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February 22

What else is there?

As a non-physics type reflecting on the "What exactly is a magnetic field" thread of Feb 15, when a person asks whether something's animal, vegetable or mineral, what else is there? How close is energy (like a force field) to being matter – can you say that? Julia Rossi (talk) 04:21, 22 February 2008 (UTC)[reply]

It depends on one's definition of mineral. If you're using mineral to mean "anything that isn't plant or animal", it's sort of lost all meaning. A true mineral is a solid substance "formed through geological processes". A computer isn't animal, vegetable, or mineral. There are also non-physical things such as thoughts, emotions, dreams, etc... -- MacAddct  1984 ^{(talk  contribs)} 05:59, 22 February 2008 (UTC)[reply]

Thoughts, emotions, and dreams are sort of physical, in that they are an abstraction that only exist as a physical represention, as an activation pattern of neurons, and/or a pattern of efficacy of synapses. Neurons and synapses are of course physical. It's very much like the movie Blade Runner is an abstraction that sort of isn't physical, but all of its representations are physical, such as a pattern consisting of the presence or absence of pits on a polycarbonate disk (a DVD), or a pattern consisting of the presence or absence of various pigments on a strip of acetate (film).

A physicist wouldn't look at everything that exists physically as being animal, vegetable, or mineral. Rather, everything that exists physically ultimately consists of elementary particles, which includes matter (quarks and leptons) and energy in the form of gauge bosons. MrRedact (talk) 08:37, 22 February 2008 (UTC)[reply]

Nice pick of Bladerunner in this context, by the way. Emotions seem more like energy that results from other things being activated, say by a thought, is that what's meant MacAddct?. And MrRedact, are you saying everything is comprised of particles (of one kind or another) of matter? Then does the question, animal, vegetable or mineral need to be upgraded to – well, you name it, what would you say? Is it molar, molecular or action? The article says "all force carrier particles are bosons" can we take it that forces are still separate but show up through the particles and that it's not the forces, but the particles that could give the impression that a force field (with its pressure) seems almost material? (Is the sound that knocks out a candle flame say, a proper example?) Julia Rossi (talk) 09:13, 22 February 2008 (UTC)[reply]

That's sort of what I mean. Things that happen in the brain, while they are all a result of electrical activity, we still recognize them as unique properties (e.g., separating dreams from thought). But when you boil everything down, as far as we know, everything is made up of the particles that MrRedact mentioned. -- MacAddct  1984 ^{(talk  contribs)} 14:14, 22 February 2008 (UTC)[reply]

I didn't realise that the particle of matter extended so far, even to their effects and things between them. Thanks so much, it's engrossing stuff. Julia Rossi (talk) 23:32, 22 February 2008 (UTC)[reply]

Belated bruise

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This may not seem like asking for medical advice to you, but it sure seems like it to me. You should ask your doctor as to whether that's normal, and what if anything you should do about it. MrRedact (talk) 07:47, 22 February 2008 (UTC)[reply]

It sent me to the Bruise article which threw some light on the nature of bruising and its indications are as per above and get it straight from the medico mouth - should be very informative. Julia Rossi (talk) 09:19, 22 February 2008 (UTC)[reply]

3600rpm 1000 HP electrical motor. Need bibliography. Vibration

I have three of theese motors installed. one of them has vibration values that jump up and down. I've heard this is normal and that this is NOT normal. Which is true. How do I justify? —Preceding unsigned comment added by Arielerosa (talk • contribs) 05:11, 22 February 2008 (UTC)[reply]

This is not a place to obtain professional advice related to safety or possible economic loss. Have you brought this concern to the manufacturer or vendor? You might wish to consult a qualified electrical engineer who is knowledgable about the vibration expected from motors. Excess vibration, of course, can cause bearing damage and further deterioration. Edison (talk) 19:02, 22 February 2008 (UTC)[reply]

Power factor in electric circuit

How can be use a capacitor to improve the power factor of a parallel ac circuit? —Preceding unsigned comment added by Meetpramendra (talk • contribs) 05:34, 22 February 2008 (UTC)[reply]

In an AC circuit with resistance and inductance, such as a motor, the current waveform lags behind the voltage waveform. The total current is larger than necessary, producing lower voltage at the motor terminals than if the current and voltage were in phase. A properly sized capacitor can correct the power factor, improving the voltage, and reducing the current which must be supplied by transformers and service conductors. For a more thorough discussion, see Power factor correction. Edison (talk) 07:11, 22 February 2008 (UTC)[reply]

The way I understand power factor is very simple. When power factor less than one occurs, it means extra power is needed but those extra power (technically electrons) is not being used to do useful work instead they bounce back and forth between the load (aka electric motor) and the generating station (aka power plant). In an ideal world, this does not matter because the transmission lines have zero resistance. But in the real world, transmission lines have non-zero resistance and it means power is being lost moving back and forth between the load and the generating station. Since the customer does not pay for power loss on the transmission lines. The electrical companies FORCE the customer to "tune" the power factor of a load to one. 122.107.226.136 (talk) 22:34, 22 February 2008 (UTC)[reply]

Well, "close" to 1, anyway. Nimur (talk) 22:12, 27 February 2008 (UTC)[reply]

