A question about current....
 

Current flows from positive to negative and is not the flow of electrons right? Its the flow of positive charge. Im so confused. I have two books that sort of give conflicting information.

Re: A question about current....
 

Conventional current is in the direction that positive charges would flow. "Real" current can be either the flow of positive or negative charges. Remember, sometimes its ions like (Ag⁺) that are positively charged and are flowing. So, the information is not conflicting, as long as negative current is opposite than positive current.

Re: A question about current....
 

Like silverstar said, Conventional current is the idea that current flows from positive to negitive.

In reality, charge flows from negitive to positive (electrons being negitively charged and all). But, for many reasons, it is easier to think of it the otherway. I found this extreamly confusing at first to. I couldn't figure out why my multimeter was giving me negitive voltages for everything.

*sigh* conventions can be so tiresome.

-Andy A.

Re: A question about current....
 

No, in reality, charge flows from positive to negative or negative to positive (see my explanation in the post above).

Re: A question about current....
 

hmmm, that brings up an interesting question. Does current flow the same way regardless of wether ions or electrons are carrying the charge? ie, are there ion resistivity constants for each ion and medium material (the "wire") that can be used to calculate resistances and such? Will current flow at (approximately) the speed of light as with electrons (i'd think so)?

Re: A question about current....
 

I remember we spent a week on this topic in physics class, but that was 3 years ago so I don't remember too much of it. What I do remember is the teacher explaining the differences between conventional current and actual current...

Conventional current is what most people recognize- electricity flowing from positive to negative, as it makes logical sense- higher concentrations of things/surplus (positive) moving towards a lower concentration/deficit (negative) to balance out.

On a technical level though, the actual charge is negative- as electrons are generally negatively charged. Electrons are much much less massive than protons, and hang out on the fringes of the atom, and so are much easier to toss around. Therefore, it's actually the negative charge that's traveling through the wire.

If that makes no sense, or is completely wrong, please correct me... this sort of thing has always fascinated me.

Re: A question about current....
 

ACTUALLY, in a galvanic or electrolytic cell (yeah for AP Chem + AP Physics) the positive ions flow also.

Current flows in opposite directions for positive ions than for electrons. Current never travels even close to the speed of light (remember, current is in Columbs per second, not meters per second, so that's an incongruous dimensional comparison). EMF travels close to the speed of light. And yes, you can find resistance using the following equation:
R=rho * length/ Area
Just replace "rho" with the resistivity of the ion/wire combo.

Re: A question about current....
 

Yes, you are right, i should have said emf instead of current, that is what i really meant. I always find it kind of surprising how slow electrons actually travel through a wire. (on the order of mm/s, if im not mistaken)

here's a quick little explanation

Re: A question about current....
 

Hello All,
There are generally two conventions for electrical current. "Electron Current" follows the flow of electrons that emit from the negative terminal of the battery and are attracted to the positive terminal. This current is more easily understood in terms of vacuum tubes where electrons are generated at the cathode and flow to the plate. The plate is always more positive than the cathode when current is flowing. Unfortunately, meters that measure current flow, indicate the opposite polarity when measuring current compared to electron flow. Most electrical people are referring to "conventional current" when they speak about current flow. This current appears to flow from the positive terminal to the negative terminal of the battery but is in fact electron current. An ammeter with the positive lead connected to the positive terminal of a battery (when inserted into a working circuit) will show positive current.

Re: A question about current....
 

Calarification for my earlier post (above):

The formula for resistance I gave is only applicable for metal wires. In metal wires you'll probably never have positive ions moving. Since pos. ions can only move in solutions, gel, and salt bridges, there is no valid "length" or "area" of the solution.

Re: A question about current....
 

Ok its time for a little historical honesty in this thread. The concepts for voltage, current, power... were all standardized on before we really knew about electrons and the subatomic particles.

I dont know who established them, but we had things like batteries and static charge generators long before we knew that electrons even existed. Its impossible to look at an arc of electricity and see which way its flowing, so at some point some scientist called one end of a battery the positive side, and using magnets to sense current flow, using the N pole of the earth as the basis for which end of a magent is the North end, we ended up with amp meters that would deflect to the right when connected to the "postive" side of a battery

so all this equipent started to be manufactured, the conventions were already in place, and it wasnt until much later that the structure of atoms was theorized and verified that we learned that, well.... we got it backwards

in 99.999% of the cases, current is the movement of electrons, and they move from - to +. It was too late to change it.

