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Lightning Flash

Why does lightning flash ?

During a storm, flashes of lightning followed by thunder, light up the sky like fireworks. It is an impressive and sometimes frightening spectacle. The flash occurs for several reasons. As the air heat and cools, it expands and contracts, and this cause changes in the movement of air and pressure.The water droplets at the top of a cloud have a positive electrical charge, while those at the bottom of a cloud are negatively charged.
   When the clouds are low enough, the negative charge in the water droplets attract a positive charge from the Earth. As a result, electrical energy is released with a flash. This causes the air to be heated tremendously high temperature, which in turn, causes the air to expand suddenly with an explosive noise that we call thunder. Though thunder and lightning occur at the same time, we see lightning first, and then hear thunder, because light travels faster than sound.

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