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Q & A: Energy in Lightning

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Most recent answer: 10/22/2007
Q:
what is the potential and kinetic energy for lightning?
- Demetrios (age 14)
Brier, Washington, United States of America
A:
Dear Demetrios,

Potential energy is a nice way to understand the reason that lightning happens. During a thunder-storm, the bottoms of clouds tend to become negatively charged, which causes the ground (where we live) to become positively charged. In the language or electricity we say that there is a potential difference between the clouds and the ground, which just means that the positive charges on the ground (and the negative charges on the cloud bottoms) have lots of potential energy.

Usually when things have lots of potential energy they will start moving if you let them. In the case of the charges in the cloud, they will try to move to the ground. Normally, this is difficult since air is a very good electrical insulator, but if the difference in potential between the clouds and the ground gets big enough (often many millions of volts) the charges can jump, resulting in lightning.

As the first electrons jump, they will leave a small trail of ionized gas in the air. This trail is a pretty good conductor of electricity, so the rest of the charges in the cloud will quickly follow down this path, causing the lightning bolts that we often see.

The potential energy that was present to begin with will be reduced by this motion of charges, and instead there will be lots of kinetic energy (heat) produced as the lightning ionized the air and slams into the ground.

Mats

(published on 10/22/2007)

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