Ask A Scientist
How does electricity get into the sky and form lightning?
Asked by: Raghav Pallapothu
School: African Road Elementary School, Vestal
Teacher: Kelly Wood
Hobbies/Interests: Piano, science
Career Interest: Surgeon
Answer from Ziang (John) Zhang
Assistant Professor of Electrical and Computer Engineering
Research area: Power system operation, renewable energy integration, distributed control system Interests/hobbies: Swimming, ice skating, soccer
You have asked two great questions! Storm clouds contain the electricity that forms lightning, but scientists haven’t reached a consensus on how storm clouds get charged. There are several theories yet to be proved. One theory states that the electrical charges are formed by collision of water droplets and ice sleet. Storm clouds are very tall compared with normal clouds, which can be as high as 70,000 feet. Within the storm cloud, there is turbulence constantly moving up and down; there are updrafts carrying tiny water droplets up and downdrafts containing ice sleet going down. When water droplets and ice sleet collide, electrons are knocked out from these small water droplets and travel towards the bottom of the storm cloud. And the bottom becomes the negative end of the cloud.
Consider a storm cloud as a giant rechargeable battery. The separation of electrons happening in the cloud is gradually charging this battery. We know atmosphere is not conductive in normal conditions. But the earth is a massive conductor. As you can imagine, if the voltage potential between the cloud and the earth is high enough, electrical charges can break through the air. And that’s how lightning is formed.
No two lightning flashes have the same shape. That is because when electrons are looking for a path to escape, they always looking for the shortest path between the cloud and the ground. The top of a building, a wet tree, or a person holding an umbrella on a flat land are all good short cuts between clouds and the ground. None of these environments are identical to each other; as a result, no lightning bolts are identical.
Lightning is an amazing phenomenon. An average lightning bolt contains about 5 billion joules of energy—that’s 1,389 kWh! In 2014, the average U.S. residential house uses 911 kWh per month. The energy in one lightning bolt is able to power a house more than a month.