What make the electrons to move in conductor with current?

[scientist91]

What make the electrons to move in conductor with (direct) current? Is the magnetic field exciting the electrons or what? Please if you know explain deeply.

 

[ZapperZ]

Look at the Lorentz force equation.

F=qE.

E is the electric field provided by whatever power source. So where do you not understand the mechanics here?

If I may make a suggestion. You have a series of rather basic questions that require more than just a question and answer session like this. I strongly suggest you open an intro physics text, such as Halliday and Resnick, or even some high school physics text. Or look at several website that provide really basic intro physics, such as the http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html" website. This is the most effective way to learn stuff systematically, especially on the questions that you have asked a few times on here.

Zz.

 

[Hootenanny]

Firstly, current is the actual flow of electrons or charge. If we take a microscopic view, then we can relate the current (I) to the number of free charge carriers (n), the individual charge of these charge carriers, which in the case of a wire is e, their drift velocity v_d and the cross sectional area thus;

$$I = neAv_d$$

Or more generally we can define the current density $\vec{J} = ne\vec{v_d}$ and represent the current through a surface $\vec{S}$ thus;

$$\int_{S}\vec{J}\cdot d\vec{S}$$

What makes the electrons flow, is not the magnetic field, but the electric field created by the potential difference induced across the conductor (by a battery for example). So roughly speaking when you place a potential across a wire, the electric field at the end of the wire changes, this causes the electrons at the end of the wire to move (recall F = qE). Once these electrons have moved, they change the electric field experienced by the neighbouring electrons, which as a result feel a net force causing them to move, thus again perturbing the field for their neighbouring electrons. This affect is repeated down the whole length of the wire, each electron perturbing the field of its neighbours causing it to move, like a line of dominos. This is the reason why signal transmissions is electric wires are significantly faster than the actual drift velocity of the individual electrons. Although the actual electrons 'drift' relatively slowly, the perturbation in the electric field is transmitted down the wire at virtually the speed of light.

I hope this was helpful

Edit: Zz beat me to it :sad:

 

[scientist91]

Firstly, current is the actual flow of electrons or charge. If we take a microscopic view, then we can relate the current (I) to the number of free charge carriers (n), the individual charge of these charge carriers, which in the case of a wire is e, their drift velocity v_d and the cross sectional area thus;

$$I = neAv_d$$

Or more generally we can define the current density $\vec{J} = ne\vec{v_d}$ and represent the current through a surface $\vec{S}$ thus;

$$\int_{S}\vec{J}\cdot d\vec{S}$$

What makes the electrons flow, is not the magnetic field, but the electric field created by the potential difference induced across the conductor (by a battery for example). So roughly speaking when you place a potential across a wire, the electric field at the end of the wire changes, this causes the electrons at the end of the wire to move (recall F = qE). Once these electrons have moved, they change the electric field experienced by the neighbouring electrons, which as a result feel a net force causing them to move, thus again perturbing the field for their neighbouring electrons. This affect is repeated down the whole length of the wire, each electron perturbing the field of its neighbours causing it to move, like a line of dominos. This is the reason why signal transmissions is electric wires are significantly faster than the actual drift velocity of the individual electrons. Although the actual electrons 'drift' relatively slowly, the perturbation in the electric field is transmitted down the wire at virtually the speed of light.

I hope this was helpful

Edit: Zz beat me to it :sad:

Thank you very much, but I still can't understand . Can u explain simpler than this. Why the electric field makes them move, is it excites the electrons or what? Is the electric field fixed or it is moving with the electrons? Thank you again.

 

[marlon]

Thank you very much, but I still can't understand . Can u explain simpler than this. Why the electric field makes them move, is it excites the electrons or what? Is the electric field fixed or it is moving with the electrons? Thank you again.

When you apply an E-field onto a free electron, this electron will feel a force equal to F=qE (q is the electron charge). Whenever a force is exerted on such a free electron, it will move. To calculate the velocity and trajectory of this electron motion caused by F=qE you need to integrate this equation with respect to time once, to get the velocity and twice , to get the trajectory.

