Voltage and Current w/in a 9V battery vs. Voltage and Current Produced by Transduction

Thread Starter

Dolmetscher007

Joined Mar 21, 2019
34
There are four terms in physics/electronics that I understand in a certain context, but not at all in another. Those terms are:
  1. Positive
  2. Negative
  3. Neutral
  4. Ground
Positive and negative seem to be the least difficult for me to understand. A 9V battery has two terminals, a positive and a negative. The battery uses a chemical reaction to create the conditions at the positive terminal whereby the atoms have fewer electrons than those gathered at the negative terminal. Correct?

So, when a conductor is placed across the two terminals, the atoms at the negative terminal want to equalize the difference in electrons. The "surplus" of electrons at the negative terminal, flow through the conductor over to populate the electrons that have a relative "deficiency". (I understand that surplus and deficiency are quantitative distinctions and not a qualitative truth. So that is how a 9V battery works. Correct?

Assuming, for this example, there are no volume or tone potentiometers, you solder one end of the pickup's coil-wire to the positive lug of the jack, and you solder the [???] end of the coil-wire to the [???] lug of the output jack. Just like a 9V battery pushes electrons across a conductive wire... through transduction, a guitar pickup can also push electrons along a conductive wire. Do they both have a positive and a negative terminal?

With a guitar pickup's transduction, I cannot envision how the "positive" end of the wire relates to the [???] end of the wire. (P.S. I keep using [???] because, I do not know if the other wire would be referred to as a negative, neutral, or ground wire.) I always imagined "transduction" kind of working like this: You have a water hose that is filled with water, if you stomp on it at some point along it's length, you create pressure that causes the water to squirt out the hose harder. If you get 20 people to all line up with hammers, and everyone starts whacking on the hose, that is kinda like the string wagging around inside the magnetic field. The magnetic force acting on the electrons inside the copper wire is analogous to the bunches of hammers waking the water-hose. That analogy breaks down in my head, however, because the copper wire has two ends, and if you "stomp" on it, it should cause the electrons to flow outwards away from the "stomp" in both directions.

In a simple circuit with a 9V battery and a light bulb, when the circuit is closed, the battery, wanting to equalize the number of electrons across it's two terminals, will push electrons from the "surplus" at the negative pole, through the light bulb, to the positive terminal, and continue doing so until the chemical reaction is spent, and the positive terminal equals the negative terminal in charge.

If you remove the 9V battery, and you replace it with a transducer (guitar pickup) that is large enough to generate 9V (much larger than a guitar pickup), and you vibrate the metal string within the mag field of the transducer, there is no "surplus" or "deficiency" at either end of the coil-wire. So... I guess... my two questions are...
  1. How the hell does a guitar pickup actually work on an electron level?
  2. What does neutral, negative, and ground mean?
 

nsaspook

Joined Aug 27, 2009
8,278
Stop thinking about water and physical electrons. The property of charge (particles) works as a system to transfer electrical energy into and out of circuits while the actual number of charged particles (electrons in most cases) remain the same but move in response to forces.

Start thinking about ferromagnetic properties, changing flux, induction, changing fields and energy flows that result in electrical potentials.

 
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MrChips

Joined Oct 2, 2009
23,248
What does neutral, negative, and ground mean?
You may as well add "positive" to that list.

For the time being, don't get too hung up on the meaning of these terms.
It is like North Pole and South Pole. It doesn't mean much. You might as well call it X-Pole and Y-Pole.

For now, focus on understanding current flow and potential difference.
 

crutschow

Joined Mar 14, 2008
27,008
I know some don't like a water analogy, but here's a simple one that may help.
Think of a closed pipe loop filled with water connected to a pump.
The water molecules represent the electrons in the wire and the pump represents a battery, power supply, guitar transducer, etc that has a voltage between its positive and and its negative end.
(Remember that a voltage is always referenced between two nodes just like a pump's pressure. You can't have a voltage at just one node. And the water won't circulate or the current won't flow unless there's a return path.)
So the pump generates a pressure across it (the voltage) and the amount of water that circulates depends upon the resistance in the pipe (such as a valve).
Notice that the amount of water molecules in the pipe (or the electrons in a wire) does not change. All they do is move because of the pressure (voltage).
So all the electrons do is move is response to a voltage. The don't pile up or become significantly deficient at any connection node.

