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So, this demonstration is meant to
illustrate how current flows in a wire.

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I have here a table, which represents a
wire, and remember that

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a wire is a piece of metal, which is not
perfectly crystalline, it

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has defects, and when electrons run into
those defects, that impedes their

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flow, and that gives rise to what we call
resistance in the wire.

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So, these golf balls, symbolize my
electrons.

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And these cups, symbolize defects.
And when I release

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a flow of electrons, you're going to see
that

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some of them will flow unimpeded, not
running

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into anything, but some of them will run

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into defects, and their flow will be
impeded.

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So let's see how that works.

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[SOUND]

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Now, another thing to remember, is that
the defects that form

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in a wire, are located randomly with a
certain average density.

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So as the wire becomes smaller and

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smaller, eventually you might reach a
point where,

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it's so small that the probability of
finding

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a defect inside that wire, is very low.

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And, so that's the next thing we want to
try.

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So, now instead of having a big wire, we
have a small wire.

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Maybe a nanowire.

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And, because the wire is small, the
probability of

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finding defects inside the wire is lower
and so you

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have a smaller number of defects, and
therefore the flow

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of current is impeded less by collisions
with the defects.

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[NOISE]

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And

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most of my electrons make it to the end of
the wire without running into anything.

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So now, we've made our wire even smaller.

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Now we can consider it to be a one
dimensional conductor.

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And in this case defects become a real
problem, because if you do have a

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defect in the middle of a one

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dimensional wire, then every electron
ecnounters that defect.

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[SOUND]

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Even, one defect, in a one-dimensional
wire, can make a big difference.

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So we've seen that defects in the crystal
structure of

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a metal can play a critical role in
determining the

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resistance of a wire, as you go from a
large

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wire, to a nanowire, and down even to a
one-dimensional wire.

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This turns out to be one of the crucial
challenges that

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one faces when one tries to

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construct electrical circuits using
nanoscale components.