Lighting is one of the most important and powerful display of electrostatics. The concept behind lighting is still not fully understood but the cloud build up a positive charge and a negative charge. When lighting is formed it is most common that on the bottom, the cloud is negatively charged and the top is positively charged. Now where does thunder come from? The electrons are rapidly moving and the air along the path emits light. While the electrons are rapidly moving it creates heat that rapidly expands creating thunder.