current flow concept

[John Frum]

My simple understanding is in a dc circuit current flows out the positive terminal of charge source and back to the negative terminal of the same charge source.
If... the voltage is sufficient to overcome the resistance along the path.
If the path is air the resistance if relatively high.
If the path is copper the resistance is relatively low.
Is it conceptually valid to imagine the charge source sucking up electrons on the negative terminal?
Like negative pressure?

 

[dgjonesy]

Conventional current flow is positive charge flowing from the positive terminal (cathode). For metals this is equivalent to electrons (negative charges) flowing into the positive terminal. A good overview is here

 

[Pierre]

Electricians prefer conventional current flow i.e from +ve to -ve. Electronics guys like myself understand electron flow better as an electron is negatively charged and it is attracted to +ve terminal.

 

[John Frum]

Conventional current flow is positive charge flowing from the positive terminal (cathode). For metals this is equivalent to electrons (negative charges) flowing into the positive terminal. A good overview is here

ok so the positive terminal is sucking up electrons?

 

[dgjonesy]

ok so the positive terminal is sucking up electrons?

Yes you are exactly correct.
The positive terminal is attracting or sucking up negatively charged electrons.

 

[John Frum]

Yes you are exactly correct.
The positive terminal is attracting or sucking up negatively charged electrons.

So voltage is suckage? :D

 

[dgjonesy]

So voltage is suckage? :D

Yes kinda like the earth sucking you in

 

[upnorthandpersonal]

One thing to keep in mind in all of this is that the actual electrons move very slowly (drift velocity), in the order of millimeters per second. What actually happens is that through the electromagnetic field, energy is transferred close to light speed. This is what Maxwell's theory is about.

 

[John Frum]

and the energy is flowing from positive to negative but the electrons are flowing from negative to positive?

 

[upnorthandpersonal]

Actually, the energy is flowing from both directions if you look at the Poynting vector.

 

[John Frum]

I'm saying OK and backing away slowly

 

[Pierre]

Actually, the energy is flowing from both directions if you look at the Poynting vector.

Do not get too technical for us mere mortals Theoretical physics is not in my wheelhouse.

 

[dgjonesy]

I'm saying OK and backing away slowly

As I am a simple minded person, I can offer a simple analogy :

Electrons are moving to a state of lower potential energy much like a ball rolling down a hill.

 

[Pierre]

Yes you are exactly correct.
The positive terminal is attracting or sucking up negatively charged electrons.

Now for further confusion : As the electrons move they leave a +ve 'hole' behind so electrons flow from -ve to +ve and the holes flow in the opposite direction which is conventional current flow

 

[upnorthandpersonal]

Physics and math time, yay!

The Poynting vector for a simple DC power source and a resistive load with ideal conductors looks as follows:

S = (1/μ0) (ExB)

Where μ0 is the permeability and E and B the Electric and Magnetic components of the EM field respectively. If you draw this out for a simple circuit (and using conventional current), you get this:

​

As you can see, the Poynting vector at every point in the circuit is directed to the resistor from the source. This makes sense if you think about it: energy only goes from source to destination, it doesn't come back. It is transformed into e.g. heat in the resistor.

You can actually derive the commonly known P=RI^2 formula from this principle as well, but I'll leave that as an exercise to the reader

 

[Pierre]

Physics and math time, yay!

The Poynting vector for a simple DC power source and a resistive load with ideal conductors looks as follows:

S = (1/μ0) (ExB)

Where μ0 is the permeability and E and B the Electric and Magnetic components of the EM field respectively. If you draw this out for a simple circuit (and using conventional current), you get this:

View attachment 10471
​

As you can see, the Poynting vector at every point in the circuit is directed to the resistor from the source. This makes sense if you think about it: energy only goes from source to destination, it doesn't come back. It is transformed into e.g. heat in the resistor.

You can actually derive the commonly known P=RI^2 formula from this principle as well, but I'll leave that as an exercise to the reader
I will wrestle with this tonight and report back tomorrow before Lesson #2

 

[John Frum]

On point with animation

 

[erik.calco]

So voltage is suckage? :D

There is actually no such thing as suckage, except in very old professions. A vacuum when opened to high pressure molecules gets filled because the high pressure molecules are in motion and basically push each other into the vacuum, like a crowd dispersing.

Not sure how to apply that to electrical theory, though I've heard voltage described as a force or pushing. Every time I read up on it it begins about how wrong we were, then how less wrong we were. So, you can only wonder how wrong we are.

 

[John Frum]

There is actually no such thing as suckage, except in very old professions. A vacuum when opened to high pressure molecules gets filled because the high pressure molecules are in motion and basically push each other into the vacuum, like a crowd dispersing.

Not sure how to apply that to electrical theory, though I've heard voltage described as a force or pushing. Every time I read up on it it begins about how wrong we were, then how less wrong we were. So, you can only wonder how wrong we are.

Loose analogy on my part. :D

 

[Pierre]

Loose analogy on my part. :D