Wikipedia:Reference desk/Archives/Science/2007 August 1

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 1

The Nile River

Is there a current consensus about the "false" source of the White Nile? Is it in Rwanda or in Burundi?

Help!!!!!anyone help me with this question....i have an exam just few hours to go....i need the anwser as quick as possible

this is a practice b4 exam...the question goes like this:

Why do aquatic veterbrates have smaller skeletons than land vertebrates?

although this question might not pop up during the exam but i was curious to noe the anwser... this question was found in the notes given by the teacher.

60.48.92.187 01:38, 1 August 2007 (UTC)zhiting

As the top of the page says, Do your own homework. Although this should be really, really, really obvious --Longing.... 01:48, 1 August 2007 (UTC)

That seems harsh... the questioner isn't asking for help with homework, but with studying. And we don't know his or her age or background. To the questioner: try looking at buoyancy and skeleton. --Allen 01:53, 1 August 2007 (UTC)

It is homework, though. It has nothing to do with age or background, just thinking about it scientifically would lead you to "What's different about these two creatures?" which would you lead you to the obvious answer --Longing.... 01:57, 1 August 2007 (UTC)

Well part of what the class is probably trying to teach them is to "think scientifically" which clearly the poster can't do (how easy it is to forget that we didn't all think scientifically once! how quickly we take as natural what took centuries for humans to develop!). I don't think there's anything wrong with just pointing them in the right direction. --24.147.86.187 02:02, 1 August 2007 (UTC)

And in that direction...try thinking about the purpose of a skeleton, and the different needs the two types of animals would have for anything that fulfilled that purpose. Someguy1221 02:32, 1 August 2007 (UTC)

Too late for the exam now, but is this statement even true? Does it mean as a proportion of body weight? After all, the largest vertebrates are blue whales and their skeletons are enormous! I would suggest though, lightness for buoyancy, and the natural support of the water means not as much strength is needed in the skeleton. Cyta 07:10, 1 August 2007 (UTC)

Cyta: yes. From what I remember talking to a friend (who keeps fish and knows everything anyway), most fish have far less dense or narrower bones than we do, because they're underwater, they don't have to support as much weight. The above link to buoyancy would help here. Although, you are correct, that whales have much much larger skeletons than we do, proportionally. --Longing.... 11:16, 1 August 2007 (UTC)

I think the amount of weight that underwater vertebrates have to support is always zero, because they achieve neutral buoyancy in the water instead of being forced down upon the ground by gravity as land vertebrates are. I guess the backbone is for rigidity purposes, so that the vital organs don't get crushed when the animal is maneuvering violently. --Bowlhover 21:10, 2 August 2007 (UTC)

Blindness from birth affecting how one learns body language, etc.?

I have been searching, including on your pages regarding autism spectrum disorders and congenital blindness, and I'm still a little confused. Is body language something learned through observing others in the first few months of life? And, if it is, how is it that blind people are able to pick up, if not all the visual cues, at least enough nonverbal cues to not be labeled as having a PDD, if they can't see to pick up those cues? Is it the context of a situation that blind and visually impaired people can pick up if they don't have an autism spectrum disorder? Or, do most visually impaired people also lack some social skills based on the fact they'd can't pick up body language well? I know a few, and they seem to be okay with social situations, though of course they have to be told if someone is leaving a room, etc.. I would think the problems with social skills, making friends, etc., with those with autism spectrum problems would be all traced back to the inability to read such langauge.DTF955 02:43, 1 August 2007 (UTC)

I think you are making several quite large assumptions. One factor that you seem not to be taking into consideration is just how highly a sight able person would modify their own behaviour and theibeing recognised would most likely offer a more then compensatory lenience in that regard. Vespine 06:07, 1 August 2007 (UTC)

Good point - being partly blind myself, I guess I don't really consider how that would differ fromt he way a sighted person would do it. (Or, maybe I have a PDD :-)

Amesbury Archer had unusual configuration to the bones in his feet.

Apparently the body buried near the Archer is presumed to be a relative because they shared this configuration.

