Thunder is the loud sound you hear after a lightning flash. Lightning is a bolt of very hot electricity that also makes the air around it very hot. In fact, that air can get as hot as 54,000 degrees. That’s about 44,000 degrees hotter than the surface of the sun!
When air gets hot, it gets bigger. A balloon that has been stretched over the mouth of an empty plastic bottle will inflate when the bottom of the bottle sits in a bowl of hot water, heating up the air in the bottle. This happens because the air has warmed up, expanded, and the bottle can’t hold it all.
Just like the air in the bottle, the air around lightning gets bigger, too. But this happens really fast, like a giant blast, because it’s so hot. It smashes into the colder air around it, cools off fast, and shrinks again quickly, making a sound wave that we hear as thunder.
Picture Credit : Google