Where Do Electrons Come From in DC Generated Current?

[yoga face]

in DC there is a movement of electrons

IE in a battery there is an excess of electrons chemically stored in one end that desire to travel to the other side of the battery where there are a shortage of electrons

where do the electrons come from in a DC generated current ?

if electrons do not travel down the line to the resistance in generated DC is this not AC ?

 

[Dundeephysics]

What do you mean by DC generated current? a battery current?

AC is the movement of electrons through a resistance in an alternating manner, unlike in DC where electrons move in one direction.

I think you need to have an understanding of AC and DC.

 

[CWatters]

where do the electrons come from in a DC generated current ?

A DC generator doesn't need to create a bucket full of "new" electrons. Metal atoms readily give up their outer shell electrons. The generator just needs to push these so called "free" electrons around.

Consider a central heating system. That has a pump which circulates water around the system from the boiler (called a kettle in some countries) to the radiators. The pump doesn't need to create "new" water it just pumps water already in the pipes around.

 

[yoga face]

A DC generator doesn't need to create a bucket full of "new" electrons. Metal atoms readily give up their outer shell electrons. The generator just needs to push these so called "free" electrons around.

Consider a central heating system. That has a pump which circulates water around the system from the boiler (called a kettle in some countries) to the radiators. The pump doesn't need to create "new" water it just pumps water already in the pipes around.

understood

what i do not understand is the following

there was a great debate among Edison and others as to what electricity Niagara falls should produce (AC or DC)

AC won out because it loses less power in the transmission of it down the wires (energy loss comes mostly through heat loss which is why they cannot bury transmission wires as they would catch on fire)


If they had decided to produce DC where were the electrons going to come from that moved down the current ? Would there have to have been a complete circuit bringing the electrons back to the generating plant at Niagara ?

thx

 

[CWatters]

If they had decided to produce DC where were the electrons going to come from that moved down the current ?

DC vs AC it makes no difference.

The electrons would come from the metal wire. See my previous reply.

Would there have to have been a complete circuit bringing the electrons back to the generating plant at Niagara ?

Yes but again that has nothing to do with AC vs DC. A return path is needed for BOTH.

The planet Earth can be used for the return path.

 

[nsaspook]

If they had decided to produce DC where were the electrons going to come from that moved down the current ? Would there have to have been a complete circuit bringing the electrons back to the generating plant at Niagara ?

thx

They would come from the same place they do in a AC circuit, the wiring.

http://www.physicsclassroom.com/Class/circuits/u9l2e.cfm

 

[yoga face]

DC vs AC it makes no difference.

The electrons would come from the metal wire. See my previous reply.



Yes but again that has nothing to do with AC vs DC. A return path is needed for BOTH.

The planet Earth can be used for the return path.

Mr watters i am lost

In a DC battery there are excess electrons at one end and a negative supply at the other

when the circuit is complete the electrons flow from excess supply to negative supply

when they have established equilibrium the battery is "dead"

how would this "flow" of electrons happen if Niagara Falls produced DC?


the way i understand it the electrons in AC come from the metal in the wire (as you pointed out) but they do not flow through the wire they agitate back and forth as the generator changes north pole to south pole agitating the electrons


in DC the electrons flow from one atom to the next (in AC they stay in their original orbit) so there has to be a starting point for the electron

once having left its starting point it needs to be replaced so we need an excess of electrons or a circuit that returns the electrons



where in my thinking am i wrong?


thx

 

[CWatters]

Go back to the central heating model I posted earlier..

DC - the pump runs in one direction all the time.
AC - the pump changes direction at regular intervals.

In neither case does there need to be new water added to the pipework, nor an "excess of water". Nor does there need to be a "starting point".

It's also wrong to think of electrons as flowing all the way around a circuit. Even for DC it's best to imagine it as a queue of electrons. When you push the first one in the queue a wave travels down the line until the one at the end moves. It appears as if one electron has made the trip but that's not the case. Only the wave has made the trip. The waves moves very fast but electrons actually move quite slowly down the wire - it varies but it's on the order of mm per second.

 

[CWatters]

In a DC battery there are excess electrons at one end and a negative supply at the other

There isn't a huge pile/excess of electrons sitting in the battery ready to go. Think of it as a chemical reaction that's capable of generating electrons one at a time. There is a limit to how fast the chemical reaction can go and that limits how much current the battery can deliver.