"An analysis of the bones later showed that he and the Archer were related as they both had the same unusual bone structure in their feet – the heel bone had a joint with one of the upper tarsal bones in the foot."

Is there a diagram of what this looked like? How unusual or rather, how common would this be in the human population? Have other examples of this trait been discovered in other ancient skeletons? If so, which ones?

Is this trait common to a particular group of people or region of the world?

Weaver137 03:31, 1 August 2007 (UTC)

It is not clear from the Amesbury Archer article and what's available from the Wessex Archaelogy website exactly what the variation seen is. It appears to involve the calcaneus (heel bone) and navicular, a bone on the instep side of the foot. This is called calcaneonavicular coalition. If it is a complete fusion (synostosis), it is exceedingly rare ( 0.03%). If it is a partial articulation (synchondrosis or syndesmosis), it would occur about 5.6% of people.[1] It is not specific to people from a region, but there is a heritable aspect to their occurrence, especially the 0.03% event. There are radiographic images in the link above, but they are seen from a 45 degree angle, so they look odd. Here are another few images. Flyguy649 ^talk _contribs 05:14, 1 August 2007 (UTC)

I%, which is pretty small although not beyond the realms of possibility. The argument that they are related likely has to do not only with this statistical probability, but also with respect to their features. I believe they had the same colour hair. Flyguy649 ^talk _contribs 13:57, 1 August 2007 (UTC)

Wormholes

What is the debate about wormholes? What do scientists and people think about wormholes?Invisiblebug590 04:15, 1 August 2007 (UTC)

Have you read wormhole? --TotoBaggins 04:47, 1 August 2007 (UTC)

The physics pretty much says that they could exist - but we have never found one and we know we couldn't possibly create one - so as a practical matter, they aren't all that interesting. (except of course to SciFi writers!) SteveBaker 10:46, 1 August 2007 (UTC)

I found one yesterday, in an apple of all places. Gzuckier 14:40, 1 August 2007 (UTC)

Had you already eaten half of the apple with no sign of the worm in what remained? Nil Einne 15:42, 1 August 2007 (UTC)

Reminds me of the joke:

Q:"What is worse than biting into an apple and finding a worm?".

A:"Finding half a worm !"

--WikiCheng | Talk 05:04, 2 August 2007 (UTC)

Also, when selecting apples, avoid the ones with odd numbers of wormholes! SteveBaker 01:30, 3 August 2007 (UTC)

Or better yet, avoid the ones with wormholes! --antilived^{T | C | G} 05:14, 3 August 2007 (UTC)

Solar Cells

Hi, just wondering if someone can answer this question (I've had a look at the solar cell article buion just occur within the cell, and how come in most diagrams I've looked at the electrons flow through the external circuit from the n to the p half, effectively travelling from a region of conventional high potential to a region of conventional low potential (the opposite direction to which they should be travelling)?. Thanks Guycalledryan 05:02, 1 August 2007 (UTC)

Once the pair has separated, the n side has one more electron and the p side one fewer than before. Since with no current flow (a dark cell) the potential at the two ends of the cell must be the same, with the new arrivals the potential at the n end is now lower than at the p end. Since electrons flow "uphill", an electron at the very end of the n region (there are plenty there!) and a hole from the end of the p region traverse the wire and the load and annihilate somewhere outside the cell. This is simply the path of least resistance: the depletion zone is an insulator, so the restorative current flows through the load instead. --Tardis 15:18, 1 August 2007 (UTC)

human anatomy

some anatomical part that begins with the letter y

See List of subjects in Gray's Anatomy: Alphabetical: Y (plus you might also find some Yersinia bacteria in a human body) and List of acupuncture points has quite a lot that start with y. JMiall₰ 12:31, 1 August 2007 (UTC)

Your arm, your leg, your head, your foot and so on and so forth :P Lanfear's Bane 12:49, 1 August 2007 (UTC)

