Friday, November 28, 2008

Capacitor: An Overview

Author: James Monahan

Anybody in the field of electronics would doubtless be familiar with a capacitor, but what exactly is it?

A capacitor is, simply, a gadget that is capable of storing energy in an electric field between two conductors on which equal but opposite electric charges have been placed.

It is sometimes also called a condenser. Every multi-conductor geometry has capacitance, even though intentional capacitors have thin metal plates that are placed one on top of the other to form a compact device. But that is getting ahead of the story. Let us first start with the capacitor's history.

The ancient Greeks were ingenious not only in the arts and culture but also in the sciences. They also knew how to create sparks by rubbing amber balls on spindles. This was chronicled by Thales of Miletus around the year 600 B.C.

They were however, unaware that by placing the insulator in between the two metal plates, the charge density would be increased exponentially. It wasn't until the 18th century that this potential was exploited.

Ewald Georg von Kleist of Pomerania was credited for inventing the world's first capacitor in October 1745. His capacitor could be described as a glass jar coated with metal both on the inside and on the outside. The coating on the inside was connected to a rod that passed through the lid and ended in a metal ball.

Several years later, Benjamin Franklin investigated the Leyden jar created by Pieter van Musschenbroek, a Dutch physicist of the University of Leyden and discovered that the charge was stored in the glass, and not in the water as others had previously assumed.

This was the reason why the original unit of capacitance was in ""jars"". A jar is equivalent to 1nF.

As mentioned earlier, a capacitor is also known as a condenser. This term was coined by Volta in 1782, and referred to the device's ability to store a much larger density of electric charge than a usual isolated conductor.

You can compare a capacitor like a battery, in that they both store electrical energy, although the former is a much simpler device. It cannot produce new electrons; it only stores them.

A capacitor has two terminals connected to two metal plates sandwiching a dielectric. Working on this premise, a rough version of a capacitor can be created with the use of just two pieces of aluminum foil and a piece of paper.

A natural example of a capacitor is lightning in the sky. The plates are the cloud and the ground, and the lightning is the charge. You can just imagine the amount of charge released by the two plates.

Someone once made an accurate way of visualizing how a capacitor works. One can pretend it is a cistern that is hooked to a pipe.

A cistern, which naturally has water pressure, stores excess water pumped from the water system. This excess water then flows out of the cistern when needed, and keeps the pressure up in the process. In much the same way, a capacitor can be likened to the cistern.

An important thing to remember is the unit of capacitance, which is a farad. A 1-farad capacitor can store one coulomb of charge at 1 volt. An amp is the rate of electron flow of 1 coulomb of electrons per second, so a 1-farad capacitor can hold 1 amp-second of electrons at 1 volt.

An interesting thing to know is that 1-farad capacitor can actually be pretty hefty, depending on the voltage it is required to handle.

About the author: James Monahan is the owner and Senior Editor of CapacitorBase.com and writes expert articles about capacitors .

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