Current Flow

[GoldDigger]

And yet, in a resistive load the electrons are constantly accelerated by the electric field and then slowed by collisions within the conductor, generating heat....
The "zero electric field" inside a conductor is clearly just an approximation and does not apply when current is flowing.

 

[mivey]

And yet, in a resistive load the electrons are constantly accelerated by the electric field and then slowed by collisions within the conductor, generating heat....

Yes, the conductor is a small load itself.

The "zero electric field" inside a conductor is clearly just an approximation and does not apply when current is flowing.

Of course. Who said there was zero electric field inside the conductor?

The electric field in the conductor is only zero at electrostatic equilibrium (polarization has settled). For charge flow, there is a distribution of surface charges yielding a voltage gradient that makes the charges move. I have discussed this before and a complete discussion can be found in the physics text "Matter & Interactions" by Chabay and Sherwood.

 

[jason619]

The best non-electrical analogy is the pump and pipes.
The source of pressure (analogous to voltage) pushes water down the pipes. The flow is current.
More pressure from the pump results in more flow, all other things being equal.

So the pump(which is the voltage source) pushes the water(electrons) through the pipe.
so all the electrons which are being pushed come back to source and this process is repeated 60 times
in one second..am i correct here?

 

[Smart $]

So the pump(which is the voltage source) pushes the water(electrons) through the pipe.
so all the electrons which are being pushed come back to source and this process is repeated 60 times
in one second..am i correct here?

To answer this question, I have to rescind my honoring of Charlie's request, as noted at that time... though I will try to avoid a technical discussion of drift velocity.

Several parameters of the closed-loop system will determine what water molecules (electrons) actually return to the pump (voltage source). Water molecules (electrons) fill the piping (wire) at all times. As molecules exit the pump, molecules enter the pump. The molecules exiting and entering are different molecules. The parameters?pressure, pipe size and length, restrictions (impedance), etc.? determine whether any molecules which exit the pump actually return to the pump during each cycle.

Jumping to the electrical side, in most cases other than extremely high current and small, short wires, the actual electrons (if you could manage to label each and every one) leaving the voltage source (pump) do not return to the voltage source within each cycle. This is analogous to water molecules leaving the pump at the end of a cycle must remain in the pipe to maintain its full-of-water status.

 

[Besoeker]

So the pump(which is the voltage source) pushes the water(electrons) through the pipe.
so all the electrons which are being pushed come back to source and this process is repeated 60 times
in one second..am i correct here?

For AC, they shuffle back and forth a bit. Actually, a very little bit.

And it's pretty much irrelevant for understanding control circuits.

 

[Sahib]

Not enough mass to get it done.
Even if for some strange reason we would group the energy stored in the magnetic field with the moving electron QM mass (and ignoring that for other type conductors we have charge carriers that display less QM type behavior than electrons), we have left out the energy stored in the electric field.

Why?
Consider Einstein equation:Energy=Mass*constant. So if an electron is given an amount of energy, be it magnetic or electric, there is a corresponding increase in mass.

The energy propagates through the field connected to the electrons. It does not move along with the electron and thus does not move along with the current.

The field does not move in step with current. Each moves at different speeds along the conductor with rate of change of electrons mass equaling the field speed and heat release along the conductor.

 

[mivey]

So the pump(which is the voltage source) pushes the water(electrons) through the pipe.
so all the electrons which are being pushed come back to source and this process is repeated 60 times
in one second..am i correct here?

For AC, they shuffle back and forth a bit. Actually, a very little bit.

And it's pretty much irrelevant for understanding control circuits.

Jason,

For AC, think of a rope saw where you just saw back and forth while the blade in the middle makes the cut. The rope does not traverse a loop but just moves back and forth like a jig saw but the energy from your hands still gets delivered to the load (the saw on the limb).

With AC, the electrons wiggle back and forth but don't actually traverse the loop. The energy stills gets delivered to the load.

 

[mivey]

Why?
Consider Einstein equation:Energy=Mass*constant. So if an electron is given an amount of energy, be it magnetic or electric, there is a corresponding increase in mass.

Charlie,
Do you see the problem now with making electrons race around the circuit at the speed of energy delivery? People just get things like that in their mind and can't seem to get away from trying tie the energy to the electron. It is just cementing bad fundamentals.

Sahib,
Don't forget the electric field is involved as well.

If we have a crowd of people crowd-surfing a large object overhead do we increase the people's mass accordingly? Do you think the electrons in a wave guide increase their mass to equal the EM wave traveling through? What electrons are present to carry the energy when the EM wave is traveling through the vacuum of space?

If we pick up an EM wave with an antenna, run the signal through some wires for measurement or whatever, then send it out the other end through another antenna the wires are just acting like a wave guide. Why do you feel the need to increase the electrons mass to somehow equate the energy to a particle?

The field does not move in step with current.

So you agree there is no need for an analogy of electrons racing around a circuit at near light speed.

Each moves at different speeds along the conductor with rate of change of electrons mass equaling the field speed and heat release along the conductor.

Just do the math and see how that works out for you.

 

[GoldDigger]

Charlie, I find it simplest to accept that energy (not necessarily "electrical" energy) can be carried by the Newtonian motion of charged particles in an electric field, and that energy can also be moved great distances by neutral particles with no rest mass (photons).
I will not accept trying to force one mechanism into handling both.