 

[yoga face]

Go back to the central heating model I posted earlier..

DC - the pump runs in one direction all the time.
AC - the pump changes direction at regular intervals.

In neither case does there need to be new water added to the pipework, nor an "excess of water". Nor does there need to be a "starting point".

It's also wrong to think of electrons as flowing all the way around a circuit. Even for DC it's best to imagine it as a queue of electrons. When you push the first one in the queue a wave travels down the line until the one at the end moves. It appears as if one electron has made the trip but that's not the case. Only the wave has made the trip. The waves moves very fast but electrons actually move quite slowly down the wire - it varies but it's on the order of mm per second.

thx

i am starting to understand

i just read where actual electron movement down the line is called "drift flow" and is very, very slow

it is the excitment of electrons that travels quickly because of the potential difference between the ends of the circuit

however, there is some movement down the line of electrons in DC where

these electrons move into the orbit of another atom (unlike AC where the stay in the same orbit) but unlike AC there is a "drift flow" down the line so do they not have to be replaced?

 

[yoga face]

There isn't a huge pile/excess of electrons sitting in the battery ready to go. Think of it as a chemical reaction that's capable of generating electrons one at a time. There is a limit to how fast the chemical reaction can go and that limits how much current the battery can deliver.

ok

there is a potential difference between the ends of the battery ie the ability to excite the electrons into movement with an electronic signal

when the circuit is turned on an electric signal travels at the speed of light charging the electrons(the charge itself does not travel)

 

[Drakkith]

however, there is some movement down the line of electrons in DC where

these electrons move into the orbit of another atom (unlike AC where the stay in the same orbit) but unlike AC there is a "drift flow" down the line so do they not have to be replaced?

Not true. Individual atomic orbitals have little to nothing to do with this. In a solid metal the moving electrons all occupy the conduction band (which is shared by the entire metal) and easily flow everywhere throughout the metal. This happens in both AC and DC circuits. The only difference is that AC circuits alternate the polarity of the voltage and thus the direction of current.

ok

there is a potential difference between the ends of the battery ie the ability to excite the electrons into movement with an electronic signal

when the circuit is turned on an electric signal travels at the speed of light charging the electrons(the charge itself does not travel)

To understand how batteries work you would need to understand the chemical reaction taking place inside it. I leave that to someone more experienced that myself.

 

[yoga face]

Not true. Individual atomic orbitals have little to nothing to do with this. In a solid metal the moving electrons all occupy the conduction band (which is shared by the entire metal) and easily flow everywhere throughout the metal. This happens in both AC and DC circuits. The only difference is that AC circuits alternate the polarity of the voltage and thus the direction of current.

then please explain this

"You never need to replace electrons because they always come back.
This is why you need two prongs on a plug for it to work. Electrons go in one and out the other. Passing through the device is what allows energy to be transferred."

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College here Dr Mellendorf states electrons flowing down the line (from high to low potential difference I presume) is what causes electricity to do its work does he not?
clearly i am not well anointed in physics and greatly admire those who are

 

[nsaspook]

here Dr Mellendorf states electrons flowing down the line (from high to low potential difference I presume) is what causes electricity to do its work does he not?

No wonder you are confused.
http://www.ratemyprofessors.com/ShowRatings.jsp?tid=405572
http://www.Newton.dep.anl.gov/askasci/phy00/phy00989.htm

 

[yoga face]

i am trying real hard "The electrons do indeed flow. When the circuit is closed, an electric field is set up in the entire wire from the generating plant to the user and back again on another wire -- a closed circuit is required! A wire is a conductor precisely because some of the electrons are free to move when pushed by an electric field.

The closed circuit is required so the electrons can flow in a closed circuit; no electrons are lost! "

Dick Plano, Professor of Physics emeritus, Rutgers University so you do need a complete circuit

grounding will not suffice (is Plano referring to DC or AC or both?) is the circuit needed to capture drift ( electron flow down the line )?

is it the charge of each electron that transfers energy to the resistance?

