The sound of thunder is produced when a strike of lightning produces a huge amount of heat. Heated to a temperature of around 30,000°C (54,000T), the air around the lightning expands very quickly — faster than the speed of sound. This rapid expansion of air causes the crashing thunder sound.
1. The electricity passes through the air and causes air particles to vibrate. The vibrations are heard as sound.
2. The lightning is also very hot and heats up the air around it. Hot air expands, and in this case the air expands very quickly, pushing apart the air particles with force and creating more vibrations.
This is what we hear and call thunder – the rumbling of thunder is simply caused by the vibration or sound of the air affected by lightning. If you’re nearby to a lightning strike, you may have heard thunder as a really loud crack, almost like the sound of a whip being cracked. But, most of the time we hear thunder as a loud, long rumble.
In fact, the crack sound is the direct sound of the lightning near us, reaching our ears. The more common rumbling effect happens when thunder echoes off objects all around us. This happens a lot in towns and cities, where there are lots of buildings for the noise to bounce off. However even in flat areas of land, with no trees or other objects, there is quite often a rumble as the thunder simply bounces off the ground on its way to our ears. All this echoing transforms the original ‘crack’ sound into a longer ‘rumble’!
Thunder is the sound produced by rapidly expanding and contracting pockets of air associated with lightning. So to understand thunder, it helps to know a little about lightning.
Lightning is an electrical discharge that occurs within a cloud, between clouds, from clouds to the ground and even from the cloud top into the surrounding atmosphere. Within a developing thunder cloud (cumulonimbus), there are millions of tiny ice crystals and super-cooled water droplets rubbing up against each other as they move up and down. This causes a positive charge to develop at the top of the cloud and a negative charge at the bottom. If this build-up of charge grows large enough, a discharge can occur—lightning. The thunder sound is the explosive expansion of air, heated to around 30 000 °C (hotter than the surface of the sun!) directly around the lightning bolt, generating an audible shock wave. Thunder can usually be heard up to 15 km from the lightning, but under optimum conditions, such as on a still night, it can sometimes be heard as far away as 25 km.
Picture Credit : Google