BTW current and voltage travel at the speed of light - when you connect a voltage source to a long wire you dont have to wait for the 1st electron to make it all the way to the other end before current flows - its not like an empty hose

its like a full hose. Current responds at the speed of light, the individual electrons however do not travel down the wire at that speed.

Re: A question about current....
 

Actually, current moves quite slowly... It's electromagnetic radiation that moves at the speed of light (radio waves, light waves, microwaves, etc).

Electricity is very analagous to water in a hose. Only difference is wires are not empty like a hose would be- the metals inside are chock full o' electrons (water) already. When electricity is applied, electrons sitting there are just pushed through the wire (as water would be if a hose were already filled), giving the instant response.

This site has some good info on how fast current actually moves.

Re: A question about current....
 

Franklin was the person that invented the convention of positive to negative. Joseph Thomson discovered that it was backwards. Unfortunately, formulas by that time had been using Franklin's standard.

Re: A question about current....
 

Okay, so can someone explain a bolt of lightning to me?

-dave

Re: A question about current....
 

I'm not quite sure, but i think it's the flow of electrons from earth to the sky.

Re: A question about current....
 

All sorts of different stuff happens in lightning- I found this and it seems to do a good job explaining it.

From the article:

Four primary types of lightning- each of which has different properties.

Re: A question about current....
 

I dont understand what they mean by positive lightning?

what is it that travels? air molicules with a positive charge? the amount of mass in motion would be huge compaired to electrons.

Last time I looked into how lightning happens scientists were at a loss to explain it all - there is not enough voltage present to strike an arc several miles long, so something else is going on.

Lightning is scary stuff - esp Blue Lightning :^)

Re: A question about current....
 

Somethings about "Positive Strikes:" (from http://www.ucar.edu/communications/i...tning/faq.html)


What is a positive flash?

The renegade of the lightning family is the positive flash--one that lowers positive charge to earth. Comprising 10-20% of all cloud-to-ground flashes, these powerful bolts carry as much as ten times the current of negative CGs and often last longer. They frequently emerge from the cirrus anvils that sweep downwind of thunderstorms, rather than from a storm's core. Some storms feature many more positive flashes than usual. The presence of smoke, dust, or pollution (such as downwind from urban areas) seems to encourage the development of positive flashes. This is probably because of the particles' effect on the number and sizes of ice crystals within storms. A study in the journal Science (10/2/98) examined thunderstorms in the Southern Plains during the spring of 1998, when smoke from Mexican forest fires was flowing northward over the region. Up to three times the usual number of positive flashes were observed in these smoke-altered storms.

Re: A question about current....
 

Well we've already seen that electrons travel pretty slowly so why not have some o3+ traveling even slower?

This article also has some more explanation, but it it doesn't really explain how it happens. The fact that the very first part of the discharge is stepped is very interesting. Its just my speculation, but maybe this indicates that there is some sort of brief moment were just enough current can travel to ionize a piece of air and that the steps occur because the bolt sort of needs to recharge after each high current ionization period.

Re: A question about current....
 

I think that in a lightning strike, or an arc in general, electrons actually are travelling the distance from one end to the other very quickly

lightning does not travel at the speed of light like an EMF wave through a conductor, but it travels very fast - I think lighting IS like water flowing through an empty hose - the electrons from the clouds are physically moved to the surface of the earth in a fraction of a second.

Re: A question about current....
 

That defenitley must be true because lightning is caused by a charge difference and the charge difference won't go away until charge is transferred.

Re: A question about current....
 

