mej@hlwpc.UUCP (Michael Jacobs) (10/28/85)
*** REPLACE THIS LINE WITH YOUR MESSAGE *** A question came up over the weekend about electricity. If you put a live electrical wire into a large swimming pool, what happens to the current? Does it flow in a localize region around the wire? Does it distribute evenly over the volume of the pool? Does it peter out slowly over distance from the wires, due to the resistance of the water? Please post replies. And thanks. .
ralphd@teklds.UUCP (Ralph Durtschi) (10/29/85)
> A question came up over the weekend about electricity. > If you put a live electrical wire into a large > swimming pool, what happens to the current? My guess is that, if you could see it, the current would look something like fuzzy lightening between the wire and ground (probably the drain). Bye, Ralph
ayers@convexs.UUCP (10/30/85)
>A question came up over the weekend about electricity. >If you put a live electrical wire into a large >swimming pool, what happens to the current? >Does it flow in a localize region around the >wire? Does it distribute evenly over the >volume of the pool? Does it peter out slowly >over distance from the wires, due to >the resistance of the water? it just drips off the end of the wire and collects in a pile at the lowest point of the pool... So come and walk awhile with me and share The twisting trails and wondrous worlds I've known. But this bridge will only take you halfway there-- The last few steps you'll have to take alone. <Shel Silverstein> (EE bygum 'e's a bad 'un) <Shush, Centerfold!> Dangermoose (& blues, II)
mwg@petrus.UUCP (Mark Garrett) (10/30/85)
++ > If you put a live electrical wire into a large > swimming pool, what happens to the current? This is just an educated guess but, I would think that the current would flow from the point of the end of the wire to the ground in a quickly widening cone. Since the electons repel each other, the main current would take up as much of the conductor as it can while still having some component in the direction toward the ground. In addition, there might be eddy currents all over the place, especially if it is AC or (worse) lightning, which is why you would probably get electrocuted no matter where you were in the water. -Mark
sgcpal@watdcsu.UUCP (P.A. Layman [EE-SiDIC]) (11/01/85)
In article <662@petrus.UUCP> mwg@petrus.UUCP (Mark Garrett) writes: >++ >> If you put a live electrical wire into a large >> swimming pool, what happens to the current? > >This is just an educated guess but, I would think that the current >would flow from the point of the end of the wire to the ground in >a quickly widening cone. Since the electons repel each other, the >main current would take up as much of the conductor as it can while still >having some component in the direction toward the ground. In addition, >there might be eddy currents all over the place, especially if it is >AC or (worse) lightning, which is why you would probably get electrocuted >no matter where you were in the water. >-Mark Guess is right. Althougth their is no simple answer to the question, we can quickly approximate 2 cases, using the point form of ohm's law, which is: _ _ J = 1/p E. _ _ In this equation J and E are current density(A/(cm**2)) and electric field (volts/cm) and are Vectors. p is the resistivity(ohm-cm) and is a scalar. If we assume the walls of the pool to be an equipotential surface of 0 volts, and the conductor to be insulated except for the end which is situated the middle of the pool at some potential V, we find that near the end of the conductor the equipontential surfaces are roughly spherical, and thus E is roughly uniform, and J will be constant in all directions. Since the total current flowing through an equipotential surface will be constant we quickly see that J will decrease as 1/(x**2) as x, the distance from the conductor increases. Near the pool walls things are quite different beacause the equipotential surface now follows the pool walls rather than being spherical. The current density will be much lower in the corners, than along flat walls. If we now consider the walls of the pool to be insulating, and the drain pipe as the zero potential we get the second simple case. Remember shaking iron powder over a bar magnetic and observing the magnetic field pattern. The lines of electric field observed between the conductor and the drain will be very similar to the magnetic field lines observed between the north and south poles, except they will be 3-dimensional. Highest magnitude of electric field will be in the straight line joining the wire and the drain, and thus so too will the current density. As we move out from this line, the lines of the electric field become longer, and thus the magnitude of the