Figure 23.2 When a glass rod is
rubbed with silk, electrons are
transferred from the glass to the
silk. Because of conservation of
charge, each electron adds negative
charge to the silk, and an equal
positive charge is left behind on
the rod. Also, because the charges
are transferred in discrete bundles,
the charges on the two objects are
$e, or $2e, or $3e, and so on.