From what I'm reading, it seems like these "streamers" are doing most of the work, setting the stage for the discharge. Perhaps the streamers are caused by subtle shifts in electromagnetic fields. My best guess is as a cloud gains more and more negative particles (electrons), the sheer volume creates a large enough electromagnetic field to influence the electrons on the surface. Like charges repel, so the field of influence of the cloud's electromagnetic field would drive away the better portion of the negative particles on the ground. That assumed, with mostly positive particles left on the surface, and mostly negative particles in the cloud, opposite charges attract. Just like a magnet would start to pick up iron shavings from a distance, either the cloud starts to draw up positive particles from the ground (perhaps oxygen ions who lost their electrons to the ground?), or the ground starts to yank at the electrons in the cloud. Either or both ways at once, you have these Streamers of charge reaching for each other. If they get close enough to initiate a discharge, bam- lightning (rather, flash, then bam... thunder results from superheated/rapidly expanding gas due to lightning).

Therefore, I'd imagine the bulk of the buildup (creating the path to the ground) happens without notice, until they're close enough to strike an arc. Once an arc is in place, I'd guess the charges will want to flow whichever way is necessary to balance out the charges, until there's no longer enough of a differential for the magnetic fields to support the streamer. In any case, I don't think the particles would have to run the entire length of the arc (potentially a mile, but most likely less), but only bump into the next atom in the streamer, which in turn bumps the next atom, and so forth, until enough charge is transfered where it has to go. Think domino effect. So in essence, the water/hose analogy still holds true, but instead of a solid wire as a hose, the streamers/charged particles pulled by electromagnetic fields serve as the medium...

IANAM, (I am not a meteorologist), but from reading the information in the posted links, that's the most logical explanation I can infer.

Re: A question about current....
 

Guys,
What you need to remember is that air acts like an insulator. But like any insulator, (glass, or PVC around a wire) high voltage can break the material down and turn it into an conductor. Air also contains a lot of conductive particles and in a storm the air that is in motion picks up static just like the cloud. In the case of lightning, the high voltage potential between cloud and ground builds up to a point where it is capable of jumping from conductive particle to conductive particle at which point the flash begins and the air molecules are ionized allowing current to flow in the material. At some point, enough current has passed through the conductive path that the potential difference between cloud and earth can no longer cause the jump between gap(s) in conductive particles in the air, and the current flow stops. During that brief time that current flows, there are in the order of several million amps flowing.
As with any electric circuit where current flows, a magnetic field is created around the flow path. It is this induced magnetic field which couples into nearby electronics and disrupts them. Also remember that ground is not a perfect conductor. As the lightning bolt enters the earth, current flow through the ground resistance causes a potential difference on the surface. Using Ohm's law, what voltage will be generated through a one ohm resistor when one million amps flows through it? That is why many people are hurt in near strikes that are never hit by a direct strike. They are bridging enough ground resistance to have several hundred to several thousand volts present across their feet. Any conductive devices in the general vicinity of a lightning strike will be subject to this potential and that is another reason why electronics and power is disrupted during storms.
The same voltage potenetial difference on the ground injures people near a high voltage wire that has fallen. If electric power lines have dropped in a storm or other damage, stay away! If you are close, keep your feet close together and shuffle away.
Lastly, there is only one thing you can predict about lightning and that is it is unpredictable. I can tell you many stories of ham radio operators and broadcasters who have gone to great lengths to lightning protect their shacks only to have a storm come along and burn it to the ground. I have a picture of what was left or a bird that was sitting on a wire that was struck I will have to find. The potential difference between it's feet caused it to vaporize.

Re: A question about current....
 

electricity will arc when you have 1000 volts within one centimeter

that means to strike an arc 1 meter long you need 100 thousand volts

and to strike an arc 1 kilometer long you would need 100 million volts

lightning often travels 3 or 4 miles, so you are looking at several billion volts - and the measurements they have taken during thunderstorms dont support that

I dont think rain helps the equation very much, because pure water is not conductive - as I mentioned before I think something else is going on - once you have charges up in the millions of volts I think some secondary effect is happening, something we cant measure or observe in a laboratory, and the 1000V per centimeter rule gives way to something else.

We had a big T-storm here last night. I never get tired of watching lighting - sure beats any pyrotechnic display that we are capible of.

Re: A question about current....
 

