Return to my Physics pages
Go to my home page

Lightning

© Copyright 1998, Jim Loy

What causes lightning? Well, strong electrical charges build up in the clouds (usually cumulonimbus clouds), because of the motion of water, both upward and downward. In general, the top of the cloud becomes positively charged, and the bottom becomes negatively charged. When the charge at the bottom of the cloud becomes strongly negative, a positive charge tends to move along the ground, to a point directly under the cloud. So, we have a strong negative charge above, and a strong positive charge below.

The air in between is normally a very good insulator. It does not conduct electricity. But the two strong electrical charges, which I described above, pull the electrons right out of the air molecules (more or less). This air is "ionized." And it can conduct electricity, just like a metal wire (but not as easily). And a huge current (actually several short bursts of current) of electricity (lightning) goes from the cloud into the ground, momentarily neutralizing the charge, and returning the situation to normal. Lightning often goes from cloud to cloud, as well.

Some people live through being hit by lightning (Lee Trevino, for example). But, lightning is often fatal. Those who survive probably did not get the full blast of the lightning. Anyway, we are advised not to be under a tree during a storm. The inside of a car is very safe, as the electrical charge stays on the outside of the car.

There's an old saying that lightning never strikes twice in the same place. This is false. Lightning "seeks" out the high points on the ground, usually hills and trees and buildings. The Empire State Building has been hit hundreds of times in the same storm.

Lightning is accompanied by thunder. Lightning heats the air, rapidly. And thunder is the sound of the rapid expansion of the air. It is just like the little zap you sometimes hear when you touch a door knob. And, since light travels much faster than sound, there is a delay between seeing the lightning and hearing the thunder. You can measure the distance to the lightning, by counting the seconds of delay. Sound normally travels about 1100 feet per second.

Say the word "unionize." It's a trap, into which physicists and electronic (electrical) engineers and electricians (and people who read this article) can fall. These people may, without thought, pronounce it uhn-I-uhn-ize (with the I syllable pronounced like the English word "eye"). The word is, of course, pronounced YOON-yuhn-ize, and has nothing to do with ions.

How does a lightning rod (invented by Benjamin Franklin) protect a building? Doesn't it attract lightning? Yes, it attracts lightning, which goes through a wire into the ground, instead of into the building, and through your electronic equipment. But the lightning blast is not as strong an usual, because the lightning rod is very sharp, and it tends to soak up much of the charge before the cloud/ground situation is fully charged.

Franklin discovered that lightning was electricity, just like the static electricity that he could produce and store in his laboratory. To do this, he flew his kite in a storm. Wasn't that dangerous? Well, his kite was not struck by lightning, it slowly bled off electricity from the air with his lightning rod; the electricity traveled down the string, and charged a metal key tied to the bottom of the string. Franklin was able to store the electricity from the charged key. But, to answer your question, yes it was dangerous. Several scientists died trying to duplicate Franklin's experiment.

Return to my Physics pages
Go to my home page