Lightning conductors

Lightning. A fascinating, beautiful, scene. But it can also be dangerous, even deadly. Thousands of people die each year from being struck by lightning. What is lightning, really, and how can you protect yourself from it?

It all starts in the clouds. Warm, humid air rises in the atmosphere, where it condenses and forms clouds. As tiny water droplets move about in the cloud, they get electrically charged. If a lot of the water droplets are electrically charged this way, we've got ourselves... Thundercloud!

Negatively charged particles gather mostly at the bottom of the thundercloud, and positive ones at the top. The potential difference, between the cloud and the ground can be hundreds of millions of volts. That's a very high voltage. It's so high, that the negative charge in the thundercloud repels the negatively charged particles in the ground. As they are pushed deeper, the ground under the cloud becomes positively charged.

Normally, air cannot conduct electricity. It's an insulator. But when the voltage is high enough, a bolt of lightning can strike through the air. It is a complex chain of events, which allows electricity to jump through the air like this, and scientists are still struggling to explain exactly what happens. Anyway, lightning is a sudden...

electrostatic... discharge... through the air. The discharge can happen between two regions in the same cloud, or between two clouds. But it's lightning that strikes between a cloud and the ground, that we need to look out for.

Lightning is lazy, like most things in nature: It takes the easiest path it can find between the negatively and the positively charged areas. The easiest path often means the shortest path. That's why lightning is more likely to strike tall buildings and trees, than it is to strike the ground in between houses and trees. But you can't be too sure. Other things - like the humidity in the air - also affect which path is the easiest for lightning to take.

Since we know that lightning is lazy, we can use this knowledge to protect ourselves from it. Take this building for instance. It stretches high in the sky, providing a short and easy path from the cloud. If lightning strikes the building, an electrical shock of several hundred million volts will run through it, which could destroy electronic equipment, electrocute people, and possibly set the entire building on fire. To make sure that doesn't happen, we have to provide an even easier path for the lightning to take to the ground.

At the very top of the building we place a steel rod: a lightning rod. The pointed ends makes this an especially easy path for lightning to take. From it, runs thick metal wires -- lightning conductors -- along the sides of the building, all the way down to the ground. The wires continue down into the ground, where they are attached to a large metal object, from which the charged particles can enter the ground. This is the ground - or earth - terminal.

These three components make up a lightning protection system. Often we use the term lightning conductor to mean the entire system. Next time a bolt of lightning strikes between the cloud and the building, it will take the easiest path -- the path of least resistance. And now, there is no easier path for the electricity -- than through the lighting conductor.