Old voice recordings

When I hear very old recordings of American voices (early 20th cen.), they sound distinctly different from modern voices. I don't know how to describe it other than to say they sound more "nasal" and higher pitched. I'd like to know if this is due to the recording technology of the era, or a true change in the way Americans speak. ike9898 (talk) 13:05, 22 February 2008 (UTC)[reply]

It's changes in the technology. Specifically, older recording methods did not record much bass, so all you hear is the treble component. If you adjust your radio to all treble and no bass, modern voices will sound similar. Unfortunately, it isn't reversible, so adjusting the radio to all bass and no treble won't do much to improve an old voice recording, as there isn't enough bass there to begin with for this bass magnification to do much good. StuRat (talk) 13:19, 22 February 2008 (UTC)[reply]

Surely part of it must also be that people really did speak differently then. Maybe not so much their voice per say, but their form of diction and register might be significantly different from what it is today. -- MacAddct  1984 ^{(talk  contribs)} 14:21, 22 February 2008 (UTC)[reply]

I highly doubt that's a contributing factor - It's audio technology advances - Reel tapes for recording back then as opposed to digital today. Wisdom89 _{(_T / ^C)} 17:39, 22 February 2008 (UTC)[reply]

Analog reel-to-reel is capable of capturing speech with as high of a fidelity or even better than current digital methods. So, whatever the technology change was that improved vocal capture, it was something earlier than the use of analog reel-to-reel tape. StuRat (talk) 01:44, 23 February 2008 (UTC)[reply]

Could it have been the introduction electrical recording as opposed to purely acoustic recording? Sound_recording_and_reproduction#4 —Preceding unsigned comment added by 79.76.211.150 (talk) 20:18, 24 February 2008 (UTC)[reply]

Wasn't the sound the OP describes usually recorded onto wax cylinders and early phonograph records? 206.252.74.48 (talk) 18:11, 22 February 2008 (UTC)[reply]

I believe so yes, dating back to the 1940's and 50's? Wisdom89 _{(_T / ^C)} 18:15, 22 February 2008 (UTC)[reply]

There are changes in the accents within a population over time. I have listened to many recordings from the 1890's on and recordings of radio programs and news broadcasts as well as sound movies (sound on film) from the late 1920's on. Some speakers engaged in a style of "elocution" to make themselves heard without public address systems which would sound odd and contrived today. Many singers did in the 1920's and earlier in fact use a degree of nasality which sounds wierd today. The switch in the 1920's from acoustic recording to electrical recording improved the fidelity without really changing the nasal quality. It is not just the greater audio fidelity of today's recordings. I have listened to a cross section of Americans recorded in fairly high fidelity by a radio station on the day the end of World War 2 was announced in 1945, and their accents departed from what I would expect to hear today: more regional variation. The speech sounded "dated" and quaint. There has been a levelling of speech in America, with fewer "hick" or "rube" accents and fewer plummy accents indicating high socioeconomic status. Broadcast media is likely a big factor in producing more standardized general American speech. Edison (talk) 18:54, 22 February 2008 (UTC)[reply]

Actually, studies have shown that radio, television, etc have no effect on a speaker's or speech community's accent. This is related to the fact that children don't learn to speak from such devices. There have been changes in pronunciation of English since the 1890s, but the "leveling" of which you speak, if even present, would be pretty minor and due more to people moving about the country. What Ike9898 is asking about has much more to do with the technology than diachronic change. — Æµ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 01:24, 23 February 2008 (UTC)[reply]

Also note that the lack of bass in early recordings effects sounds other than just voices, such as music. StuRat (talk) 01:49, 23 February 2008 (UTC)[reply]

I am not that impressed by studies which "prove" a negative such as is claimed above. "Studies" have also shown that an individual's speech is not frozen when he learns from his parents how to speak. Thus broadcast influences could well affect speech. One multi-decade study in Philadelphia noted speech changes in the same individuals over time. There was also the "great vowel shift" centuries ago in which the pronunciation of English changed, with "mice" having the vowel sound change from the older "mees" to the present pronunciation, with one writer at the time marvelling about how the language had changed since he was a youth, his own pronunciation included. In recordings from the 1930's and 1940's, for example, I note more speaker in the U.S. pronouncing "r" sounds in a more British "ah" way. Bass/treble balance has no effect on such linguistic variation. Edison (talk) 20:51, 23 February 2008 (UTC)[reply]

Ahem, mouse was pronounced like moose, not mees. This change did not occur over a single generation. No one is arguing that language doesn't change over time, and of course we can spot phonetic differences from recordings a hundred years ago. — Æµ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 23:45, 23 February 2008 (UTC)[reply]

You are confusing the pronunciation shift of "moose" to "mouse" and "meese" to mice." And as I recall, it happened in the life of publisher William Caxton. See The Learning Company's course on the history of the English language, or see [1] and [2]. Edison (talk) 05:16, 26 February 2008 (UTC)[reply]

