Aquila Children's Magazine The Electric Issue - Page 6

According to the Institute of Physics , a single lightning bolt contains enough energy to toast 100,000 slices of bread . That ’ s a lot of toast ! ( or 50,000 toasted sandwiches . How many panini ? Ed )

Thunderclouds , or cumulonimbus ( cumulus - heap ; nimbus - rainy cloud ) are often referred to as anvil clouds because they are a similar shape to a blacksmith ’ s anvil .

They form over the warm surface of the Earth on humid days . They are very tall , stretching above other clouds .
It is very cold inside a thundercloud ( -15 to -25 ° C ), which means you get a mixture of supercooled water droplets , ice crystals and hail . Warm air from the land causes updrafts inside the cloud that carry some of the lighter ice crystals and water droplets upwards , while the heavier droplets and hail stay still or fall from the cloud .
Words : Dr Sarah Bearchell . Illustration : Sophie Bryant-Funnell
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The particles crash into each other and , as they move , some electrical charge is transferred . Exactly how it happens is not understood but the top of the cloud becomes more positively charged compared to the bottom of the cloud . This separation of charge makes an electric field .
The thundercloud also causes a positive charge beneath it . So now we have positively charged Earth , a relatively negatively charged cloud base and a positively charged cloud top . Some lightning travels from cloud-to-cloud or within a single cloud . We know most about cloud-to-ground lightning , simply because it is easier to predict and measure .
When the electric field is strong enough , a leader of charged air is formed ; it often branches in a tree-like shape . The cloud leader may join an upwards leader from the ground , usually coming from a tall object such as a flag pole . When the two leaders meet , the path is complete from cloud to ground and the electric current flashes through as it discharges .
The massive flow of electricity makes the leader channel become hotter than the surface of the sun and we see a flash of brilliant blue-white lightning . The sudden heating of the air makes it expand explosively and this causes a shock wave , which we hear as thunder .
Light travels at about 300 000 000 metres in a second , but sound travels at just 340 metres in a second . This is why the lightning flash reaches us before the rumble of thunder . The further we are from a storm , the greater the delay between lightning and thunder . A one-second gap means the storm is about 340 m ( 0.21 miles ) away and a five-second gap means the storm is about a mile away .