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Apr 22, 2019

Lightning

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By Allen Martis, USA [ Published Date: November 23, 2004 ]

Lightning is one of the most beautiful displays in nature. Since there is an enormous amount of current in a lightning strike, there is also an enormous amount of heat.  This heat is the actual cause of the brilliant white-blue flash that we see as a lightning bolt.

Lightning originates around 15,000 to 25,000 feet above sea level when raindrops are carried upward until some of them convert to ice. A cloud-to-ground lightning flash originates in this mixed water and ice region. The charge then moves downward in 50-yard sections called step leaders. It keeps moving toward the ground in these steps and produces a channel along which charge is deposited. Eventually, it encounters something on the ground that is a good connection. The circuit is complete at that time, and the charge is lowered from cloud to ground. The return stroke is a flow of charge (current) which produces a luminosity much brighter than the part that came down. This entire event usually takes less than half a second.

During thunderstorm conditions the turbulence in the cloud causes the charges to separate in such a way that the negative charges concentrate in the base of the cloud. Since like charges repel, some of the negative charges on the ground are pushed down away from the surface, leaving a net positive charge on the surface.

Opposite charges attract, so the positive and negative charges are pulled toward each other. Since the negative charges (electrons) are many thousands of times smaller than the positive charges (ions--charged atoms) they move much more easily and cover most of the distance. This first, invisible stroke is called a stepped leader.  As soon as the negative and positive parts of the stepped leader connect there is a conductive path from the cloud to the ground and the negative charges rush down it causing the visible stroke.

Lightning comes from a parent cumulonimbus cloud. These thunderstorm clouds are formed wherever there is enough upward motion, instability in the vertical, and moisture to produce a deep cloud that reaches up to levels somewhat colder than freezing. These conditions are most often met in summer.
Flashes that do not strike the surface are called cloud flashes. They may be inside a cloud, travel from one part of a cloud to another, or from cloud to air. Cloud-to-ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole, or other tall object. 

If you are caught outside in a storm, always look for appropriate shelter. Lightning can use you as a path to the earth just as easily as it can use any other object. Appropriate shelter would be a building or a car. If you do not have anywhere to go, then you should avoid taking shelter under trees. Trees attract lightning.

Never lie down on the ground. After lightning strikes the ground, there is an electric potential that radiates outward from the point of contact. If your body is in this area, current can flow through you. You never want the current to have the ability to pass through your body. This could cause cardiac arrest, not to mention other organ damage and burns.

If you are indoors, stay off the phone.  If you must call someone, use a cordless phone or cell phone. If lightning strikes the phone line, the strike will travel to every phone on the line (and potentially to you if you are holding the phone). Stay away from plumbing pipes (bath tub, shower). Lightning has the ability to strike a house or near a house and impart an electrical charge to the metal pipes used for plumbing.

With lightning bolt temperatures hotter than the surface of the sun and shockwaves beaming out in all directions, lightning is one of the most deadly natural phenomena known to man.

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