Ken et al,
One reference on the Intenet lists the conduction of air in the 20kv/cm range but as you suspect there are other factors involved. The polution (particles) present in the air and the ionized gas molecules that make up the atmosphere all cause that value to change to much lower values. As the static builds up (a potenetial difference between cloud and ground or cloud to cloud) energy is imparted to the air molecules causing electrons to begin to move between atoms. This "ionization" imparts conductive paths from molecule to molecule. Remember that a good conductor is one in which the applied voltage is capable of adding energy to an electron to cause it to move to another atom or raise it to a higher energy level within the atom. So the static discharge is not one that jumps several miles but millions that jump micro inches until a conductive path is formed, creating a pipe of ionized (conductive) gas which is sufficient to cause current to flow. A high voltage source causes great deals of ionized gas to be formed near the source. High voltage power lines produce this ionizing voltage sufficient on very high voltage power lines of jumping fourteen feet. Remember when looking at the insulators on power lines that the total path length is the surface path around each section of the insulator not the tip to tip length. Power lines do produce some current flow between the wires and ground and anyone standing underneath can hear the discharge as a constant crackle which becomes worse on humid or rainy days.

Re: A question about current....
 

That stepped ionization is what i gathered from the page referenced in one of my earlier posts. You had the idea correct, but the page claims that the steps happen in 50 ft sections. This is reasonable when lightning strikes are in the million volt range so 50*2.54*12*1000 = 1.524 million. At the Boston Museum of Science (or whatever its called), they have a show about electricity (the one with the enormous Van der Graaf generator that makes 12 foot arcs.) and they mention that lightning usually requires 1 million volts per mile. The longest recorded bolt was something like 6 or 7 miles.

Re: A question about current....
 

Hwello,

Electrical arcs and lightning bolts across substances are governed by Paschen's law. Each scenario has a breakdown voltage, above which electricity can flow through a material. This voltage is related to the distance across the gap, gas density, and other properties that I have forgotten. Once this breakdown voltage has been crossed, the gap allows electricity to flow. This is the basis for Jacob's ladder demonstrations. Take a look here for more information:

http://home.earthlink.net/~jimlux/hv/paschen.htm

Also, electrons do not actually move to carry charge. The current moves at a speed called propagation speed, which is dependant upon the medium in which the current is flowing. Electrons move at a speed called drift velocity, which is equal to the magnitude of the current divided by the number of charge carriers times the magnitude of the charge on each charge carrier times the area of the conductor.

v = I / nqA,
where v = velocity of electron, I = current, n = # of charge carriers, q = magnitude of charge on carriers, and A = conductor area.

I have always found a water system analogy very useful for explaning basic electrical concepts to people. Think of water flowing in a pipe. The pressure on the water is equivalent to the voltage and the amount of water crossing a point at a given time is analogous to the current. This model is not wholly accurate, but it makes sense to people who used to ask "How many volts is an amp?"

Re: A question about current....
 

This why lightning tends to be one of those phenomena that is actually quite difficult to explain in entirety. It is an extremely complex dynamical system which is why no two lightning bolts ever look the same. Take a year of upper level E&M and then also a year of upper level Statistical Mechanics and you might be on the right track for describing how a one inch spark propagates. You cannot take a general solution of dielectric breakdown as 20kv/cm (for dry air) to be a solution for 6 miles of air that has varying pressure gradients, temperature gradients, varying air currents, changes in air composition and varying humidity, etc.... Thanks Al, for setting us straight on this.

The electric field from the power line to the ground is quite substantial and now easily measurable with digital multimeters. For those of you with power lines nearby; obtain or borrow a digital multimeter and set it to measure voltage, place one lead in (near) the ground and simply raise the other lead over your head (6-8 feet off the ground) - REMEMBER NEVER TO GET TOO CLOSE TO OR PLAY NEAR POWER LINES - YOU SHOULD ALWAYS BE AT LEAST 25 FEET AWAY (OR MORE, IF ITS HUMID OR RAINY)!! So with that disclaimer, your voltage lead should still be at least 25 - 30 feet below the power line! Hmm, what's the voltage? Lightning strikes are common when the voltage near the ground 18 KV/m or higher. Hopefully you never measure this - If you do you are in danger and I'd put down the voltmeter probes and then bring your feet close together, curl into a ball, and stay away from trees or tall objects. Lightning kills the most people each year, more than all other natural weather phenomena put together (hurricanes, tornados, floods, etc..)!

