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# Capacitor : Uses, Unit and Formula

## What is Capacitor

• 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.

## Uses of Capacitor

(1) The main purpose of the capacitor is to store charge . If an instantanous strong current is to be flown in a  circuit,the best way would be to connect the terminals of the circuit to a charge  capacitor

(2) A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)

(3) Capacitor are used in many electrical intstruments like ignition systems of the motor engines.It is also employed in Electric fan

(4) Because capacitors pass AC but block DC signals (when charged up to the applied dc voltage), they are often used to separate the AC and DC components of a signal. This method is known as AC coupling or “capacitive coupling”. Here, a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the signal frequency, is employed.

(5) Capacitors are also used in Scientic Study.Using plates of different size and shape,different electric field configuration are established between the plates and the behavior of dielectric sunstances placed in these field are studied

(6) Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor banks) are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming,pulsed lasers ,pulse forming networks, radar, fusion research, and particle accelerators.

## Unit Of Capacitance

Unit of capacitance is Farads(F) or C/V
1F is very large unit of capacitance. Practically capacitors with capacitance of the order of micro farads ($\mu F$) are used in circuits of radio recivers , transmitters etc. Thus,

$1 \mu F=10^{-6}$ (micro)
$1nF=10^{-9}$ (nano)
$1pF=10^{-12}$ (pico)

## Capacitance Formula’s

For Parallel Plate Capacitor

$C= \frac {k \epsilon _0 A}{d}$

Cylinderical Capacitor with radii a and b ( b> a)

$C= \frac {2 \pi k \epsilon _0 L}{ln (b/a)}$

Spherical Capacitor with radii a and b ( b> a)

$C= \frac {4 \pi k \epsilon _0 ab}{b-a}$

Capacitance in Series

$\frac {1}{C} = \frac {1}{C_1} + \frac {1}{C_2} + \frac {1}{C_3}$

Capacitance in Parallel

$C= C_1 + C_2 + C_3$

Energy of the Capacitor

$E= \frac {QV}{2} = \frac {CV^2}{2}= \frac {Q^2}{2C}$

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