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I know that current is produced due to potential difference which makes the free valence electrons being passed on in a copper wire(or am i wrong, plz crt me if so). Each copper atom provides a single free electron. When a voltage is connected across a piece of copper, it pushes the free electrons so that they flow through the metal – that's an electric current.

But what happens to it when one end of the wire is left open (in air not touching ground). what happens to the free voltage or free electron ?? It stays der ? How ?

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    $\begingroup$ The end of the wire will get on the same potential as the current driving side, therefore bringing current flow to an end. If the potential is very high, an air gap to ground might be bridged if the breakdown voltage of air is reached. Then ionized air will carry the current on...etc. $\endgroup$ – mikuszefski Nov 3 '16 at 8:56
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    $\begingroup$ "The end of the wire will get on the same potential as the current driving side, therefore bringing current flow to an end" ... Can you be more precise on how the current flow will end ? $\endgroup$ – VisheshRaju Nov 3 '16 at 9:58
  • $\begingroup$ Well, what makes the current flow in the first place? Current typically flows due to a potential difference. If, e.g., an accumulation of charge removes that difference, current flow stops. $\endgroup$ – mikuszefski Nov 3 '16 at 10:20
  • $\begingroup$ Yes, thats right but from what i have known ... The potential diff will move the valence electron of one atom of copper to another and so on ..... So what happenes to this electron as it reaches and which is open to air ? $\endgroup$ – VisheshRaju Nov 3 '16 at 11:02
  • $\begingroup$ for dc current, if the wire ends in air there will be no current . A sudden break might generate a spark but the current will stop, electrons will no longer be drifting because there will be no potential difference . If it is ac current then it is an antenna, and the electrons drift back and forth. $\endgroup$ – anna v Nov 3 '16 at 11:57
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Since the final state might well be that no charges are moving you could treat it as a question about electrostatics.

You have an uncharged wire and as you bring it close to the negative terminal of a battery (surplus of electrons here) then charges are induced on the wire by the free electrons in the wire mooing away from the negative terminal leaving a surplus of electrons at the other end of the wire.
This movement of the free electrons continues until the electric field inside the wire is zero and one end of the wire is connected to the negative terminal of the battery.

The air around the wire could become a conductor if the air is ionised accompanied by the production of mobile electrons.
The ionisation of the air can be achieved by having a radioactive source close by, by heating the air or by having a fairly large electric field around the end of the wire which then ionise the air via an avalanche process.

The free electrons in solid and liquid metals are there because it is energetically favourable for a lattice of positive ions to form with the liberated electrons being able to wander throughout the metal.
This is the essence of a metallic bond.

However the electrons are confined within the metal as it requires energy to remove them electron from the solid.
The photoelectric effect, thermionic emission and field emission are all examples of electrons being given enough energy to escape from the metal.

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  • $\begingroup$ "Field emmision" Is what i expected ..... that gives answer on how the ectrons escape from metal. But just to confirm does this cause the ionisation effect in air close to the wire ? $\endgroup$ – VisheshRaju Nov 5 '16 at 14:44
  • $\begingroup$ Field effect is usually in a vacuum so it is literately pulling out electrons from the metal surface. I provided links for each of those effects. $\endgroup$ – Farcher Nov 5 '16 at 14:52
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Electrons are not free to move. The system is governed by force in an electric field, and the system is either endothermic or exothermic due to attraction and repulsion. Systems are usually operated in exothermic states with a load dominating direction of attraction. The circuit must be closed to move electricity or otherwise you have an electrostatic field or open voltage.

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