Capacitor and it's types | Electronics Component And Material

Capacitance

Two metallic surfaces with a gap between them are capable of storing electrical charge and an electrical field can be created in the gap. The gap may be filled up with air or with any other insulating material, often called the dielectric. The complete device is known as capacitor. When voltage is applied across the plates, an electric field exists between the two surfaces and charges are developed across the parallel surfaces. If the charge stored at the two surfaces be + Q and -Q coulombs and potential difference of V volts be existing between them, then the ratio between Q and V is defined as the capacitance of the capacitor. Thus

Q/V = C

The SI unit of capacitance is called Farad.

[Farad] = [Coulomb] / [Volt]

One Farad is too large. Hence much smaller units like microfarad (uF), nanofarad (nF) or picofarad (pF) are used .

Capacitance of Parallel plate

where

d = distance between the plates

A = Area of one of the plates

€ = permittivity of the dielectric

To achieve reasonable value of capacitance the area of the plates must be large, €r high and dielectric thickness small. Dielectric constants of different materials have been enlisted in table.

Capacitance of two Concentric Sphere Shells

If a charge Q is distributed uniformly over the outer surface of the inner shell of radius 'a', there will be equal and opposite charge induced on the inner surface of the outer shell (radius b). The Field at any point between is shell is given by