How you label the polarities is just convention.
Conventional current flow is from plus to minus.
Electron flow is minus to plus.
You can use either convention as long as you use it consistently in all you calculations. The results will be the same.
(I prefer current flow because the arrow on transistors and diodes indicates the direction of current flow.)

Ground/common is just an arbitrary reference point that is considered to be 0V with respect to all other voltages. It has no other significance.
Neutral is used mostly in AC mains power, where it refers to the line that is referenced to earth/safety ground.

(Note that "transduction" is not a word commonly used in electronics. ;))
 
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nsaspook

Joined Aug 27, 2009
8,278
One of the problems I have with the closed loop water analogy is that pressure = voltage is wrong even in a loose analogy. Pressure is energy per unit volume independent of position with no need for a reference point. Voltage/Potential and potential energy are position dependent. Potential is the potential energy per unit charge or unit mass. IMO pressure is something you measure locally and doesn't translate well to voltage. If you must use water then the gravitational potential of a reservoir is a better analogy to voltage.

https://en.wikipedia.org/wiki/Pressure
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html
 

crutschow

Joined Mar 14, 2008
27,008
Pressure is energy per unit volume independent of position with no need for a reference point. Voltage/Potential and potential energy are position dependent.
Really?
You going to make a fuss about the analogy because the energies don't correspond? :rolleyes:
It's a very simple analogy to help basically visualize what's happening, and what the energies are doing is not important for that.
I think you are being way too pedantic in your objection.
IMO pressure is something you measure locally and doesn't translate well to voltage.
I have no idea what that means. :confused:
Pressure is relative, just like voltage.
 

nsaspook

Joined Aug 27, 2009
8,278
Really?
You going to make a fuss about the analogy because the energies don't correspond? :rolleyes:
It's a very simple analogy to help basically visualize what's happening, and what the energies are doing is not important for that.
I think you are being way too pedantic in your objection.
I have no idea what that means. :confused:
Pressure is relative, just like voltage.
Yes, really. A plumber might use "pressure" as how strongly (the pressure gradient indicates how strongly and in what direction the water is pushed) the water is pushed but really pressure is a specific thing like Newton Per Square Meter (the distribution of a force over an area).
The way to understand electricity is by using system (two effects) energy analogies like between gravitational PE per kilogram of water and electrical PE per coulomb of charge.

http://www.abc.net.au/science/articles/2014/02/05/3937083.htm
 
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BR-549

Joined Sep 22, 2013
4,938
Current can't flow like water. It flows like a fan belt or a bicycle chain. It rotates. An electron can not flow out of a battery, without an electron flowing into the battery.

When a magnetic field cuts a conductor, an electron has to flow in one end, as an electron flows out the other end of the conductor.

It's a complete rotation. A complete circle. Water does not need a circle.

Battery current is DC current. Induction current from a vibrating string.....is AC current. Both the voltage and the current in AC circuits, stops, and turns around. It alternates.
 

nsaspook

Joined Aug 27, 2009
8,278
Sorry, but that's making it way more complicated then it needs to be.
Water analogies are for children or non-electrical laymen. Yes, it's too complicated for a child with no electrical interest but I taught my then 12 yo child the "Maxwell-lite" (electrical energy travels between the conductors, guided by the surface of the conductors.) version of electricity easily. I would bet most electrical beginners don't understand closed loop hydraulic systems to the point the inconsistencies are obvious. So they end up learning bad conceptual frameworks of electrical energy flow in particles (energy is delivered when water fills the bucket at the far end) and other circuit theory misconceptions that eventually will need to be relearned in a engineering/physics compatible way to progress beyond simple battery and lamp circuits.
1st year electrical apprentice: "Now tell me again, how does that voltage and current stuff work?"

