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bigsplit
2006-Aug-17, 03:47 PM
What cause an "up" quark to be positively charged and a "down" quark to have a negative charge?

I once heard an electron has a "pull" force and a proton has a "push" force, what common variable would illustrate the pull/push?

Peter Wilson
2006-Aug-17, 06:59 PM
What cause an "up" quark to be positively charged and a "down" quark to have a negative charge?
According to String Loop Quantum Theory of Everything Gravity, it has something to do with renormalization of the 11th dimension's intrinsic charge morphilization of the Eigen-value attractors :eh:

Of course Brian Green, who is better with the math, explains it a little more clearly...;)

bigsplit
2006-Aug-18, 02:15 PM
According to String Loop Quantum Theory of Everything Gravity, it has something to do with renormalization of the 11th dimension's intrinsic charge morphilization of the Eigen-value attractors :eh:

Of course Brian Green, who is better with the math, explains it a little more clearly...;)



Thanks, I think.

Wait a second, the idea of charge has been around for quite some time.... The answer has not been "mainstreamed"?

Ken G
2006-Aug-18, 02:34 PM
Charge is the ability to generate, and couple to, the electromagnetic force. Thus charge is as charge does. Asking why different quarks have different charges is much harder, I don't know, I doubt anyone knows at this stage, and it is certainly possible that we will never know. By the way, you cannot associate "pull" and "push" with charges-- like charges repel, and unlike charges attract. It is completely symmetric with regard to protons and electrons, and indeed it is pure convention that protons have positive charge and electrons have negative charge (indeed, the far greater mobility of the electron, coupled with our experiential preference for positive numbers, means that a far more convenient convention would have been the opposite, so much so that this is essentially what electrical engineers do.)

bigsplit
2006-Aug-18, 06:01 PM
Charge is the ability to generate, and couple to, the electromagnetic force. Thus charge is as charge does. Asking why different quarks have different charges is much harder, I don't know, I doubt anyone knows at this stage, and it is certainly possible that we will never know. By the way, you cannot associate "pull" and "push" with charges-- like charges repel, and unlike charges attract. It is completely symmetric with regard to protons and electrons, and indeed it is pure convention that protons have positive charge and electrons have negative charge (indeed, the far greater mobility of the electron, coupled with our experiential preference for positive numbers, means that a far more convenient convention would have been the opposite, so much so that this is essentially what electrical engineers do.)


I have read that originally what is called the positive/negative charge where "corrected" and vica/versa....does anyone know what this is based on? Something to do with Franklin and rubbing different materials together producing charge....there is some independent effects that would make the conclusion a catagorization was backwards?

Ken G
2006-Aug-18, 07:27 PM
It can't be "backwards", as it is a pure convention, but the issue is whether is the most convenient choice. I think you are right that the history goes back to Franklin and a lack of knowledge about the charge carriers, though I don't know the details. Now we know that electrons are what carry charge from place to place, and unfortunately normal currents are a negative flux of charge because electrons were given a negative charge.

jlhredshift
2006-Aug-18, 08:16 PM
When a battery is connected to two plates emmersed in water hydrogen forms on the elctrode connected to the terminal labeled negative. The negative plate is providing electrons to the hydrogen ions. Therefore, electrons are flowing from the negative terminal into the plate and subsequently the water.

Which is the opposite of what most people think.

Ken G
2006-Aug-19, 03:46 AM
What I find surprising is that the automobile battery has the negative terminal attached to ground. It seems kind of backwards to run a car's electronics by immediately driving a bunch of electrons into the frame of the car! Thus as I understand it, your car's electronics don't run by driving electrons through them, they run by creating a dearth of electrons on the positive terminal and waiting for electrons from the frame to rush in to try and fill the void when you close the circuit. What is the reason for this choice of polarity, is it a safety or efficiency issue?

snarkophilus
2006-Aug-19, 12:43 PM
What I find surprising is that the automobile battery has the negative terminal attached to ground. It seems kind of backwards to run a car's electronics by immediately driving a bunch of electrons into the frame of the car! Thus as I understand it, your car's electronics don't run by driving electrons through them, they run by creating a dearth of electrons on the positive terminal and waiting for electrons from the frame to rush in to try and fill the void when you close the circuit. What is the reason for this choice of polarity, is it a safety or efficiency issue?

This used to confuse me as well, but I'm reasonably sure that it doesn't matter. You don't get significant electron flow without a closed circuit, partly due to capacitance issues, and partly because the charge in the battery itself is strongly predisposed to being balanced.

Suppose in a simple (short) circuit, you first "charge" the wire, so it's connected to the negative terminal (this is really a very small charge, but assume it's significant). When you close the circuit, electrons get pulled from the wire, dropping the amount of charge in it, let's say by some amount C. If you don't have a charged wire, when you connect it to the negative terminal, it will gain some charge... but that amount of charge is also C.