This is basic classical physics. You should study this stuff from a good book like Zz has already told you ! The hyperphysics website can help you as well.

greets
marlon

 

[scientist91]

When you apply an E-field onto a free electron, this electron will feel a force equal to F=qE (q is the electron charge). Whenever a force is exerted on such a free electron, it will move. To calculate the velocity and trajectory of this electron motion caused by F=qE you need to integrate this equation with respect to time once, to get the velocity and twice , to get the trajectory.

This is basic classical physics. You should study this stuff from a good book like Zz has already told you ! The hyperphysics website can help you as well.

greets
marlon

Ok, thank you very much, now I understood it, but why (for ex.) the magnetic field is not exerting force on the electrons?

 

[marlon]

Ok, thank you very much, now I understood it, but why (for ex.) the magnetic field is not exerting force on the electrons?

What magnetic field ? The external applied field onto the electrons is an electric field.

marlon

 

[scientist91]

What magnetic field ? The external applied field onto the electrons is an electric field.

marlon

Yes, but also that electric field creates magnetic field like the magnetic field which is creating electric field.

 

[scientist91]

So how that is going? First the electric field force makes the electrons to move, so did the electric field moves with the electron together?

 

[Manchot]

For direct current, the time derivative of the electric field is zero (by definition). Therefore, there is no displacement current, and the only source of magnetic field is the current itself.

 

[marlon]

Yes, but also that electric field creates magnetic field like the magnetic field which is creating electric field.

But that is why i asked you about the magnetic dipole thing. Why did you not answer to my question ?


The electric field does not generate a magnetic field, the electron current DOES, as described by the laws of Maxwell. Do you know these laws ? Do you know the concept of displacement current etc etc ?

You need to study those introductory concepts.


marlon

 

[scientist91]

Can somebody explain how does the current is gained with electromagnet induction and what happens inside of the conducor when you move the magnet among the conductor? Thank you very much. Please if you can explain with simpler words and simpler text.

 

[The_Thinker]

I think what your fundamentally asking is... if the electricity is electrons moving... then "What is voltage?" Well think about it this way.. the magnet moves, because of this relative motion between the magnets and the electrons, the electrons feel a force. Dictated by the laws that are fundamentally stated in any intro physics textbook. These laws dictate the movement of electrons in the conductor.

Now... since the electrons feel this force and move from their native atoms, there is now a deficiency of electrons in that atom, so.. the atom becomes +ve. So... now there is a potential difference between this atom and the neighboring atoms. This is the potential or voltage... Now... you move enough of these little critters away, then the force becomes more profound.

As to why these forces themselves exist, well they are fundamental forces and that's how nature works, or at least that's what we have observed..

If you are still interested in knowing why!? then your out of luck... physics hasn't even finished "completely" explaining the how yet, so the why!? is a question for when the hows been solved..

So, I hope this explains it...

But.. I am not sure of this explanation completely yet, tried finding these answers myself, this is the explanation i came up with...
so... Hmmmmm... Am I right?

 

[scientist91]

I think what your fundamentally asking is... if the electricity is electrons moving... then "What is voltage?" Well think about it this way.. the magnet moves, because of this relative motion between the magnets and the electrons, the electrons feel a force. Dictated by the laws that are fundamentally stated in any intro physics textbook. These laws dictate the movement of electrons in the conductor.

Now... since the electrons feel this force and move from their native atoms, there is now a deficiency of electrons in that atom, so.. the atom becomes +ve. So... now there is a potential difference between this atom and the neighboring atoms. This is the potential or voltage... Now... you move enough of these little critters away, then the force becomes more profound.

As to why these forces themselves exist, well they are fundamental forces and that's how nature works, or at least that's what we have observed..

If you are still interested in knowing why!? then your out of luck... physics hasn't even finished "completely" explaining the how yet, so the why!? is a question for when the hows been solved..

So, I hope this explains it...

But.. I am not sure of this explanation completely yet, tried finding these answers myself, this is the explanation i came up with...
so... Hmmmmm... Am I right?

Exacly I think like you, but I wanted somebody to confirm me. Thank you very much, you answered all of my questions with one post. Just I want to ask, not all of the electrons of the atoms are unbounding right?

