For what reason the lightning gets to the high and pointed objects more often, than in low and having the equal form? And what measures can be taken almost completely to avoid hit in a lightning object? Scientists found answers to these questions in the eighteenth century.
Electric current can pass not only through metals which conductivity is caused by existence in a crystal lattice of free electrons, but also through other environments. For example, through organic matter, semiconductors, a vacuum, liquids and gases. In order that gas began to carry current, it is necessary to have in it charge carriers as which ions act. It is possible to bring in gas a source of ions artificially: in its role the flame or a source of alpha particles can act. If electric current in gas only uses the available ions from a third-party source, but does not create own, such category is called dependent. It does not radiate own light. At the certain density of current it accepts ability to create new ions and to immediately use them for own passing. There is an independent category which is not demanding additional sources of ionization and supporting itself until sufficient tension is attached to electrodes. Electric discharge, depending on density of current and pressure of gas, is divided into crown, smoldering, arc and spark. All of them, except crown, have so-called negative dynamic resistance. It means that with increase in current resistance of the channel of the ionized gas falls. If not to limit current artificially, it will be limited only to the internal resistance of the power supply. The lightning is an example of the spark category. This category considerably surpasses all artificial spark categories in the parameters: it is characterized by tension in tens of millions of volts and currents in hundreds of thousands of amperes. It is known that any spark interval is characterized by the so-called tension of ignition. It depends not only on distance between electrodes, but also on their form. The electric field strength around sharp electrodes at the same tension is more, than around spherical or flat. For this reason the lightning more likely gets to the pointed subject, than to equal which is nearby. The height of an object also increases the probability of hit in it of a lightning as it is equivalent to reduction of distance between electrodes. The lightning rod invented in the middle of the eighteenth century by the physicist Benjamin Franklin works as follows. On its edge there is a crown category which as it is stated above, is the only thing from all gas categories which does not have negative dynamic resistance. Therefore current does not increase to catastrophic sizes that is equivalent to the slow category of the condenser instead of fast. It is possible to give such analogy: if slowly to pour out all water of the vessel suspended on thin thread, it is possible not to be afraid any more that under weight of water thread will break and all vessel will fall. Being during a thunderstorm on the open area far from the buildings equipped with lightning rods for minimization of probability of hit of a lightning it is necessary to depart from trees and to hide an umbrella.