Look at it this way: suppose you touched the negative terminal and a bunch of electrons rushed into you. Would that be any worse than if you touched the positive terminal and it sucked a bunch of electrons out of you? It makes no difference. All that matters is the number of electrons passing a point at a given time.

I'm not a member of the automotive industry, so I could be wrong, but the reason must just be that it's the EE convention to have negative = ground.

Ken G
2006-Aug-19, 02:46 PM
There might be other issues though, related perhaps (?) to the fact that they recommend you attach the ground wire last when jumping a car battery. That way the circuit closes at a point that is far from the battery itself. Also, by attaching the negative terminal to ground, you have no electron buildup anywhere when you first close the circuit when you turn your car on, and perhaps that limits sparks/shocks and that sort of thing. The basic asymmetry is that positive and negative charges work the same in the circuit mathematics, but the fact that the negative charges are the mobile ones breaks the symmetry in practical applications when circuits first close, and I suspect it must be related to that but I don't really know.

publius
2006-Aug-19, 06:45 PM
All,

I swear, there ought to be a rule that thread titles should be updated to reflect the lastest content. :) I almost missed this.

The question of why automotive manufacturers chose negative ground is one of those things that is endlessly debated, with various stock answers given that aren't really true. [This is right up there with another notion that is debated back and forth, which is that a lead-acid battery will rapidly go dead on a concrete floor -- that's wrong, with modern batteries at least, but it persists. I know it is wrong myself, but nonetheless I'll always put a piece of wood between a battery and concrete, because it was drilled into me!]

In the old 6V days, positive grounds were extensively used. The switch to negative ground occured about the time they went to 12V systems, and there's a lot of debate about it.

Ken, 12V is so low there is no spark or other hazard due to capacitive effects. Using frame return, that is, using exposed metal parts as part of the current carrying circuit would be dangerous for voltages high enough to shock you. If there is a bad connection, you could have dangerous voltages between exposed metal parts. That is why you never do that with household AC voltages and higher. You have one wire to carry the return current, and another for safety grounding purposes.

But 12V is so low it's not a safety problem. It will however make for very some strange behavior when you have a bad ground, such as with tailight circuits grounded to thin sheet metal. It will blow your mind when you turn on a turn signal, and see many lights that shouldn't be on glowing dimly. :)

And there is pretty much no difference between using a positive current convention. That's what we "pretend" in just about everything, except for electrochemical circuits where the fact that is electrons moving that is important.

Back to the ground polarity question. Most old 6V systems used a postive ground, and they switched to negative ground with 12V. However, there were some 12V positive ground systems and my father and I have one in a very old piece of farm equipment.

There are two standard reasons for a negative ground thrown out that are the "strongest" possible reasons, but I'm still not sure of either, and you can't even get an authoritive answer from the automotive engineers -- it's been too long since it was decided and the people involved are gone.

One is the radios. About the time of the 6 to 12V switch, transistors and solid state components were coming out and the common configurations would've required a "hot chassis" design for the radio on a postive ground system.

Second is galvanic corrosion that can occur with moisture and loose connections. The more positive metal will be the one that gets "eaten away". So if you have a positive ground system with a ground wire connected to the frame or sheet metal, it will be the frame that corrodes. With negative ground, the wire lug will be the side that corrodes.

Those two are the most plausible stock answers that are given, but I'm not sure. It would take a lot of corrosion to be a problem, and 6V positive ground systems were used for years.

And finally, they may be about to up the voltage again. 12V is getting too low, and requiring too high a current. Every year, the electrical load increases, with more and more electronic and electrical gizmos added. The biggy was fuel injection, with solenoid fired injectors.

100A+ alternators are standard, and that's a lot of current (and heat for the small package alternators). Now, if you have a dead battery and boost it off, the additional charging load of discharged battery (40A+ at typical regulator voltages) can easily exceed the alternator's rating and you'll burn it up.

In the old generator days, the regulator had a current regulator circuit as well as voltage, which would keep generator output current below the maximum. Modern systems are not current regulated, just voltage. I left the switch on one of my vehicles a few weeks ago -- I needed to raise the power windows and forget to turn the switch off -- and ran the battery down. It was sitting too far away from an outlet to put a charger on it, so I boosted it off, then quickly moved it where it could plug the charge in.

The thing ran less than a minute, and just in that short time, the alternator was already too hot to touch.

And so they are thinking about going to higher voltage systems, 48V being discussed. That is just about the highest you go can without having a shock hazard, although some people can feel that. DC is a bit different in how it feels -- no "vibrating" sensation, just sort of a "pinch" feeling, but my threshold is about 50VAC. I've played with low voltage transformer systems, stacking 12/24/48V systems, and I can feel the slightest tingle at 48VAC.