Y chromosome. FYI, the reason you won't find many such words is that in ancient Greek, from which most English anatomical terms are derived, a word starting with Y was always spoken with a "rough breathing", which means it would be transliterated into our Roman alphabet with an initial "H". This explains why there are so many medical words beginning with "hy" and almost none beginning with "y". --TotoBaggins 13:13, 1 August 2007 (UTC)

yeux (if you're French). Physchim62 (talk) 14:08, 1 August 2007 (UTC)

natural abundance

I need to learn how to compute the natural abundance of an isotope. Anyone wanna share? --MKnight9989 13:49, 1 August 2007 (UTC)

The natural abundance of an isotope is just how much of it is found somewhere (in the universe, in the solar system, on the Earth, in Iowa, etc.). You can't compute it any more than you can compute "how long is a piece of string?"; you just have to measure it. --TotoBaggins 14:08, 1 August 2007 (UTC)

Sorry to be a real pain, but you can compute how long a piece of string is, in many ways. You'd have to measure something else, but you could compute it (for example, make it into a pendulum, or use some trigonometry and some other measurements, or burn it and another piece of string of known length, etc.). However, you cannot compute the natural abundance of an isotope, unless you know the standard atomic weight and the relative atomic mass of all the other isotopes, as stated below. --80.229.152.246 22:14, 1 August 2007 (UTC)

If you don't want to measure it, you can look up terrestrial values in a table such as this one. Physchim62 (talk) 14:12, 1 August 2007 (UTC)

As much as I'd love to, I have to know how to calculate myself for school. Thanks anyway though. --MKnight9989 14:50, 1 August 2007 (UTC)

Using the table linked to by Physchim, Standard Atomic Weight = the sum of [(Relative Atomic Mass of isotope 1(RMA1) x Isotopic Composition of isotope 1(IC1)) + (RMA2 x IC2) + ...]. I'll let you plug in the values, and figure out what you have to do if you are given different variables. Using Helium as an example may be the simplest. Flyguy649 ^talk _contribs 15:13, 1 August 2007 (UTC)

Maybe what you're looking for is how to calculate abundances from mass spectrometry data? You will find an example mass spectrum of neon at this link. What you have to do is add together the heights of all the peaks to find a number which I shall call total height. The abundance of each isotope is height of isotope peak/total height. For the neon example, total height is 110.5 units, while the height of the peak for neon-22 is 10.2 units: hence the abundance of neon-22 is 10.2/110.5 = 9.23%. Note that I didn't choose neon as an example by chance... Physchim62 (talk) 02:21, 2 August 2007 (UTC)

Frog

In Upstate New York in the Catskill Mountains, I often catch and release a kind of frog that are simmilar (but not the same) in shape and colouring to the leopard frog, but much smaller. Anyone have any ideas on what kind of frog it might be? If so, thanks a lot! --Gbgg89 14:48, 1 August 2007 (UTC)

Federal forest service lists the following toads/frogs in the area: American toad, green frog, gray treefrog, northern spring peeper, and Fowler's toad. -- Kainaw^(what?) 14:53, 1 August 2007 (UTC)

There are other frogs found in New York state than listed above. The species closest in appearance to the Leopard Frog (Lithobates pipiens) is the Pickerel Frog (Lithobates palustris). It is similar to the Leopard Frog, but the dark brown spots are more rectangular than circular, and it is smaller with an average body length of 2.5 inches (as opposed to the Leopard that is 3-4 inches). Check out the website at nyfalls.com/wildlife for a complete list of New York amphibians. --Eriastrum 17:04, 1 August 2007 (UTC)

Thank you so much! Yes, the Pickerel Frog is the frog that I have caught there. I have been wondering what it was for a while, so thank you so much! --Gbgg89 20:41, 1 August 2007 (UTC)

residue left when bleach dries

Help please!!!!!

When belach dries it leaves a white crystline residue. My boss wants it removed from painted surfaces, ceramic tile and chrome. Any suggestions that will save minimum paid employees hours and hours of scrubbing uselessly to remove the stuff?

Many thanks on any help that you can give.

Don't you mean The Boss? *joking* Nil Einne 15:29, 1 August 2007 (UTC)

On a more serious note, does ordinary water not work? Perhaps you should try a greater dilution? Nil Einne 15:42, 1 August 2007 (UTC)

It is possible the bleach has etched or corroded the surfaces rather than left a residue. Lanfear's Bane

use a bathroom cleaner such as vim (cleaning product) or flash, cif whatever you call it, plus water - you'll still need to scrub.83.100.138.237 16:39, 1 August 2007 (UTC)

White stuff on old batteries

Are the white crystalline residues on old batteries harmful?

