Science
How does lightning form?
Lightning forms when charges separate inside a storm cloud — light positive charge near the top, heavy negative charge near the bottom. When the difference grows large enough, it overcomes the air's resistance and discharges as a giant spark.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how lightning works.
Step by step
- 1Rising and falling ice and water in a cloud separate electric charge.
- 2Negative charge builds at the cloud base, positive on the ground below.
- 3When the voltage is high enough, air breaks down and a spark jumps.
- 4The bolt heats air so fast it explodes outward as thunder.
Frequently asked questions
- What causes lightning?
- A buildup of separated electric charge in storm clouds that discharges as a massive spark.
- Why does thunder follow lightning?
- Lightning superheats the air, which expands explosively and creates the sound wave we hear as thunder.
- Why do we see lightning before hearing thunder?
- Light travels far faster than sound, so the flash reaches us almost instantly while the sound lags behind.