Does anyone know why there are these + - two symbols at the two ends of a power source?
Does it mean that one side has a deficiency and the other an excess of electrons?

 

Exactly so.. the -ve has excess electrons, and they (conceptually) flow round to the +ve - contrary to 'conventional' current flow from + to -. Confusing huh?!


Welcome to AAC btw,

 

"Conventional current" flow (+ to -) was established long before it was recognized that current is a flow of electrons from - to +.

 

Not necessarily so. Think of electric current as marbles in a tube.



Electricity is the motion of electrons along a conducting material. Electrons don't move very fast, about 2cm per hour. When one electron moves, another one follows behind to take its place. Hence, no, there is not an excess of electrons in one place and a deficiency in another.

They move because there is an electric field that pushes them along. The positive sign says that that part in the circuit is at a higher potential than the part with the negative sign. This is by convention. It is similar to why England is north of the equator and Australia is to the south. This is simply conventional.

 

Hmmm, how do you explain the charge on plates of a capacitor - is not the electric field the result of one plate having an excess and the other a deficit?

 

Not necessarily so. Think of electric current as marbles in a tube.

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Electricity is the motion of electrons along a conducting material. Electrons don't move very fast, about 2cm per hour. When one electron moves, another one follows behind to take its place. They move because there is an electric field that pushes them along.
Hence, no, there is not an excess of electrons in one place and a deficiency in another.

Tell that to a battery or capacitor.

The OP was asking about a source not a conductor.

 

Does anyone know why there are these + - two symbols at the two ends of a power source?
Does it mean that one side has a deficiency and the other an excess of electrons?

Basically, but the amount of charge that is separated is miniscule. What it really means is that positive work will done on a positive charge as it moves from the positive terminal through some external path to the negative terminal. Conversely, positive work will also be done on a negative charge as it moves from the negative terminal to the positive terminal.

 

Hmmm, how do you explain the charge on plates of a capacitor - is not the electric field the result of one plate having an excess and the other a deficit?

Yes, but he was asking about a power source, not a capacitor. How do you explain a DC generator? Does it have an excess of electrons on the negative terminal?

 

This discussion could go a lot of different directions.

Such as...is a generator actually a power source or is the actual power source what is turning the generator?

But I agree with the idea that there is little or no charge separation at the terminals of a generator,

 

Basically, but the amount of charge that is separated is miniscule. What it really means is that positive work will done on a positive charge as it moves from the positive terminal through some external path to the negative terminal. Conversely, positive work will also be done on a negative charge as it moves from the negative terminal to the positive terminal.

I have a question.

How does positive charge and negative charge get past each other on the way to their respective destinations?

 

I have a question.

How does positive charge and negative charge get past each other on the way to their respective destinations?

Is that a rhetorical question?

You’ve heard of holes? Whether or not they actually exist, positive is the absence of electrons. There are not two physical “charges” that need pass by each other. Yes, there are protons, but as long as we’re not talking about an atom bomb, I think they pretty much stay put.

 

I have a question.

How does positive charge and negative charge get past each other on the way to their respective destinations?

That is where the conversion from some other form of energy to electrical potential energy comes in.

In a typical chemical battery, it is a diffusion process in which positive and/or negatively charged ions diffuse from a region of higher concentration to lower concentration. Conceptually very similar to the diffusion of electrons and holes across a PN junction. As the diffusion action produces a charge separation, that separation produces an electric field that is trying to draw them back where they came from. At some point (almost instantly) an equilibrium is established and the chemical reactions producing the ions stops. As electrons exit the negative terminal and other electrons enter the positive terminal due to the external circuit connected between them, the electric field within the cell diminishes and the chemical reaction once again can produce the ions that then diffuse and reach an equilibrium again.

 

I wasn't speaking of battery chemistry, I was talking about these 2 opposite charges getting past each other in a conductor as implied in post #7.

 

I wasn't speaking of battery chemistry, I was talking about these 2 opposite charges getting past each other in a conductor as implied in post #7.

Where was that implied at all? All I stated is the definition of what a voltage difference is. There is NOTHING in that statement that implies that opposite charges are getting past each other in a conductor.

 

Ok, you did say "external path" not conductor.

 

Ok, you did say "external path" not conductor.

I also did not say that there was any requirement for both types of charge to be flowing at the same time. Either by itself is perfectly acceptable (and would be the case the vast majority of the time).

 

you will find this site is a great place to ask questions. I am one of those people that believe there are no stupid questions. Do you know what a DVM is?

 

Does anyone know why there are these + - two symbols at the two ends of a power source?
Does it mean that one side has a deficiency and the other an excess of electrons?

Perhaps y'all in your ongoing debate are addressing something well beyond the intent of the question (not that that EVER happens here).

+ (plus) is the positive terminal of the power supply.

– (minus) is the negative terminal of the power supply.

 

I have a question.

How does positive charge and negative charge get past each other on the way to their respective destinations?

Hi,

This is possible but mostly only in theory. The reason for this is just so we can calculate things sometimes. The net algebraic sum is actually what would really 'flow' in a wire.
For example, if you have 3 to the right and 1 to the left, there is a net flow of 2 to the right, or a net flow of -2 to the left.
You can assign signs if you like. If you have 3 to the right and -1 to the left, there is a net flow of 4 to the right, or a net flow of -4 to the left.

 

Forget the question...Apparently, I don't know how to read and understand English.