Oh, yeah....

The terms Positive and Negative originated before the electron was discovered. Positive and Negative were used to simply describe excess and deficiency of a mysterious substance known as charge. + was more than normal and - was less than normal. I like to think of it in terms of pressure differences High and Low. Thus "current" was used to describe the flow of "charge" from high "pressure" (+) to low "pressure" (-). But then the electron was discovered and everything had to fit within the well known model. (Gee, thanks Franklin!) This has caused an enormous amount of confusion especially when today we realize that what actually travels in a current carrying wire is electrons which DRIFT from (-) to (+). They drift on average of 0.1 mm/s at 1 Amp through 18 AWG solid copper wire. However in a plasma (ionized air) the mobile charge carrier can be electrons AND positively charged ions. Now which way does it go?? (Take an upper level plasma physics class!!) Just remember that the term "current" was defined by someone who didn't know the whole story and now we're stuck with it. Use the term "electron flow" or "electron current" if you feel a need to describe the direction electrons are going!

Just another thought ... What would happen if you held a 4 foot flourescent tube underneath a power line??? (make sure it is a dark, moonless night, and please don't drop / break the flourescent tube - mercury vapor is a known carcinogen) REMEMBER MY SAFETY DISCLAIMER STATED ABOVE!!!

That's enough of me rambling on and on and on....

Re: A question about current....
 

Not quite. The electrons move, but not the ions, so therefore the charge of the ions are meaningless. Electricity always moves from neg to pos.

Sparks

Re: A question about current....
 

Yes, in wires, electrons are the mobile charge carriers. But I must warn you to stay away from using ambigous terminology like "electricity.. moving...". It just perpetuates common misconceptions about electricity.

In a wire, current, by definition, is from pos. to neg. Whereas electron flow is from neg to pos. Understanding this subtle difference is vital when you try and use applications where bias is important or say when your doing circuit analysis with Kirchoff's Laws. Remember, current was defined before they knew the electron existed and now we're stuck with it.

Re: A question about current....
 

An arc between two charged regions across an insulating region is extremely difficult to model. The ability of an arc to cross a region is dependent upon the difference in Voltage across the region and several other factors, including gas density and distance. Also temperature and humidity are important factors to consider.

The reason for breakdown is explainable. When tremendous voltage differences appear between surfaces, the Townshend (sp?) effect occurs in gases. In this effect, outer electrons disassociate (or lose some of their bond strength) in gas molecules. These newly-freed electrons can now carry charge, and allow for conduction.

Imagine two electrodes a distance r apart from one another, with a gas whose density is p. There is a law, Paschen's law, which states that the required breakdown voltage, the voltage at which electric current can flow across the insulator, is a function of p and r. This function is not linear and is
dependent upon the type of gas, geometry of the setup, etc. And furthermore, it is only truly useful at pressures near 1 atmosphere and distances of roughly 1 centimeter.

In air, an approximation exists that is often used on short distances.

Breakdown_Voltage = 366 (V/(cm*torr)) * gas density * (distance/(1.18 + ln(distance * gas density)))

where distance is measured in centimeters.

There is also another effect at work, wherein air will not break down, regardless of distance, unless a certain threshold voltage has been crossed. In air, this voltage is approximately 330 volts. This threshold voltage is affected by the chemical composition of the involved electrodes; for example Aluminium electrodes in pure air result in a breakdown voltage of 352 volts.

There are a few fun demos possible with Paschen's law. If you have ever seen a Windhurst machine, that is one of them. This machine uses two spheres mounted such that the distance between them can be controlled. Also, a human spins a crank, which has two brushes attached, which build up
very massive voltages on the two spheres. Eventually the breakdown voltage is reached and crossed, and "lightning" appears. (Side note: Try placing a plastic ruler with a hole in it inbetween the two spheres, and watch the lightning jump through).

One other note: When the Townshend effect results in the breakdown of air in a large area, radio communications become extremely difficult to sustain. I have done some experiments trying to sustain FHSS walkie-takies through a row of Jacob's ladders, trying to see how well radio works with that much ionization occuring. Maybe because I was using terrible units or maybe because ionization is that good at stopping radio, but very little communication made it through.

