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atmosphere are mainly due to troposphere and stratosphere. The troposphere extends up to 12 km from the surface of earth, while the stratosphere extends from 12 km to about 50 km from the surface of the earth. The earth is good conductor of electricity and at low altitude, atmosphere is poor conductor of electricity. The small conductivity of the atmosphere is due to the ionization produced by the high energy particles of the cosmic rays, which are constantly hitting the earth from the outer space. The conductivity of space is greatly influenced by the presence of dust particles and by the humidity conditions. However as we go up the conductivity of the atmosphere goes on increasing. At the top of the stratosphere i.e. at a distance of 60 km from the surface of the earth, the atmosphere is quite a good conductor of electricity. The electrical phenomena in atmosphere take place between the surface of earth acting as one conducting layer's and the top of the stratosphere (acting as the other conducting layer), which are separated by a thick atmosphere of varying conductivity. The two layers form a spherical capacitor of large capacitance which can be calculated. Now we state a few experimentally observed facts about electrical properties of atmosphere: 1. Ar ground level, there is a downward electric field of about 102
m'all over the earth. This goes on decreasing with height. At 10 km above the surface of earth, it becomes quite small, while at end
it is negligible. . 2. There is a potential difference of the order of 4X10' V between
the surface of earth and that of the stratosphere. Most of the - potential difference occurs at low altitudes. 3. Due to downward electric field at ground level, earth has a negative
surface charge density over the surface of earth. The negative surface charge density of the earth is 10-9 cm?
total charge on the surface of the earth is = - 5 x 10' C 4. The top of the stratosphere has an equal positive charge i.e. + 5 x
10'C the potential difference between the earth's surface and that of the stratosphere should be 5 x 10RV However, the observed value (4x10'v) is much lesser. The explanation for this difference is the fact that the intervening air becomes more and more conducting as we go up.
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GEHT WEIT SUR 122
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