Wikipedia:Reference desk/Archives/Science/2008 February 18

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February 18

Tube guitar amplifier humming/rustling sound problem

Hello, perhaps this should be in miscellaneous but it deals with the internal components of an amplifier and speaker. Yesterday I purchased a Peavey Classic 30 guitar amp, a 30-watt all tube amp with one 12" speaker, 3 preamp tubes and 4 power tubes. It sounds fine except for a few quiet rattles: sometimes the amplifier makes a very low pitched crackly rustling sound that kind of sounds like the wind blowing. It is peculiar because it happens whether my guitar is plugged in or not, and it is at the same volume no matter what the volume of the amp is. I've turned it up very loud and I've turned the volume as low as possible and the volume of this little crackling hum has not changed at all. It's very quiet and I only hear it while playing quietly or not at all but while the amp is still on. Does this problem sound familiar to anyone, if so, does anybody know what causes it and, most importantly, how to fix it? NIRVANA2764 (talk) 02:11, 18 February 2008 (UTC)

Is it a bug or a feature? I thought it was little quirks like that that made tube amplifiers attractive in the first place... —Steve Summit (talk) 02:56, 18 February 2008 (UTC)

Try "tapping" the power tubes one at a time to see if any tube "responds" as sometimes a tube can become microphonic and generate unwanted background noise. Seems like a fine piece of equipment that you've gotten, have fun and good luck! --hydnjo talk 05:51, 18 February 2008 (UTC)

Googling suggests that the Classic 30 has a spring reverb: analog reverbs are always prone to hum (from transduction and interference). Does the hum persist if you take the reverb out of the circuit (assuming the amp has a "reverb on/off" button) as opposed to just turning the reverb knob down? Depending on its design, a spring reverb can sometimes act as an antenna, capturing unwanted RF interference from neighbouring devices. Try turning off everything electrical nearby (TVs, monitors, fans, AC units, and transformers in particular). If you can't be sure the reverb is off (as opposed to just dialled down) whack the amp (gently) - a whacked spring reverb makes a horrible noise like an explosion in a scrapyard. -- Finlay McWalter | Talk 15:23, 18 February 2008 (UTC)

I've never seen that sound so eloquently described! --hydnjo talk 15:39, 18 February 2008 (UTC)

I tend to agree with that as well. Especially since I've heard both that amp sound and an explosion in a scrapyard in real life. 206.252.74.48 (talk) 20:27, 18 February 2008 (UTC)

Hydnjo is right. I know that sound, too. There is a schematic diagram here. You have a transistor or two in there, you know. I would try freeze spray on Q2, being careful not to break a tube with it or electrocute myself (tube amps bite hard). You can pull tubes one at a time (unplugging the amp and letting it sit awhile between pullings) to narrow down the circuit the noise is coming from. Don't pull an output tube. Freeze capacitors one at a time and listen. It might be normal for this amp. --Milkbreath (talk) 16:56, 18 February 2008 (UTC)

Besides microphinics in tubes, the connection between the tube pins and the socket can be imperfect due to dirt or corrosion. With the power off, wiggling the tube in the socket or removing and replacing a few times may 'wipe" the contack and improve the noise level. Volume controls are another suspect. They can be cleaned with appropriate spray (power off)or replaced. Connects and things that plug into them are the third area where imperfect contactor frayed wiring can create noise. Edison (talk) 19:55, 18 February 2008 (UTC)

Hmm. Sounds like brown noise to me caused by a noisy output stage —Preceding unsigned comment added by 79.76.226.64 (talk) 03:46, 21 February 2008 (UTC)

Since the op states that the noise is not affected by the volume control then, the noise is most likely contributed by the power amplifier section (not the preamp). (I am assuming the noise has been shown not to be coming from the reverb amp, but this could easily be checked.)

