What causes Sparks and Lightning?

Description
Here electric field for asymmetrical conductor is calculated. Tendency of charge to accumulate near amore curved part of a body is demonstrated by charging up a pot and examining its charge at various parts.Due to this property of charge it leaks from sharp ends. This helps in explaining the lightning and sparks in atmosphere

Prof. Walter Lewin, 8.02 Electricity and Magnetism, Massachusetts Institute of Technology: MIT OpenCourseWare), http://ocw.mit.edu (Accessed January 14, 2011). License: Creative Commons BY-NC-SA: http://ocw.mit.edu/terms/#cc