Basic theory question-- "positive ground"

[plexi12000]

we all know electrons flow from negative to positive.  so how is it possible to have a pos. ground circuit?  -lol   how does that work?

[R.G.]

Ground has nothing to do with electron flow.

Ground is a REFERENCE POINT. It's the place in the circuit we designate with the voltage of 0.00000000000V. A battery can have its negative terminal connected to ground, leaving the + end free to power the circuit. This is negative (battery terminal) ground(ed). It can also have its positive terminal tied to the reference voltage point, leaving its negative terminal free to power the circuit. This is positive (battery terminal) ground(ed).

[merlinb]

The situation is not helped by the silly name 'positive ground' which is deliberately designed to confuse beginners:
http://www.diystompboxes.com/smfforum/index.php?topic=110232.0

[induction]

Nor by the fact that electron flow is the opposite direction of current flow. We can blame Benjamin Franklin for that one.

[greaser_au]

Nor by the fact that electron flow is the opposite direction of current flow. We can blame Benjamin Franklin for that one.

Nothing wrong with the concept of conventional current (hole) flow - makes NPN design a LOT easier to follow. 

david

[Brisance]

Also the concept of cathode and anode can cause confusion especially to people with a chemistry background(since cathions are positive and anions negative)

I work around this problem by remembering diode polarity in a way that the symbol is like an arrow pointing in the current flow direction and are marked on "bar" side with a line. ( and for leds, longer lead goes to positive ) crude and lame, but that avoids "hooked up the wrong way" problems for me.

[merlinb]

Nor by the fact that electron flow is the opposite direction of current flow.

No it isn't. Electrons are negative charges, so the current flowing in the direction of the electrons is negative. Conventional current agrees precisely with electron flow (yes, most hobby websites miss this point). Saying that positive current flows in the opposite direction is exactly the same thing, but more convenient because it's easier to work with positive numbers.

[induction]

Nor by the fact that electron flow is the opposite direction of current flow.

No it isn't. Electrons are negative charges, so the current flowing in the direction of the electrons is negative. Conventional current agrees precisely with electron flow (yes, most hobby websites miss this point). Saying that positive current flows in the opposite direction is exactly the same thing, but more convenient because it's easier to work with positive numbers.

Electric current is defined in terms of the amount of positive charge moving past a given point over time. Its units are coulombs per second. If you draw a current vector, the arrow will point in the opposite direction of electron motion. If referring to magnitude alone and you want to specify negative current, you must explicitly indicate that, or suffer the wrath of the examiner. I stand by my statement.

And I mean no disrespect to holes. The OP specified electrons.

[merlinb]

Electric current is defined in terms of the amount of positive charge moving past a given point over time.

Is it? Check you textbooks!  

[Tony Forestiere]

I may be stupid. Is there really such a thing as negative current? I can imagine a negative voltage in reference to another point in a circuit, but negative current sounds like like an impossibility to my tiny understanding unless the measurement of current is an absolute value. (ie. I = |I|).

[merlinb]

I may be stupid. Is there really such a thing as negative current? I can imagine a negative voltage in reference to another point in a circuit, but negative current sounds like like an impossibility to my tiny understanding unless the measurement of current is an absolute value. (ie. I = |I|).

Negative just means "the opposite direction". Current is a bit like speed; it is the 'rate of change' of something with time (rate of change of charge, to be exact). If you drive your car forwards then it may attain a certain speed. If you put it into reverse then you can say its speed is negative with reference to your chosen 'reference vector' (i.e. forwards). It's a purely mathematical concept. Current doesn't really 'go' anywhere, just like 'speed' doesn't go anywhere; it is a scalar quantity, i.e. just a number.

[Tony Forestiere]

I guess I am dense. (No surprise there!). Using your automobile analogy: Forward and reverse driving would be positive or negative with respect to a linear reference (distance traveled from point X), but wouldn't the speed of travel in either direction from point X (MPH or KPH) still be a constant absolute positive value?

[induction]

Electric current is defined in terms of the amount of positive charge moving past a given point over time.

Is it? Check you textbooks!  

No need. The answer is in the units.

Current is a vector, not a scalar. It has both magnitude and direction. The relavant quantities are charge, direction, and time. A negative sign can indicate the negation of any of these three: negative charges following the vector, positive charges moving in opposition to the vector, or positive charges following the vector, but moving backwards in time (eg. positrons; their usage is usually reserved for virtual particle pairs that spontaneously pop into and out of existence in vacuum. This is is one of the contenders for explaining dark energy.)

In electronics, statements about current are usually phrased in terms of magnitude only (eg. 'how much current'). But when direction is part of the statement (eg. 'electron flow is the opposite direction of current flow'), the statement is necessarily about vectors.