When an electron transfers energy does it lose its charge? then recapture it from the potential difference? i am getting contradictory answers but i suspect this is because each answer by itself is an incomplete picturecheers

 

[nsaspook]

i am trying real hard

i am getting contradictory answers but i suspect this is because each answer by itself is an incomplete picture

cheers

I know you are and it really is a shame that you have to.
You might start here for a fresh start with good answers: http://amasci.com/miscon/eleca.html#cflow
http://amasci.com/miscon/elect.html

 

[tiny-tim]

Yes but again that has nothing to do with AC vs DC. A return path is needed for BOTH.

The planet Earth can be used for the return path.

does the Earth act as a wire that is part of the circuit, or as a capacitor inserted into the circuit?

 

[yoga face]

I know you are and it really is a shame that you have to.
You might start here for a fresh start with good answers: http://amasci.com/miscon/eleca.html#cflow
http://amasci.com/miscon/elect.html

thx a bunch my preconceptions are wrong (thank the public schools )have i got this right in your link it is stated

"A battery can send electric energy to a light bulb, and the bulb changes electrical energy into light. "

so what is energy?

Energy is Charge * Voltage. correct?

You need both the current flow and the voltage differential for the bulb to light up.

Also

the magnetic fields contain the energy, however they will not light something up until a potential change (voltage) in the field takes place.

In short, energy causes the filament to light up, however one of the components of electrical energy is the existence of charge flow (current).

so what kills you the energy (charge flow ie current * voltage ie potential diffeence) in the electro magnetic field or is it the current (charge flow) alone and separate from the energy ?

in the link he says "When lightning strikes , the spreading electric currents in the ground can kill anyone standing nearby"

he does not say the current times voltage (energy) kills youcheers

 

[Naty1]

In some commercial power systems, the return [negative] path is earth...in others it is ground wires..in either case the electric potential moves electrons along a CLOSED circuit..a continuous path.

Energy is Charge * Voltage. correct?

ok...
But CHARGE is not current flow...current flow is ' i'...or 'I'...

...POWER is current times voltage: P = IE, and charge, Q, is IT

You need both the current flow and the voltage differential for the bulb to light up.

exactly...

In short, energy causes the filament to light up, however one of the components of electrical energy is the existence of charge flow (current).

Close, but you again have energy and power mixed up. POWER causes the filament to light.
WATTS, for example, a common measure of bulb strength, is a measure of POWER. Power is energy per unit time.

 

[yoga face]

In some commercial power systems, the return [negative] path is earth...in others it is ground wires..in either case the electric potential moves electrons along a CLOSED circuit..a continuous path.

tremendous NATY

getting the concepts is tricky for a Canadian from the country

one more

in commercial power stations the power is AC

in AC i thought electrons move back and forth while staying within their own orbit (unlike DC where you do have drift) negating the need for a return wire whose job it is to return the electrons that have drifted

if the power station produced DC (which can easily be done) then you would need a return wire(by ground wire do you mean return wire that goes back to the power plant to complete the circuit?)cheers from Canada

 

[Drakkith]

in AC i thought electrons move back and forth while staying within their own orbit (unlike DC where you do have drift) negating the need for a return wire whose job it is to return the electrons that have drifted

Get rid of this idea of electrons in 'orbits'. The electrons within the metal that move are NOT bound to individual atoms. They are bound to the material as a whole. If they were bound to individual atoms, the resistance would be extremely high, as in an insulator.

See the following link: http://en.wikipedia.org/wiki/Conduction_electron
And here: http://en.wikipedia.org/wiki/Electrical_conduction#Band_theory_simplified

if the power station produced DC (which can easily be done) then you would need a return wire(by ground wire do you mean return wire that goes back to the power plant to complete the circuit?)


cheers from Canada

You need a return path for both AC and DC. You CAN do this with the Earth itself, and it is indeed done in certain situations, but you almost always have a metal wire running from the generators, out to the distribution system, and then back again to complete the circuit.

 

[Naty1]

Draakith posts

You need a return path for both AC and DC. You CAN do this with the Earth itself, and it is indeed done in certain situations, but you almost always have a metal wire running from the generators, out to the distribution system, and then back again to complete the circuit.

yes.
If you look in an electrical outlet in a home in the US, you'll find standard color wiring:

Black is 'hot', say plus 120 volts,..that's the one which may SHOCK you directly.

white is 'neutral'...actually the return wire,

and is also connected to ground in your fuse or circuit breaker main electrical panel.

green is ground for safety...it does NOT normally carry any current.

