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Getting a shock from the doorknob after rubbing your foot on a floor carpet is due to discharge of electric charges. Discharge occurs when the electrons on your hand are quickly pulled to the positively charged doorknob. The movement of electrons, which is felt as a shock, causes the body to lose a negative charge. Electric discharge takes place mostly in gases (fluids).
Touching the doorknob
Lightning is another example of discharge that takes place in clouds.
  • The discharge of electric charges produces lightning from cloud to cloud or from cloud to ground. During a thunderstorm, the air moves upward rapidly.
  • The air that rushes carries small ice crystals upwards. Simultaneously, small water drops move downwards.
  • When they both collide, ice crystals become positively charged and move upwards, and the water drops become negatively charged and move downwards.
  • The upper portion of the cloud is positively charged, and the lower portion of the cloud is negatively charged. When they both come into contact, electrons in the water drops are attracted by the ice crystals' positive charges. Thus, electricity is generated, and lightning is seen.
  • Sometimes the lower portion of the cloud, which is negatively charged, comes into contact with the positive charges accumulated near the trees, mountains, and even people on the earth. This discharge produces a lot of heat and sparks that result in lightning.
Huge quantities of electricity are discharged in lightning flashes and can reach temperatures of over \(30,000°C\). This intense heating causes the air to expand explosively fast, and then it contracts. This expansion and contraction create a shock wave that turns into a booming sound wave known as thunder.
Sometimes we may see lightning before the thunder is heard. It happens due to the distance between the clouds and the surface is very long, and the speed of light is more than the speed of sound.