I would have to agree it sounds bizzare to suggest broadcast media could not affect the way people speak because it's not how they learn to speak. Accents are not static. Immigration would seem to disprove this claim immedietly. Most immigrants (especially those who emmigrate in their early 20s or 30) will, while retaining an accent with some charateristics of where they grew up, also have changes in their accent based on where they now live. Indeed in some cases their accent may be similar enough to a 'native's' accent that it will be indistinguisable to all but the extremely trained ear. These obviously depend greatly on the level of interaction the person has with native speakers. And I'm talking about immigrants who grew up speaking English (or whatever language were referring to). For that matter, people can learn multiple accents whether conciously (as actors/actresses, call centre workers, etc show)or subconciously. Speaking of immigrants again, many may be able to speak with an accent more similar to their original accent if they desire and may for example, even do it fairly subconciously if they go back to their native country for a holiday or whatever. This obviously doesn't prove people learn from broadcast media, but it does suggest it's ludicrious to suggest only what people learn in childhood matters. Nil Einne (talk) 08:00, 26 February 2008 (UTC)[reply]

Modem

Sir, I want to know wat a modem in engineering sense with some examples and illustrations its use etc... Thanku —Preceding unsigned comment added by 117.196.162.187 (talk) 14:28, 22 February 2008 (UTC)[reply]

Have you reviewed our article on modems? Also, please don't type in ALL CAPS; not only is it more difficult to read, it is seen as YELLING and isn't considered polite. TenOfAllTrades(talk) 14:40, 22 February 2008 (UTC)[reply]

I would also recommend not to yell yourself. Don't break rules to illustrate a point. 64.236.121.129 (talk) 17:14, 25 February 2008 (UTC)[reply]

Electromagnet

We were doing an experiment with electromagnets using a coil of wire, an iron nail, a 9V battery, and a paperclip. When we created the electromagnet by generating a current through the wire, it picked up the paper clip, of course. But, after we removed the current, the nail acted as a working magnet. What has happened here? Nick (talk) 16:02, 22 February 2008 (UTC)nicholassayshi[reply]

Are you sure the nail wasn't steel? AlmostReadytoFly (talk) 16:05, 22 February 2008 (UTC)[reply]

The difference is not between iron and steel, but between hard and soft. A soft iron core will lose magnetism as soon as the electricity is switched off, a hard iron core will retain some magnetism. (If someone more knowledgeable can write helpful things for those links to point to, that would be lovely). A soft iron core, as well as only being magnetic when the current is flowing, will provide a stronger magnet than a hard iron core. If I recall from my school days, the difference between them is down to how quickly they are cooled when being made. I think soft iron is the one that is slowly cooled, taking hours or even days, giving a different structure to hard iron which is cooled much more swiftly. Unless the manufacturer is making the iron for an electromagnet, they are probably going to make hard iron as it is easier and cheaper. Skittle (talk) 17:49, 22 February 2008 (UTC)[reply]

What happened was ferromagnetism, which is the phenomenon by which materials, such as iron, in an external magnetic field become magnetized and remain magnetized for a period after the material is no longer in the field. MrRedact (talk) 17:52, 22 February 2008 (UTC)[reply]

If you had measured the actual strength of the magnet's pull, you would probably have found that the pull with current off was way lower than with current on. Even an iron ("soft" ferromagnetic material) nail can retain a bit of the magnetization. A piece of steel{"hard" ferromagnetic material) would have retained a much higher degree of magnetization. Lifting one paperclip may not have been a severe enough test of the magnet's strength. Steel has greater Retentivity than iron. Edison (talk) 18:46, 22 February 2008 (UTC)[reply]

Not wishing to quibble, but you seem to be suggesting the difference is between iron being 'soft' and steel being 'hard'. I'm really pretty sure that you can get soft iron and hard iron, and that good soft iron retains almost no / no magnetism while cheap hard iron retains a noticeable magnetism. While I have no doubt that steel has a higher retentivity than iron, the retentivity of iron is highly dependent on its structure which is, in turn, highly dependent on the cooling conditions. I seem to recall doing an entire module on this. Skittle (talk) 00:07, 23 February 2008 (UTC)[reply]

Paper Clip Capacitor

A long time ago I had a physics teacher who had an old hand crank generator in their room to show how magnets can generate electricity. One day me and some fellow students where playing around with it and one of them took a paperclip and placed it on the two contacts (where it stuck due to magnetism) and I started cranking the generator like crazy. Nothing happened (some of my peers thought the clip would melt, which I thought was ridiculous) so I reached for the clip to remove it so we can attach something else. As soon as I touched it I was literally thrown back so hard that I (in a spinning office chair) hit the opposite wall. Obviously I was electricuted, and I've experienced a shock of almost the same strength with a vacuum cleaner. I am wondering how a paperclip could store so much charge, or how it could store charge at all. This generator can barely make a small light bulb glow and yet it could throw me across a room and even temporarily paralize the left side of my body for a minute (something that I should have told someone, maybe. I'm fine 4 years later, so I doubt it was a problem). How is this possible? 206.252.74.48 (talk) 16:45, 22 February 2008 (UTC)[reply]

