How an electric current passes through air during lightining??
Answers
It is true that air is a poor conductor of electricity. That could change if electrons or ions or both are present in air in sufficient numbers. What happens during a thunderstorm is roughly as follows: Charges build up at the bottom of the cloud to such an extent that the cloud bottom could be billions of volts with respect to the surface of the earth. In such a situation, charges accumulate on the surface of the earth too. These two sets of charges create a high electric field between them. As a result of the high electric field, air can get ionised, especially near pointed objects (what is sometimes called "St. Elmo's fire"). Once such ions are formed, they get accelerated in the high electric field, acquiring a lot of energy quickly. When these ions or electrons collide with other molecules of air, they also get ionised and go through the same process. Thus, the number of ions increases very fast (the process is known as an "avalanche"). These ions and electrons provide the necessary impetus to start forming a conducting path between the earth and the cloud. Once a conducting path is formed then discharge can happen easily.
Lightning is not “normal circumstances”.
When electrical voltage exceeds more than 3 million volts per meter, then the air literally FAILS as a insulator. The air literally ionized and becomes conductive and that what you witness with lightning - a voltage breakdown of air. The electrical current literally jumps the breakdown gap with spectacular light and sound effects due to the high energy involved.
For lightning to jump 1000 meters from a cloud to ground involves 3 billion volts!
And that is lightning - spectacular failure of air as an insulator becoming a conductor if the voltage if allowed to build up too high (by charged winds in clouds).
