G azərbaycan respublikasi təHSİl naziRLİYİ azərbaycan texniKİ universiteti M. M. QƏNDİLova e. Q. İsmayilova

Generation of Electricity
It is fundamental law of nature that energy cannot be created; however, it can be converted from one to another. Friction, pressure, heat, light, chemical energy, and mechanical and magnetic energy can all be converted into electrical energy. Although most of these six methods of producing electricity have little or no practical application today, they are all discussed because of their historical or potential significance.

Static Electricity
Static electricity is sometimes called electricity of friction. Some examples of the production of electricity by friction are rubbing an amber rod with fur or wool, walking across a wool carpet with rubber-soled shoes, the flexing of tires as a car travels on a highway, discharging liquids through a pipe or hose, and by a static machine built for this purpose and used in laboratory experiments.

Static electricity occurs because of the phenomenon of the attraction of unlike charges. This attraction is readily demonstrated by the behavior of pith balls suspended on threads and charged by a static machine. The pith balls are uncharged at the left; they are neither attracted to nor repelled by each other. In the next diagram, one ball is given a positive charge and the other is given a negative charge; the balls move toward each other. When both balls are given likes charges, they move away from each other.

Static electricity has no practical application outside the laboratory, and although it occurs in many ways, it is often a hazard and is seldom welcome when it does occur. A bolt of lightning between clouds or from a cloud to earth during a thunderstorm is the most spectacular occurrence of static discharge. Less dramatic are sparks and minor shocks that accompany the discharge of static electricity from one person’s hand to another’s or from a hand to a doorknob.

Disastrous fires have resulted from the ignition of oil or gasoline by static electricity. In most cases of static discharge, the electricity is seeking the shortest and easiest path to the earth. Therefore, when a static charge accumulates on hose connections of a gasoline truck, the charge may leap across an air gap to reach the ground if no other path is provided. This creates an arc-the familiar spark-that could start a fire. Prevention of arcing is possible by providing a “ground” in the form of a conductor from the truck hose to the ground, preventing arcing, and thereby diminishing the possibility of a fire.

Lightning is a gigantic arc similar to that described in the preceding paragraph. Lightning roads are the “grounds” used on farm houses and other structures to provide a safe path for the lightning to follow to the earth.

In dry atmospheric regions, static charges accumulate on metal bodies of cars because there is insufficient atmospheric moisture to provide for a gradual discharge of the static electricity, and the insulation of the car’s rubber tires prevents it from reaching earth. Most drivers are familiar with the arc that leaps from the door handle of a car to the hand of person about to open the door. That charge, too, is simply seeking a path to the earth.

If a static charge that may be hazardous to discharge by means of an arc is suspected, the presence of the charge can be verified, by using a pith ball and the principle illustrated in figure 5.1. Apply a static charge to the pith ball suspended on a thread, and bring the ball near the surface where the charge is suspected. If the surface is charged, the ball will be deflected either toward or away from it.

Early laboratories used Leyden jars to store static electricity. A Leyden jar has a tin or lead foil coating both inside and outside of glass jar. The outside foil is connected to the ground (represented by the symbol); the inside foil is connected to a rod that projects through the cork of the jar, with a ball on the end of the rod to receive the static charge. The Leyden jar was the forerunner of present-day condensers and capacitors, which are used extensively in radio, power factor correction, and on many electrical apparatus.