A capacitor needs two things, an electrical conductor to hold the charge, in this case the metal paper clip, and an electrical insulator to prevent discharge. Air makes for a minimal insulator, allowing the conductor to hold the charge for a few minutes as it slowly bleeds off. The clip might also have had a coating on it which worked as an electrical insulator. Contact with a better conductor, in this case you, allowed the paper clip to rapidly discharge. I must comment that touching the clip immediately with a bare hand was not at all a wise thing to do. Even if it hadn't retained the charge, it could have been hot enough to burn you severely, this could have happened if the clip had more electrical resistance or only had intermittent contact with the generator (you would get sparks in this case). Also, the term "electrocuted" means killed due to an electrical shock, and this obviously was not the case here. StuRat (talk) 18:00, 22 February 2008 (UTC)[reply]

I've never been one to use common sense. I've been injured countless amounts of times in high school, and this just happens to be a notable one. Curiously, the paper clip wasn't hot when someone else took it off. Maybe they just ignored the pain, such is the strength of conformity. 206.252.74.48 (talk) 18:09, 22 February 2008 (UTC)[reply]

If this was a standard steel paper clip, directly touching both contacts, I wouldn't expect it to get very hot from the amount of current produced by a hand generator, as steel has a fairly low electrical resistance. The electrical charge would have been largely dissipated (into you) by the time your friend touched it. Maybe it's time to use a bit more common sense before you get seriously injured or killed. StuRat (talk) 18:20, 22 February 2008 (UTC)[reply]

While there was likely some capacitance somewhere in the system, the paperclip definitely wasn't it. The capacitance of a few centimeters of wire (insulated or in air) is going to be somewhere in the very approximate neighbourhood – give or take a couple orders of magnitude – of one picofarad. Even charged to an utterly implausible potential, the paperclip isn't going to store an appreciable amount of energy. (Consider—has anyone ever gotten an electric shock from touching the exposed terminals of an isolated extension cord immediately after unplugging it from the receptacle? Lengths of wire are pathetic capacitors.) TenOfAllTrades(talk) 18:25, 22 February 2008 (UTC)[reply]

I would argue that the wires in an extension cord could hold a substantial charge for a short period of time, but that normal use of an extension cord doesn't cause that to happen. (The charge flows in one end and out the other, and none is retained.) I'm not sure if this retention of charge in electrical conductors qualifies under the definition of a capacitor, however. StuRat (talk) 18:38, 22 February 2008 (UTC)[reply]

You could argue that, but you'd be mistaken—electricity can be a bit counterintuitive sometimes. The self-capacitance of modest lengths of wire is almost trivially tiny. (Coaxial cable typically has a capacitance of about 100 pF per meter[3]; the capacitance of a paperclip wire will be less than that.) For the record, capacitance is defined as the amount of charge stored divided by the electrical potential: C = Q/V. You just can't cram many surplus charges into a wire at any reasonable potential, so it has a very low capacitance. TenOfAllTrades(talk) 19:26, 22 February 2008 (UTC)[reply]

Actually, electrocuted means killed or harmed by electric shock. -80.229.152.246 (talk) 18:14, 22 February 2008 (UTC)[reply]

Actually actually, electrocution means being killed by electric shock or damage due to electric charge [4] —Preceding unsigned comment added by 79.76.197.6 (talk) 00:09, 23 February 2008 (UTC)[reply]

I was thinking about that, thanks for clearing it up. So what is the term for what happened to me? Just "shocked"? 206.252.74.48 (talk) 18:19, 22 February 2008 (UTC)[reply]

Yes, or "electrified". StuRat (talk) 18:22, 22 February 2008 (UTC)[reply]

Whether or not "electrocuted" implies being killed is one of those things that varies according to who uses the word, or possibly by country. Anyway, we've cleared it up now. --Anon, 18:24 UTC, February 22, 2008.

Some dictionaries only say kill, others include injury. It's clear, however, that it originally meant death only, as the origin of the word is "electro-execution", referring to execution using the electric chair: [5]. I therefore consider the "injury" usage to be a modern misunderstanding of the word. Unfortunately, this misunderstanding is widespread enough to have now gathered some level of acceptance. StuRat (talk) 18:31, 22 February 2008 (UTC)[reply]

The term "Westinghoused" just never caught on for electrocution. I can't rule out the possibility, from your description, that the generator had a capacitor somewhere in the circuit hooked to it at the time you got the shock. Of course, if the generator were still being cranked and you touched two fingers across the terminals, even an old wall telephone magneto could generate sufficient current and voltage to produce a painful shock that you would long remember. Was it a telephone magneto or some other sort of generator? I have used a hand cranked resistance tester called a "Megger" which produced 1000 volts DC. A Wall phone magneto would have produced probably tens of milliamps at around a hundred volts max, depending on the speed it was cranked. If a capacitor were connected to such a phone magneto,or a Megger, it could store enough charge to produce a fatal electrocution. I would not expect an accidental capacitor in the form of a paperclip to store much electricity at the voltages produced by a hand cranked generator. If it were an extremely high voltage static generator, such as a Van de Graaf or Wimshurst machine, then a capacitor such as a plastic film container filled with water could act as a Leyden Jar or capacitor and store a painful or dangerous charge. Edison (talk) 18:38, 22 February 2008 (UTC)[reply]