From the circuit diagram here , it appears the main voltage amplification (a few thousand times) in the power amp is provided by V3A,B (a 12AX7 double triode). I would investigate initially in this area. I'm sure I used to hear tales in the old days of faulty grid leak resistors causing noise problems. These resistors are R48 and R47 (both 1 Mohm). You could initially try tapping these gently with an insulated tool to see if they are microphonic. (Remember there are lethal voltages in this circuit). If they are noisy, then replacement of these may be in order (especially if they are carbon composition types which are known to be noisy anyway). —Preceding unsigned comment added by 79.76.226.64 (talk) 13:50, 21 February 2008 (UTC)

bug/insect identification

Can someone tell me which bug this is? http://farm3.static.flickr.com/2411/2272801999_ed19224b97_o.jpg It was about the size of a dime or a nickel. This is the underside: http://farm3.static.flickr.com/2119/2272814521_32f6c5f0b5_b.jpg Sorry for the blurriness. Thank you. --Rajah (talk) 04:08, 18 February 2008 (UTC)

Looks like a member of the Pentatomidae family. They're called shield bugs or stink bugs. This one might be the Brown marmorated stink bug, but many of the species in this family look similar. Sancho 05:51, 18 February 2008 (UTC)

Thanks! --Rajah (talk) 13:05, 18 February 2008 (UTC)

Volume of solution

Does the volume of water change when NaCl is added to it? What about solutions in general? Does the volume of solution change when solute is added to solvent? Kushal 13:06, 18 February 2008 (UTC)

In general, the volume of a solution changes when solute is added. That's why, for example, a molar solution is always prepared by putting the solute in the flask first, rather than starting off with a known volume of solvent and adding the solute. MrRedact (talk) 16:40, 18 February 2008 (UTC)

Yes, the volume of water changes when dissolving solutes as (in your example for instance) the NaCl displaces water molecules. Wisdom89 _{(T / ^C)} 18:49, 18 February 2008 (UTC)

By changing, I think you mean increase, it's important to realize that there some solutes which will decrease the volume of the solution. This is a particular chestnut of many physical chemistry courses. --Rajah (talk) 02:21, 19 February 2008 (UTC)

Sorry I can't find a reference, but I remember that it was either a solution of water and small amount of alcohol added or vice versa. In at least one of the cases, you can show that the volume of the solution decreases, because the solute and solvent are attracted to one another and pull the molecules closer together. --Rajah (talk) 02:50, 19 February 2008 (UTC)

And a followup point is that I would think, but am not sure, that if you can increase or decrease a solution volume by adding solute, then sometimes when you add a solute (or combination of solutes), the volume of the solution will remain the same. --Rajah (talk) 02:51, 19 February 2008 (UTC)

So, in no case involving a single solute and a single solvent does the solute just go in the intermolecular space of the solvent? I mean, if the solute were to go in the intermolecular space of the solvent, the volume would not change, would it? Kushal 17:57, 19 February 2008 (UTC)

It would be rare that the solute would be small enough and the spaces between the solvent molecules large enough and the interactions between the solute and solvent molecules be net-zero-effect. Things usually don't "just fit in and that's the whole story", but there could certainly be a net zero change in volume (balance of all interactions). Consider that if there's a (relatively) large space between solvent molecules, that means there's a strong (repulsive) force between them, so there's probably going to be a strong interaction (of uncertain direction) between those molecules and a solute molecule wedged between them. Cage-like molecules (cryptands, crown ethers, buckyballs) would be interesting exceptions: solute fits inside a single "solvent" cage, but it's perhaps rigid and so cannot change size/shape when the solute is present vs absent. Though it depends on how one defines "solvent" a bit. DMacks (talk) 19:28, 19 February 2008 (UTC)

Thank you very much. Kushal 11:22, 21 February 2008 (UTC)

I want an stream eletric generator to produce 80000 units of current annually

I want an stream eletric generator to produce 80000 units of current annually which is run by an cocentrated solar type stream producer.please help me. —Preceding unsigned comment added by 58.68.95.56 (talk) 14:16, 18 February 2008 (UTC)