Electrical instructor: "It's simple. Just think of it like water."

Meanwhile, over at the plumbers apprentice school:

1st year plumbing apprentice: "Now tell me again, how does that pressure and flow stuff work?"

Plumbing instructor: "It's simple. Just think of it like electricity."
https://pdfs.semanticscholar.org/56d2/230c4f9fdb8409f897220aedc959ff4f365d.pdf
 
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nsaspook

Joined Aug 27, 2009
8,278
My analogy uses a closed loop pipe, so the water does need a circle.
We must be having a meeting of the pedantics here. :rolleyes:
That's a low blow, I'm not at his meeting. My meeting is based on good science as you well know because we've had this conversation before.
https://forum.allaboutcircuits.com/threads/when-does-water-analogy-to-electricy-break-down.75499/

I understand you don't like the message but I'm not alone in the good science and not liking water analogy club.

https://dailybritain.wordpress.com/2017/11/06/6th-november-1913-drain-pipe-theory/
Preece who worked briefly under the great Michael Faraday (2) was famous for what was disparagingly called the Drain Pipe Theory, from rivals in the field such as Oliver Lodge and Heaviside, and his ‘Thought Experiments’, which included an analogy between the flow of electricity and water.
The water analogy makes it easy to understand a very limited view of electricity that is mostly wrong but useful in a limited way.
 
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crutschow

Joined Mar 14, 2008
27,008
Some further thoughts:
One of the problems I have with the closed loop water analogy is that pressure = voltage is wrong
The power transferred by water flow in a closed pipe is pressure times flow.
How is that fundamentally different from volts times current?
taught my then 12 yo child the "Maxwell-lite" (electrical energy travels between the conductors, guided by the surface of the conductors.) version of electricity easily.
Yes, I learned that back in the distant past and haven't really thought about it since. It's an interesting theory, but what does that mean in a typical circuit design unless your are perhaps dealing with RF.
I've never needed that information to design any of my circuits or to understand how a circuit works.
energy is delivered when water fills the bucket at the far end
Absolutely no buckets in my analogy.
The water circuit is always closed loop, no leaks.
 

nsaspook

Joined Aug 27, 2009
8,278
Some further thoughts:
The power transferred by water flow in a closed pipe is pressure times flow.
How is that fundamentally different from volts times current?
Because it leads to a fundamentally wrong conclusion about power, energy and the mechanism of power transfer unless you are very careful to first explain the flow/current in a electrical circuit does not contain the energy of circuit. If you explain this very important fact the analogy gets messy.

Some analogies are better and usually don't lead to questions like this.
"If flow of electricity in wires is like flow of fluid in pipes why can I get fluid out of a single pipe, when I can't get electricity out of a single wire"
 
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Thread Starter

Dolmetscher007

Joined Mar 21, 2019
34
Oh Boy! So much to unpack! I LOVE this. Thank you so much guys. I am an Instructional Designer for a very large and well known software company. My entire job is to examine, create, revise, and fine tune analogies that help teach people very complex concepts using understandable comparisons. This means that I am absolutely... 100%... a through-and-through Pedant. I love getting into the muck of minutia and granularity so that I can deeply and fully understand something. THEN I am usually pretty good at developing an iron clad analogy. It is a very thin needle to thread sometimes. I find that people who use flawed analogies tend to be less interested in deeply understanding something, and are more goal-focused in general; which is an awesome thing! And I find that people who want to discuss everything under absolutely accurate terms and conditions tend to not engage their creative side as often as their analytical side, so... I try to be the buffer between these two "types" and the lay person that just wants to learn.