From what I recall, the generator was a bunch of "U"-shaped magnets (each about the size of a horseshoe) attached to a board, with a length of metal covered in copper wire suspended inside it that was attached to the crank. The two terminals were made out of screws, and the gear assembly and the crank were taken from an old pencil sharpener. It was basically made out of scratch sometime in the 1950s. Also, no one was cranking the generator at the time of contact. 206.252.74.48 (talk) 19:22, 22 February 2008 (UTC)[reply]

The voltage it produced should have dropped to zero as soon as it stopped spinning unless there was a sizeable capacitor attached. If it was used to power an electromagnet, it was probably not designed to create extremely high voltage at extremely low current like the Megger. There might have been a rectifier to supply DC to the electromagnet, unless it was a DC generator with a built in comutator. I can't see how a paper clip connected to such a generator could store enough charge to zap you. Even if a capacitor were solidly connected across the output terminals, its charge should have drained away through the fairly low resistance of the winding. Some wall phone magnetos disconnected the winding from the output terminals as soon as you stopped cranking, to prevent the winding draining away the voice current when you talked. Some old wall phones also had capacitors to help operate the bells on the front. All the elements are there for there to have been a capacitor charged by the spinning armature and disconnected and waiting to zap you, if the thing was taken from an old wall phone. See telephone magneto and another telephone magneto. See wall phone for a diagram including the capacitor or condensor. Edison (talk) 20:34, 22 February 2008 (UTC)[reply]

I don't think the electricity threw you across the room, it was probably your muscles seizing + numbness/paralysis that caused the illusion of being "thrown back" :D\=< (talk) 23:01, 22 February 2008 (UTC)[reply]

What do you mean by "small light bulb"? --Milkbreath (talk) 23:10, 22 February 2008 (UTC)[reply]

A telephone magneto will light a 7.5 watt 120 volt bulb, but not (in my experience 40 watts or larger. Just saying. Edison (talk) 23:51, 22 February 2008 (UTC)[reply]

the answer here is clearly nothing to do with capacitance as many have pointed out. It is more likely the energy stored by inductance in the generator coils. The paperclip is shortcircuiting the output, but steel is not that good a conductor so it will take time for the magentic energy stored in the coil to drain through the resistance of the paperclip. Removing the paperclip breaks the circuit, but inductors are not able to instantly change the current flowing through them. The terminal voltage will consequently instantly rise to a potential that can sustain (for an instant) the previous current. As you are an even poorer conductor than the paperclip, this probably required a rather substantial voltage for a short period, then the current would rapidly decay. Conversly, if the paperclip had not been there, then there would have been no output current and hence little energy stored in the coils, and the terminal voltage would decay much faster, making it safe to touch immediately. I am astounded by the number of different dangerous things that can be done with a paperclip. Somebody should write an article on it. SpinningSpark 16:34, 23 February 2008 (UTC)[reply]

Yes, the inductance explanation seems much more plausible than the capacitance explanation. However, the resistance of the paper clip is negligible in this problem. The resistivity of steel is greater than some other metals, but it isn’t that high. Depending on the alloy, it’s around 10^-7 to 10^-6 Ωm.[6] The resistance of a paper clip is just a very small fraction of an ohm. I tried measuring the resistance of a paperclip using an ohmmeter, and I couldn’t detect a value different from zero. What’s really limiting the current in this circuit is the resistance of the coils, not the resistance of the paperclip. MrRedact (talk) 18:21, 23 February 2008 (UTC)[reply]

No, no, no. Inductance doesn't store anything. Inductors take energy from the current and put it into a field around them. The instant the current stops, the field collapses. It takes no time at all, almost literally. A coil will ring as the collapsing field induces a cuurent which creates a field which collapses, etc., but that, too, happens in an instant. The only way I can think of for our boy to be telling the truth is if there was a great big capacitor across the terminals, the paperclip wasn't making contact between the two terminals for whatever reason (paint?), and he got across the cap. This is supposing that the generator could produce enough EMF to jolt a person. I got 300V from a big filter cap hand-to-hand one time, and I can confirm that it will light up your life. --Milkbreath (talk) 20:11, 23 February 2008 (UTC)[reply]

I do not expect that the current would continue through the winding of the magneto for more than milliseconds after the thing stopped turning. If it were being cranked with a paperclip shorting it, there might indeed be a very high voltage when the circuit was broken, perhaps hundreds of volts, due to self-induction, if the inductance of the winding was high enough. Once it has stopped, I would not expect a shock from breaking the circuit. Edison (talk) 20:22, 23 February 2008 (UTC)[reply]

As of the instant the generator was stopped, the circuit can basically be modeled as a closed loop consisting of an inductor (representing the inductance of the coil) in series with a resistor (representing the resistance of the coil). I think any stray capacitances involved are going to be negligible. There wouldn’t be any ringing in this idealized circuit, because ringing requires a circuit governed by a second-order differential equation, and this simple RL circuit is only first order. What will happen is that after the generator is stopped, the current in the circuit will decay exponentially, with a characteristic time of L/R. So for example, if the coil has an inductance of 1H and a resistance of 1Ω, then a second after the generator was stopped, the circuit will still have a current going through it that’s e^-1 = 0.368 times as big as the current in the circuit as of the instant the generator was stopped. I’m guessing the coil probably has an inductance of less than 1H, and a resistance of greater than1Ω, so the OP would have less than a second after stopping the generator to break the circuit, in order to get a jolt that’s close to the amount of current that was in the circuit originally. However, the currents involved are going to quite large (albeit at initially quite low voltages), due to the generator being shorted out. MrRedact (talk) 21:04, 23 February 2008 (UTC)[reply]

