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explain, how a charged cloud passing over a tall building causes lightning?
Lightning is an electric discharge in the atmosphere between oppositely charged clouds.
A cloud is a visible mass of condensed water vapours floating in the atmosphere, high above the ground. A heavy, dark, rain cloud is called storm cloud. When a storm cloud develops in the sky, strong winds move upwards through the cloud and make the water drops present in the cloud to rub against one another. This rubbing together of water drops produces extremely large electric charges in the cloud due to friction. The small water drops acquire a positive charge and, being lighter, more to the upper part of the cloud with rising wind. On the other hand, the larger water drops acquire a negative charge and, being heavier, come down in the lower part of the cloud. In this way, the top of the cloud becomes positively charged whereas the bottom of the cloud becomes negatively charged.
When the amount of opposite electric charges on the top and bottom of a storm cloud becomes extremely large, then electric charges start flowing with high speed through the air between them.
Storm clouds carry electric charges. Now, if a storm cloud having negative charges at its bottom passes over a tall building, it induces positive charges on the roof of the building. when the electric charges on the bottom of the cloud become extremely large, then these tremendous electric charges present on the bottom of the charged cloud suddenly flow to the roof of the building and we see a flash of lightning coming towards the building. We say that lightning has struck the building. Thus, lightning strikes the earth or its tall structures when electric charges flow between the cloud and the earth through a tall building, a tree or any other object.


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