field is reduced, and so too the current density. As far as being electrocuted is concerned for 120 volts in a reasonably sized pool you probably wouldn't be anywhere *inside* the pool. However in a plastic lined pool, the danger is stepping out and providing a lower resistance than the drain, in which case you might. The only eddy currents that will be observed are those near the filter outlet, and those will be water, not electron current. There is no magnetic field to induce currents in a conductor in the pool. You might want to have a look at "Engineering Electro-Magnetics" by Hayt, a basic EE text, which describes some simple graphical methods of solving this type of problem Paul L. (EE at waterloo) sgcpal@watdcsu.UUCP
wmartin@brl-tgr.ARPA (Will Martin ) (11/01/85)
In article <662@petrus.UUCP> mwg@petrus.UUCP (Mark Garrett) writes: [Carried-forward query] >> If you put a live electrical wire into a large >> swimming pool, what happens to the current? [Extract] >In addition, there might be eddy currents all over the place, especially >if it is AC or (worse) lightning, which is why you would probably get >electrocuted no matter where you were in the water. >-Mark Hmmm --- if a person is immersed in the water, why would they be electrocuted at all? If they were between the wire and the point of greatest ground potential, like a metal drain, I could see it (but wouldn't the current tend to flow AROUND the body, through the water which has less resistance than the body [considering skin resistance]). If they were in the pool, at another spot, why would there be any potential across their body at all? They wouldn't have any current flow through their body in this case, would they? Will
makaren@alberta.UUCP (Darrell Makarenko) (11/01/85)
> ++ > > If you put a live electrical wire into a large > > swimming pool, what happens to the current? > > a quickly widening cone. Since the electons repel each other, the > main current would take up as much of the conductor as it can while still > having some component in the direction toward the ground. > -Mark I remember doing experiments in grade 12 science showing that pure water does not conduct electricity. Salt water did conduct because of the Na+ and Cl- ions. Of course air does not conduct electricity either but lightning still hits the ground. Question: Does pure water conduct electricity? If it does not (as I believe) why does one have to be extra carefull about getting elecrocuted when standing in a puddle of water??
levy@ttrdc.UUCP (Daniel R. Levy) (11/03/85)
In article <714@alberta.UUCP>, makaren@alberta.UUCP (Darrell Makarenko) writes: > > I remember doing experiments in grade 12 science showing > that pure water does not conduct electricity. Salt water did conduct > because of the Na+ and Cl- ions. Of course air does not conduct > electricity either but lightning still hits the ground. > Question: Does pure water conduct electricity? If it does not > (as I believe) why does one have to be extra carefull about getting > elecrocuted when standing in a puddle of water?? If you had tested tap water too you would have found it to be a pretty fair conductor. It doesn't take much impurities to do this. You can pretty well count on all naturally occurring water to have enough impurities to be a good enough conductor to allow dangerous amounts of current to pass at house- hold power voltages, given the usual small distance in the puddle between your skin and a good conductor, namely the ground, at an opposite potential to a "live" wire (since most electrical systems have one side of their voltage source tied to an earth ground somewhere). You touch the other side of the voltage source while standing in such a puddle, and you get shocked or worse. The lightning mechanism is different. The voltage difference between cloud and ground or cloud and cloud is sufficient to ionize the air, whereupon it WILL conduct electricity (very simplistic explanation; the ionization occurs in steplike stages) sort of like neon does in a neon lamp. Now the question of how the cloud achieves that voltage is a different one and I understand there are several explanations (anyone care to elaborate?). -- ------------------------------- Disclaimer: The views contained herein are | dan levy | yvel nad | my own and are not at all those of my em- | an engihacker @ | ployer or the administrator of any computer | at&t computer systems division | upon which I may hack. | skokie, illinois | -------------------------------- Path: ..!ihnp4!ttrdc!levy
slg@ukma.UUCP (Sean Gilley) (11/04/85)
Pure water (H2O) does not conduct electricity. The reason you need to
be careful with electricity around water is that the minerals in solution
within the water are conductors.