I think it’s time to go numeric, in order to get an order-of-magnitude estimate to see if the inductance hypothesis is plausible. It sounds like the generator can only produce a relatively small amount of power, like in the ballpark of 10 watts. My guess is the coil has a resistance of more than an ohm, but it only consists of wire, so its resistance can’t be that high; let’s call it 5Ω. From the equation P=I²R, that means that the shorted-out generator was initially producing about 1.4A of current. The two coils on this little inductor[7], that’s only a fraction of an inch big, total close to 0.1H, so an estimate of 1H for the generator coil, that’s presumably much bigger, seems like a not unreasonable estimate of the generator coil’s inductance. For the OP to have considered the generator to have for sure have been stopped, there must have been a time in between when the generator was stopped and when the circuit was broken that’s not unreasonably small on a human time scale; let’s call it half a second. The amount of current that the OP would have received when he opened the circuit is I₀e^{-t R / L}, which, plugging in the above values, comes to about 0.1A. Given that a shock of 0.1A can kill you, it seems quite plausible that the inductance explanation is sufficient to explain how the OP could have gotten one heck of a jolt under the circumstances described. MrRedact (talk) 23:11, 23 February 2008 (UTC)[reply]

By the way, when I said that “the inductance explanation seems much more plausible than the capacitance explanation,” I was in that sentence only referring to the very implausible explanation that it was due to capacitance of the paper clip or of the wiring. Edison’s telephone magneto explanation is also a perfectly reasonable explanation, although it doesn’t match up as well with the OP’s memory of the device. I guess I’ll ask the OP (if he’s still watching): How long was it between the time the generator was stopped, and the time you removed the paper clip? If it was just a fraction of a second, then the inductance explanation is plausible, and matches better with your not remembering any capacitors. If it was like a half a minute or something, then Edison’s telephone magneto explanation is more plausible. Looking at this picture of a telephone magneto, I can see how you might be under the impression that someone had hand-made the thing from scratch, using the gear assembly and crank taken from an old pencil sharpener. MrRedact (talk) 01:06, 24 February 2008 (UTC)[reply]

Thank you for all your incredibly detailed answers. Also, it was a telephone magneto, the pictures match perfectly (as does my description somewhat). As for the delay between cranking and touching the paperclip, I figure it was about 1 second - and since my memory is fuzzy it could very well have been myself that was cranking the magneto before attempting to remove the paperclip. 206.252.74.48 (talk) 14:03, 25 February 2008 (UTC)[reply]

Medicine

North American Symptomatic Carotid Endarterectomy Trial: Carotid endarterectomy was found to be beneficial for symptomatic patients with carotid stenosis greater than 70%. Does this measurement of 70% stenosis refer to a relative stenosis in diameter or area? 50% stenosis in diameter = 75% stenosis in area. Which is the measurement that tips the scale towards surgery? —Preceding unsigned comment added by 69.74.62.226 (talk) 16:46, 22 February 2008 (UTC)[reply]

It is the area that is measured, and 70% is considered to be the standard threshold for surgical intervention. Though for those who have symptoms between 50-69% surgery may be considered if other treatments fail. Fribbler (talk) 17:17, 22 February 2008 (UTC)[reply]

(ec) Link to NASCET article in Stroke (no subscription required): HTML, PDF

The methods section describes one eligibility criterion as "...a stenosis of 30% to 99% in the ipsilateral carotid artery based on linear diameter reduction" (my emphasis). There's a more detailed description of the eligibility criteria in an earlier volume of Stroke: PDF. This article also includes diagrams of what was measured.

Note that stenoses aren't necessarily uniform, and that the unobstructed lumen won't necessarily be circular in cross-section. In other words, the relationship between linear stenosis and area stenosis isn't perfectly-behaved, mathematically. TenOfAllTrades(talk) 17:36, 22 February 2008 (UTC)[reply]

answers plz (refrigeration vs. air conditioning)

what is the difference between refrigeration and air conditioning? —Preceding unsigned comment added by 202.83.173.61 (talk) 20:57, 22 February 2008 (UTC)[reply]

They're the same concept. The function of a refrigerator is to remove heat from one system, and place it in another. In the case of your typical kitchen refrigerator, heat is removed from the inside, and dumped into the outside. A house with central air conditioning is basically a gigantic refrigerator, which removes heat from the house and dumps it into the air outside. This is why you can't, for example, keep your fridge open and expect it to cool the house down. Someguy1221 (talk) 21:30, 22 February 2008 (UTC)[reply]

If the refrigerator is cooler than the house then the average temperature of the house and the refrigerator is less than the temperature of the house.. if you let them equalize then it would in fact cool down your house. But I guess refrigerators do create waste heat cause they use electricity.. but for a little while at least it would cool your house. :D\=< (talk) 22:57, 22 February 2008 (UTC)[reply]

You're house would have to be incredibly small for that to work...Someguy1221 (talk) 00:42, 23 February 2008 (UTC)[reply]

