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To repeat, skim over 24.5 but don't spend too much time on this.

The last section is about conductor in electrostatic equilibrium. Really that means with no electric current!

The most important points here are (all derived from Gauss' Law)

the electric field is zero inside the conductor.
the electric field at the surface is perpendicular to the surface.
the magnitude of the electric field at the surface is E =\eta/\epsilon_0 where \eta is the surface charge density of the conductor.

This implies that if there is a hole in a conductor (with no charge in the hole), the electric field must be zero inside, always.

Faraday's Cage

This is the principle behind the Farady's cage whereas we make the electric field zero in some area by surrounding the area by a conductor.

Charge inside

if they are charges inside the hole, then there will a surface charge density on the inner surface in order for the electric field in the conductor to be zero.

Remember that we know all these facts simply by using that electrons can move freely and Gauss' law tell us that if the E field is zero, the charge inside the gaussian surface must be zero!

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