So... here are a few things that I do not fully understand.
(Remember that a voltage is always referenced between two nodes just like a pump's pressure. You can't have a voltage at just one node. And the water won't circulate or the current won't flow unless there's a return path.)
The word "referenced" here doesn't click with me. A lot of the time, using the passive-voice to explain something, it throws me off. Crutschow, do you mean "You can only measure a voltage between two nodes."? Or are you saying, "You must have two nodes in order for a voltage to exist."? Just to make sure I am understanding the term "Nodes" properly, I created this little circuit schematic and laid out what I consider to be its nodes:



IMAGE URL: https://i.ibb.co/mtQRTYz/NODES.jpg

So, are you saying that the only way that you can describe "voltage" is by comparing the measurement of some value that exists within the wire of node 1 with the measurement of the same value that exists within the wire of node 2? I hate to be so picky, but the word "referenced" is a block for me.

Pressure is energy per unit volume independent of position with no need for a reference point.
nsaspook... Water pressure, as best as I can tell, is a measurement of the force exerted by the water against the inner wall of a fixed diameter (i.e. rigid) pipe. I am not familiar enough with the basic laws of physics to understand your point about pressure being "independent of position." I imagine you mean something like the following:
If you have several 1/2" metal pipes and 4x 90-degree connector elbows, you can connect the pipes into a closed loop. Then you cut out a section of pipe and insert a water pump. Finally you cut out three or four other sections of pipe randomly along the closed loop, and you insert water pressure meters in each of these places, you the water pressure should read the same psi at all of the water pressure gauges, regardless of how far away from the pump's output they are located. Is that what you are saying?

The way to understand electricity is by using system (two effects) energy analogies like between gravitational PE per kilogram of water and electrical PE per coulomb of charge.
nsaspook... I don't seem to understand your use of the word "system (two effects)." I have also always had a hard time understanding the term "Potential energy". I think I understand the concept. If you have a rock sitting at the edge of a cliff, everyone knows that if you were to push that rock off the cliff, it would fall. So that rock has the "potential" to exhibit energy. But... I think I don't fully understand the term "energy" either then. Because if the rock falls off the cliff, it's potential energy has been converted to kinetic energy (movement). But if you measure kinetic energy, what are you measuring? The the force that the rock is exerting against the air molecules as it falls through the air? The force the rock exerts against the ground when it lands? Is it a measurement of how hard gravity is pulling it downwards as it falls? I think it is imperative that one understand basic potential and kinetic energy of a rock before they can convert that knowledge to understanding electricity.
Likewise, with the water analogy... If you have a fish aquarium that is only 1/4 full of water, as long as it is laying flat there is no kinetic energy within the water (I believe, anyway). But if you raise one side of the tank up 6 inches, the water molecules located at the side that raised will be pulled by gravity into moving towards the lower side of the tank. That analogy confuses me, in that I can only see a case for kinetic energy. If you insert a vertical divider into the water tank that divides it in half between left and right, and then you lift one side of the water tank, I can see then that the divider is holding back the water, so that water now has "potential energy" in that, if you were to yank out the divider, the water would instantly move, i.e. its potential energy would be converted into kinetic energy. But how can you measure something's "potential to move?"

An electron can not flow out of a battery, without an electron flowing into the battery.
BR-549... are you saying that electrons do NOT flow in and out of a battery? If you plug a 9V battery into a circuit do electrons not flow out of it's negative terminal and back into its positive terminal? If they do not, then I really have misunderstood a lot of things about direct current.

flow/current in a electrical circuit does not contain the energy of circuit.
Current is a rate. Correct? 1 Amp describes 1 Coulomb of electrons passing a fixed point every second. amps = (coulombs per second). A watt is a joule every second. One measures force and the other a quantity, right?
 
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BR-549

Joined Sep 22, 2013
4,938
If you understood my post to say that current does not flow........then my comments serve no purpose here.

I wouldn't know how to write any clearer. Rotation is an easy concept for most.

Good luck.
 
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