General Physics Questions

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nacnud

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<font color="yellow">What would you do with all those pesky electrons coming out of your socket</font><br /><br />That's why you should always switch your sockets off at the wall when you are not using them, otherwise when you get up in the morning there will be a puddle of electricity all over the floor! You can see this in some people’s houses when you walk around in your socks on the carpet the electricity makes little sparks as it squelches out of the way.<br />
 
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siarad

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Not trying to be nastily picky but it's the RMS voltage 0.707 of the peak, average is 0.632peak for sine waves.<br />
 
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siarad

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Yes + & - but remember energy is always positive so when the current flows one way & then reverses it's still energy. Take care as integrating a sine wave through one cycle gives 0 unless you appreciate this.<br />Further you don't consume electricity you just measure it's passing. As you seem to be in the USA look upon it as the way in which the 'Frisco trams clutch onto the circulating wire where nothing is removed from it.
 
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Saiph

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There are two types of current, DC and AC.<br /><br />Direct Current creates a bias, that slowly shifts the current in only one direction. This setup is fine for short distances. However, the voltage requirements to keep the current from dropping off rapidly over distance is immense. The solution used to be to have lots of small independent power stations all along the grid (Thomas Edison's solution). Basically, everybody has their own generators.<br /><br />AC current, however, doesn't need to shove all the charge down the wire. It merely makes all the charge in the wire twitch, first one way, then the next. This can be "transmitted" much easier, over greater distances. Also, most power production equipment naturally produce electricity in this fashion (anything that spins a magnet in a coil of wire...basically everything).<br /><br />It works, because you only need the charge to move, the direction doesn't matter.<br /><br />If the device requires the current to go in a single direction (quite a few, such as battery chargers) a DC converter is put into the circuit, but by the device, not the power producing equipment. These are forms of a wave rectifier, using a) Resistors and capacitors or b) one way "gates" called Diodes (yes, the same sorta thing as an LED) which turn the oscillating current into a steady one way current (with some power loss usually). <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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AMeece

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<p><font color="#008000"><strong>In absolute terms, there's no telling how big anything in this universe is because there's no absolute yardstick. The wavelength of sodium light is one of our local meters long but for giants living outside our universe, one of our meters might equal the length of their tongues.</strong></font></p><p><font color="#008000"><strong>&nbsp;&nbsp; Which is to say; everything we know might fit into a thimble in a larger universe which may or may not include this one.</strong></font></p><p><font color="#008000"><strong>&nbsp;&nbsp;&nbsp; Which means; distance is an illusion. It could be simply the way we perceive the force which creates the perception of separation in space.</strong></font></p><p><font color="#008000"><strong>&nbsp;&nbsp;&nbsp; We have no way of telling how long any distance really is. So why pretend that we do? Job security for scientists?</strong></font><img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-money-mouth.gif" border="0" alt="Money mouth" title="Money mouth" /> </p><p>&nbsp;&nbsp; <br />&nbsp; </p>
 
