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Lightning

 

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Overview
Scientists know that lightning results from a complicated interplay of positive and negative electrical charges occurring in the 2,000 or so thunderstorms taking place on Earth at any given moment. To learn about what causes lightning, scientists had to learn about the interaction of electrons and positive ions. Electrons, tiny particles orbiting the outside of atoms, carry a negative charge. Positive ions are atoms or molecules that have lost an electron. Atoms and molecules normally have equal positive and negative charges, making them neutral. When different materials come in contact, electrons are transferred and one of the materials gains an excess of electrons and becomes negatively charged. When an object with a lot of positive or negative charges gets close to an object carrying the opposite charge, a spark jumps across the space between them to neutralize the charges. In a thunderstorm, that spark is a lightning bolt. It's only a couple of inches wide, but it leaps between the clouds and the earth at a remarkable 90,000 miles per second. The power in the stroke is three million megawatts, comparable to all the power generated in the United States at any one instant. The separation of positive and negative charges necessary for lightning begins during a thunderstorm, when rising water droplets collide with falling hailstones in the middle of the cloud. The hail strips electrons from the droplets and the top of the cloud becomes positively charged, while the bottom becomes negatively charged. What we see as lightning happens in a two-step process. Static electricity builds up between the earth and the cloud and a spark in the form of an invisible lightning bolt comes down from the cloud. Just before this bolt reaches the ground, it is met with an upward moving, positively charged spark. When the two collide, an explosion occurs as the return stroke travels up the bolt-the result: a visible flash called lightning.

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