Re: A question about current....
 

Venkatesh,
True, arcs are extremely hard to model because there are so many variables. What practice dictates is the safety margins involved to protect persons and property. Power line height is dictated by the known breakdown characteristics under the worst rain ever encountered with the most conductive particles contained in the water plus a safety margin to make up for those variables that can all combine to cause an arc and/or personal injury.
As Doug has stated above, there are fields surrounding power lines. Since they are AC fields, placing a wire in such a field will cause current to flow in the wire. The field will also induce current flow in the ground under the wires and in the towers that the wires hang on.
As to interference, the arc is a current flow. Current flowing in a conductor (in this case ionized gas) produces a field about the conductor. An arc is not a steady state or DC current (even it is generated by a DC source) but wildly alternating in nature. This field is the same as takes place in an antenna. The arc produces a very large and wideband electromagnetic field and as such overpowers the radios in your experiment. Spark gap transmitters were the source of Marconi's radio waves at the beginning of the last century. The energy produced by the gap was also wideband and Marconi and others attempted to narrow the output to a smaller range of frequencies using what are now known as tuned circuits. As broadcasting progressed, the spark gap transmitter fell out of favor and was eventually outlawed as using too much spectrum. To overpower your little handhelds (radios) takes a field strength of just a few millivolts per meter at the distances you suggest.

Re: A question about current....
 

I've "heard" lightning on my radio many of times! You can also take 9 Volt battery and connect one end to a metal file and the other end to a wire. Run the free end of the wire across the file and watch all the little sparks and listen to your radio too (try the AM band).

Re: A question about current....
 

Doug,
You are quite right. I will try to stay away from ambigous terminology in the future. (It's something that drives everyone around me nuts!!)

Sparks

Re: A question about current....
 

I have read with interest the discussion on this thread. However, it appears to have gotten a bit off topic… At issue is “why does current flow from positive to negative and electrons flow from negative to positive?” As I am letting my Thanksgiving dinner digest, let me take a stab at this by using an analogy to make a complex subject more (I hope) understandable.

Imagine a telephone pole lying on the ground. As an observer, you are standing off to the side so that you can see the whole pole. Now we strike the end of the pole to the left of the observer with a sledge hammer. The pole moves one centimeter to the right of the observer when hit.

In the fraction of a second before the hammer impacts the pole there is a 1 cm “hole” at the far right end of the pole where the wood ends. A fraction of a second after impact, that hole is replaced by wood and the 1 cm “hole” has appeared at the end of the pole to the left of the observer.

The wood flow is from left to right and the hole flow is from right to left. You can not have one without the other.

The observer can define positive flow as wood flow (and therefore negative flow is the hole flow) OR he can define positive flow as hole flow (and negative flow as wood flow). It makes no difference as long as he or she is consistent.

To continue this concept, let’s assume that the hammer is invisible and that most of the pole is hidden from view by a pipe which encloses the pole. Now he or she sees wood being injected into the tube from the left and exiting to the right. He or she also sees a hole being injected from the right and exiting from the left.

The wood is, of course, analogous to the electrons in a wire (the pipe) and the hammer is analogous to a (negative) voltage.

Realize that a positive voltage attracts electrons and repels holes. A negative voltage attracts holes and repels electrons.

Holes are actually the absence of an electron in the outer shell of an atom of a conductor or semiconductor. Holes are every bit as important as electrons to the function of electricity.

A single electron exists in the outermost electron shell of an atom of copper, the most common conductor we use. We tend to call this single valence electron a “free” electron. While a copper atom with 29 electrons is electrically neutral, its outer shell wants to either give up an electron (the shell would be empty) or gain an electron (the shell would have two electrons). Thus we can inject a hole (take away an electron) to get a balanced outer shell (empty) but negatively charged atom or inject an electron to get an equally balanced outer shell (two electrons) but positively charged atom.

This delicate balance of electrons and holes makes the magic of electronics work. When you complete the circuit of wire from positive to negative of a voltage source, the number of positively and negatively charged atoms is constrained by the fact that the wire is a short circuit. The atoms want to be at a neutral charge so a heavy current flows as the electrons migrate from negative to positive and the holes migrate from positive to negative.