Sean.
--
Sean L. Gilley Phone: (606) 272-9620 or (606) 257-4613
{ihnp4,decvax,ucbvax}!cbosgd!ukma{!ukgs}!slg, slg@UKMA.BITNET
Watches are a conspiracy by Swiss confidence men.mls@husky.uucp (Mark Stevans) (11/05/85)
The question of how atmospheric electricity is generated has been raised by the referenced article: > Now the question > of how the cloud achieves that voltage is a different one and I understand > there are several explanations (anyone care to elaborate?). Here is the best theoretical explanation of cloud electrification that I know of: Clouds are made up of droplets of water. If there is a lot of water in the cloud, larger droplets may fall out of the cloud as rain. If the cloud is relatively calm, the droplets usually stay in one piece as they travel about. In stormier conditions, water droplets break up and recombine as they get blown about in the cloud. There are some free electrons in every droplet of water. They naturally collect around the outside of the droplet, due to mutual repulsion. If a droplet begins to break up into two sub-droplets, the electrons tend to stay on the larger droplet (statistically and fluid-dynamically speaking, droplets usually don't break up into exactly equal sub-droplets), because during this period (envision the process as similar to a yeast cell budding) the larger sub-droplet has less surface area per unit volume. We end up with a relatively positively charged small sub-droplet, and a negatively charged large sub-droplet. Due to their greater weight to surface area ratio, the large, negatively charged droplets tend to sink in the cloud, perhaps hitting the ground as rain, while the small droplets stay suspended in the air currents. Since the free electrons in the cloud are moving to lower altitudes, a potential difference is generated. Most lightning strokes are between upper and lower parts of a single cloud, and not between cloud and ground. The potential difference per unit distance increases until it is sufficient to ionize a "finger" of air about an inch wide. This highly conductive finger, which typically snakes from a positively charged region towards a negatively charged region, lengthens at a speed on the order of a thousand miles per hour. When the end of the finger gets close enough to its target, the potential difference between the end of the finger and the target causes free electrons on the target to arc across the gap into the ion finger. This "return stroke" is what we know as lightning. Mark Stevans ritcv!husky!mls
sgcpal@watdcsu.UUCP (P.A. Layman [EE-SiDIC]) (11/06/85)
In article <2358@ukma.UUCP> slg@ukma.UUCP (Sean Gilley) writes: > > > Pure water (H2O) does not conduct electricity. The reason you need to >be careful with electricity around water is that the minerals in solution >within the water are conductors. > I'm afraid your wrong Sean. Pure water is a conductor. It's conductivity is enhanced by certain impurities, in the same way that silicon's conductivity is increased by certain dopant's. Paul L.
jmc@riccb.UUCP (Jeff McQuinn ) (11/06/85)
> > A question came up over the weekend about electricity. > > If you put a live electrical wire into a large > > swimming pool, what happens to the current? > The current will take the shortest path from the wire to the nearest ground (probably the drain) assuming the water is a homogenous mix of contaminates. Jeff McQuinn just VAXing around
elf@cylixd.UUCP (Leonard Bottleman) (11/06/85)
In article <2358@ukma.UUCP> slg@ukma.UUCP (Sean Gilley) writes: > > Pure water (H2O) does not conduct electricity. The reason you need to >be careful with electricity around water is that the minerals in solution >within the water are conductors. > > Sean. Water self hydrolyzes into H and OH ions: so even if you managed to get pure H2O, it wouldn't remain that way for more than an instant. Leonard Bottleman ihnp4!akgua!cylixd!elf
jbs@mit-eddie.UUCP (Jeff Siegal) (11/07/85)
In article <2358@ukma.UUCP> slg@ukma.UUCP (Sean Gilley) writes: > > > Pure water (H2O) does not conduct electricity. The reason you need to >be careful with electricity around water is that the minerals in solution >within the water are conductors. > > This is not quite correct. Pure water (H2O) DOES conduct elecricity. However, the conductivity is sufficiently low that it can often be ignored. What causes aqueous solutions to be conductive is the ions which present in the solution. If I remember correctly, water is itself partially ionized. The concentration of H+ (and other complexes, H3O+, etc.) is 1 x 10**-7 mole/L. The pH is defined as - LOG10(concentration of H+ ions). Thus the pH of pure water is 7. Jeff Siegal - MIT EECS (jbs@mit-eddie)
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (11/08/85)
In all this talk about whether water is a "conductor" or not, people sound like they think this is an all-or-nothing proposition. Pure water has fairly high (but not infinite) resistivity, but it doesn't take much in the way of ionic impurities to reduce its resistivity substantially. Since a swimming pool (postulated in the original problem) would have hypochlorite salts dissolved in it, it would conduct electricity much better than pure water.