The area in front of the refrigerator would certainly be cooled significantly- that's why you feel a blast of cold air when you open the freezer.. :D\=< (talk) 00:47, 23 February 2008 (UTC)[reply]

That would only work if the waste heat from the fridge was being expelled outside the house. If you're doing that, you basically have an air conditioning unit. Just to avoid confusing the anonymous person with Froth's silliness. Skittle (talk) 23:24, 24 February 2008 (UTC)[reply]

I think there's a slight diff in the terms in that the goal of refrigeration is only to lower the temperature, while the goal of air conditioning also includes lowering the humidity. That said, refrigeration often causes a reduction in humidity, whether that is the goal or not. StuRat (talk) 01:34, 23 February 2008 (UTC)[reply]

It's in the names themselves. The goal of a refrigerator is to lower the temperature, or refrigerate, the contents. The goal of an air conditioner is to condition the air by controlling the temperature (by heating and/or cooling as needed), humidity (a cooling system will also pull moisture, often a closed system will include a humidifier downstream of the cooling coils) and quality (by filtering dust and debris, and often scrubbing chemicals).

Note that humidity is often automatically controlled by a sensor called a humidistat; linking to that word redirects to the WP article for humidifier, which has a link to humidistat...... -SandyJax (talk) 21:30, 26 February 2008 (UTC)[reply]

Chemical reaction question

KCl + HNO₃ → NR

Why? I figured, since KCl is ionic, and HNO₃ is ionic (right?), HCl (which is covalent) would be formed:

KCl + HNO₃ → KNO₃ + HCl

Well, I was wrong, but why? I guess it's because K is more reactive than H? If so, how do I know when the driving force to form a solid/covalent compound "wins"? Thanks in advance. :) -- Aeluwas (talk) 21:53, 22 February 2008 (UTC)[reply]

HCL is a strong acid, which means it just about completely dissociates in water, just like an ionic compound (so you can think about it behaving like one). HNO₃ by the way is also a strong acid. HNO₃ is also an oxidizer and is some situations will undergo an oxidation reduction reaction to form NO₂ gas and other things, but it doesn't seem to be the case here. What you would get in the solution is the following Sifaka ^talk 22:50, 22 February 2008 (UTC)[reply]

Cl^-(aq) + NO₃^-(aq) + K⁺(aq) + H⁺(aq) (or H₃O⁺(aq) if you prefer)

HCl is a covalent compound, but it is also highly water soluble. In addition, it is a strong acid, which means that when you put it into water, it is almost completely deprotonated (i.e. the H⁺ is removed from the Cl^-). Actually, (pure) HNO₃ is also a covalent, highly water soluble strong acid, just like HCl. When you mix KCl (ionic and highly water soluble) with HNO₃ in water (from the HNO₃ solution you're using), the compounds rapidly dissociate into K⁺, Cl^-, "H⁺" (see hydronium ion for why I put it in quotes), and NO₃^-. What happens next is determined by the solubility product constant for each of the potential products in this double displacement type reaction. We already know that KCl and HNO₃ are highly water soluble, so they will not precipitate. We also know that HCl is also highly water soluble, so it will stay in solution too. That leaves the KNO₃. Potassium nitrate, like KCl, is also a highly water soluble salt, so if you mixed dry KNO₃ with water, it would rapidly dissolve, forming K⁺ and NO₃^- ions. Since we already have K⁺ and NO₃^- ions, nothing further will happen in our reaction. Most potassium and sodium salts are highly water soluble, so no matter what you mix with them, they tend to stay in solution. Contrast that with something like silver salts. AgNO₃ is water soluble, but AgCl₂ is not. If you mix AgNO₃ with a hydrochloric acid solution, you'll see the formation of AgCl₂ as a solid, and you'll have the formation of HNO₃, which will stay dissolved (as H⁺ and NO₃^-). -- 128.104.112.47 (talk) 22:59, 22 February 2008 (UTC)[reply]

Nice answer by the way. Sifaka ^talk 23:01, 22 February 2008 (UTC)[reply]

Great answers, both of you! Thanks a lot. -- Aeluwas (talk) 09:58, 23 February 2008 (UTC)[reply]

is it two seconds or four seconds to moon and back?

If you say something, will it take 2 seconds or 4 seconds to hear the other person's "yes" "no" etc response? —Preceding unsigned comment added by 79.122.91.82 (talk) 22:07, 22 February 2008 (UTC)[reply]

You're talking about sound getting to the moon? It won't get there- sound travels through air (or sometimes other matter), but not empty space. Friday (talk) 22:08, 22 February 2008 (UTC)[reply]

I assume he means via radio or something else that travels at the speed of light. In which case, it should take (less than) 1.35 seconds in either direction, or 2.7 seconds both ways. -- Aeluwas (talk) 22:10, 22 February 2008 (UTC)[reply]

Anyway, don't forget that the distance from the Earth to moon is highly variable especially between perigee and apogee. Hope this helps. Thanks. ~A H 1^(TCU) 01:02, 26 February 2008 (UTC)[reply]