For a 240 volt circuit, in addition to the above, is a second 'hot' wire which is red.

 

[anorlunda]

It may help you to consider that for each half cycle (1/120 th of a second), even AC systems are DC. By that I mean the current flows in only one direction for the half cycle. Even within that frame, no electrons a are crated or destroyed. Electrons flow put of the negative terminal and other electrons are pushed into the positive terminal instan try instant.

Try thinking of only one millisecond. Within that time, there is no difference between AC and DC, yet Ohm's Law still applies. E=I*R Also, within a milliseconds there is no appreciable electron drift. The queue analogy works well. The source pushes some electrons into the negative terminal and at the apsame time the closed circuit pushes other electrons into the positive terminal. Think of the queue as a pipe full of ping pong balls.

 

[tiny-tim]

Try thinking of only one millisecond. Within that time, there is no difference between AC and DC, yet Ohm's Law still applies. E=I*R

only for pure resistors, of course (ie, not capacitors or inductors)

 

[yoga face]

Draakith posts
yes.
If you look in an electrical outlet in a home in the US, you'll find standard color wiring:

Black is 'hot', say plus 120 volts,..that's the one which may SHOCK you directly.

white is 'neutral'...actually the return wire,

and is also connected to ground in your fuse or circuit breaker main electrical panel.

green is ground for safety...it does NOT normally carry any current.

For a 240 volt circuit, in addition to the above, is a second 'hot' wire which is red.

what is in the return white wire?

an electomagneic field wth no energy waves?

has not the energy of the electromagnetic waves been used by the resistance?is there any difference between ac and dc electron drift ?

 

[Drakkith]

what is in the return white wire?

an electomagneic field wth no energy waves?

I'm not sure, but I think the labeling of "hot" and "return" is just a matter of convenience so you know which wire is which. Both wires have full current flowing through them.

has not the energy of the electromagnetic waves been used by the resistance?

It has been consumed by the load and the circuit and turned into either work or heat.

is there electron drift in AC ?

Of course, it just alternates back and forth at the frequency of the circuit. In mains power lines in the U.S. that would be 60 hz.

 

[yoga face]

It has been consumed by the load and the circuit and turned into either work or heat.

then is the ground wire safe to touch if the energy has been used by the resistance?

 

[Drakkith]

then is the ground wire safe to touch if the energy has been used by the resistance?

NEVER touch part of the circuit unless you are certain the power has been removed. If there is a fault the current is routed to ground through the ground wire.

 

[yoga face]

NEVER touch part of the circuit unless you are certain the power has been removed. If there is a fault the current is routed to ground through the ground wire.

THX FOR THE WARNING but in theory can the return or grounded wire be touched because the resistance has used up the energy of the electromagnetic waves ?

double cheers from Canada

 

[Drakkith]

THX FOR THE WARNING but in theory can the return or grounded wire be touched because the resistance has used up the energy of the electromagnetic waves ?

double cheers from Canada

No, but I'm not sure I have the required knowledge to explain why. The following is my attempt to figure it out for myself and I don't guarantee that it is correct or accurate.I THINK it may be because there is no potential difference between the ground wire and the return wire since the live wire isn't connected to ground. (Otherwise you'd have a parallel circuit) If you were to connect a ground wire to the live wire as well as the return wire, current may begin flowing through both ground wires as a path has been created through the ground itself.

Imagine a battery with a single resistor connected between the two terminals. Take a piece of wire and connect it to the negative side and then connect the other end to ground. Current doesn't flow from the ground to the negative terminal because then you would have more current leaving the positive terminal and moving through the circuit than there is entering the negative terminal through that circuit. In other words, total current leaving the positive terminal would be less than the total current entering the negative terminal, as you would add the total current of the circuit PLUS the current of the ground wire. Obviously this cannot happen, as current leaving the positive terminal and entering the negative terminal must be equal, so there must be zero current flowing through the ground wire. Since there is zero current flowing through the ground wire, the voltage drop across it is zero and you cannot be shocked by it.

Similarly, current flowing through the live and return wires MUST be equal (unless there is a fault), so no current can flow through the ground wire as that would increase the current in the return wire. Again, since no current is flowing there must be zero voltage drop and zero potential difference. Therefore no shock.

Anyways, I hope that makes sense and I hope that's correct, but again I'm not 100% sure.