-Richard

-Richard

Ken G
2006-Aug-19, 06:53 PM
Very interesting publius, I'm glad to hear about all the issues that do into decisions like that, and all the folklore that goes with it!

Kaptain K
2006-Aug-20, 04:04 AM
IIRC, my '56 Austin-Healey 100/4 had a 12v positive ground (earth) system.

Also, the last I heard, the next planned automotive voltage upstep is to 42v. This may have to do with the voltage sensitivity threshhold mentioned earlier.

publius
2006-Aug-20, 04:29 AM
Ken,

The choice of charge sign is indeed arbitrary, but once you've chosen positive charge, then postive current follows from that. This is also related to the sign of the fields, magnetic in particular.

There is also some tricky business between sources and loads. Note that positive current goes *into* the positive terminal of a load. VI is then positive. That means absorbing power is positive. But for source, positive current comes *out of* the positive terminal. Following the same convention, power is *negative* for the source. That can get confusing.

But you can just as easily flip that sense, and that is sometimes done. If you're in a generating mindset, you might like to have positive power mean the system is supplying power, and negative mean it is absorbing power. The idea is positive is "normal" and negative is "backwards".

Now, with AC, you don't have polarity so much as *phase* to worry about (and really that is relative phase). The sign of reactive power and current comes into this as well. Traditionally, inductive current and reactive power is taken as positive, and capacitive (or charging) power is taken as negative. That is inductive reactance is positive, and the lagging current it draws is positive (in the sense of going into the postive terminal of the load). Capacitance is then negative.

This means you can think of an inductive load as "drawing" reactive power from a system, while a capacitor *supplies* it. :) In this way, one sees power-factor correction capacitors as "supplying" the magnetizing current required by your motor or other inductive loads.

But you could just as easily flip the sense, and think of motors as "supplying" charging current, and capacitors "drawing" it. At any rate, with AC generators and reactive power, a geneator supplying an inductive load looks like a capacitor, as it supplying magnetizing current.

And so, again in a "generating frame of mind", you might want to flip the sense of reactive power so that positive current is "coming out" of the generator rather than going into it. That is, a generator is "supplying" reactive power when an inductive load is connected. Put a capacitor across it, and it is then "absorbing" reactive power.

For me it's best not to think about this too much, or I'll get confused, "too clever by half" so to speak, and get it backwards anyway. :)

And finally, on the field side of things, when you're feeling frisky one day write down Maxwell, and look at what happens when you flip the sign of charge.

You'll have to put a minus sign in front of the charge density. But then you can flip the sense of the E field, and get rid of that minus sign. That is, the field arrows come out of negative charge, and we call it positive.

But look what that does to the magnetic side of things. The minus sign in the curl E equation will flip, and you'll now have a minus sign in front of the curl B equation.

You can take care of that by flipping the sign of B. Now, you're back to the original form, with a minus sign in curl E. The right hand rule would still apply, it would just make B be backwards because the direction of positive current would be backwards.

So what that means is if we wanted to flip our sense of postive and negative charge, we would have to flip the sense of North and South as well, or use a "left hand rule", with a minus sign on the curl H part. A left hand rule with a positive sign on curl E would make things sort of backwards to the way we think of it. At first blush, you'd think it would it would cause positive feedback, with the EMF supporting rather than opposing a change in a magnetic flux. But the minus sign on the curl H takes care of it, as positive current now causes the field to be backwards. :)




-Richard

publius
2006-Aug-20, 06:52 AM
IIRC, my '56 Austin-Healey 100/4 had a 12v positive ground (earth) system.

Also, the last I heard, the next planned automotive voltage upstep is to 42v. This may have to do with the voltage sensitivity threshhold mentioned earlier.

I just searched around on this a bit. Actually, they are going for 3x voltage, which will be 36V. The battery will technically be 36V, using the defintion that a lead-acid cell is 2V. Actually it's about 2.1V nomical= 12.6V up to 2.2V completely "topped off" = 13.2V

Now, the standard charging system voltage however, is consider 14V nominal. And so 3*14V = 42V. That's where the 42V comes from. So actually were going 3x, not 3.5x

A good rule of thumb for most electrical devices (very sensitive devices not withstanding) is you have +/-10% voltage tolerances. For 12V, that's 13.2V max. Incandescent bulbs are very sensitive to overvoltage however. They'll stand +10%, but they life will be greatly reduced (the newer higher efficiency "miser" type bulbs operate the filament hotter and are even less tolerant of overvoltage). So automotive light bulbs are actually rated 14V nominal, not 12V. I've got a book here with a graph of various tungsten filament variables vs. voltage in percent. The life curve goes inversely as a high power of voltage, and is almost a vertical line through the 100%V point!

