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### Capacitors

-Capacitors are important components used in electronics and telecommunication devices for example radio , television recivers , transmitter circuits etc.

-Capacitor is a device used for storing electronic charge.

-All capacitors consists of two metal plates(or conductors) separated by an insulator(air, vacuum or any other dielectric medium).

-Conventional symbol of capacitor is where T is the terminal (positive or negative) of battery joined to the plates.

-Capacitor gets charged when a battery is connected to it or when there is a potential difference between two metal plates of the capacitor.

-Capacitor gets discharged on joining two of it's plates.

-If V is the potential difference between two plates of the capacitor and q is the amount of charge developed on each plate then q/V is constant for the capacitor since q∝V.

-The ratio of charge on either plate to the potential difference between the plates is called capacitance C of the capacitor. Thus,
C=q/V
or q=CV

-Unit of capacitance is Farads(F) or CV-1.

-1F is very large unit of capacitance. Practically capacitors with capacitance of the order of micro farads (μF) are used in circuits of radio recivers , transmitters etc. Thus,
1μF=10-6 (micro)
1nF=10-9 (nano)
1pF=10-12 (pico)

-For any capacitor it's capacitance is constant and depends on shape , size , separation f the two conductors and also on insulating medium being used for making capacitor.

- Capacitance of parallel plate capacitor havinf vacuum or air acting as dielectric or insulating medium is
C=(ε0A)/d
where,
C= capacitance of capacitor
A= area of conducting plate
d= distance between plates of the capacitor
ε0=8.854× 10-12 and is known as electric permitivitty in vacuum.
-If k is the relative permittivity of the dielectric medium then
ε=ε0k
thus capacitance of parallel plate air capacitor in presence of dielectric medium of electric permitivity ε is
C=εA/d
-Capacitance of spherical capacitor having radii a, b (b>a) with
(a) air as dielectric between them
C=(4πε0ab)/(b-a)
(b) dielectric with relative permitivity ε
C=(4πεab)/(b-a)