen in this image on the right side of the "large screwdriver" about 3/4 of the way down. I searched "Leatherman diagram" until my eyes bled and none of them indicate what the heck that nub is for. Anyone? Thedoorhinge (talk) 02:28, 14 May 2011 (UTC)[reply]

Isn't it just there to give your finger something to grab onto when you want to pull out the screwdriver? Dragons flight (talk) 05:19, 14 May 2011 (UTC)[reply]

That's my guess as well. Note that unlike some of the other tools, the large screwdriver doesn't have a fingernail slot on the side of it, so some other means of grabbing onto it is needed. Red Act (talk)

Damn, I totally thought it had some obscure function. Well thanks for the info! Thedoorhinge (talk) 05:51, 14 May 2011 (UTC)[reply]

I have been told that an unidentified tool included in a Penknife is for getting stones out of horses' hooves. Cuddlyable3 (talk) 19:55, 15 May 2011 (UTC)[reply]

Cantor's diagonal argument shows that there is no Bijection between the real numbers and the integers. Therefore the infinity of the real numbers is greater than the infinity of the integers.

And for any finite number of dimensions, say N, the coordinates in the finite dimensional space (x0,x1,x2,x3,...,x(N-1),xN) can be bijected to the one dimensional real number line.

What happens when you have an infinite number of dimensions? (x0,x1,x2,x3,...) Where each coordinate x(i) is a real number. Is there a bijection between infinite dimensional space and the real number line? Hcobb (talk) 03:06, 14 May 2011 (UTC)[reply]

This would be better suited to the Math Refdesk, but the answer is yes, Cantor proved that the two cardinalities are the same. I'm not going to spell out the proof, but it involves arranging each infini-tuple of real numbers as a rectangular array by writing them in decimal form and lining up the digits vertically, then applying a pairing function to map the whole rectangular array into a linear sequence of digits. Any textbook on Cantor theory should include this proof. (The logic is very similar to the proof that the set of rational numbers is countable.) Looie496 (talk) 03:33, 14 May 2011 (UTC)[reply]

If x(i) is a real number, then x0 is a real number, so there's a bijection between (x0 in R, 0, 0, 0, ...) and R, but I don't know how to construct the full bijection between the infinite real vector and the reals, and I doubt it's very easy unless there's a diagonalization as Looie implies. Perhaps the more interesting question is if x(i) are in the integers or rationals instead of reals. In that case, I think the vector is still uncountably infinite, but again I don't know the bijection. Ask the Math Reference Desk. 173.8.151.126 (talk) 05:00, 14 May 2011 (UTC)[reply]

Can electrons in rest may set to motion using a magnetic field? —Preceding unsigned comment added by 175.110.91.49 (talk) 10:23, 14 May 2011 (UTC)[reply]

Not with a fixed magnetic field. However, a time-varying magnetic field creates an electric field, which of course will exert a force on stationary electrons. See Faraday's law of induction#The Maxwell-Faraday equation. Red Act (talk) 10:50, 14 May 2011 (UTC)[reply]

I've always assumed I have normal colour vision, but I just came across this, which is making me wonder. Can you read what this says? (There is actually a partial caveat on the associated explanation page, but that reveals the answer, and it's best to first try to read it without already knowing.) 86.181.206.103 (talk) 12:27, 14 May 2011 (UTC)[reply]

I can read it, but it is certainly not clear. I got the "right" answer, but I wasn't all that confident before I looked. And I know I am not color blind. --Jayron32 12:36, 14 May 2011 (UTC)[reply]

We don't answer medical questions. For what it is worth, you would need to look at a properly printed card anyway. Also, the color profile of your monitor may be way off giving a false rendition.--Aspro (talk) 13:14, 14 May 2011 (UTC)[reply]

Oh for goodness sake. —Preceding unsigned comment added by 86.181.206.103 (talk) 13:31, 14 May 2011 (UTC)[reply]

We do answer medical questions. We don't give medical advice, but that isn't the same thing. --Tango (talk) 16:43, 14 May 2011 (UTC)[reply]

Also keep in mind that there are numerous fake 'diagnostic' graphics that circulate. My WP:OR indicates this 'test' uses much less color contrast than the other tests I've seen. SemanticMantis (talk) 14:57, 14 May 2011 (UTC)[reply]

I can't read it and I'm colorblind. I've read that this may explain why my night vision is so good. Count Iblis (talk) 14:57, 14 May 2011 (UTC)[reply]

I think it's a psychological hoax to make us immagine we see something that's not there.190.56.112.55 (talk) 15:32, 14 May 2011 (UTC)[reply]

You can open the image in Photoshop or Gimp, and play with the Hue, Saturation, Contrast, and other parameters. Particularly, boost the saturation; then rotate the hue axis ("slide the hue bar") to rotate the red/green to a different axis in HSV space. This will assist the image in "popping out" perceptually. The image is very noisy and the purported "9" lacks a clean completion. That effect is independent of your ability to perceive red/green as separate colors. The image is therefore poor test of color-blindness; it conflates color-perception with outline-detection. Nimur (talk) 16:19, 14 May 2011 (UTC)[reply]