You will note that we've pretty much standardized on multiples of 12, or 120, 1200V for our voltage levels (with factors of the square root of three with three-phase thrown in). But sometimes the base is 110 or 115 (occasionally you will see a 117V rating)

Supply systems are now using a base of 120V, but you'll note motor ratings use a base of 115V. This puts the motor's nominal rating and the +/-10% at nice spot to allow for voltage drop (and +5% is actually a "sweet spot" in terms of efficiency and current draw, but power factor does decrease, and this can confuse some people. Basically 9A at 95% power factor is better than 10A at 100%, but some people get it in their heads that power factor is always the be all and end-all). But +anything is not a sweetspot of any sort for incandescent bulbs, and they are designed for the actual nominal supply voltage. If you can stand the dimmer light, go with 130V rated bulbs, which are becomming even more popular for these reasons. They are running filaments hotter now, and they are less tolerant to slight overvoltages.

-Richard

DALeffler
2006-Aug-20, 06:48 PM
There might be other issues though, related perhaps (?) to the fact that they recommend you attach the ground wire last when jumping a car battery.



Ken, 12V is so low there is no spark or other hazard due to capacitive effects.

I think both Ken G and publius are partly right: Connecting two new, fully charged, 12V batteries together in series or in parallel should pose no spark hazard but "jumping" a dead car battery with a car battery in a running automobile is not at all the same thing.

Jumping a car battery from a running auto to a dead battery in a non-running auto is connecting an undercharged or "dead" battery to a "hot" charging system: sparks are likely.

Ken G
2006-Aug-20, 07:06 PM
The danger that is referred to tends to be exploding the battery. I don't know what that likelihood is. Perhaps negative ground helps with that, as there is never a wire rife with extra electrons close to a battery. But I think publius's point is that the number of extra electrons is so small it poses no threat until the circuit is closed, at which point it doesn't really matter which way the current flows.

publius
2006-Aug-20, 07:31 PM
Ken and all,

The danger is indeed making sparks right next to the battery and exploding any H2 that might be liberated inside the battery and coming out the vent holes. That danger is normally small but it is there, and batteries do explode. In fact, I've had two battery explosions/fire with me, and my father had about the same number himself. But we mess with a lot of batteries. Ground polarity doesn't make any different with this danger.

I mentioned this in this post here along with details of how it happened, and uploaded a picture of a burned battery. Now, the funny thing is this battery still worked after I put the fire out!
http://www.bautforum.com/showpost.php?p=805998&postcount=11

Once you've had a battery explode, it makes you more careful because you know "cow horns will hook" as my grandmother would say.

Basically, with 12V, sparks are only made with conduction current, not charging transients, because the typical capacitance is so low. And note there is a difference between DC and AC with capacitive circuits. With AC, you have a continuous charging current, but with (dead constant) DC, you only have a brief charging transient.

With 120VAC, with a reasonably long circuit, you can actually the charging current make a spark when you connect it. It's very weak, but in the dark you can see. And warning, don't be messing around with your electrical panel in the dark! :) This capacitive reactance is also on the order of a good meter's internal impedence (megaohms), and it will make for some strange, range dependent voltage readings.

The capacitance of various parts of a car frame are very small, and the brief charging transient will be very small. However, a large capacitor will make quite a spark with a 12V battery. Case in point is some 12V-120VAC inverters designed to give you 120V off a car battery. These things have large capacitors on the input 12V side, and will pull one heck of spike when you first connect it to the battery. The on-off switch is basically a low current "side circuit" to avoid having a large switch on the 12V, very high curent side and so the capacitors are always across the input. I have a 1kW model (makes a rough "stair step" output waveform), and you'll note that 1kW at 12V is 83A, and that's over 100A when you figure efficiency.

Low voltage is high current. Me, I'm a high voltage, low current kind of guy. :)

-Richard

Dr Nigel
2006-Aug-20, 08:07 PM
Here's another thought about the origin of the +ve / -ve convention.

If I understand correctly, the first evidence that electricity involved something actually moving was the observed movement of coloured ions (e.g. Cu2+, Ni2+ or Co3+) through a wet filter paper when a voltage was applied.

Since these are all positively charged ions (and no common negatively-charged ions are coloured unless you count ions of some quite complex dye molecules), it seems reasonable to posit that this gave rise to the "current flows from +ve to -ve" convention.

Only later was the electron discovered, and the means by which metals conduct electricity was uncovered later still. It is my guess that the convention was already established by then.

Ken G
2006-Aug-20, 09:30 PM
And it's too bad how often convention trumps logic.

swansont
2006-Aug-21, 02:06 PM
And it's too bad how often convention trumps logic.


And does so by convention...