It's probably some of the electrolyte and generally won't be that harmful but I would recommend you wash your hands afterwards and definitely don't lick it. But for more info, you need to say what old batteries? Alkaline? Lead acid (car etc batteries)? NiMH? NiCad? Li-ion? Lithium? Zinc-carbon? Where on the old batteries? Terminals? External covering? On the electrodes (for lead acid batteries)? Nil Einne 15:16, 1 August 2007 (UTC)

Just a regular AA battery. I left them in my wireless mouse for long after they were dead. The stuff was most abundant around the metal +/- things where the batteries connect to the device. Some actually creeped outside the battery container. 128.163.224.198 16:29, 1 August 2007 (UTC)(original poster)

If they were alkaline it's probably potassium carbonate - slightly corrosive and not for eating as said above, it's a good idea to clean it out of your mouse (use wet rag, then dry) as it can encourage further corrosion of the terminals. No more harmful than strong floor cleaner...83.100.138.237 16:37, 1 August 2007 (UTC)

Alkaline batteries use potassium hydroxide as an electrolyte, which will turn into a white residue if the water is evaporated. Potassium hydroxide is a very strong base used in high-duty drain cleaners, so although there isn't enough in a battery to cause serious harm, throw the battery away! --Bowlhover 21:21, 2 August 2007 (UTC)

Entry of blood from marrow to circulatory system

How does blood generated in bone marrow enter into the circulatory system? Morton00 16:46, 1 August 2007 (UTC)

Bones aren't simply dead things; they contain a matrix of living cells and these cells have the usual blood supply that connects with the rest of the circulatory system. So marrow cells also have access to the circulatory system.

Atlant 17:15, 1 August 2007 (UTC)

Understood. It's the path that the blood takes that I wonder about. Is the bone porous enough? Do arteries and veins enter the bone at some point?

Bones are filled with blood vessels. They travel in longitudinal and transvers "canals". See images at Bone#Macrostructure, for example. Flyguy649 ^talk _contribs 19:24, 1 August 2007 (UTC)

How many human diseases are there?

Any numbers/estimates?128.163.224.198 16:58, 1 August 2007 (UTC)

A way to get an estimate is to look at ICD9 codes. They codify each disease and subsection of diseases. If you can find a count of how many ICD9 (or ICD10) codes there are, you'll have an estimate for the number of diseases. -- Kainaw^(what?) 17:04, 1 August 2007 (UTC)

But ICD9 codes also include injuries as well as diseases, don't they? Corvus cornix 21:46, 1 August 2007 (UTC)

Ah, yes, see List of ICD-9 codes. Corvus cornix 21:47, 1 August 2007 (UTC)

Isn't that a matter of what you consider to be different diseases? For example, is the cold one disease or do you distinguish between different types? And what about last week's outbreak in Milan (making that up), is that a separate strain? It's probably distinguishable from the strain that hit Rome a week earlier and from which it evolved. I don't know this, just wondering. DirkvdM 07:11, 2 August 2007 (UTC)

Regarding the strain, I don't know how biologists distinguish each in classifying when one becomes a "diferent" disease. I'm guessing all strains of a virus count as one disease, barring any characteristic that makes it totally different from other strains.128.163.245.13 14:45, 2 August 2007 (UTC)(question poster)

I guess there isn't a good, set estimate out there? I don't think I can count all of the codes :) (Each number sometimes correspond to many diseases). But from glancing at the list of codes, it's safe to say there are a few thousands.128.163.245.13 14:45, 2 August 2007 (UTC) (question poster)

Right - and when you start worrying about whether this years influenza strain is a different disease from last years strain - you get into some very grey areas. You also have stuff like lactose intolerance - which isn't a disease because it's 'normal' - with lactose tolerance being the newly evolved 'abnormal' thing...and then there are 'diseases' such as Asperger syndrome - where a majority of the 'victims' feel it's an advantage to have it and would not wish to be cured. How about things like Sickle-cell disease which gives the benefit of protection against malaria - at the cost of severe illness and often death for those who inherit it. How do you count a set of things like that? SteveBaker 15:28, 2 August 2007 (UTC)

I'm still really curious to know a mathematical estimate for how many diseases, illnesses and disorders etc, ie: things that can go wrong are there? (And maybe even see the answer broken down into categories, and probablities).