I could take a guess at why color blindness tests would deliberately use imperfect digits: a person who perceives the color contrast but only faintly (like me) could identify the greenest bits individually, then consciously fill in the connections, and figure out what the number is supposed to be. If the color contrast is perceived more strongly, an entirely different type of effortless edge detection is applied. Imperfections in the outline cause more difficulty for the "consciously working it out" method, thus ensuring that people who should fail the test do fail the test. I took the test with the big dots long ago, and they said I was color blind, and I remember that one of the numbers I failed on was a 6 that was pretty darn close to being a 5, which I figured out after it was too late to get credit for it. So apparently they've always been that way. 67.162.90.113 (talk) 05:34, 16 May 2011 (UTC)[reply]

Online color vision tests aren't all that great - not only is there issues with them sometimes being hacked up by amateurs, there's also issues with faithful color reproduction on computer screens, with CRT/LCD differences, differing color temperature settings, varying gamma correction, limited gamut, etc. I wouldn't trust a normal monitor to faithfully represent subtle color differences - there's a reason why imaging professional sometimes spend thousands of dollars on special color-correct monitors. That said, I was in a similar situation. I have glasses and so have been given Ishihara color tests a number of times without anyone mentioning anything, so I assumed I had normal color vision. However, like you I noticed difficulties with online color discrimination. It was only after I went to the eye doctor and explicitly asked for a thorough color vision assessment that I learned that I had slight red-green color blindness. The quick, several picture test they give you before they check your prescription is only intended to detect major, life altering color vision deficiencies (e.g. the "can't tell the red stoplight from the green stoplight" ones) - you have to use different plates to pick up the slight color vision issues (e.g. the "can't tell the difference between a bright yellow-green shirt and a bright yellow shirt" ones). Keep in mind that while many people go through life not realizing they have slight color vision issues, a change in color vision could be indicative of more serious eye problems. In my case, as I hadn't noticed any color vision issues until later in life, they scheduled me for additional tests with follow-ups a year later to check if the color vision was stable or if there was further deterioration. -- 174.31.219.218 (talk) 18:23, 14 May 2011 (UTC)[reply]

I was able to read the "49" very clearly. Maybe there is a continuum of near-colourblindness. ~AH1 ^(discuss!) 18:33, 14 May 2011 (UTC)[reply]

We are all "colour-blind" in some respects. Human perception of colour varies considerably, even between individuals considered to have "normal" colour vision. No retina detects the full gamut of colours accurately, but just takes samples in (usually three) detection ranges, These ranges vary slightly between individuals and the relative sensitivity varies enormously. For most people, the brain adjusts perception so that we believe we are seeing "normal" colours, but this is really just because we adjust our interpretation to match what other people claim they see. If one detector is unusually weak then the person is described as "colour-blind" because they are unable to detect distinctions that most other people can make, but there is indeed a continuum, and the definition of "colour-blind" will vary between cultures and tests. Dbfirs 06:42, 15 May 2011 (UTC)[reply]

It will show up more clearly on some types of monitors than others -- it is intended as a pure contrast in hue, but some monitors will show it as a difference in brightness as well, which is much easier to detect. Looie496 (talk) 19:53, 14 May 2011 (UTC)[reply]

I found this much harder than the colour blindness test that I took when I tried to join the Royal Navy many years ago - it was made up of large dots 2 to 3mm across a bit like this. I passed easily (only I failed my A Levels!). Considering the exhaustive nature of the other medical tests they did, I don't think they would have given me an easy option. Alansplodge (talk) 20:21, 14 May 2011 (UTC)[reply]

Is there any information ava;lable on the subject? This is as opposed the the phenomenon of missing time. I'm sure that there is documentation on people having experiences where a sequence of events takes place in a period of time that is far too short to account for the experiences realized. Links to this phenomenon, specific or general would be of help. There must be an explanation out there. 184.211.105.250 (talk) 15:07, 14 May 2011 (UTC)[reply]

Time perception is our overview article. Before resorting to the paranormal, you should know that experimental psychology has repeatedely demonstrated that most humans are very poor observers of time. The "perceived" amount of time can deviate from the actual duration of an event by several orders of magnitude. Our article provides several good references on the subjective nature of human comprehension of duration. Nimur (talk) 16:10, 14 May 2011 (UTC)[reply]

(And for the uninitiated, "missing time" or "lost time" typically refers to the purported UFOology/abduction-related effect of unaccounted minutes or hours). Nimur (talk) 16:11, 14 May 2011 (UTC)[reply]

See [1] Tevildo (talk) 16:23, 14 May 2011 (UTC)[reply]

There is an experiential phenomenon based around falling asleep, where whole scenarios seem to take place in the blink of an eye. I have had this for many years, and a doctor told me it was a sleep phenomenon, like lucid dreaming or the sensation of falling and waking up suddenly. However he didn't tell me the Latin name! --TammyMoet (talk) 16:33, 14 May 2011 (UTC)[reply]

See also flow (psychology) and deja vu. ~AH1 ^(discuss!) 18:31, 14 May 2011 (UTC)[reply]