Like - help you how? --hydnjo talk 14:40, 18 February 2008 (UTC)

Units of current annually? You might be able to phrase your question more clearly if you first study our articles on solar energy and Electrical Units.--Shantavira|^{feed me} 14:55, 18 February 2008 (UTC)

And SI electromagnetism units. --hydnjo talk 15:13, 18 February 2008 (UTC)

80,000 Amperes of current would require extraordinarily large conductors coming off the generator windings as well as in the windings. 80,000 kilowatt-hours per year would only require the generator to produce 9132 watts average (naturally it would have to produce much more than this during the hours the sun is shining). Before you issue bid specifications or begin construction, you should familiarize yourself with the units of measurement of electric power. Edison (talk) 19:51, 18 February 2008 (UTC)

See Russ Rowlett's pages on units of measurement: definition 6 for a "unit" is "in Britain, another name for the kilowatt hour, which was formerly called the Board of Trade unit." And by the way (to be picky) the man was Ampère but the unit is ampere without a capital letter. --Anonymous, 21:37 UTC, February 19, 2008.

claustrophobia

I am trying to find out if anxiety about being in a situation where escape might be difficult is also claustrophobia. eg being on an island or a large boat, not involving small enclosed spaces or panic attacks. thanks —Preceding unsigned comment added by 97.96.181.252 (talk) 15:38, 18 February 2008 (UTC)

I would have a look at the phobias article. Also, the DSM-IV is a good reference guide, which mentions anticipation of events. -- MacAddct  1984 ^{(talk • contribs)} 16:28, 18 February 2008 (UTC)

The Merck Manual points out a website called The Phobia List, which lists hundreds of phobias. I tried searching for "escape" and several related terms, but no hits. Based on a Google search I did earlier, it does seem that claustrophobia includes the cases you mentioned (that is, any event in which one could not escape). Sorry, I'm not an expert. (EhJJ)^TALK 17:51, 18 February 2008 (UTC)

Also take a look at agoraphobia, maybe. --Ouro (blah blah) 19:04, 18 February 2008 (UTC)

inclined planes

If you put a sledge on a steep enough ramp, it'll slide down.. but where is the horizontal component coming from? Is it electromagnetic, from friction? If I had never seen something roll I don't think I'd ever have guessed a horizontal component would appear :D\=< (talk) 16:56, 18 February 2008 (UTC)

There are two forces on the sledge. There is gravity, and there is the force of the ramp pushing back on the sledge. Ignoring friction (for a moment, I'm just trying to keep it simple), the force of the ramp pushing back on the sledge is perpendicular to the surface. Which means, since the ramp is tilted, it has a horizontal component. JohnAspinall (talk) 17:05, 18 February 2008 (UTC)

There's a nice diagram at the inclined plane article. Sancho 17:13, 18 February 2008 (UTC)

Yes, the force is electromagnetic, at the molecular level. The molecules of the surface exhibit a net positive force against the molecules of the sledge -- static friction. Once the angle is sufficiently steep, gravity overcomes static friction and dynamic friction comes into play. -Arch dude (talk) 04:25, 20 February 2008 (UTC)

Blindness versus deafness

Have any scientific studies been done on the following questions and, if so, what did they conclude?

• Which is "worse" or "harder" ... which is "better" or "easier" ... to be blind or to be deaf?

• Which is "easier" ... which is "harder" ... to be born blind ... or to have sight and then subsequently lose it?

• Which is "easier" ... which is "harder" ... to be born deaf ... or to have hearing and then subsequently lose it?

