Lightning is the result of a large charge separation within a cloud. Clouds are composed of millions of ice particles and water droplets. These particles collide with other condensing moisture as it rises, and when they do, electrons are knocked loose. These electrons build up at the bottom of a cloud and make it negatively charged. The rising moisture molecules, now missing electrons, become positively charged and gather at the top of the cloud. This creates a charge separation, which has an electric field that is negative at the bottom and positive at the top. As the collisions continue, the electric field builds so strong that it gives the planet's surface a positive charge. When these charges become powerful enough, the cloud's electricity is discharged toward the Earth's surface, which results in lightning.
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