plates. This insulator is called a dielectric. Air is one dielectric, but other dielectrics can
be used to increase the capacitance.
The unit of measure of capacitance is the farad (F), named after the physicist Michael
Faraday. A one-farad capacitor has a great deal of capacitance. It can store a lot of
charge. Many commonly encountered capacitors have capacitances ranging from
microfarads (10í^6 F) down to picofarads (10í^12 F). However, capacitors with greater
capacitances certainly exist: car audio enthusiasts often boast systems employing one-
farad capacitors.
The movement of electrons creates the charges on the two plates of a capacitor. They
move away from one plate, leaving a net positive charge behind, and go toward the
other plate, which takes on a negative charge. Note that the electrons do not move
across the gap between the plates. Rather, they move along the wires whose ends you
see in the illustrations.
A source of potential difference such as a battery exerts a force on the electrons,
causing them to move. This force through a distance constitutes work. The amount of
work done during the charging process equals the electric potential energy stored by
the plates. The greater the charge on its plates, the greater the amount of energy a
particular capacitor is storing.
Capacitance
Relationship between charge, potential
difference