Corona discharge

• When an uncharged body is brought near a charged body having sharp corners there is large number of charges at the corners. Due to induction, they induce large number of opposite charges. This creates a very strong Electric field between them. Finally the dielectric strength breaks-down and there is fast flow of charges. This Spray of charges by spiked object is called Corona discharge. 
• The lightening arrester work on the principles of Corona discharge where the charge pass through conductor of arrester, and the buildings are saved