Science desk
< June 2	<< May \| June \| Jul >>	June 4 >

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

June 3

batteryless flashlights

could not find information on how batteryless flashlights work.do u have any info.on this? —The preceding unsigned comment was added by 66.174.93.98 (talk • contribs).

One method would be to generate electricity though mechanical action. A changing magnetic field (caused, say, by moving a magnet) creates a current (see Electrical generator). If the batteryless flashlight you're thinking of is one in which you pump a handle or crank to light it up, what you are likely doing is spinning a magnet around inside of a coil of wire. For more information on this, see Mechanically powered flashlight. Hope this helps. --TeaDrinker 07:58, 3 June 2007 (UTC)[reply]

The next step is to introduce a capacitor to store energy that can be released when you stop turning the dynamo. Otherwise the light goes off when you stop winding. Bendž|Ť 13:26, 3 June 2007 (UTC)[reply]

Some "batteryless" flashlights may acutally contain batteries which are charged by a hand crank generator or other mechanical means (I have one of these that really has a Lithium Ion battery inside). It is also possible that some of them don't use batteries, instead using a clockwork mechanism, perhaps storing energy in a spring (device) or flywheel, then releasign that energy into a generator which then powers the light. See Self-powered equipment and Batteryless radio. -- Diletante 15:41, 3 June 2007 (UTC)[reply]

I have one that you shake back and forth – it involves copper wire coil and presumably a magnet inside the coil. Vranak

I've just bought one that involves squeezing a lever (which I think operates a rachet, flywheel, and dynamo). I am disapointed with it: it is very noisy, it is too tiring to keep it going for long, the light is weak and intermittent. In my opinion, you are better off having a conventional torch - or flashlight in American English - plus some spare batteries. 80.0.100.234 08:27, 5 June 2007 (UTC)[reply]

plant's Water purification

It would be nice if there's links and reference: How plants can purify the solutions and water in the ground and attract necessary substances? how they can discern the particles of substances and elements , with what special characteristic of them? Is the attraction according to the requirement or instinctive?Flakture 04:58, 3 June 2007 (UTC)[reply]

Root#Root structure and osmosis are good places to start. Dr_Dima.

Sunrise Sunset Time Differences

Why is it that on June 17th the sunrise in NH is at 5:09 AM and sunset at 8:30 PM, but in FL the sunrise is ar 6:25 am and sunset at 8>24 PM. I can understand the sunrise time differences are due tot he curvature of the earth and would vary during the year, but I had expected the sunset times to also vary and be different. Dick: 209.247.23.5 10:49, 3 June 2007 (UTC)[reply]

New Hampshire is much further north than Florida, and therefore, the changing seasons have a much greater effect on day length - As it is currently summer in the Northern hemisphere, an NH day is almost an hour and a quarter longer. As we approach the summer solstice, the NH day will grow even longer compared to the Florida day, but in winter, Florida days would be much longer than Hew Hampshire days. The weather stations where sunrise and sunset are measured from are probably not on the same line of longitude; if they were, the difference between the two sunsets would be the same as the difference between the sunrises (in other words, it's just chance that the two sunsets occur at the same time). Laïka 11:06, 3 June 2007 (UTC)[reply]

Would point out that here in NH, the sun is closest to us in the winter, and furthest from us in the summer. I'm guessing that this is what is causing the unexpected sunrise/sunset differential, that the sun is physically closer to different parts of the world at different parts of the year. Maybe the Analemma is related. - MSTCrow 15:43, 3 June 2007 (UTC)[reply]

I'm not sure about the relative distance of the sun in winter or summer, but the important thing is that the axis of the earth stays at a tilt, like a gyroscope. As it goes around the sun during the year this means that one hemisphere or the other gets more or less sunshine, corresponding to summer or winter. Imagine light from a distant source falling upon a model globe with a tilted axis. One of the hemispheres will have more shadow than the other. 80.0.100.234 08:33, 5 June 2007 (UTC)[reply]

