Creative Corner

SHARPEN YOUR KNOWLEDGE
THUNDERSTORMS   DANGEROUS TO LIFE AND PROPERTY
What is thunderstorms?

A thunderstorm is a convective storm accompanied by lightning, rain and sometimes hails. Thunderstorm may be compared to the discharge of a condenser. A condenser consists of two parallel plates; held at a small distance apart. If the potential difference between the two plates is very large, the charge leaks to the plates at a lower potential and is accompanied by a sport. The nature of lightning in a thunderstorm is the same as in the case of discharging condenser
Let us see how do two different layers of a cloud acquire

Such large potential differences

Sun heats the surface of the earth more than the surrounding air. The air in contact with the surface of the earth is heated up and becomes lighter than the air above it. It, therefore rises up into a region of low pressure, expands and thereby cools. A stage is reached when the up going air cooled so much that it cannot hold all of its water in the form of vapour. The additional water vapour condenses into million of tiny water droplets to form a white fluffy cloud. The heat released during this condensation warms the air, driving it further upwards. Almost at every point the column is warmer than the surrounding air and therefore continues rising upwards. There it forms clouds of cauliflower shape, which later produce thunderstorms
In the rising cloud the water droplets turn into ice crystals, which grow until they are big enough to fall. On falling they melt into raindrops and are met by the up draughts of air from below.
Friction with air produces electric charge on these raindrops, as rubbing a piece of glass with a cloth charges the glass. The water drops, which have moved up, are positive with respect to the lower layers of the cloud. This process continues inside the cloud and potential difference between the two layers keeps on increasing. Finally a voltage is reached when the ionization starts, and the ions provide a conducting zigzag path for the charge to leak through. This is accompanied by emission of visible light and by explosive heating, which produces the cracking noise we call thunder
The potential difference between top and bottom of a thundercloud has been estimated to be of the order of a few billion volts.
The current always takes the path of least resistance. Since, the electric resistance of air is higher than that of earth, concrete or wood, lightning is more likely to strive the top of a tall building of tree than to pass through air to objects on the ground at a lower level.
Tall buildings are therefore usually provided with conduct us at their tops.These conductors are very thick,so that they can carry large current safely without melting.
In thunderstorm,it is advisable to remain inside a house .One should not stand under a tree or near metallic objects like telephone or electricity wires or water pipe.

Shivangini Patangia
Class - XI C