I thought it was like lightning, sometimes clouds are positive and negative, right? Cloud to ground--ground to cloud.

 

Exactly. It's the rate at which the electrons pass a given point which gives the 'speed' of electricity. It's a bit like watching people going through the turnstile at a football match. They come through very quickly, and the turnstile is going round like crazy. But if you watch one person moving with the queue outside, they are moving very slowly. But the O.P's instructor seems to be saying that the queue is actually moving in the opposite direction!

That's not the cause of the 'speed' of electricity but that's the subject of another thread.

 

That's not the cause of the 'speed' of electricity but that's the subject of another thread.

Ok if I start it will you explain more? I know it makes no difference to the practical results, but if the 'speed' of electricity is not about the number if electrons flowing past a certain point then I'm keen to know more. I thought that was how current was defined. That's the problem with science.. Every time you think you understand, it turns out that the truth is more complex still!

 

Ok if I start it will you explain more? I know it makes no difference to the practical results, but if the 'speed' of electricity is not about the number if electrons flowing past a certain point then I'm keen to know more. I thought that was how current was defined. That's the problem with science.. Every time you think you understand, it turns out that the truth is more complex still!

The number of charge carriers moving past a point (current) is a perfectly good way of describing the 'what' of electricity's effect on matter but it doesn't describe the 'why' very well.

This thread already exist so if you need to post use that. http://forum.allaboutcircuits.com/showpost.php?p=619118&postcount=17

 

The Wikipedia article on Coulomb says "Since the charge of one electron is known to be about 1.60217657 × 10E-19 coulombs, a coulomb can also be considered to be the charge of roughly 6.241509324 × 10E18 electrons".

A Coulomb, of course, is the charge transferred when 1 Amp flows for 1 second. (And if it flowed into a capacitor of 1 Farad, it would charge it to 1 Volt.)

An electron doesn't carry much charge. To do anything useful, you will need a lot of them.

 

The Wikipedia article on Coulomb says "Since the charge of one electron is known to be about 1.60217657 × 10E-19 coulombs, a coulomb can also be considered to be the charge of roughly 6.241509324 × 10E18 electrons".

And the Wikipedia article is deficient because it neglect the fact that charge is a signed quantity. But note that they covered that by adding, "electrons are technically represented with a charge in negative coulombs, and protons positive". They also claim "for electrical purposes charge is generally represented with an absolute value". Even if this is true (and I'm not convinced it is), that is irrelevant because the sign is inextricably linked to this discussion, and therefore can't just casually be ignore.

Consider this: If the charge on one electron is 1.60217657 × 10E-19 coulombs, then what is the charge on one proton? If you say 1.60217657 × 10E-19 coulombs, then you are claiming that a proton and an electron have equal charge, whereas we know that they have equal and opposite charge. So the charge on on of them has to be positive and the charge on the other has to be negative. The choice of which is which is arbitrary, but once you make that choice then the polarities of everything else, electric field, voltage potantial, magnetic fields, have to be defined consistently with that choice. Pointing out that the charge on the electron could have been defined to be positive, while true, changes nothing.

Now consider a more visual example: I have a sphere that has a wire going to it. The sphere is initially uncharged. Now a bunch of electrons flow onto the sphere over the wire (the sphere is actually one-half of a capacitor with something else, such as the Earth, serving as the other half) at a rate that has a magnitude of I=1mA=1mC/s and this is allowed to continue for T=1ms. What is the charge on the sphere? Is it +1μC or -1μC?

Let's look at this from both the "conventional current" and the "electron current" view. From the conventional current side you can define the symbolic direction of current however you want. If you define it to be flowing toward the sphere, then it has a magnitude of -1mA while if you define it to be flowing away from the sphere, then it has a magnitude of +1mA. In the first case the charge on the sphere is

Q = Qo + I*T = 0 + (-1mA)(1ms) = -1μs

In the latter case, the charge on the sphere is

Q = Qo - I*T = 0 - (1mA)(1ms) = -1μs

But what about the "naive" electron current view?

They claim that a current of 1mA is flowing in the direction of the sphere. This means that 1mC of charge is flowing onto the sphere every second and, therefore, after 1ms there must be +1μC of charge on the sphere. That's an inescapable consequence of claiming that a positive current is a current in the direction of electron flow. Of course, what happens is that then they want to come back and patch it up by saying that, well, yes, we conclude that there is 1μC of charge on the sphere, but that is just the magnitude. But we know that the electrons are negatively charged, and so the charge on the sphere is really negative, so its actually -1μC of charge on the sphere. But you can't have electrons be positively charged or negatively charged by convenience. If they are negative charged once they get onto the sphere, then they were negatively charged as they were flowing down the wire, and so the amount of charge that passed a given point would be -1mC/s, or a current of -1mA in the direction of the electron flow. Now go back and look at what the current was in the conventional current case when the direction was defined to be in the direction of electron flow -- it was -1mC/s. So, in either case, if the direction of current is taken to be toward the sphere, there is a current of -1mA flowing in the wire if electrons are flowing toward the sphere.

The problem is with the electron current fans that won't recognize that you can't ignore the fact that the electron is defined to have a negative voltage. More specifically, you can't treat it is positive unless you reverse the signs on everything else, namely your voltages and your fields, and that, unless you do, all your work must recognize and account for the fact that it is negative.

 

The +ve & -ve concept is a mathematical analog of the behaviour of real things in a real world.

It is in some degree flawed,as -ve signed numbers in Mathematics do not lose some part of their value which wanders across to a +ve number (or the other way round).

OK,-ve & +ve numbers cancel,but there is nothing really approaching current.

An immaculate mathematical argument may demand differently signed values for Electron Flow & Conventional CurrentFflow,but in the real world,where Engineers are supposed to exist,there is no need for such a distinction.

For years,Technicians were taught Electron Flow because it explains the operation of such things as Vacuum tubes.

They were also taught that Conventional Current Flow was used for such things as "Fleming's Right Hand Rule " & the like,so became
effectively"ambidextrous"(Yes,I have seen the "Left Hand Rule" promoted.)

Engineers,who originally were mostly Electrical Engineers,dealing with such huge things as Traction Motors,Power station Alternators.& the like.learned Conventional Current Flow.

Some Engineers,however,--------no less capable or qualified Engineers than your goodselves,delved into the innards of vacuum tubes & other thermionic emission type devices,& because of this,dealt with ,& promoted Electron Flow.

It is not just some silly idea thought up by a few old Techs brought up on tubes,but for most of the "Radio" period of Electronics was the way current was visualised by some of the "brightest & the best" of their time!