[induction]

I guess I am dense. (No surprise there!). Using your automobile analogy: Forward and reverse driving would be positive or negative with respect to a linear reference (distance traveled from point X), but wouldn't the speed of travel in either direction from point X (MPH or KPH) still be a constant absolute positive value?

Vectors vs. scalars again. Velocity is a vector (magnitude and direction). Speed is the magnitude of velocity. Velocity can be negative, speed can't. (At least not for anything in our everyday experience, like cars.)

[merlinb]

Current is a vector, not a scalar.

No, current density is a vector. Current is scalar, just like speed. It can be positive or negative relative to a reference direction, but this does not mean the current itself has a direction. e.g. speed is positive when the car move forwards, but this tells you nothing about what direction the car itself is going. We know implicitely that it is on a (two dimensional) road. Whether it is going up or down the road makes no difference to us, since the wear and tear on the asphalt (which we do care about) is just as bad ether way.

Current density is negative in the direction of the electrons, because electrons are negative. The only 'conventional' thing about conventional current is the preference to use positive numbers where possible.

[GibsonGM]

The only 'conventional' thing about conventional current is the preference to use positive numbers where possible.

I was waiting for this to go to the traditional discussion based on "ground is just a convention".  And it is.   "Positive ground" simply means "positive reference point for this circuit".    Provided you follow the laws of physics (being described above, lol), it makes no difference.   You can play basketball on a court outdoors, or on the 10th floor of a high rise - doesn't matter, as long as you know where you are      

[Some] Components are made to receive electrons at one point, emit them at another.  As long as you allow them to do this with their proper polarity, and you are aware of WHAT is common, as well as how you would interface them with circuits NOT using this reference -  there's really not much need to delve too far into the BIG theory behind it.   

Unless, of course, you want to!    Great question, things like this always make for interesting reading!

[induction]

Current is a vector, not a scalar.

No, current density is a vector. Current is scalar,

Apparently, this is something about which reasonable people can disagree. This article goes through the arguments and declares that current is a 'constrained vector'. Richard Feynman is cited as a source on the vector side. The main argument against is that current doesn't obey the laws of vector addition.

The internet is full of physics fora with people arguing back and forth on this topic. To avoid adding this site to that list, I withdraw my previous statement and offer this one in its place:
"Nor by the fact that electron flow is the opposite direction of current density. We can blame Benjamin Franklin for that one."

[merlinb]

"Nor by the fact that electron flow is the opposite direction of current density. "

But think about what you're saying there. It's equivalent to saying "traffic flow is the opposite direction to velocity". The sentence itself makes no sense. Velocity is a measure of traffic flow; velocity itself is not a moving object.

If electrons are negative (and we all agree they are) then so is the current density in the direction of electron flow. That is the construct of conventional current, and there is nothing backwards about it. The only obstacle standing in the way of newbies is accepting that a negative number in one direction is the same thing as a positive number in the opposite direction. That's just maths. They're not opposites but 'duals', two sides of precisely the same coin. The whole 'problem' of conventional current is a phantom that only exists in the minds of newbies who haven't made the mental connection between negative charge and negative current. That's why you never hear of real engineers and physicists arguing over weather to 'reverse' the definitions of current etc, because there is no problem to fix.

[R.G.]

For hundreds of years, the question of how many angels could dance on the head of a pin was a really, really hot topic among the thinkers of Europe.  
[Note: there is more to this question than the seeming inconsequentiality of it.  ]

Philosophical discussions are fascinating, but the issue of "positive ground" is simple: which side of (presumably the only) battery is connected to the ground reference point.

In the larger philosophical scheme of things, Mother Nature doesn't care what we mean by 'negative' or 'positive'. The math works the same way whether we say the charge on the electron is one unit positive or one unit negative. Things might have been simpler if the (probably apocryphal) story of Ben Franklin getting it backwards had come out differently. If he'd initiated the naming so that the charge on the electron was deemed positive, then the charge on the proton would be one unit negative, the math would still work, and we'd be having discussions about the philosophical meaning of "negative ground", since positive-charged electrons flow from positive to negative. PNPs would be NPNs, and the nominal thinking is that power supplies were naturally negative with respect to ground.

One many's ceiling is another man's floor.  

[merlinb]

Things might have been simpler if the (probably apocryphal) story of Ben Franklin getting it backwards had come out differently. If he'd initiated the naming so that the charge on the electron was deemed positive...

I've always found it remarkably fortuitous that he chose to use the words 'positive' and 'negative' at all. He wasn't using maths himself, and it was such a mysterious phenomenon that he might have named them 'wet' and 'dry', or 'strange' and 'charm' or whatever. If he had, it would be a real pain to learn electronics today and memorise the connections between the wordy descriptions and the mathematics. I guess Benny Franklin was a very perseptive guy!