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My question is how does having free electrons make something a conductor?

I know that the flow or movement of electrons create a current but can't you just add free electrons (such as a battery) to an insulator and a magnetic field making the free electrons move, thus creating a current?

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  • $\begingroup$ 'Free' electrons are, well, free to move about and carry current. Now, yes, you can add carriers. For example, low-doped semiconductors are photoconductive - shine light to create carriers and you conduct enough. No magnetic field needed, which won't interact with a charge unless it is moving. $\endgroup$
    – Jon Custer
    Commented Sep 22, 2020 at 17:01
  • $\begingroup$ So in other words you can add electrons/charge to an insulator but wouldn't that mean the insulator could conduct electricity. (since there are free electrons) $\endgroup$
    – Faheem Azeemi
    Commented Sep 22, 2020 at 17:04
  • $\begingroup$ Well, yes, but adding them may not be particularly easy and they may not last very long. $\endgroup$
    – Jon Custer
    Commented Sep 22, 2020 at 17:05
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    $\begingroup$ Q: I know that sharks need water to breathe but can't you just add water under a pergola and then the sharks will be able to breathe there? A: a pergola can't hold water, and if you make one that can, it's not a pergola. $\endgroup$
    – Criticizing Israel not allowed
    Commented Sep 22, 2020 at 17:16
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    $\begingroup$ You have two separate questions here. Which one do you want to ask? $\endgroup$
    – Criticizing Israel not allowed
    Commented Sep 22, 2020 at 17:18

2 Answers 2

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My question is how does having free electrons make something a conductor?

An applied electric field, such as that supplied by a battery, provides the force needed to move electrons which, in turn, means create current. Electrons that are not free are bound by electrostatic forces which oppose the force of the applied electric field thereby inhibiting current.

can't you just add free electrons (such as a battery) to an insulator

As pointed out in the comments, there are ways to add electrons but it is not particularly easy. Electrostatic charging one way but the current created by electrostatic discharge is usually brief. As far as batteries go, they don't supply electrons to a circuit. They convert chemical potential energy to electrical potential energy which is then used to push free electrons in the circuit producing current.

and a magnetic field making the free electrons move, thus creating a current?

Relative motion between magnetic fields and conductors can push and pull free electrons creating current in the conductors. Examples are moving a magnet in and out of stationary coil of wire, or moving a coil of wire over a fixed magnet.

Hope this helps.

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As stated in Bob D's answer, batteries do not supply electrons to a conductor. The electrons are already present in the conductor, bound by weak electrostatic forces to the nuclei of the atoms of the conductor, so they are not entirely "free".

When a battery is connected to the ends of a conductor, it exerts a force on the electrons in the conductor (we usually say it generates a potential difference between the ends of the conductor which means the same thing as exerting a force on the electrons) and the electrons move readily since they were previously weakly bound.

An insulator also contains electrons but the electrons are bound to the nuclei of the insulator by very strong electrostatic forces. When a battery is applied to the ends of an insulator, the force exerted by the battery is not sufficient to separate the electrons from the nuclei, there is therefore no electron flow.

However, there are no absolute insulators as any material will conduct electricity if the force exerted on its constituent electrons is great enough to separate them from the nuclei to which they are bound. In order words, find a strong enough "battery" (which can supply a potential difference of tens of thousands of volts) and a substance usually regarded as an insulator will eventually conduct an electric current.

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  • $\begingroup$ @Thornah : If the battery does create a potential difference wouldn't that mean the wire would be positively charged? I also read in an article that the battery undergoes a chemical reaction in which it creates electrons that it releases into a wire. On the other terminal the battery creates an attraction between electrons. Here is the link: science.org.au/curious/technology-future/batteries $\endgroup$
    – Faheem Azeemi
    Commented Sep 22, 2020 at 19:16
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    $\begingroup$ The potential difference created does not affect the charge of the wire. The wire as a whole is neutral as it contains both negatively charged electrons and positively charged nuclei. The issue about the battery releasing elecrons into the wire is quite subtle. Though there are local movements of electrons from the negative terminal of the battery into the wire, this is balanced by the movement of electrons from the wire into the battery via the positive terminal of the battery. There is therefore no net movement of electrons into the wire from the battery. $\endgroup$
    – Toba
    Commented Sep 22, 2020 at 20:12
  • $\begingroup$ And an electric field exists emanating from the wire due to the battery potential, allowing energy flow around the wire to connected load (e.g. resistance), right? Per the Poynting vector. $\endgroup$
    – relayman357
    Commented Sep 22, 2020 at 23:43
  • $\begingroup$ Exactly. Note that the connected load also contains electrons that move due to the applied potential difference. $\endgroup$
    – Toba
    Commented Sep 23, 2020 at 17:26

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