lightning
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The build-up of electrical charge during a thunderstorm that causes lightning. Negative charge builds up at the bottom of a cloud; positive charges rise from the ground and also within the cloud, moving to the top of it. A conducting channel forms through the cloud and a giant spark jumps between opposite charges causing lightning to strike within the cloud and from cloud to ground.
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All isolated high buildings attract lightning, and particularly those of predominantly metal construction like the mainly iron Eiffel Tower in Paris, France. This photo was taken on the morning of 3 June 1902 and is one of the earliest photographs of lightning in an urban setting (although that setting has changed fairly radically in the intervening century).
High-voltage electrical discharge between two rainclouds or between a cloud and the Earth, caused by the build-up of electrical charges. Air in the path of lightning ionizes (becomes a conductor), and expands; the accompanying noise is heard as thunder. Currents of 20,000 amperes and temperatures of 30,000°C/54,000°F are common. Lightning causes nitrogen oxides to form in the atmosphere and approximately 25% of atmospheric nitrogen oxides are formed in this way.
According to a 1997 US survey on lightning strength and frequency, using information gathered from satellite images and data from the US Lightning Detection Network, there are 70–100 lightning flashes per second worldwide, with an average peak current of 36 kiloamps.
| Lightning kills more than 200 people per year in the USA and causes extensive damage to property and lost revenue due to power cuts. |
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