Significant time-delay for radio propagation may occur as the signal passes through the ionosphere. In this region, the speed of light (or radio waves) is variable based on direction, frequency, temperature, butterfly-wing-flaps, etc. (Note that the speed of light is constant in a vacuum, but the region of charged particles near earth is decidedly not a vacuum!) Nimur (talk) 22:20, 27 February 2008 (UTC)[reply]

Unrelated to the original question

Anyway electromagnetic radition could never escape the gravitational field of the earth.. you should be thankful for that, or we'd all be scorched to a crisp by the untempered fury of the Sun.. not to mention the roar of noise from nuclear fusion in the core, which would be overwhelming without any atmosphere in space to slow it down. :D\=< (talk) 23:32, 22 February 2008 (UTC)[reply]

What on earth are you talking about? Your post, as far as I can understand it, is completely incorrect. Friday (talk) 23:47, 22 February 2008 (UTC)[reply]

It is completely incorrect. Electromagnetic radiation can't leave the earth? Infared, microwaves, radio waves, and light can all leave the earth quite easily. Wisdom89 _{(_T / ^C)} 23:50, 22 February 2008 (UTC)[reply]

Seriously Froth, what's up? Been wondering for a while now if your account's been compromised. 79.74.0.57 (talk) 23:58, 22 February 2008 (UTC)[reply]

The wrong crowd :/ Who are you by the way? :D\=< (talk) 00:46, 23 February 2008 (UTC)[reply]

I'm confused. You used to be a computer science student named Brian and now you're "54-year-old grandmother writing a novel in her spare time"? It looks to be like we need an admin to shut down this account until the real Froth can provide his user committed identity. (EhJJ)^TALK 04:48, 23 February 2008 (UTC)[reply]

I've sent a ~~request of administrative action.~~ ~~Please comment there, whether you agree or disagree.~~ (EhJJ)^TALK 14:12, 23 February 2008 (UTC)[reply]

lol metadiscussion. Yeah it's me, don't mind me. I blanked my userpage to change from the well-behaved Froth persona to the still-helpful EFG persona that's not afraid to screw around for lulz. I guess it's a stage of my life spiraling downward. *shrug* Also why were you going to ban me.. if my account was compromised the real me would come forward with the hash text to reclaim my account. All aboard the light-current's fate train, toot toot! :D\=< (talk) 15:42, 23 February 2008 (UTC)[reply]

Someone knocking on my coffin? Be careful: you might bring me back to life 8-)--HideousCrumpet (talk) 22:22, 23 February 2008 (UTC)[reply]

:O :O :O :O :O :D\=< (talk) 05:16, 24 February 2008 (UTC)[reply]

Also the grandmother thing was because I had asked a perfectly legitimate medical information question regarding the novel I'm writing. I could very well have been some casual user very offended by the accusation that I'm seeking free medical help. :D\=< (talk) 15:46, 23 February 2008 (UTC)[reply]

Yeah, this should have been moved to the talk page a long time ago. Anyway, I've dropped my original complaint. (EhJJ)^TALK 16:36, 23 February 2008 (UTC)[reply]

Purple veins

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

A thinly-disguised request for a diagnosis is still a request for a diagnosis. Have your novel's character (ha, ha) see a doctor. MrRedact (talk) 01:36, 23 February 2008 (UTC)[reply]

Well I never! I'm a 54-year-old grandmother writing a novel in her spare time. At the next bridge tournament, I'll be sure to tell all the ladies never to ask for help from Wikipedia. Hmph! :D\=< (talk) 04:04, 23 February 2008 (UTC)[reply]

I also have a large purple vein on the underside of my cock that seems to be getting bigger. Should I see the nurse to reduce the swelling, or should i take matters into my own hands?

What makes protiens

I read the page on protiens. It explained what protiens were made of but not what made them. Also, do single cell organisms have DNA & RNA? cris —Preceding unsigned comment added by 75.145.213.217 (talk) 23:16, 22 February 2008 (UTC)[reply]

Yes all single cell organisms have both DNA and RNA. Viruses, which are not considered living organisms may have only one of the two. Ribosomes make proteins. The info you were looking for in the protein article is found here Sifaka ^talk 23:24, 22 February 2008 (UTC)[reply]

(ec) Yes. What you are describing is the central dogma of molecular biology. That is, all cells (single-cell and multicellular organisms) have DNA. They transcribe this DNA into mRNA and then that mRNA is translated into proteins. (EhJJ)^TALK 23:26, 22 February 2008 (UTC)[reply]

Thank you! —Preceding unsigned comment added by 75.145.213.217 (talk) 00:01, 23 February 2008 (UTC)[reply]

Is the unknown information transfer from protien to RNA and protien to DNA how science speculates that DNA and RNA first formed? (Central dogma of molecular biology) —Preceding unsigned comment added by 75.145.213.217 (talk) 01:01, 23 February 2008 (UTC)[reply]

RNA can have enzymatic functions. There is a suggestion RNA may have originally performed the function of proteins and DNA [8]. This would have transitioned to RNA and proteins then probably RNA, proteins and DNA Nil Einne (talk) 01:12, 23 February 2008 (UTC)[reply]

This is called the RNA world hypothesis. (Internal Wikipedia link for those interested, the link posted by Nil Einne is good too.) -- 128.104.112.47 (talk) 21:22, 23 February 2008 (UTC)[reply]