Trolleybus/Trackless Trolley

Can a trolleybus run off from underneath the transmission wires above? What happens if this occurs? How is it reattached to the electrical distribution system? Thanks. - MSTCrow 19:02, 1 August 2007 (UTC)

It happens frequently, often at junctions for the wires, IIRC. The bus stops quickly, the driver gets out and replaces the trolley poles onto the wire. (there are spring-loaded ropes at the back of the trolley that attach to the poles that the driver uses to pull down and move the poles. You can see them in this Image:Translink-2744.jpg) Because there are two poles, one is usually stowed first. It takes about a minute. Flyguy649 ^talk _contribs 19:18, 1 August 2007 (UTC)

That's the primary answer all right, although it should be said that there have been trolleybuses without the retriever ropes (I've been told that this was usual in Britain when they were used there), in which case a long, lightweight pole with a hook would be used instead. But the primary method only works if the trolleybus is close enough to the wires for the poles to reach. If a driver is new to the route, or otherwise absentminded, it's possible that they will do something like going straight ahead at an intersection where the wires turn left. By the time they've braked to a stop, the wires are out of reach of the poles. I've seen it happen once (involving parallel bus driveways, some wired and some not, rather than a street intersection). In that case the solution is simply to push the trolleybus back under the wires with a non-electric vehicle, like a truck.

I also once saw a trolleybus stopped with a pole sticking up the middle of the diamond where two pairs of wires crossed! (This was at the same place, in fact.) Presumably when stopping the trolleybus after the pole had come off, the driver had let it roll backwards a little on a slope, creating a position where the usual retrieval by rope was impossible. I didn't have time to stick around and see how they dealt with it, but I assume a repair person was sent out and either (1) removed the pole from the trolleybus, (2) removed one side from the diamond, or (3) lifted the wires above their usual level so the pole could be retrieved by rope, whichever was easiest.

Incidentally, I once saw a different use of retriever ropes, after a trolleybus had failed in the street. This was a 4-lane street and the normal procedure would be to just lower the poles; if the failed vehicle was in the right lane, following trolleybuses would pass it on the left, and if in the left lane, they would pass it on the right. But this one had been in the middle of changing lanes, so it could only be passed by swinging out into the other side of the street, which would have taken the following trolleybus off the wires. So what they did was, they did exactly that -- with a man running along behind it! Oncoming traffic was stopped, and at the critical position the running man pulled down the poles while the trolleybus was moving; then the driver steered into the opposite side of the road, coasted past the obstacle, and returned to the correct side, then stopped for the poles to be put back on the wires.

In some cities they use trolleybuses with batteries that can power the vehicle for a short distance off the wires. They're missing all the fun.

--Anonymous, August 2, 2007, 04:59 (UTC).

Here in Innsbruck, the buses seems to have a small auxiliary Diesel engine. They make a lot of noise and smoke but move the bus only very slowly, but I've seen them used only once. In general, the buses don't seem to loose grip on the wire very rarely -- I haven't seen it happen yet and suspect that they use their Diesel engine mainly when parking in their bus park. Simon A. 07:04, 2 August 2007 (UTC)

Type of thought disorder?