 

[The_Thinker]

"Unbounding??" hmmm... well Let me just tell you that you are not using the right terms... And this can cause confusion because specific terms, mean specific things in physics and using them will nilly can cause problems.

Anyway... no not all of them move, only the outer, "valance" electrons... But let me just ask you straight up... What are you getting at?

 

[scientist91]

"Unbounding??" hmmm... well Let me just tell you that you are not using the right terms... And this can cause confusion because specific terms, mean specific things in physics and using them will nilly can cause problems.

Anyway... no not all of them move, only the outer, "valance" electrons... But let me just ask you straight up... What are you getting at?

Look the electrons are kinda connected with the protons, they are holding each other (opposite charges), so that's why I said unbound. Ok, I understand all of your explanation.

 

[heafnerj]

In a DC circuit, mobile electrons flow in response to a uniform electric field created by a gradient in surface charge distribution over the outside of the circuit.

See http://galaxy.cofc.edu/circuits.html for simulations and some discussion, although you won't find much about this in traditional introductory textbooks and not much more at the graduate level. It's a shame since is a simple and correct model.

 

[scientist91]

But I can't understand that, from the one side there are moving valence electrons and from another not (potential differences). When you move the magnet, you move it from both sides, how is that possible? PLease explain. THank you.

 

[Doc Al]

I'm having a hard time understanding what it is you are trying to ask. Realize that electrons in a conductor are free to move when subjected to an electric field. Are you trying to understand how an applied voltage source (battery) creats an electric field in a conductor?

 

[scientist91]

I'm having a hard time understanding what it is you are trying to ask. Realize that electrons in a conductor are free to move when subjected to an electric field. Are you trying to understand how an applied voltage source (battery) creats an electric field in a conductor?

I am trying to realize when moving the magnet among conductor and creating voltage, from the one side there are valence electrons which are moving (- potential), and from the other there are not moving electrons (+). Why on the + potential there is not moving electrons, when the magnet is moving on whole conductor?

 

[Doc Al]

Are you talking about the induced EMF (and current) when a magnet is moved towards a conducting ring? Please state a specific example of what you mean. (A diagram or link would help.)

In the case of a battery attached to a wire, realize that at one end of the wire the surface charge will be positive (which just means a relative lack of electrons) and at the other it will be negative.

 

[Astronuc]

I think there is mix of concepts in this thread. The OP starts with a question on the mobility of electrons in a conductor and a reference to DC. Along the way, the concept of magnetic induction is introduced.

Perhaps these would help -
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magint.html
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elewor.html
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/conins.html

The electrons in a conductor are 'loosely bound' to the atoms, as opposed to insulators in which the electrons are tightly bound. In conductors, the loosely bound electrons can move in response to a electric field which develops in response to a potential difference, or if there is a 'moving' or 'varying' magnetic field (and either the conductor moves (e.g. homopolar generator) or the magnetic field moves (induction generator)).

Also, the atoms of the conductor remain stationary since they are held via atomic bonds.

 

[scientist91]

But man, why from the one side of the conductor there will move electrons (+) and from the other not (-) ? (potential difference) How is that possible? I am talking about electromagnetic induction, concretely induction generator.

 

[The_Thinker]

Are you trying to ask, why if the current are electrons moving from the -ve ly charged atoms to the +ve ly charged atoms, then why is it that the convention says that current flows from the +ve of a battery to the -ve of the battery?

Well, the answer to this is that, its a "convention" that current flows from a +ve to a -ve of a battery even though in fact the electrons flow from -ve to +ve. The electrons flow in this direction... -ve to +ve. But its a convention to say that current flows from +ve of a battery to the -ve of the battery.. that's all.. it started with that way, saying it flows from +ve to -ve, then when it was found out what was going on... they kept the convention, and that's what remains...

I hope this clears it up...

 

[The_Thinker]

I am talking about electromagnetic induction, concretely induction generator.

by the way... what is a concretely induction generator?


The +ve side is the side that has a deficiency of electrons and the -ve side is where there is an excess... So... the electrons flow from -ve to +ve... Is what you wanted to know?

 

[scientist91]

by the way... what is a concretely induction generator?


The +ve side is the side that has a deficiency of electrons and the -ve side is where there is an excess... So... the electrons flow from -ve to +ve... Is what you wanted to know?

