as we know that air is insulator of electricity.
when lightnening happen in the sky , how it strikes on the earth?(while air is present as a medium between sky and earth ,and air is an insulator. 

Asked by dvd.ravi | 2nd May, 2017, 10:28: AM

Expert Answer:

Air is an insulator, i.e. current cannot readily flow through open air—the charge in the clouds must reach large values before it will arc across the air. So when the electrical potential builds up, small charges leak out from the negative areas and flow swiftly and invisibly through this insulating air, form conductive channels through which the current flows.

Answered by Yashvanti Jain | 2nd May, 2017, 11:32: AM