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AMeece

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So if the current is going back and forth then how does it get to our houses, it seems like the electrons/holes would be boing back and forth and not getting anywhere. <br /> Posted by ScottCarlin</DIV></p><p>&nbsp;&nbsp; Yu have to realize they are going back and forth really strongly. [if the load resistance is smallish. If the resistance is huge, the voltage can't push many electrons back and forth.] </p><p>It's like a hydraulic car jack handle goes up and down and that motion is converted by a cylinder which only goes in one direction but really strongly.&nbsp; </p>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>actually, the "mass" increase is a misnomer. The inertia of an object, that is the objects resistance to a change in velocity (to acceleratioN) increases. Normally, this is what mass measures. However, the "mass" increase due to velocity does not exert gravitational forces, only an objects "rest mass" does. <br />Posted by Saiph</DIV></p><p>Sorry Saiph, but that is not correct.&nbsp; The mass/energy gain is real and it does exert gravitational force.&nbsp; In fact one can in theory construct an object from pure light that exerts enough gravity (warps space sufficiently) to hold itself together.&nbsp; John Archibald Wheeler studied such objects and named them geons.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>good question scott. The current is alternating (notice I said current, not voltage), and so shifts from going one way to another. Depending on the device, this is a good thing. If it isn't, you'll see a DC converter in the circuit somewhere (often the big "box" part of a plug that isn't just two prongs, or buried in the device). As for voltage, it too oscillates. It does go from positive to negative, but it actually goes from +170 to -170. The reason it's usually refered to as a 120 or 110 v outlet is that'the average voltage. It doesn't spend much time at 170, and even less at 0 (the voltage drops rapidly through that point) giving us a 120 v average. <br />Posted by Saiph</DIV></p><p>The average voltage is actually zero.&nbsp; The root mean square of the voltage is about 110 volts (or 120 )and the peak is SQRT(2) times that.&nbsp; What you receive in your home is one branch of a 3-phase supply, and to get 220 you take the voltage across 2 branches.</p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>There are two types of current, DC and AC. Direct Current creates a bias, that slowly shifts the current in only one direction. This setup is fine for short distances. However, the voltage requirements to keep the current from dropping off rapidly over distance is immense. The solution used to be to have lots of small independent power stations all along the grid (Thomas Edison's solution). Basically, everybody has their own generators. AC current, however, doesn't need to shove all the charge down the wire. It merely makes all the charge in the wire twitch, first one way, then the next. This can be "transmitted" much easier, over greater distances. Also, most power production equipment naturally produce electricity in this fashion (anything that spins a magnet in a coil of wire...basically everything). It works, because you only need the charge to move, the direction doesn't matter. If the device requires the current to go in a single direction (quite a few, such as battery chargers) a DC converter is put into the circuit, but by the device, not the power producing equipment. These are forms of a wave rectifier, using a) Resistors and capacitors or b) one way "gates" called Diodes (yes, the same sorta thing as an LED) which turn the oscillating current into a steady one way current (with some power loss usually). <br />Posted by Saiph</DIV></p><p>Actually DC transmission is more efficient than AC transmission due to skin effect losses and inductive coupling with the ground in AC transmission.&nbsp; This assumes that you can transmit the DC current at high voltage so as to transmit high power at relatively low current.&nbsp; The Los Angeles&nbsp;Department of Water and Power takes advantage of this effect with aDC &nbsp;transmission line that runs from hydroelectric sources in Oregon to an inverter station in Sylmar where it is converted to AC.&nbsp; AC is much more convenient for distribution because it is easily transformed to useful voltages.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;&nbsp; Yu have to realize they are going back and forth really strongly. [if the load resistance is smallish. If the resistance is huge, the voltage can't push many electrons back and forth.] It's like a hydraulic car jack handle goes up and down and that motion is converted by a cylinder which only goes in one direction but really strongly.&nbsp; <br />Posted by AMeece</DIV></p><p>It is more like rubbing your hands back and forth against one another to warm them up.&nbsp; It is not necessary to have a steady river of electrons to obtain energy from the current.&nbsp; Movement back and forth is quite adequate.&nbsp; In fact you can show that the energy is really contained in the electromagnetic field that is associated with the current and voltage.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In absolute terms, there's no telling how big anything in this universe is because there's no absolute yardstick. The wavelength of sodium light is one of our local meters long but for giants living outside our universe, one of our meters might equal the length of their tongues.&nbsp;&nbsp; Which is to say; everything we know might fit into a thimble in a larger universe which may or may not include this one.&nbsp;&nbsp;&nbsp; Which means; distance is an illusion. It could be simply the way we perceive the force which creates the perception of separation in space.&nbsp;&nbsp;&nbsp; We have no way of telling how long any distance really is. So why pretend that we do? Job security for scientists? &nbsp;&nbsp; &nbsp; <br />Posted by AMeece</DIV></p><p>Your assertions lack precision.&nbsp; But you are correct that there is no such thing as absolute distance.&nbsp;&nbsp; That is one lesson of special relativity.</p><p>No one is pretending anything.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Sorry Saiph, but that is not correct.&nbsp; The mass/energy gain is real and it does exert gravitational force.&nbsp; In fact one can in theory construct an object from pure light that exerts enough gravity (warps space sufficiently) to hold itself together.&nbsp; John Archibald Wheeler studied such objects and named them geons. <br /> Posted by DrRocket</DIV></p><p><br />Saiph's description pretty much parallels how I would describe it, too.&nbsp; I've seen geons mentioned before, but always shuffled it aside as being in the same category with the likes of Tachyons and such.&nbsp; <br /><br />I found this:<br /><br />Geons, Blackholes & Quantum Foam, by John Archibald Wheeler, with Kenneth Ford, page 236, para 2.<br /><br />"This hypothetical entity, a gravitating body made up entirely of electromagnetic fileds. I call geon(g for the gravity, e for electromagnetism," and on as the word root for"particle"). There is no evidence for geons in nature and later was able to show that they are unstable-they would quickly self-destruct if they were ever to form. Nevertheless it is tempting to think that nature has a way of exercising all the possibilties open to it. Perhaps geons had a transitory exitance early in history of the universe. Perhaps(as some students and I speculate much more recently), they provide an intermediate stage in the creation of the balckholes."<br /><br /><br />Is it something worth exploring other than just being familiar with it? </p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Saiph's description pretty much parallels how I would describe it, too.&nbsp; I've seen geons mentioned before, but always shuffled it aside as being in the same category with the likes of Tachyons and such.&nbsp; I found this:Geons, Blackholes & Quantum Foam, by John Archibald Wheeler, with Kenneth Ford, page 236, para 2."This hypothetical entity, a gravitating body made up entirely of electromagnetic fileds. I call geon(g for the gravity, e for electromagnetism," and on as the word root for"particle"). There is no evidence for geons in nature and later was able to show that they are unstable-they would quickly self-destruct if they were ever to form. Nevertheless it is tempting to think that nature has a way of exercising all the possibilties open to it. Perhaps geons had a transitory exitance early in history of the universe. Perhaps(as some students and I speculate much more recently), they provide an intermediate stage in the creation of the balckholes."Is it something worth exploring other than just being familiar with it? <br />Posted by derekmcd</DIV></p><p>No reason to chase it.&nbsp; I brought it up to illustrate that "gravity" can come from energy as well as rest mass.&nbsp; Those photons (i.e. the electromagnetic field) have no rest mass. <br /></p> <div class="Discussion_UserSignature"> </div>
 
