What is capacitor?



Capacitor Definition: The charge necessary to raise the potential of a conductor by units is numerically equal to the capacitance of the capacitor.

q=cv                                       q=charge
It is a scalar quantity.
Factor affecting conductors:       
1.Greater the size of conductor, larger is its capacitance.
2.Greater the surface area of the conductor,larger its capacitance.
3.More the di-electric constant of the surrounding medium more the capacitance of the conductor.

Capacitor unit     

S.I unit = Farad 
C.G.S unit=Stat Farad
Point to be noted:
1 micro farad= 10 ̄6 Farad
1 nano farad=10 ̄9 Farad
1 pico farad=10 ̄12 Farad
Elastance: Reciprocal of capacity of a conductor ⇒ S=1/C
Unit: F ̄1  (Some times called ‘daraf ‘) 
Dimension: [C] = [M ̄1 L ̄2 T4 A ]

Capacitor symbol

Capacitor History
In October 1745, Ewald Georg von Kleist of  Germany, found that charge could be stored by connecting a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar. Von Kleist’s hand and the water acted as conductors, and the jar as a dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist found that touching the wire resulted in a powerful spark, much more painful than that obtained from an electrostatic machine. The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leiden where he worked. He also was impressed by the power of the shock he received, written, “I would not take a second shock for the kingdom of France.
Daniel Gralath was the first to combine several jars in parallel to increase the charge storage capacity. Benjamin Franklin investigated the  Layden jar and came to the conclusion that the charge was stored on the glass, not in the water as others had assumed. He also adopted the term “battery” (denoting the increasing of power with a row of similar units as in a battery of cannon), subsequently applied to clusters of electro chemical cells. Leyden jars were later made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils. The earliest unit of capacitance was the jar, equivalent to about 1.11 nano farads.

Types of capacitor:

Polar and non polar
One of the main difference between various types of capacitor is whether they are polarized or not.
polarised capacitor is one that must be run with the voltage across it in a certain polarity.
Some of the more popular types of polarized capacitor include the aluminium electrolytic and tantalum. These are marked to indicate the positive or negative terminal and they should only be operated with a voltage bias int his direction – reverse bias can damage or destroy them. As capacitors perform many tasks like coupling and decoupling, there will be a permanent DC voltage across them, and they will pass only any AC components.
The other form of capacitor is a non-polarized or non-polar capacitor. This type of capacitor has no polarity requirement and it can be connected either way in a circuit. Ceramic, plastic film, silver mica and a number of other capacitors are non-polar or non-polarized capacitors.

Leaded and surface mount capacitors

Surface-mount technology (SMT) is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred to as a surface-mount device (SMD). In industry, this approach has largely replaced the through-hole technology construction method of fitting components, in large part because SMT allows for increased manufacturing automation. Both technologies can be used on the same board, with the through-hole technology often used for components not suitable for surface mounting such as large transformers and heat sinked power semiconductors.

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