A convention was adopted long ago where a positive current was defined as the current which flows from a positive voltage to a negative voltage. Positive conventional current is hole flow.

This convention was, in all fairness, arbitrary but convenient for 95% of all electrical engineering. An engineer who is designing electron guns for cathode ray tubes, for example, may want to use non-conventional current (electron flow), however, this is more of a rarity as we become more and more dependent on semiconductor technology.

Last notes:

In type P semiconductors, the material used requires less electrons be lost (more holes be added) to make a stable outer shell than the number of electrons added (holes lost). N type material is the opposite. This difference in materials and valence electrons is why you may hear of majority carriers and minority carriers. In conductors, the holes and electrons have equal billing.

Lastly, the telephone pole analogy points out another curiosity. If you were to lay down and put your head against the far right end of the pole and I were to hit the left end with the sledge, the wood will only move 1 cm but you will get a headache instantaneously. The actual speed of migration of electrons in a 2 mm diameter copper wire passing 1 ampere of current is just under 9 cm per hour yet the signal travels at about nine tenths the speed of light… Cool eh?

Re: A question about current....
 

Mike,
I go back a bit further in electronics and for the most part "hole" theory didn't really become part of my education until semiconductor discussions. It was simple enough to know that a conductor when connected to a voltage source (i.e. battery) would draw electrons from the outer shell of the atoms at the positive terminal of the battery. Those atoms now wanting an electron to stabilize the outer shell in turn stripped them from neighboring atoms and so on until the battery was required to give up electrons at the negative terminal. Since I had a healthy background in vacuum tubes, (electron flow from cathode to plate is essential to their operation) I always have that mode stuck in the back of my head. The cathode generates excess electrons through the act of heating a material. When you introduce a positive voltage to the plate these electrons then migrate through the tube elements causing current flow.
Conventional current flow is a way for users to easily measure and predict other phenom. An ammeter will deflect "up" when the positive lead is connected to the more positive part of the circuit. The "right hand" rule for magnetic fields works with conventional current. Most electronic circuits consider the positive portion of the circuit at a potential above ground and so therefore current flows into the ground. Interfering signals are thought of as moving into a shielding material at ground potential, etc. Most of which are conventions used in the US but are different in other parts of the world.
Whatever method you use of analyzing a particular behavior is just a tool in your toolbox that helps you get the job done. Multiple tools makes the work easier. My dad was fond of telling me to use the "right tool for the right job."

Re: A question about current....
 

Al,

I also started with vacuum tubes (electronics technician school in 1971) and understand well... I thought that introducing the concept of hole flow would be helpful to today's generation.

BTW, my 1959 Austin-Healey is a positive ground system...

Re: A question about current....
 

Mike,
Austin dual 6 volts, one under each seat? Makes it hard to put a CD player in doesn't it. (Of course what am I saying, there is no room!)

Re: A question about current....
 

Al,

Mine is a 100-6 two-seater. The batteries are indeed dual sixes located behind the seats. Did I mention how much I love Lucas regulators? :D

Re: A question about current....
 

Are you having problems? I have never personally worked on one but if they are anything like GM regulators, I know the contact spacing and alignment were crucial. I worked in a GM parts store in high school back before Delphi when GM ignition and electrical parts were Delco Remy. The store had this panel that helped in alignment. As I remember it had about three round meters and several switches. I had a friend who finally found an interesting problem with an MG and the two batteries. The springs in the seat were broken or worn and they would occasionally short a cell or two on top of one of the batteries. Until it started a small fire there was no indication that the seat was the problem.

Re: A question about current....
 

Al,

The truth be told, I have not had it running for over 10 years. Before I started dismembering it, I used to carry a small tack hammer and bang on the the top of the regulator when the battery started discharging...

Mike

Re: A question about current....
 

Back on topic... I've heard via PM from a few engineers about my telephone pole analogy. I'd like to hear from students...

There are no more fundamental concepts in EE than current flow, Ohm's law, grounding, et cetera. These can also be some of the most confusing... You guys and gals must have more questions...

Bring 'em on now... In about 6 weeks we mentors will be to busy to type up lengthy answers.