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In a DC current in a conductive wire, is it more accurate to think of one electron wiggling its way through a sea of electrons... or to think of one electron bumping into another, which bumps into another, which bumps into another, which eventually causes an electron on the other end of the wire to "pop out" like the initial electron "popped in?"

Does the answer change for DC current flowing through a semiconductor?

Does the answer change for AC current in a conductor?

Does the answer change for AC current in a semiconductor?

DJG
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2 Answers2

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You are close.

For all of your questions, the answer is the same and relatively simple.

The short answer I was taught is here:

Although the energy in an average electric circuit can seem to flow very rapidly, a significant fraction of the speed of light in a vacuum, around 70-80%, the actual electrons do not physically move that fast.

Instead, say in a regular copper wire as an example, the electrons move from the power source to an atom of Cu, which, in turn, causes an 'over-balance' of electrons in the atom which repels another electron outward. This chain-reaction is what causes electricity to flow.

I am currently studying in a secondary school and I will hopefully get to know more about the subject next year, I do not know much as of the moment.

I found another stack exchange forum that should provide a sufficient and a detailed answer:

https://electronics.stackexchange.com/questions/72875/do-electrons-actually-flow-when-a-voltage-is-applied

Julius
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I believe the basic answer to your question (how to think of electrons moving in a current) has been addressed in the link @Julius provided. But you also asked whether there was any distinction for different frequencies of conduction or different material classes.

As mentioned before, the short answer is no, there is generally no difference in how one conceptually thinks about conduction for AC or semiconductors, etc. But I would make some qualifications:

  1. There are many models of conductivity, each of which is appropriate for different systems (although the general idea of charge carriers transmitting an electromotive force down the wire without moving much themselves applies to virtually all of them). In some exotic systems, conduction is more complicated. For example, in superconducting or quantum Hall states, the standard intuition of electrons randomly bouncing around into each other with an average drift in the direction of the current can be pretty much thrown out. Also sometimes the mobile charge carrier in a solid state system is more complicated than an electron (e.g. polarons, trions, and other coupled excitations).

  2. AC conductivity is exactly the same as DC conductivity until the frequency is high enough to reach some relevant time scales in the conductor. An important one here is the time scale for scattering of electrons. If you switch the direction you are pushing electrons faster than they scatter off of things, conduction is no longer Ohmic. Metals have scattering times of ~10 femtoseconds, so if you wiggle electrons in them faster than ~100 THz (say, with visible light) it turns out that the resulting current is more or less out of phase with the driving field, which may seem counterintuitive. Optical and infrared conductivities of materials can have rich physics.

  3. Semiconductors behave the same as conductors, but they have fewer charge carriers and typically less scattering. This combination reduces semiconductors' conductivity in comparison.

But for general intuition, remember that a voltage is an electromotive force. This force is transmitted by all charge carriers collectively.

Gilbert
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