How does the electric field propagate in a circuit?

[pardesi]

how does an electron 'flow' in a circuit ...can someone please explain me the detailled mechanism ...

 

[member 11137]

So far I understand applied physics, when you close the electrical circuit (you switch on the light), you create a difference of potential (given by the generator) and you create a polarization that can be strong enougth to expulse electrons; these electrons propagates and create a polarization in their neightborought and so and... Perhaps someone else can explain quite better than me the mechanism at atomic level.

 

[pardesi]

thanks but i really want an atomic level explanation

 

[russ_watters]

That was an atomic level explanation! What part are you confused about?

 

[pardesi]

can't it be more detailled?as to how when connected toa battery the electrons start flowing?

 

[ice109]

can't it be more detailled?as to how when connected toa battery the electrons start flowing?

there's a voltage potential between the negative and positive termal of the battery. if you want to know how a battery makes a voltage potential look up electrolytic cells.

 

[pardesi]

no problem with battery functioning but i want an explanation on the bais of field not potential concept

 

[ranger]

If you have two parallel plates; one plate more negative than the other. We have an electric field. Its direction is determined by the direction a positive test charge will move. What would happen if you drop a negative test charge in between the plates? Remember that since the plates are not at the same potential, there also exist a potential difference and cloumbic interactions.

You will notice that an electric potential difference and an electric field go hand in hand in this situation.

http://www.tpub.com/neets/book10/39i.htm

 

[pardesi]

well i still don't get it why do the elctrons ever move insid ethe wire..if it is due to the field due to battery or any other source then that should depend on orientataion of wire...so what actually does make the electron move

 

[russ_watters]

What you are saying seems to imply you think there is a field emitted by the cell that directly pushes on electrons in wires, so if a wire looped back toward the cell, it would push the electrons backwards. That's not how it works. Each electron is pushed by the electrons sitting next to it.

 

[Doc Al]

surface charge gradient along the wire

well i still don't get it why do the elctrons ever move insid ethe wire..if it is due to the field due to battery or any other source then that should depend on orientataion of wire...so what actually does make the electron move

What happens is that as soon as you hook up the wire to the battery, electrons move onto the surface of the wire at one end (and off of the wire surface at the other end), just as they would on any conducting surface. A small charge gradient is quickly built up along the surface of the wire, which creates the electric field within the wire that drives the current.

I don't think it's useful (or accurate) to think of the electrons in the wire as pushing each other along. Any repulsion between the moving electrons is balanced by an attraction to the positive lattice--the average net charge on a small volume within the wire is zero.

 

[pardesi]

thank u all

 

[rcgldr]

There are free electrons bouncing around almost randomly at high speed, with a slow net component of velocity in the direction of electron "flow". The negative end of the energy source supplies the free electrons, while the positive end absorbs them.

 

[robphy]

Possible interesting reading and viewing:

http://www4.ncsu.edu/~rwchabay/mi/circuit.pdf
from http://www4.ncsu.edu/~rwchabay/mi/mi_docs.html

http://galaxy.cofc.edu/circuits.html
http://galaxy.cofc.edu/rcircuits.html

 

[Doc Al]

Good links, robphy! I hope pardesi reads the first one as it states clearly what goes on in a circuit. (And what I had tried to summarize.)

I remember reading some excellent pedagogical articles by Sherwood several years ago regarding pseudowork versus "real" work. (Confusing those two is one of my pet peeves.)

 

[pardesi]

robphy thanks they are really wonderful
@Doc Al yes indeed i will go through the first just got a glimpse of it


u all have been wonderful this has been bugging me for a time
yet again thanks

 

[ice109]

why doesn't it suffice to say that the field is conducted by the wire? propagated by the electrons themselves, if i am correct the first article robphy posted implies that the field from a capacitor propagates through air, impinges on parts of the circuit and induces a charge distribution on parts of the circuit? that seems extremely silly to me.

 

[Emanresu]

What happens is that as soon as you hook up the wire to the battery, electrons move onto the surface of the wire at one end (and off of the wire surface at the other end), just as they would on any conducting surface. A small charge gradient is quickly built up along the surface of the wire, which creates the electric field within the wire that drives the current.

Doc Al, I always thought that the field in a circuit propogated at c such that a bulb many kilometers away from a switch would turn on almost instantly. Can the gradient you talk about really propagate that fast ?

E.

 

[Doc Al]

Doc Al, I always thought that the field in a circuit propogated at c such that a bulb many kilometers away from a switch would turn on almost instantly. Can the gradient you talk about really propagate that fast ?

Yes, this redistribution of charge takes place very quickly. Realize that charges don't need to travel the length of the wire, they just have to shift a bit to create the electric field.