mwg@petrus.UUCP (Mark Garrett) (11/08/85)
++ > Hmmm --- if a person is immersed in the water, why would they be > electrocuted at all? If they were between the wire and the point of > greatest ground potential, like a metal drain, I could see it (but > wouldn't the current tend to flow AROUND the body, through the water > which has less resistance than the body [considering skin resistance]). > > If they were in the pool, at another spot, why would there be any > potential across their body at all? They wouldn't have any current > flow through their body in this case, would they? > Will When I was young(er), and before so many years of education in engineering and electronics, I thought about what would happen if lightning hit the house when I was in the shower. I thought that I'd be safe since the current would much rather go through the pipe (full of water) in the wall than through me. The problem with this logic is that the two resistances are really in parallel (depending on the geometry). If I constituted a path with 1% of the total conductivity from the source to ground, then I would get 1% of the current. For lightning, even a small fraction of the current might ruin one's day. I can see that in the swimming pool case, the current density resulting from a 120 volt drop, spread out over the water might be small. But remember, that the conductivity of the water is finite, so there is a voltage difference between any two points along the current path. Therefore if you are in that path, you have some voltage across you and you will draw some current.
randy@utcsri.UUCP (Randall S. Becker) (11/10/85)
> In article <2358@ukma.UUCP> slg@ukma.UUCP (Sean Gilley) writes: > > > > > > Pure water (H2O) does not conduct electricity. The reason you need to > >be careful with electricity around water is that the minerals in solution > >within the water are conductors. > > > I'm afraid your wrong Sean. Pure water is a conductor. It's conductivity > is enhanced by certain impurities, in the same way that > silicon's conductivity is increased by certain dopant's. > > Paul L. Just to provide clarification to this point, water is an extremely weak electrolyte. Distilled water is 0.0000002 % ionized at 25C. (Ref: Chemistry: A Conceptual Approach, Mortimer, 1979) Randy -- Randall S. Becker Usenet: ..!utcsri!randy CSNET: randy@toronto
ems@amdahl.UUCP (ems) (11/12/85)
> In article <2358@ukma.UUCP> slg@ukma.UUCP (Sean Gilley) writes: > > > > Pure water (H2O) does not conduct electricity. The reason you need to > >be careful with electricity around water is that the minerals in solution > >within the water are conductors. > > > This is not quite correct. Pure water (H2O) DOES conduct elecricity. > However, the conductivity is sufficiently low that it can often be > ignored. What causes aqueous solutions to be conductive is the ions > which present in the solution. ... Hmmm. Sounds like a semiconductor. I can see it now, the next 'wave' in chips. Fluidics! No. NO. Thats been taken. Er, ah, Fluitronics!! No. no. Too hard to read... How about: aquaware !! no. sounds like a swimsuit. Hurumph. Maybe this idea is just all wet... -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems 'If you can dream it, you can do it' Walt Disney This is the obligatory disclaimer of everything. (Including but not limited to: typos, spelling, diction, logic, and nuclear war)