I assume by NH, you mean the Northern Hemisphere, not just New Hampshire. -- Diletante 15:52, 3 June 2007 (UTC)[reply]

It couldn't be the whole northern hemisphere - the sun is both rising and setting at every point in time simultaneously there! Laïka 16:50, 3 June 2007 (UTC)[reply]

Dick, see if you can find a map-tool that shows what parts of the world are in sunlight at a given time – ah, I see there's a link at terminator (solar). You'll notice that at (your) summer sunrise the terminator runs NW/SE, while at (your) summer sunset it runs SW/NE. Thus your example town in Florida can be near your sunset line but not near your sunrise line. Does that make sense? —Tamfang 01:48, 4 June 2007 (UTC)[reply]

Difference between Sagittal and Medial planes in human Anatomy

I am struggling to complete an assignment on the position and actions of muscles in the body as I can't seem to figure out the difference between the Sagittal and Medial Planes in the human body.

Having scoured the net, the information I have found seems to be at best unclear and at worst contradictory.

Please could someone clarify this for me?

Thanks Becks.

A mid sagital line is a medial line. However, not all sagital lines are mid-sagital therefore they are parallel and only very by a X intercept. 68.41.155.159 13:07, 3 June 2007 (UTC)[reply]

See Gray's anatomy online and this illustration. There is only one median plane. It divides the body into two roughly symmetrical halves. Any plane parallel to the median plane is a sagittal plane. Thus, the median plane is a sagittal plane (and is therefore also called the mid-sagittal plane). For an example of a sagittal plane that is not the median plane, see this illustration. --NorwegianBlue^talk 13:45, 3 June 2007 (UTC)[reply]

Another way to put it is the median plane is a sagital plane which divides the body into equal left and right symmetrical pieces. --24.147.86.187 17:01, 3 June 2007 (UTC)[reply]

Careful about spelling. I believe "medial plane" is a common improper designation for the "median plane" (much like the "median nerve" is often mistakenly called the "medial nerve"). As others have described, the sagittal plane divides an object into two sides, right and left. Sagittal planes can be moved in a horizontal direction to change the size of the right and left sides. The position of the sagittal plane that divides the object into equal right and left halves is called the midsaggital (or median) plane. Cheers, David Iberri (talk) 20:06, 4 June 2007 (UTC)[reply]

Catheter ablation

Is catheter ablation effective for the treatment of arrhythmias?

Depends on the type of arrythmia. It is the treatment of choice for re-entry tachycardias, which are caused by abnormal signal transduction from the ventricles to the atria. However, whether it is possible or not depends on the localization of the abnormal pathway. See Wolff-Parkinson-White syndrome, Treatment. --NorwegianBlue^talk 14:39, 4 June 2007 (UTC)[reply]

Radiofrequency abalation is also coming into use in the treatment of atrial fibrillation. A Maze procedure - previously performed by scalpel - can now be performed via catheter to isolate spots prone to fibrillation.

Frogs and lily pads

I was at a lake this weekend that had many lily pads, but I never saw a frog on any of them. Do frogs really sit on the lily pads or is that just something that people always assume from cartoons and popular culture? --Catrina

From what I remember (and I've never really paid attention to frogs since I was a kid), they don't really 'sit' on them for extended periods of time - but they do climb over/through them... --Kurt Shaped Box 23:03, 3 June 2007 (UTC)[reply]

I have seen many frogs sitting on tree leaves, presumably to take advantage of the natural camouflage. In a lake, hiding under the water may be the safest place, but while on the surface, the frog will try to seek a low-visibility spot such as a background it blends with. Nimur 01:17, 4 June 2007 (UTC)[reply]

I've seen small frogs sitting on lily pads before, hanging out and doing their frog thang. --24.147.86.187 15:08, 4 June 2007 (UTC)[reply]