Lightning is a powerful electric discharge. It occurs when a strong electrification of clouds or the earth. Therefore, the lightning strikes can occur or within clouds, or between adjacent electrified clouds, or between electrified cloud and earth. The lightning discharge is preceded by the appearance of the electric potential difference between adjacent clouds or between a cloud and the ground.
Electrification, that is, the education of the forces of attraction of an electrical nature, all familiar from everyday experience.
If you comb through clean, dry hair with a plastic comb, they are attracted to her, or even spark. After this comb can attract, and other small objects such as small pieces of paper. This phenomenon is called electrification by friction.
What causes the electrification of clouds? Because they do not RUB against each other, as occurs in the formation of an electrostatic charge on the hair and comb.
Storm cloud is a huge amount of steam, a portion of which is condensed in the form of fine droplets or ice particles. Top storm clouds may be located at a height of 6-7 km and down to hover over the earth at a height of 0.5-1 km 3-4 km Above the clouds consist of ice particles of different sizes, because the temperature is always below zero. These icicles are in constant motion, caused by rising currents of warm air from the heated surface of the earth. Small icicles easier than large, are fond of ascending currents of air. Therefore, the "nimble" small pieces of ice, moving in the upper part of the cloud, all the time facing large. Each such collision leads to electrification. With large icicles are charged negatively, and small - positively. Over time, positively charged small icicles appear at the top of the cloud, and negatively charged large at the bottom. In other words, the top of the storm clouds charged positively, and the bottom is negative.
The electric field of the clouds has a huge tensions are about a million V/m When large oppositely charged region come close enough to each other, some of the electrons and ions, running between them, creating a glowing plasma channel, which for them rush the other charged particles. So is lightning discharge.
During this discharge is allocated an enormous amount of energy - up to one billion joules. The temperature of the channel reaches 10 000 K, which gives rise to the bright light that we see when the lightning. Clouds constantly discharged through these channels, and we see symptoms atmospheric phenomena in the form of lightning.
A red-hot environment vzryvoobrazno expands and causes a shock wave that is perceived as thunder.
We can simulate lightning, let miniature. Experience should be in a dark room, otherwise nothing will be seen. We will need two elongated balloon. Try and inflate'll wrap a mesh around them. Then, making sure they do not touch at the same time we shall RUB them with woolen cloth. The air was full of them electrified. If the balls to pull together, leaving between them are minimal gap, from one to another through a thin layer of air will begin to slip sparks, creating flashes of light. At the same time we will hear a faint crackling - a miniature copy of the thunder during the storm.
Everyone who has seen the lightning have noticed that this is not a bright straight line and broken line. Therefore, the formation of a conducting channel for lightning call it "stepped leader". Each of these "steps" is a place where accelerated to relativistic velocities of the electrons are stopped due to collisions with air molecules and changed direction.
Therefore, lightning is a breakdown of the capacitor dielectric is air, and the plates - clouds and the earth. The capacity of such a condenser is small - approximately 0.15 UF, but energy is huge, as the voltage reaches a billion volts.
Lightning usually consists of several categories, each of which lasts only a few tens of millionths of a second.
Most lightning occurs within the cumulonimbus. Lightning happens when volcanic eruptions, tornadoes and dust storms.
There are several types of lightning on the form and direction of discharge. Discharges can occur:
- between a storm cloud and the ground,
- between two clouds,
- inside the cloud,
- get away from the cloud in a clear sky.