Asked by pritam | 28th May, 2010, 01:53: PM

Expert Answer:

Dear student,

The sky is filled with electric charge. In a calm sky, the positive (+) and negative (-) charges are evenly spaced throughout the atmosphere. Therefore, a calm sky has a neutral charge.

Inside a thunder storm, the electric charge is spread out differently. A thunderstorm is made up of ice crystals and hail stones( precipitate in pellets of ice and hard snow). The ice crystals have a positive charge, and the hailstones have a negative charge.

An updraft(upward current of air) pushes the ice crystals to the top of the thunderstorm cloud. At the same time, the hailstones are pushed to the bottom of the thunderstorm by its downdraft(A strong downward current of air). These processes separate the positive and negative charges of the cloud into two levels: the positive charge at the top and the negative charge at the bottom.

During a thunderstorm, the Earth's surface has a positive charge. Because opposites attract, the negative charge at the bottom of the thunder cloud wants to link up with the positive charge of the Earth's surface.

Once the negative charge at the bottom of the cloud gets large enough, a flow of negative charge rushes toward the Earth. This is known as a stepped leader. The positive charges of the Earth are attracted to this stepped leader, so a flow of positive charge moves into the air. When the stepped leader and the positive charge from the earth meet, a strong electric current carries positive charge up into the cloud. This electric current is known as the return stroke and we  see it as lightning.



Answered by  | 29th May, 2010, 11:46: AM

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