An electric current in a wire occurs when...

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An electric current in a wire occurs when...
A. electrons move in the wire as a result of getting pushed along from a neighboring electron.
B. electrons move in the wire as a result of the repelling force from the negative battery terminal and the attractive force from the positive battery terminal.

This was a multiple choice question on my Physics test.
The other answers were not included because they were obviously incorrect (e.g. the protons move in the wire, etc.) I had to decide between A and B.

Here's how I thought of the question: I knew that without a voltage source, there would be no current.

However, if there were no electrons at all, there wouldn't be a flow of electrons in the first place, since it is the electrons themselves that go from atom to atom (like a game of hot potato).

Would it be accurate if I think of the electrons as train cars (which are pushing one another) being pushed by a locomotive (except the locomotive itself doesn't move)?

So, what do you think? Is the correct answer A or B?
 

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  • #2
kuruman
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The closest analogy I have seen is that of a pipe filled with water (an incompressible fluid) with a pressure difference between the ends. There is enough friction so that the water moves with constant speed (drift velocity for electrons) through the pipe.

How you model electron flow should not be a key factor to answering the question. Think of it this way: No matter how you model electron flow, electric current has a direction. Which of the possibilities that you are left with best conveys the idea of direction?
 
  • #3
Drakkith
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Would it be accurate if I think of the electrons as train cars (which are pushing one another) being pushed by a locomotive (except the locomotive itself doesn't move)?
Only vaguely. Electrons don't occupy set positions like chain links or train cars do. They are moving in random directions, bouncing and scattering off of electrons and ions in the lattice, and it is a net motion in their their bulk movement that results in current flow.

All in all I think it's a poor question. Both A and B have some truth to them, but neither is particularly accurate. The repelling force from the negative terminal and attractive force from the positive terminal only propagate through the conductor because the conductor contains mobile charges (electrons). An insulator would not confine and conduct the electromagnetic field in the way that a conductor does. I would guess that the correct answer on the test is B though. The mere presence of electrons in a wire doesn't create current, you need something to provide the force to make the charges move, which is what B is about. Hence I would guess that B is the answer the test is looking for.
 
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The question lacks clarity, and option (B) seems more relevant in the given context.
 

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