CBSE Class 12-science Answered

Measurements show that there is an electric field surrounding the earth. Its magnitude is about 100 N/C at the earth's surface and points inward toward the earth's center. so the Earth is negatively charged.

The Earth is electrically charged and acts as a spherical capacitor. The Earth has a net negative charge of about a million coulombs, while an equal and positive charge resides in the atmosphere.

The electrical resistivity of the atmosphere decreases with height to an altitude of about 48 kilometres (km), where the resistivity becomes more-or-less constant. This region is known as the electrosphere. There is about a 300 000 volt (V) potential difference between the Earth's surface and the electrosphere, which gives an average electric field strength of about 6 V/metre (m) throughout the atmosphere. Near the surface, the fine-weather electric field strength is about 100 V/m.

The atmosphere is not a perfect insulator, and there is a small current between the electrosphere and the Earth. Negative charge leaks from the Earth and rises to the electrosphere. This is called the fair weather electric and it is about 2000 amperes (A) at any given moment. At this rate, the Earth's charge would dissipate in less than an hour, but, as it turns out, lightning recharges the Earth's surface by delivering negative charges back to the surface.