No, I wanted to know how is possible from the one side to flow electrons (+) and from the other not (-)?

 

[Sojourner01]

No, I wanted to know how is possible from the one side to flow electrons (+) and from the other not (-)?

Not sure what you're asking here. Why shouldn't electrons flow?

 

[scientist91]

Not sure what you're asking here. Why shouldn't electrons flow?

OMG man, look, from the one side the electrons are flowing (positive pole) to the other bounded electrons(negative pole). My question is how is possible to have to different poles when all of the atoms and the electrons are same in the conductor? So all of them should have positive pole when they move.

 

[Doc Al]

But man, why from the one side of the conductor there will move electrons (+) and from the other not (-) ? (potential difference) How is that possible? I am talking about electromagnetic induction, concretely induction generator.

Again, not sure what you are referring to. A changing magnetic field induces an EMF in a conductor; if there's a complete path, current will flow.

OMG man, look, from the one side the electrons are flowing (positive pole) to the other bounded electrons(negative pole). My question is how is possible to have to different poles when all of the atoms and the electrons are same in the conductor? So all of them should have positive pole when they move.

What poles are you talking about? What do you mean by "bounded" electrons?

 

[scientist91]

Again, not sure what you are referring to. A changing magnetic field induces an EMF in a conductor; if there's a complete path, current will flow.


What poles are you talking about? What do you mean by "bounded" electrons?

Look, how is possible some of the electrons to flow and on that section of the closed loop to miss electrons (+) and on the other side to have only electrons?(-)

 

[Hootenanny]

Look, how is possible some of the electrons to flow and on that section of the closed loop to miss electrons (+) and on the other side to have only electrons?(-)

Look, an emf is induced in the loop and electrons will flow around the loop. Beyond that I have absolutely no idea what your asking.

 

[Astronuc]

Look, how is possible some of the electrons to flow and on that section of the closed loop to miss electrons (+) and on the other side to have only electrons?(-)

I believe one is referring to Faraday's Law with respect to a conductor moving in a magnetic field -
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html

There doesn't have to be a loop. There can be conductor and the electrons are forced to one end where they accumulate and provide a net negative charge, with a corresponding + charge at the other end of the conductor - and that establishes a potential difference. If a load is put across the conductor, one obtains a current.

And there is a similar effect for a current in a conductor called the Hall effect.
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/hall.html

The one may ask - how does a magnetic field impart a force on a moving charge (Lorentz force), or how does a changing magnetic field or moving magnetic field impart a force on a charge, moving or not.

 

[scientist91]

Voltage is from the one side there are missing electrons and from the other there are electrons so there is potential difference.
The atoms and electrons in the conductor are all same. So when you force them with the magnetic field all of them should move not part of them.

 

[Astronuc]

Voltage is from the one side there are missing electrons and from the other there are electrons so there is potential difference.
The atoms and electrons in the conductor are all same. So when you force them with the magnetic field all of them should move not part of them.

The electrons are bound to atoms with different energies. Many electrons will move, but then Coulomb repulsion (force) prevents more from moving. One can increase the magnetic field which increases the number of electrons that can be 'forced' to the same end of the conductor. Turn off the magnetic field and the electrons rapidly return to the atoms from which they had escaped.

It's a bit like pushing a box up frictionless (or perhaps very low friction) slope. One pushes the box up the gravity field so far and then stops. One still has to push against the force of gravity even when stopped. Then remove the pushing force and the box slides down the slope. A somewhat crude analogy.

 

[scientist91]

The electrons are bound to atoms with different energies. Many electrons will move, but then Coulomb repulsion (force) prevents more from moving. One can increase the magnetic field which increases the number of electrons that can be 'forced' to the same end of the conductor. Turn off the magnetic field and the electrons rapidly return to the atoms from which they had escaped.

It's a bit like pushing a box up frictionless (or perhaps very low friction) slope. One pushes the box up the gravity field so far and then stops. One still has to push against the force of gravity even when stopped. Then remove the pushing force and the box slides down the slope. A somewhat crude analogy.

Which is that Coulomb repulsion, explain please. Thank you.