Lightning, Earthing and Staying Safe: Concept Map

Concept Map

Organise the vocabulary, quantities and relationships into a connected model.

This extension applies that lens specifically to Lightning, Earthing and Staying Safe.

Lightning is static electricity on an enormous scale. Inside a thundercloud, ice crystals and hail rub past each other in violent updraughts and transfer charge, so the bottom of the cloud builds up a huge negative charge while the ground below becomes positively charged.

Air is normally an insulator. But when the build-up becomes big enough, the charge tears a path through the air and neutralises in a fraction of a second — a lightning flash. The flash heats the air along its path so violently that the air explodes outwards, and that shock wave is thunder.

This matters here: the South African Highveld has one of the highest lightning-flash densities in the world, and lightning kills people in this country every summer.

Earthing is how we make the charge take a path we choose. A lightning conductor is a metal rod at the top of a building connected by a thick metal strip all the way into the ground. Metal conducts far better than brick or wood, so the charge runs down the strip and spreads harmlessly into the earth instead of blasting through the building.

Worked example — how far away is the storm? Light travels so fast that you see the flash effectively instantly, but sound travels at about 340 m/s, so it takes roughly 3 seconds to cover 1 km.

You see a flash and count 9 seconds before the thunder.

Check it the long way: $340 \times 9 = 3\,060$ m, which is about 3 km. If that gap gets shorter with each flash, the storm is coming towards you — go inside.