i. During the development of a thunderstorm, the air current moves upward and the water droplets move downward.

ii. These movements of air and water droplets cause charge separation.

iii. The positive charges collect at the upper edges of the clouds.

iv. The negative charges collect at the lower edges of the clouds.

v. There is an accumulation of positive charges near the ground also.

vi. When the magnitude of the charges become too large, negative and positive charges meet.

vii. This produces streaks of bright light and sound.

viii. Hence, lightning causes by the accumulation of charges on the clouds.