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Still a metal?

by karen03grae
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karen03grae
#1
Jan16-05, 04:16 PM
P: 82
Q: When just one end of a wire is connected to a positive terminal of a battery, don't the free electrons in the wire get pulled into the positive terminal?

If these valence electrons did get pulled, what would this make the wire? Still a metal? No valences? Would the wire have a net "+" charge?

Reasoning: My book says when a wire is first connected (both leads), the free electrons at one end of the wire are attracted to the positive terminal, & at the same time, electrons leave the negative terminal of the battery and enter the wire at the other end. Continuous flow of e's.

Maybe since, in my question, there is no negative terminal connected, therefore no electrons being added to the wire, the free valences in the wire would rather 'just chill' and float around than be pulled into the positive terminal.

what do yall think?
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kirovman
#2
Jan16-05, 05:47 PM
P: 75
Quote Quote by karen03grae
Q: When just one end of a wire is connected to a positive terminal of a battery, don't the free electrons in the wire get pulled into the positive terminal?
No.
You need to have both terminals connected to induce an emf and make a current. And even then, the moving electrons will need to be replaced by more electrons, from the -ve terminal. I'm pretty sure the terminals aren't charged on their own, can someone confirm?
Even if the electrons were slightly attracted to the positive terminal, it would be negligible to the number of valence electrons.


The free electron model describes the metal as periodic +ve ions with many delocalised electrons.

Sure the electrons are delocalised, but the ionic lattice will not give up it's valence electrons so easily.

You'd have to get substantial positive charge to steal the electrons from metal.
Gokul43201
#3
Jan16-05, 08:58 PM
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Quote Quote by karen03grae
Q: When just one end of a wire is connected to a positive terminal of a battery, don't the free electrons in the wire get pulled into the positive terminal?
No, electrons do not get pulled. Just imagine the wire as an extension of the terminal that it is connected to. The whole terminal-wire assembly is at the same potential. You must have a potential gradient (difference) to make electrons flow.

karen03grae
#4
Jan16-05, 10:31 PM
P: 82
Still a metal?

Okay. So they don't get pulled because as soon as the wire is connected to the + terminal, the wire and terminal are equipotential surfaces. So do the valence electrons float just keep floating around the copper atoms...
.................................
.CuCuCuCuCuCuCuCuCuCu. <--copper wire segment composition
.CuCuCuCuCuCuCuCuCuCu. . = electrons
.................................

That is supposed to be the copper atoms with their free electrons being shared. Sorry if this is leaning more toward chemistry than physics...but if anyone knows if this picture is correct then please let me know.
Gokul43201
#5
Jan16-05, 11:24 PM
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Yes, the free electrons float about the copper atoms "freely". Their motion is random, and so there is no net velocity in any particular direction.

But keep in mind that these free electrons are not valence electrons anymore. They are refered to as 'conduction electrons'.
chris1234
#6
Jan17-05, 05:37 AM
P: 7
I think this isn't quite right.

Say I have a copper wire and I plug it into a terminal. Then some charge moves from the wire to the terminal until the wire and terminal come into equipotential. Now, the number of electrons that move into the terminal will probably be quite small compared to the number of free electrons. So the wire still acts like a metal.

This is how a capacitor works.
osskall
#7
Feb4-05, 03:16 PM
P: 48
Quote Quote by chris1234
I think this isn't quite right.

Say I have a copper wire and I plug it into a terminal. Then some charge moves from the wire to the terminal until the wire and terminal come into equipotential. Now, the number of electrons that move into the terminal will probably be quite small compared to the number of free electrons. So the wire still acts like a metal.
But I guess this has nothing to do with the potential difference over the battery terminals, i.e. what makes the battery a battery, but only with the potential at this one terminal, which makes your point relevant not only to batteries.

Quote Quote by karen03grae
Q: When just one end of a wire is connected to a positive terminal of a battery, don't the free electrons in the wire get pulled into the positive terminal?
What makes the electrons flow is 1) the potential difference over the two terminals, but this is not enough; 2) a path for them to flow and lower the potential difference. So obviously no current will flow if you just connect a wire at one terminal, except for the small flow of electrons to cancel the potential difference between end terminal and the copper wire.
Antiphon
#8
Mar16-05, 03:44 PM
P: 1,781
Some will get pulled. As they do, the voltage will go up and meet the
battry potenetial and no more will get pulled.

This is called "charging a capacitor."
nebulan
#9
Mar29-05, 10:51 AM
P: 6
no negative not true
nebulan
#10
Mar29-05, 10:58 AM
P: 6
lets say we want to put batteres in a toy so it can work..ok

we take advantage of the loss of elctrons

wen the positive pole unleshes elctron its like energy for the toy
and after it out of energy it losses it powers and go to the negative poles
and if some one said or meend this then he is correct


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