For lack of better words, I use the terms easier / harder / better / worse to generically mean ... the ease/difficulty a person has adjusting, getting by, everyday living, accomodating, adapting, etc., in a world today where most people are not deaf or blind ... physically, mentally, socially, psychologically, etc. Thanks. (Joseph A. Spadaro (talk) 17:33, 18 February 2008 (UTC))

I doubt the first question is even a matter of studies- its' obviously far harder to be blind than the be deaf :D\=< (talk) 18:19, 18 February 2008 (UTC)

Well, I don't know. There is a story (which I haven't tracked down but is referred to here) that Helen Keller would have preferred to have her hearing back instead of her sight if she could have only one: "... because when you lose your sight, you lose things. When you lose your hearing, you lose people." Also, "The problems of deafness are deeper and more complex, if not more important, than those of blindness. ... Deafness is a much worse misfortune. For it means the loss of the most vital stimulus – the sound of the voice that brings language, sets thoughts astir and keeps us in the intellectual company of man." Of course, this was before the internet and texting. --Milkbreath (talk) 19:11, 18 February 2008 (UTC)

Also the phrase "tis better to have loved and lost then to have never loved at all" may provide answer to the second query. Although similarly so could the lines "if i hadn't seen such riches I could live with being poor" from James Sit Down...I guess it depends on an individual's perspective. I recall reading a story about a man who had been blind from birth, was getting rather old and was gardening with his wife, helping to turn over the soil when his eyes focussed and he saw for the first time - bold yellow flowers. The most beautiful thing, the flower he had loved that his wife had described on many occasions was the first clear vision of his life. A nice story I always thought, but i'm not sure if vision can just 'return' like that? ny156uk (talk) 18:50, 18 February 2008 (UTC)

My impression from the recent Gallaudet University presidential succession controversy is that if you don't learn sign language as a mother tongue, you may have trouble integrating fully with other deaf people, just as an adult who goes to a foreign land might never overcome the language barrier. --Sean 19:16, 18 February 2008 (UTC)

Considering that 80-90% of the average person's sensory information comes from sight, it's probably more difficult to be blind than deaf. —Lowellian (reply) 20:59, 18 February 2008 (UTC)

There are ranges of degree for both deafness and blindness. Total deafness is, as I understand, quite rare. Also, if we are talking about being born or becoming deaf or blind at an early age, then for most of history and to the present in parts of the world, deafness is far worse. See Prelingual deafness and History of the deaf -- until surprisingly recently in history being prelingual deaf (total or profoundly deaf), meant never learning language and never acquiring symbolic thought. This is far far worse a fate than being blind in any form. But as I said, profound prelingual deafness is rare compared to most kinds of hearing impairment. Still, since the question didn't specify I thought I would point out this example in which being deaf is worse than being blind, no contest. A book that explores this particular topic in some detail is "Seeing Voices" by Oliver Sacks. Pfly (talk) 04:38, 19 February 2008 (UTC)

If you never even develop symbolic thought that's not such a bad fate.. it might be pretty confusing but you don't know what's going on or that you can't think properly. Same as those quotes above, you wouldn't know or care what you're missing. Also it reminds me of the Futurama episode where the professor gives a martian monkey superintelligence and it's smart enough to see that knowing things sucks and it was happier in the jungle, so it takes off its brainwave hat and returns to the wild as a stupid monkey :D\=< (talk) 05:04, 19 February 2008 (UTC)

For humans there is no wild to return to. Not having language does not mean you not want to be among other humans, to have social feelings and emotions, etc. If your needs were taken care of by kind loving people, then perhaps it would not be so bad. The norm, however, for most of history, was isolation, abuse, scorn, and such like. Pfly (talk) 00:17, 20 February 2008 (UTC)

Thanks for the great input. Much appreciated! (Joseph A. Spadaro (talk) 01:04, 24 February 2008 (UTC))

Non-foaming shampoo on first wash, explosion of foam second wash.

