Tuesday, March 17, 2015

CAPACITOR

A capacitor is a device for temporarily storing electric charge.

In October 1745, Ewald Georg Von Kleist of Pomerania in Germany found that charge could be stored by connecting a 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. Von Kleist found that touching the wire resulted in a spark even after removing the generator.


In a letter describing the experiment, he said "I would not take a second shock for the kingdom of France."

In 1746, the Leyden jar was invented by Pieter van Musschenbroek at the University of Leyden in Holland. It was a glass jar wrapped inside and out by a thin metal foil.

The two layers of electrically conducting material that is metal foil here were separated by layers of a non-conducting material that was glass in the case of the Leyden jar, but it can also be wax, mica, oil, paper, tantalum, plastic, ceramic material, or even air.


The outer foil was connected to the ground, and the inner foil was connected to a source of electricity such as an electrostatic generator.

The plates will become charged, one positively and one negatively. If the externally applied voltage is then removed, the plates of the capacitor remain charged, and the presence of the electric charge induces an electrical potential between the plates.

 Daniel Gralath was the first scientist to combine several Leyden jars in parallel into a "battery" to increase the charge storage capacity.

Benjamin Franklin checked the Leyden jar, and proved that the charge was stored on the glass, not in the water as it was assumed.

He used a Leyden jar to store electricity from lightning in his famous kite flying experiment in 1752. By doing so he proved that lightning was really electricity.

He deviced the idea of a parallel or flat plate capacitor & developed the first flat plate capacitor called the Franklin Square.

Leyden jars began to be 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 Nano farad.

Years later, Michael Faraday experimented and made the first practically viable capacitor. Faraday’s pioneering role in capacitor technology has been honoured by naming the SI unit of Capacitance as ‘Farad’.

Leyden jar or flat glass plate construction was used until about 1900.

The invention of wireless (radio) created a demand for standard capacitors, and the steady move to higher frequencies required capacitors with lower inductance.


A flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, rolled or folded into a small package were constructed.

Early capacitors were also known as condensers, this term is still used occasionally now.

It was coined by Alessandro Volta in 1782.

 It was derived from the Italian word “condensatore”, with reference to the device's ability to store a higher density of electric charge than a normal isolated conductor. 

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