I was wondering if there was a recognized type of thought or general disorder where the afflicted had uncontrollable thoughts. The types of thoughts could include reoccurring phrases and other things that annoy the afflicted person or that they disagree with. Sorry for the ambiguity. --74.97.142.249 20:30, 1 August 2007 (UTC)

There's a WP article on intrusive thoughts. Haven't read it myself. --Trovatore 20:34, 1 August 2007 (UTC)

Thanks Trovatore, that seems like a good place to start. --74.97.142.249 20:54, 1 August 2007 (UTC)

Yes, this is rather ambiguous, and could apply to any number of mental disorders (to be honest I think most, if not all, people experience uncontrollable thoughts, which is not to say these thoughts adversely affect their normal life, which is I guess where it would become a disorder). It certainly would seem to relate strongly to schizophrenia, and I'd have to say, even depression. --jjron 09:10, 2 August 2007 (UTC)

I seem to remember seeing a documentary about Obsessive compulsive disorder which referred to some extreme cases whereby sufferers who can't help imagining the worst possible outcomes from any scenario, however outlandish, along the lines of "there's the breadknife, that's dangerous, wouldn't want to hurt anyone, my wife's over there, I mustn't kill my wife with the breadknife". This was some time ago, I have no medical knowledge and a dodgy memory, so someone who knows what they're talking about is welcome to put me right. --Dweller 13:24, 2 August 2007 (UTC)

Ah! I see from our article on OCD (that I so helpfully wikilinked, lol) that my memory may not be so flawed after all, though I suppose my example might be. --Dweller 13:25, 2 August 2007 (UTC)

What is the definition of ORTHODOSES?

What is the definition of ORTHODOSES?

Are you sure you don't mean Orthoses? --Mdwyer 22:00, 1 August 2007 (UTC)

Or Orthotics, which is basically the same thing, but a far more detailed article. --jjron 08:50, 2 August 2007 (UTC)

Laser Pointers

I have a 532 nm, <50 mW laser pointer that takes 2 AAA batteries. I have two questions about it:

1. What will happen if I stick an extra little button-cell battery in series with the other two AAA batteries and press the "on" button?
2. How can I make this laser more powerful?

Thanks. Steevven1 ^{(Talk) (Contribs) (Gallery)} 22:03, 1 August 2007 (UTC)

If it is a red laser pointer, you cannot make it more powerful regardless of anything you do. It isn't truly an authentic laser. It is, if memory serves, a gallium arsenide LED shining through a small hole. The best you could do is try to get three or four in perfect phase with one another with mirrors - but only being off by a fraction of a nanometer will weaken the whole beam. -- Kainaw^(what?) 01:30, 2 August 2007 (UTC)

A laser shining through a hole is still a laser. What is it that makes you think it is not a laser?Edison 02:19, 2 August 2007 (UTC)

532 nm is green, btw. And, sorry I can't answer the other questions. Flyguy649 ^talk _contribs 02:26, 2 August 2007 (UTC)

Er, I'm not quite sure where you're coming from on this, Kainaw. As far as I know, even the cheap little keychain laser pointers use a laser diode—not to be confused with a light emitting diode (an LED). (This page has some pictures and information.)

I agree - I've owned half a dozen of these things over the years and I've never seen a 'laser pointer' that was just a non-laser LED shining through a small hole - such a cheap trick wouldn't work anyway - the light would still diverge too rapidly to be useful as a pointer. The thing User:Kainaw is looking at is a laser diode - not a regular LED. They look kinda similar...but they aren't at all the same thing. Laser diodes are used (for example) in CD/DVD players. SteveBaker 12:00, 2 August 2007 (UTC)

Apparently marketing-speak is worse than I thought. A laser is "light amplification through stimulated release of radiation". In essence, light of the same frequency is bounced back and forth inside an enclosed area until the waves are in sync and powerful enough to push through a semipermeable barrier. Those little red laser pointers use an LED. It is often called a "laser LED" because it emits one specific frequency of light. However, it does not create this light through stimulated release of radiation. It does not amplify the light. It just emits a single frequency. Also, the light waves are not in sync with one another. So, if you point one of those red laser pointers at a spot a couple inches away, you get a very tiny dot. If you point it at a spot a hundred yards away, you get a much larger spot - because it is not a laser. It just an LED emitting a single frequency of light. I know that the marketing people behind those things will never understand the difference, but scientists should be offended that the term "laser" is used for them. -- Kainaw^(what?) 13:18, 2 August 2007 (UTC)

