Chapter: Rain, Thunder, and Lightning
CBSE Class 8 Science Notes
Thunderstorms are caused by the rapid upward movement of warm, moist air into cooler air.
Cumulonimbus clouds are responsible for producing thunderstorms. These clouds grow vertically, towering into the atmosphere.
Thunderstorms usually occur in summer when warm, humid air rises above heated ground.
The rising air cools and condenses to form tiny water droplets, which eventually grow into larger droplets or ice crystals.
Hailstones may form if ice crystals fall to the ground.
Thunder is produced when lightning heats the air rapidly, causing it to expand explosively.
Lightning occurs due to electrical discharges between clouds or from a cloud to the ground.
Lightning is a powerful discharge of electricity caused by the accumulation of negative charges at the bottom of a thunder cloud. These charges build up due to the separation of particles inside the cloud.
When the electric field becomes strong enough, it breaks the air's resistance, allowing a flash of electricity to jump between the cloud and the ground or between clouds. Lightning is accompanied by thunder due to the rapid expansion of heated air.
Benjamin Franklin, through his famous kite experiment, demonstrated that clouds contain electric charges.
Electric charges can be positive or negative. When two objects are rubbed together, they acquire equal and opposite charges. Like charges repel each other, and unlike charges attract each other. The separation of charges during a storm creates the conditions for lightning to occur.
Voltage refers to the difference in electric potential between two points. It measures the force that drives electric charges to flow from one point to another. During a thunderstorm, the voltage difference between the cloud and the ground can become extremely high, leading to the discharge of lightning.
An electroscope is a device used to detect, measure, and determine the nature of the charge on an object. It consists of a metal rod connected to two thin metal leaves that spread apart when charged. The electroscope shows the presence of static electricity, such as that present in thunderstorms.
The Earth's atmosphere is filled with electric charges that play a significant role in weather phenomena like thunderstorms. Atmospheric electricity builds up due to the movement of air and water particles in the atmosphere, creating charges within clouds.
Benjamin Franklin demonstrated the presence of electrical charges in the atmosphere using a kite during a storm. Lightning can cause serious damage, including burning trees, destroying buildings, and killing people or animals.
Lightning conductors are used to protect tall buildings by safely conducting the electric charges to the ground. It is important to take safety precautions during thunderstorms, such as staying indoors and avoiding tall structures.
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