Question

How lighting and thunder occur? What is the reason behind it?

Answer 1

Lightning is a huge electrical discharge that flows between clouds, from a cloud to air, or from a cloud to the ground. The charge develops because of the collisions between tiny ice particles within thunder clouds.
How does lightning form?
As tiny water droplets form inside a storm cloud, they are propelled towards the top of the cloud by strong internal winds (updraughts) where they turn to ice. Some of the pieces of ice grow into hail, but others remain very small. Some of the hail that forms becomes too heavy to be propelled by the updraughts and so begin to fall back through the cloud, bumping into smaller ice particles as they do so. During these collisions, electrons are transferred to the hail giving the hail a negative charge, while the ice particles that have lost electrons gain a positive charge.

The updraughts continue to carry the ice particles upwards, giving the top of the cloud a positive charge. The hail continues to fall through in the lower part of the cloud, giving it a negative charge. As well as being attracted to the positive charge in the top of the cloud, the surplus of electrons in the cloud base are attracted to positive charge in other clouds and on the ground. If the attraction is strong enough, the electrons will rapidly move towards the positive atoms. The path they make in doing so forms the channel we see during a flash of lightning.

As negative charge builds at the base of the cloud, the electrons near the ground's surface are repelled. This leaves the ground and the objects on it with a positive charge. As the attraction between the cloud and the ground grows stronger, electrons shoot down from the cloud cutting through the air at around 270,000 miles per hour.

Thunder is created by a rapid expansion of air. Think of a balloon popping. There is a sudden release of noise due to the rapid expansion of air. When lightning moves through the air it increases the temperature of the air dramatically in a very short period of time. The air then cools rapidly. This rapid expansion and contraction of the air gives off the sound waves that is heard from the lightning.