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qso1

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<p>With all the discussion about speed of light travel and current scientific understanding that this speed cannot be exceeded, or even closely approached. I have a question that I posted about two years ago and nobody was able to answer it. I mean, I had several responses, and some better than others, but not the one I was looking for.</p><p>Here goes:</p><p>The whole SOL thing is based on Einsteins equation as I undestand it. Probably the most widely recognized equation in the world...E=MC2.</p><p>Shouldn't this equation read E=MC if we cannot even exceed light speed, let alone light speed squared. If someone does answer it, point me to a source ref, thanks..&nbsp;</p> <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>With all the discussion about speed of light travel and current scientific understanding that this speed cannot be exceeded, or even closely approached. I have a question that I posted about two years ago and nobody was able to answer it. I mean, I had several responses, and some better than others, but not the one I was looking for.Here goes:The whole SOL thing is based on Einsteins equation as I undestand it. Probably the most widely recognized equation in the world...E=MC2.Shouldn't this equation read E=MC if we cannot even exceed light speed, let alone light speed squared. If someone does answer it, point me to a source ref, thanks..&nbsp; <br />Posted by qso1</DIV></p><p>The inability to exceed the speed of light is not dependent on E=Mc^2.&nbsp; It in fact comes from the assumption that the speed of light is the same in all reference frames.&nbsp; If you assume that any speed is constant in all reference frames then that speed becomes a maximum.&nbsp; The fact that it is the speed of light that is invariant comes from&nbsp;a couple of places.&nbsp; It was demonstrated experimentally in the Michaelson-Morely experiment.&nbsp; It is implicit in Maxwell's equations.&nbsp; You can from Maxwell's equations derive a speed for the electromagnetic wave in a vacuum.&nbsp; It turns out that this speed is the same as the speed of light, and that was one of the first clues that radio waves and light were really the same thing.</p><p>Added in edit: As far as an equation like E = Mc goes, it fails the test of having consistent units.&nbsp; If you recall the equation for kinetic energy in Newtonian mechanics, 1/2 Mv^2, you can see by example that energy has dimensions of mass times velocity squared.&nbsp; This can also be seen from dimensions of work which is force x distance and from the equation F=ma force has units of massxdistance/time^2.&nbsp; So work or energy has dimensions of massxdistance^2/time^2 which is massxvelocity^2.</p> <div class="Discussion_UserSignature"> </div>
 
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primordial

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Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>An observation is any event that interacts with the wave form directly, ie the screen of your two slit experiment. It does not mean a human observation. <br />Posted by nacnud</DIV><br />&nbsp;Yes that is correct.
 
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