It is possible for the electric field between the plates of the capacitor to
decrease if the total number of electric field lines between the capacitors
will decrease.
This is a device which stores electrical energy in an electric field. It has two
terminals which aids its storage characteristics.
When the dielectric is inserted, it completely fills the space between the
plates which leads to a decrease in the electrostatic potential energy of
the capacitor. This leads to the electric field and field line experiencing a
corresponding decrease.
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