In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge. Capacitance is also a measure of the amount of electric charge stored (or separated) for a given electric potential. A common form of charge storage device is a parallel-plate capacitor.In a parallel plate capacitor capacitance is directly proportional to the surface area of the conductor plates and inversely proportional to the separation distance between the plates.If the charges on the plates are +Q and −Q, and V gives the voltage between the plates, then the capacitance is given byC=Q/V
Isolated conducting sphere: may be taken as a capacitor if we
imagine that there is a spherical conducting shell at infinity. In this case, C = 4*pi*epsilon_0*R, where R is
the radius of the sphere.
Spherical capacitor: composed of a conducting sphere of radius a
surrounded by a spherical conducting shell of radius b. To find C, we put +Q on the sphere, -Q on the shell, and
calculate the potential difference V. Then C = Q / V. We find that the capacitance is given by C =
4*pi*epsilon_0*a*b / (b a).
Parallel-plate capacitor: C = epsilon_0 * A / d, where A is the
plate area and d is the separation between the plates.
Cylindrical capacitor: A conducting cylinder of radius a surrounded
by a coaxial cylindrical sheel of radius b. The capacitance per unit length is
C / L = 2*pi*epsilon_0 / ln(b / a)
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