Capacitance

Capacitance, ability of a system to store an electric charge, measured by the charge that must be communicated to a body to raise its potential 1 unit. Electrostatic unit capacitance is that which requires 1 electrostatic unit of charge to raise the potential 1 electrostatic unit. The farad = 9×10¹¹ electrostatic units. A capacitance of 1 farad requires 1 coulomb of electricity to raise its potential 1 volt. A conductor charged with a quantity Q to a potential V has a capacitance C = Q/V. The capacitance of a spherical conductor of radius r is C = Kr. The capacitance of 2 concentric spheres of radii r and r' is C = K[rr'/(r−r'). The capacitance of a parallel plate condenser, the area of whose plates is A and the distance between them d, is C = KA/4πd. Capacitances are given in electrostatic units if the dimensions of condensers are substituted in cm. K is the dielectric constant of the medium.