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Equations 2-23 and 2-24 show that the charge and voltage of the sphere are proportional to each other. The ratio of charge to voltage is called the capacitance. Hence

Q = Cv [2-25]


q = the charge in coulombs
v = the voltage in volts
C = the capacitance in farads.
Thus the capacitance of the isolated sphere is expressed by

C = 4πkrε0r1

Energy is required to charge the sphere to the potential r and the energy is considered to reside in the electric field that occupies the medium, known as the dielectric, external to the sphere. The capacitance of a certain configuration depends in general upon the dimensions and the dielectric constant that is a property of the dielectric in which the energy is stored. The dielectric constant and the dielectric strength are the properties of the dielectric that determine the energy that can be stored electrically in a given volume of material.

Last Update: 2011-08-01