Careful...Laser diode specifically explains how "laser diodes" work, and it's exactly in the terms you expect for a laser (optical cavity, stimulated emission, etc). Whether a cheap laser pointer keychain actually has one, and what MarketSpeak is used to make a "really bright LED" sound like it's actually a laser? A different matter entirely. DMacks 15:29, 2 August 2007 (UTC)

Reading the article, it explains that it uses "laser diode" to refer to a specific type of LED that may be used in a laser to provide a coherent light source. To create a laser, more than the diode is required. The examples in the article are the classic laser design - the diode between a solid mirror and a partially silvered mirror. Laser pointers do not have the two mirrors - just the LED. Because it produces coherent light (as I stated, light emitted all of the same frequency), there is very little collision in the light beam compared to a normal light source. That allows the beam to travel a long way without much spread. However, it is not a laser in the proper sense of the term. It is, more precisely, a "coherent light pointer". Of course, this is way off topic for this question. -- Kainaw^(what?) 16:46, 2 August 2007 (UTC)

Kainaw, seriously, you have no idea what you are talking about. Laser diodes of the common type have an optical cavity built into the semiconducting material. That is, photons bounce back and forth within the semiconductor, hence there is no need for additional mirrors. That bouncing stimulates recombination of electrons and holes giving rise to additional light with exactly the same aspects as normal stimulated emission (i.e. coherent in phase and direction). Emerging from the semiconductor introduces a large diffraction effect, and hence common laser diodes spread much more than typical lasers, but that doesn't change the fact they operate through stimulated emission within an optical cavity. Also, I have no idea what you mean by "very little collision in the light beam", since photon-photon interactions are neglible. Dragons flight 17:28, 2 August 2007 (UTC)

Scientists should be offended in your utter bungling of the science! (Are you just making this up as you go along?) A laser diode is a laser (an injection laser). It is a different type of laser than you find in a lab (an optically pumped laser), but it is a laser. The beam grows in the air because of diffraction — it has nothing to do with it "not being a laser". All lasers will diffract, the degree to which is determined by their diameter—obviously a tiny laser diode will refract more readily than a large laboratory laser. Laser diodes are similar to LEDs but the key difference is that LEDs do not have a feedback cavity, where as a laser diode does, causing it to "lase", and is thus a laser. That's the essential scientific difference; there are loads of technical differences as well (LED spectra is much wider than a laser diode; laser diodes are loads more efficient than LEDs; laser diodes come from a point source and so even with diffraction are able to be far, far more focused than any LED can be). Get your facts right before invoking what scientists should be offended by! --24.147.86.187 16:48, 2 August 2007 (UTC)

There's very little that you can do to make a diode laser more powerful (brighter). If you push more current through it (which you can probably do with a cheap laser pointer by stacking additional batteries in series to increase the supplied voltage) you will get more light output for a while, but the higher current and higher operating temperature will tend to degrade the laser diode rather rapidly. TenOfAllTrades(talk) 02:57, 2 August 2007 (UTC)

We wired one of the laser key chain pointers into a mains supplied power pack while trying to build a simple laser telecommunications transmitter (incidentally I don't recommend trying this if you don't know what you're doing). However, in the interests of science, and not really caring if we burnt the laser out, we did pump it right up as far as 12V. It was clearly brighter, but I must say not very transportable any more :) --jjron 09:03, 2 August 2007 (UTC)

Laser pointers have a legally limited maximum brightness because if you have them any brighter they become more of a danger to eyesight than they already are. So unless you have some legal reason for doing this - don't! So clearly, increasing the voltage increases the brightness - but to what degree and how far you can push it before the thing overheats or something probably depends on the precise laser diode your laser pointer has. You'll probably have to experiment. But just be REALLY careful - lasers (even laser pointers) really can mess up your eyesight. SteveBaker 12:00, 2 August 2007 (UTC)

Returning to the original question - to make it more powerful you could add additional cells in parallel to increase the current - and hence light intensity - in all likely hood this would just cause the led to overheat and break.87.102.67.227 16:57, 2 August 2007 (UTC)

More ill-informed speculation! Adding additional cells in parallel won't do a thing to the current that a conventional circuit draws. The circuit draws whatever it draws (unless the original battery is so under-specified that its internal resistance limits the current, but that would be a silly and stupid design). If you add cells in parallel in the supply to a conventional circuit, both the voltage and the current will be unchanged.

