What is Lightning? - Definition, Types & Causes

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  • 0:03 What Is Lightning?
  • 0:44 How Does Lightning Form?
  • 2:56 Types of Lightning
  • 4:05 Lesson Summary
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Lesson Transcript
Instructor: Linda Fye
Have you ever wondered what lightning is and how it forms? In this lesson, you'll learn how lightning develops, different types of lightning, and what causes thunder.

What Is Lightning?

We've all heard the saying that lightning never strikes the same place twice, but is it true? The answer is absolutely not. In fact, lightning occurs so frequently that it would be hard for that to be true. At any given time, there are 2000 thunderstorms on the planet, and they produce around 6000 lightning strikes every minute. That's more than 8.5 million strikes a day. They each have 100,000 times the power of household electricity.

So, what is lightning? Lightning is a very quick electrical discharge that occurs between a cloud and the ground, between two clouds, or within a cloud. It can be seen as a bright flash and is followed by the sound of thunder.

How Does Lightning Form?

Lightning is usually associated with thunderstorms, which are short-lived localized storms that have vertical air motion, humidity, and instability. The exact mechanism of electricity developing in a storm is not very well understood. So, lightning is a bit of a mystery. However, there is a series of events that occur for lightning to develop that are known:

  • The development of a thunderstorm causes electrical charges to be separated.
  • The updraft of air carries positively charged water droplets with it.
  • The downdraft of precipitation transports negatively charged water drops downward to the bottom of the cloud.
  • The negative charges on the bottom attract positive charges on Earth's surface directly below the thunderstorm.
  • Then, the difference in charges on the bottom of the cloud and on the ground grows stronger and stronger until there must finally be a release.
  • A finger of negative electricity shoots down from the cloud and meets a finger of positive electricity that is shooting up from the ground. They connect and a surge of electricity strikes downward.

This may happen several times in rapid succession until all negative charges are gone from the bottom of the cloud. This type of lightning is called cloud-to-ground lightning. It only makes up about 20% of lightning in a storm, but it is the most destructive.

There are other types of lightning in a storm. Intra-cloud lightning happens within the same cloud. The separation of the charges from the top and bottom of the cloud produce lightning between them. Cloud-to-cloud lightning happens in storms in the same way, only the discharge occurs from one cloud to another.

Lightning is inevitably followed by thunder. When a lightning bolt strikes, it causes sudden heating and expansion of the air. This causes a shock wave that becomes a sound wave that we hear as thunder. The lightning and thunder occur at the same time, but to us it seems like the lightning is first. This is because light travels faster than sound. So, many of us have heard that you can tell how far away a storm is by counting how long it is between when you see the lightning and hear the thunder. This is true. Five seconds in between means the storm is about one mile away. If you don't hear any thunder, it means the storm is a dozen or more miles away.

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