Chapter 12: Some Natural Phenomena
Lightning: A Massive Electric Spark
Lightning is a natural electrical discharge of very high energy that occurs during thunderstorms. It is essentially a giant spark, similar to the sparks you might see from a loose electrical wire, but on a much larger scale.
The Charging Process
During the development of a thunderstorm, air currents move upwards while water droplets move downwards. This vigorous movement causes a separation of charges. Generally, the positive charges collect near the upper edges of the clouds, and the negative charges accumulate near the lower edges. There is also an accumulation of positive charge on the ground.
Electric Discharge
When the magnitude of the accumulated charges becomes very large, the air, which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. This process is called an electric discharge.
The fact that lightning is an electrical phenomenon was demonstrated by American scientist Benjamin Franklin in 1752. Through his famous kite experiment, he proved that the clouds carry electric charge.
Lightning Safety
Protecting ourselves from lightning is crucial during a thunderstorm.
During a Thunderstorm:
- Find Safe Shelter: A house or a building is a safe place. A car or a bus with windows and doors shut is also a safe shelter.
- If in an Open Area: Stay away from tall trees, poles, or other metal objects. Do not lie on the ground. Instead, squat low on the ground with your hands on your knees and your head between the hands.
- Indoors: Avoid contact with water (bathing), electrical appliances, and telephones with cords. Mobile phones and cordless phones are safe to use.
Lightning Conductors
A lightning conductor is a device used to protect buildings from the effect of lightning. It consists of a metallic rod, taller than the building, which is installed in the walls of the building during its construction. It provides an easy route for the lightning charge to transfer to the ground without damaging the building.
Earthquakes: Shaking of the Earth
An earthquake is a sudden shaking or trembling of the Earth lasting for a very short time. It is caused by a disturbance deep inside the Earth’s crust.
What Causes an Earthquake?
The outermost layer of the Earth, the crust, is made of several large and small rigid plates called tectonic plates. These plates are in continual motion. Earthquakes are caused by the sudden movement or collision of these plates. The boundaries of the plates are the weak zones where earthquakes are more likely to occur, known as seismic or fault zones.
Measuring an Earthquake
The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale, developed by Charles F. Richter in 1935. Really destructive earthquakes have magnitudes higher than 7 on this scale. The tremors are recorded by an instrument called a seismograph.
Protection from Earthquakes
Since earthquakes cannot be predicted, it is important that we take necessary precautions to protect ourselves.
Safety Measures:
- If you are at home: Take shelter under a table and stay there till the shaking stops. Stay away from tall and heavy objects that may fall on you.
- If you are outdoors: Find a clear spot, away from buildings, trees, and overhead power lines. Drop to the ground.
- Building Design: In highly seismic areas, buildings should be designed to be "quake-safe." It is advisable to make the structure simple so it is earthquake-safe. Use light construction materials like timber and avoid heavy ones like mud and brick.
Frequently Asked Questions (FAQ)
What causes the sound during a thunderstorm?
The sound (thunder) is produced by the rapid heating of air by the lightning spark. The air expands explosively, creating a shockwave that we hear as thunder.
What is a seismograph?
A seismograph is an instrument that measures and records the ground motion, including the seismic waves generated by earthquakes. The recording produced is called a seismogram.
Why are buildings in Japan often made of wood and bamboo?
Japan is in a highly seismic zone. Light materials like wood and bamboo are used because they are more flexible and less likely to cause heavy damage if they collapse during an earthquake compared to heavy materials like concrete and brick.
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