Can someone explain what's going on here? When I wash my hair in morning, the first shampoo does not foam up at all. But after rinsing and applying a second dose of shampoo, my hair explodes with lather. --70.167.58.2 (talk) 17:35, 18 February 2008 (UTC)

Lather, rinse, repeat... ;-) hydnjo talk 17:55, 18 February 2008 (UTC)

I'm not 100% sure, but I guess it's caused by saturation. The first time you apply shampoo it will mostly solve in the water and attach too the fat in your hair, but the second time most of the fat is already washed off and the water already saturized, preventing the extra shampoo from solving and thus creating foam. - Dammit (talk) 18:00, 18 February 2008 (UTC)

For this reason, i usually first take a smaller amount of shampoo and do a quick scrub and rinse through all my hair to get the bulk of the oil out, then I take a little more and have a longer and more satisfying leathering scrub. Vespine (talk) 00:36, 19 February 2008 (UTC)

Hair oils. The oils prevent it from lathering up the first time, but after they are washed away, then a nice foam can arise. bibliomaniac15 00:51, 19 February 2008 (UTC)

Note also that lather is affected by the hardness of the water. If there is a lot of Ca2+ in your water supply it may not be as easy to form a lather, obviously unless you go somewhere else with softer water you won't notice this though.

Shniken1 (talk) 02:25, 19 February 2008 (UTC)

Fundamentally, oil neutralizes soap or detergent. In the first case, most of the soap/detergent is neutralized, but it removes all of the oil from your hair. On the next application, no oil remains, so all of the soap or detergent is un-neutralized and is available to form bubbles. -Arch dude (talk) 04:15, 20 February 2008 (UTC)

Newtonian Physics

I'd like to start a space program with an objective of sending a manned expedition to Mars. The major caveat of the expedition is that I wouldn't want any of my planners or engineers to use General Relativity. I'd like the entire mission to run on the assumption that Newtonian physics is the physics of the universe. Will my crew be safe?Sappysap (talk) 18:44, 18 February 2008 (UTC)

Since I assume you're actually a world leader starting such a program and not just a student doing homework or something, I'll give you a very practical answer. Putting people on Mars is an enormous undertaking that will require the best engineers in the world. These are pragmatic and careful people who will simply refuse to be involved in such folly as to risk lives, billions of dollars, and their own reputations on something like running a space program on long-discredited science. Sorry, George. --Sean 19:27, 18 February 2008 (UTC)

Isn't space travel mostly Newtonion Physics these days? What does relativity have anything to do with launching a rocket, slingshoting it near another body of mass, and then landing on Mars? 206.252.74.48 (talk) 20:24, 18 February 2008 (UTC)

Well, or more to the point: would any of the speeds, forces, etc. that they would be experiencing come to the point where Newtonian physics wasn't a good enough approximation? GR generally only becomes a significant factor when you are talking about very high gravities, very high densities, very fast speeds. I'm not sure if anything involved in a Mars landing using modern technology would require relativistic effects to be factored in; the Newtonian might be good enough. --98.217.18.109 (talk) 20:51, 18 February 2008 (UTC)

Or not! I'd factor in anything that I knew about even if it only affected the margins. --hydnjo talk 21:13, 18 February 2008 (UTC)

Hydnjo's comment is well stated. Newtonian physics provide a very good approximation of actual orbital mechanics for present space travel. However, when you're talking about billion-dollar programs, it's sheer hubris to ignore a better approximation. Risk management is a very important part of space exploration, and excessive approximation is bad risk management. — Lomn 21:43, 18 February 2008 (UTC)

You should probably avoid anything that takes precise timing measurements on radio signals like a GPS does, and also design your computer systems so that they can gracefully handle any minor discrepancies in time-keeping. (Especially compared to ground-based clocks.) 72.10.110.107 (talk) 22:05, 18 February 2008 (UTC)

I disagree. Timing is everything! --hydnjo talk 23:37, 18 February 2008 (UTC)

Incorrect textbook?

