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Lightning - Lesson Summary

Lightning is a natural phenomenon that has fascinated people for ages. Several people thought and researched about the cause of lightning and its process. Benjamin Franklin discovered that there is an electric discharge between clouds that produces a spark, and it is the electric spark between the clouds and the earth that appears as lightning. His famous kite experiment proved this fact.

The occurrence of lightning is as follows. The formation of clouds involves friction between water droplets in the atmosphere. The friction charges the particles in the atmosphere. By a process, not yet completely understood, among the positive and negative charges, the negative charges accumulate at the bottom of the cloud and the positive charges at the top. As the accumulation of the charges increases, the cloud will induce positive charges on the ground nearby. As the amount of charge increases, the negative charges on the cloud tend to make a path towards the ground, and it results in a narrow streak of electrical discharge, which we call lightning.

An electroscope is a device that detects whether an object is charged or not, and the type of charge on a body. It consists of a glass jar fitted with a cork lid and a metallic wire passing through it. There are two metallic strips at the bottom of the wire. The upper end of the wire is connected to a metal disc. When a positively charged body is brought in contact with the metal disc, the charge is transferred to the metal strips through the wire, and the strips diverge because both the strips acquire like charges and they repel. If the metal disc of the electroscope is touched with the hand, it loses its charge to the ground by transfer of charge through the human body. This is called earthing.


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