What is the product formed from the reaction of methyl alcohol and NaH? —Preceding unsigned comment added by 109.79.6.247 (talk) 15:28, 14 May 2011 (UTC)[reply]

See Alcohol#Deprotonation. I've added a section header to your question, as well. Tevildo (talk) 16:08, 14 May 2011 (UTC)[reply]

Hello! The US and Europe have different mains voltages, so will a microphone bought in the US work properly with recording equipment in Europe if they both have XLR connectors? I assumed that the XLR specification would require a specific voltage that the recording equipment would have to provide regardless of the mains voltage, but the article XLR connector isn't clear on the voltage specification, and I haven't been able to find online the EIA Standard RS-297-A that the article references. Thank you.--el Aprel (^facta-_facienda) 18:48, 14 May 2011 (UTC)[reply]

To be clear, the recording equipment is manufactured in Europe, so it can handle the European mains voltage. I'm just concerned that it might pass a higher voltage to the US microphone. Thanks.--el Aprel (^facta-_facienda) 22:35, 14 May 2011 (UTC)[reply]

It should be fine, the article you are after is Phantom power. Vespine (talk) 01:47, 16 May 2011 (UTC)[reply]

I don't know why "Looie496" saw fit to remove this question as I'm not a "banned editor" as he/she claims, so here it is again. 92.28.246.151 (talk) 22:16, 14 May 2011 (UTC)[reply]

Why are some butterflys brightly coloured? Surely this would make them too visible to their bird predators? Thanks 92.29.120.214 (talk) 23:30, 13 May 2011 (UTC)[reply]

The colours advertise the bad taste. That's why you never see birds attack butterflies. --T H F S W (T · C · E) 23:32, 13 May 2011 (UTC)[reply]

This article is very interesting, and related to your question. Oops—I'm not sure if the whole article is available online. Bus stop (talk) 23:46, 13 May 2011 (UTC)[reply]

Well, not just bad tastes. Others use it for different purposes too - some have things that look like large cat's eyes, and other clever defenses. And some butterflies are dull coloured and use camouflage for defense. --T H F S W (T · C · E) 00:50, 14 May 2011 (UTC)[reply]

I thought it was only the nocturnal butterflies that have dull grey colors. – b_jonas 22:57, 14 May 2011 (UTC)[reply]

Editorial note: A geolocate on the IP says that this question was almost certainly posted by LightCurrent, who is banned from the reference desks and only asks questions because he enjoys bragging about getting people to waste their time answering them. Looie496 (talk) 23:39, 14 May 2011 (UTC)[reply]

Heh, joke's on him, I find the best way to learn is by answering others' questions. Gets me thinking about stuff I thought I knew.-RunningOnBrains^(talk) 10:44, 15 May 2011 (UTC)[reply]

You are mistaken. I've never heard of "Lightcurrant". He or she is certainly not me. 92.15.25.241 (talk) 15:41, 15 May 2011 (UTC)[reply]

Ditto to Runningonbrains. And @b_jones I believe there are diurnal butterflies and moths that have dull colours at well. This may work the other way around too - is the luna moth active in the night? --T H F S W (T · C · E) 03:12, 18 May 2011 (UTC)[reply]

Photons will diffract and interfere with itself if shot at slits that are of sufficient size. The same will happen for larger electrons, protons and atoms. According to a physics textbook, even Buckministerefullerene molecules will exhibit diffraction. When does this phenomenon stop? In other words, what is the largest object that will diffract and interfere with itself when shot at slits of proper size? How come I don't diffract and interfere with myself if I walk through two open doors? Thanks Acceptable (talk) 23:16, 14 May 2011 (UTC)[reply]

How can you tell that you're not diffracting? Dauto (talk) 23:24, 14 May 2011 (UTC)[reply]

The "Particle diffraction" section of our Diffraction article would be my first place to check. I think some virus-particles have been diffracted (but not mentioned there). But anyway, the article talks about the limits of size vs wavelength. You can calculate the value for any object and (as Dauto suggests) figure out what the effect would likely be. DMacks (talk) 23:27, 14 May 2011 (UTC)[reply]

The effect effectively stops when the decoherence rate becomes so large that a description of the system in terms of pure states always breaks down. You can formulate this problem as follows. If you have a superposition of an object being at position x1 and x2, how long does it take for the environment to "detect" the position of the object? You can find some formulas in e.g. this paper (formula 4.1 gives some times scales, figure 1 illustrates the intitial situation of the superposition). Count Iblis (talk) 01:13, 15 May 2011 (UTC)[reply]

You can walk through two doors simultaneously? That's one novel way to deal with the problem of The Lady, or the Tiger. Clarityfiend (talk) 03:17, 15 May 2011 (UTC)[reply]

A person can walk through two doors at once, but I think they each have to be less than about 10^-35 nanometers wide for this to work. See de Broglie wavelength. Wnt (talk) 18:28, 15 May 2011 (UTC)[reply]

A person can walk through both these doors at once. Cuddlyable3 (talk) 19:47, 15 May 2011 (UTC)[reply]