There is no electric ﬁeld inside a conductor. Suppose we bring a plus
charge near a conductor. For a very short moment, there will be an electric ﬁeld inside
the conductor. However, this ﬁeld will act on and move the electrons, which are free
to move about. The electrons will move close to the plus charge, leaving net positive
charge behind. The conductor’s charges will continue to move until the “external”
E~ -ﬁeld is cancelled out — at that point there is no longer an E~ -ﬁeld to move them, so
they stay still.

Alt text

Figure 1: Conductor near an external charge. The charges in the conductor very quickly
rearrange themselves to cancel out the external ﬁeld.

A more accurate statement of this rule is “After a very short time, there is no
electric ﬁeld inside a conductor”. How short a time is it? Recall that in cgs units,resistivity (which tells us how good/bad something conducts electricity) is measured
in seconds. It turns out that the time it takes for the charges to rearrange themselves
to cancel out the external E~ -ﬁeld is just about equal to this resistivity. For metals,
this is a time that is something like \(10^{-16}\) − \(10^{−17}\) seconds. This is so short that we
can hardly complain that the original statement isn’t precise enough!

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TopNewestThere is no electric ﬁeld inside a conductor. Suppose we bring a plus charge near a conductor. For a very short moment, there will be an electric ﬁeld inside the conductor. However, this ﬁeld will act on and move the electrons, which are free to move about. The electrons will move close to the plus charge, leaving net positive charge behind. The conductor’s charges will continue to move until the “external” E~ -ﬁeld is cancelled out — at that point there is no longer an E~ -ﬁeld to move them, so they stay still.

Alt text

Figure 1: Conductor near an external charge. The charges in the conductor very quickly rearrange themselves to cancel out the external ﬁeld.

A more accurate statement of this rule is “After a very short time, there is no electric ﬁeld inside a conductor”. How short a time is it? Recall that in cgs units,resistivity (which tells us how good/bad something conducts electricity) is measured in seconds. It turns out that the time it takes for the charges to rearrange themselves to cancel out the external E~ -ﬁeld is just about equal to this resistivity. For metals, this is a time that is something like \(10^{-16}\) − \(10^{−17}\) seconds. This is so short that we can hardly complain that the original statement isn’t precise enough!

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