A capacitor is an arrangement of conductors that is used to store electric charge. A very simple capacitor is an isolated metallic sphere. The potential of a sphere with radius R and charge Q is equal to
Equation (1) shows that the potential of the sphere is proportional to the charge Q on the conductor. This is true in general for any configuration of conductors. This relationship can be written as
where C is called the capacitance of the system of conductors. The unit of capacitance is the farad (F). The capacitance of the metallic sphere is equal to
Information provided by: http://teacher.nsrl.rochester.edu