Sorry my mistake not thinking.87.102.19.44 23:14, 3 August 2007 (UTC)

That might be a part of the design though - because there is a legal limit on the brightness of these gadgets, it might be desirable that lack of battery current would limit the light output. I doubt that's the case though because by the time a AAA is current-limiting, it's also getting amazingly hot! SteveBaker 01:26, 3 August 2007 (UTC)

What will change (and this might be just what you want) is the amount of time you can operate the thing before the batteries wear out. —Steve Summit (talk) 23:38, 2 August 2007 (UTC)

Plus, unless that is a typo, 50mW is already a VERY strong laser, in Australia, you can't own anything over 5mW without a special permit. Vespine 23:24, 2 August 2007 (UTC)

According to Laser pointer: The output power of a laser pointer is measured in milliwatts (mW). In Europe/UK the legal requirement is that laser pointer output not exceed 1 mW; in USA this output is limited to 5 mW for presentation lasers. - so 50mW is almost certainly a typo. SteveBaker 01:26, 3 August 2007 (UTC)

Actually to be technically correct you should say "in theory" the device "shouldn't" draw any more current with more cells in PARALLEL. The reality is that the device would be a small amount brighter (depending, try this with a light meter and flashlight). IE: When you check the voltage with device off, you will see more voltage then with device on. Why? Because battery voltage under load is less then not under load. Hence, More cells in PARALLEL (assuming all fully charged and all are same design voltage) makes it easier for the "working" voltage to stay higher (closer to the max voltage draw of the device) under load.

All devices have a "range" of working voltage and amps capability (ie check out Military Specs require a vastly increased "range" of operation to increase survivability in the event of too much or too little "juice" ) being supplied. Too many watts ( amps x voltage) will burn it out like a very expensive fuse. If you put cells in SERIES you quickly begin overdrive the device actually "forcing" thru more electrons than was designed for. This can lead to thermal breakdown (burnout) if prolonged or if too high or both typically.

BUT the reality is YES you can 'force' it to be "some" brighter (with less lifetime) by adding to the voltage and or amps. Don't do this with a laser for legal reasons as they say above! Motors can actually take advantage of this situation too, in fact some controllers add amps (and sometimes volts too) to increase motor speed. One patent I worked on recently actually uses this idea to have a low, med, high, (power saver/stealth mode, medium, and search "high" ) intensity for electric portable lights. See my censored non-user page TripleBatteryLife 14:33, 5 August 2007 (UTC)

Angular momentum

How does this work? Is it just a coriolis sort of effect since the half of you is farther away from the equator than the other? And if you stop spinning doesn't that counter any effects you've had? --froth^t 22:26, 1 August 2007 (UTC)

Of course it doesn't really work, but here goes... total angular momentum is conserved, so when you start spinning, you push the Earth a little bit the other way. It's much simpler than a Coriolis effect. If you're right on the equator, you will give the Earth a little bit of a "polar" roll (i.e. shift the poles a tiny amount). If you're right on one of the poles, you will leave the Earth spinning on the same axis, but make it go a mite faster or slower. And in between, you do a little of both. Now as you noted, once you stop spinning, the Earth's rotation goes back to what it was originally... but as long as you keep spinning, its angular velocity is different. Imagine that you stood on the North pole and spun around fast enough to slow the Earth's rotation by 10%, and you kept going for an hour. Then you stop. At the end of the hour, the Earth is rotating like normal, but it has only gone through 13.5° instead of the usual 15°! So the dawn will come later. (It's probably unnecessary to point out that the effect you really have by spinning around is so tiny it's basically zero). --Reuben 23:13, 1 August 2007 (UTC)

Hmm, most disk drives are in hte northern hemisphere, spin the same direction, and are oriented the same way relative to local vertical, and are currently powered on. Still no real effect, but fun to think about.-Arch dude 01:20, 3 August 2007 (UTC)