My textbook on geography states:

“ If Earth did not rotate on its axis - creating day and night - only the half facing the Sun would receive solar energy. ... The half of the planet facing away from the Sun would always be dark and cold. ”

I agreed with this statement until the word always; if the Earth did not rotate, at least at some point, the other side would be exposed to the Sun's energy within the year. Is this correct? --~~MusicalConnoisseur~~ Got Classical? 19:30, 18 February 2008 (UTC)

I agree with your assessment of their wording. They may have been trying to describe tidal locking. --Sean 19:50, 18 February 2008 (UTC)

Yes, but nowhere in that paragraph does it mention tidal locking (though that idea did enter my mind). Its topic is a totally hypothetical situation - if the Earth did not rotate, period, unlike the moon. --~~MusicalConnoisseur~~ Got Classical? 20:13, 18 February 2008 (UTC)

Well, the side of the Earth that is not facing the sun is dark and cold(er). Nobody said that side ever stayed over the same geographic location. —Preceding unsigned comment added by 206.252.74.48 (talk) 20:55, 18 February 2008 (UTC)

Yeah, I agree. As it reads, there's nothing wrong with the statement in the textbook, since it doesn't specify that the side facing away from the sun is always the same part of the Earth. —Lowellian (reply) 21:01, 18 February 2008 (UTC)

It's a textbook. They get things wrong. Don't hold them to the same standards as Wikipedia. Considering some of the anti-Wikipedia articles linked to in the In the News section of the Wikipedia Signpost (not necessarily today), no one else does. — Daniel 21:14, 18 February 2008 (UTC)

It's a classic frame-of-reference question, isn't it? When we say that an orbiting body "doesn't rotate", do we mean that it always keeps the same face towards the body it's orbiting, or that it always keeps the same face towards 0° longitude in the "fixed" frame of the body it's orbiting?

Supposedly there was an ancient Greek philosopher whose lifelong, quixotic quest was to find students who had not been "brainwashed" otherwise by his peers, and teach them that the moon does not rotate as it revolves around the earth... —Steve Summit (talk) 23:09, 18 February 2008 (UTC)

A rotating reference frame is non-inertial. From any inertial frame, a body with a tidal lock is rotating. — Daniel 00:30, 20 February 2008 (UTC)

Is it physically possible...

To die from the loss of the will to live?

Assuming that the person doesn't commit suicide, eats properly, sleeps properly, does not OD on medicine, and is perfectly healthy in every way...

could it happen?

Thanks!

❦ECH3LON❦ 23:41, 18 February 2008 (UTC)

I doubt that anyone would respond by saying "that's impossible". --hydnjo talk 23:49, 18 February 2008 (UTC)

I think most normal people would not have the ability to will themselves to death, or in this cases unwill themselves from life. There are many people, for example in jail that wish they could will themselves to death, but they still usually have to resort to more physical measures. Don't hear too many cases of death by lack of will to live. On the otherhand, it seems quite common with old couples that seem to keep them selves going, but once one dies the other soon follows, seemingly having "lost the will to live".. Vespine (talk) 00:32, 19 February 2008 (UTC)

...But, similar to the idea of hypocondriacs and the Nocebo effect, if it is possible to have a disease that is self-procured, then surely, isn't it possible to have that same "illness" kill someone? I'm not sure if this complicates the question though. ❦ECH3LON❦ 02:30, 19 February 2008 (UTC)

Of course, everyone has many diseases at any given time, which are wiped out by our immune system before they become noticeable. So, all that's necessary to die from disease is to suppress your immune system to the point where the diseases win the battle. I'm not sure if this is possible, but it might serve an evolutionary purpose, if individuals which no longer contributed to the survival of the group were to have killed themselves in this way, thus enhancing the chance that others in the group carrying their genes would survive. StuRat (talk) 09:38, 19 February 2008 (UTC)

Kurdaitcha might be of some interest. In these cases, the person doesn't just decide of their own volition to give up the will to live, it's externally imposed; but the effect is the same. We need a better article (or any article) on Pointing the bone, so I can't say how widespread this practice was or, indeed, if it's still practised at all. -- JackofOz (talk) 23:31, 19 February 2008 (UTC)

So...It's like the horror story 'The Candidate by Henry Slesar in which the main character is told of a way to kill people by using wishes, or willpower, and then later die of "Natural Causes"?

That's interesting...❦ECH3LON❦ 00:46, 20 February 2008 (UTC)