CBSE Class 12-science Answered
As the storm of the cloud established in the sky, Heavy wind moves towards up through the cloud and rub over the water drops present in the cloud, due to friction between them electric charge produces in the cloud. Lighter drop late carries positive charge, place at upper part of the cloud and heavier drop late carries negative charge, place at the lower part of the cloud. In this way, top of the cloud become positive whereas, bottom of the cloud become negative.
The electric charges start flowing with high speed when amount of the top and the bottom charges becomes large enough. As these positive and negative charges meet, spark gets produced. When the negative charges passes at its bottom over a ground or tall building, it induces positive charge on the top of the building. As the amount of charge increases, the cloud will create a negative charge that tends to make a path towards the ground which results in a narrow streak of electrical discharge.