Ch 15 covers two powerful natural phenomena — lightning and earthquakes. Students learn about electric charges, how lightning forms, lightning safety, the causes of earthquakes, and how to stay safe.
Clouds become charged due to friction between water droplets and air. When the charge difference is large enough, an electric discharge occurs — lightning. It can occur between clouds or between cloud and ground. Lightning conductor: metal rod on buildings provides a safe path for lightning current to reach the ground.
Earthquakes are caused by the movement of tectonic plates. When plates push, pull, or slide against each other, tremors occur. Seismograph records earthquake intensity. Richter scale measures magnitude. Earthquake-resistant buildings and safety drills save lives: Drop, Cover, and Hold On.
Download: https://ncert.nic.in/textbook/pdf/hesc115.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
Lightning tends to strike tall, pointed objects. Trees are tall and can be struck easily. If you're under a tree hit by lightning, the current can jump to you. The safest place is inside a building or car (metal body acts as a Faraday cage).
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