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Chapter Analysis
Intermediate14 pages • EnglishQuick Summary
Chapter 12 of the Class 8 Science textbook titled 'Some Natural Phenomena' covers the natural occurrences of lightning and earthquakes, explaining their causes, effects, and safety measures. The chapter describes the types of electrical charges, the transfer of charge, and explains the phenomenon of lightning and how it can be mitigated with lightning conductors. Additionally, it covers earthquakes, detailing their causes, effects, and safety precautions during such disasters. It's an essential chapter that blends scientific explanations with practical safety advice for natural phenomena.
Key Topics
- •Types and interaction of electrical charges
- •Transfer of charge and earthing
- •Action of lightning and its safety measures
- •Phenomenon of earthquakes and their causes
- •Effects and safety measures for earthquakes
- •Use of seismograph for measuring seismic waves
- •Role of lightning conductors
Learning Objectives
- ✓Understand the types of electrical charges and their interactions
- ✓Explain the process of transferring charges and the concept of earthing
- ✓Identify safety precautions during lightning and thunderstorms
- ✓Describe the causes and effects of earthquakes
- ✓Understand the use of a seismograph and the Richter scale
- ✓Implement safety measures to mitigate earthquake damages
Questions in Chapter
Which of the following cannot be charged easily by friction?
Answer: A copper rod
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When a glass rod is rubbed with a piece of silk cloth the rod
Answer: becomes positively charged while the cloth has a negative charge.
Page 163
Write T against true and F against false in the following statements.
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Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
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Explain why a charged body loses its charge if we touch it with our hand.
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Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
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Suggest three measures to protect ourselves from lightning.
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Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
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Describe with the help of a diagram an instrument which can be used to detect a charged body.
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List three states in India where earthquakes are more likely to strike.
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Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
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The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Page 164
Additional Practice Questions
What is an electroscope and how does it work?
mediumAnswer: An electroscope is a device used to detect electric charge on a body. It consists of a metal rod with thin metal leaves at one end. When a charged object touches the metal rod, the leaves repel each other due to like charges. It's useful for observing static electricity.
Why is it advised not to use mobile phones during a lightning storm?
easyAnswer: Although mobile phones themselves do not attract lightning, they can pose a risk because lightning can pass through the wires and metal pipes in buildings. It's safer to avoid all electrical conductors during a thunderstorm.
How do tectonic movements lead to earthquakes?
mediumAnswer: Tectonic movements involve the shifting of large earth plates, and their collision or brushing past each other can cause stress that is released in the form of seismic waves, leading to earthquakes.
What steps should be taken during an earthquake if you are indoors?
hardAnswer: Take cover under sturdy furniture, stay away from windows, and keep calm. Once shaking stops, evacuate the building and move to an open area, avoiding utility lines and damaged structures.
What role do lightning conductors play in protecting buildings?
mediumAnswer: Lightning conductors are metal rods installed on buildings to direct the electrical discharge from lightning safely to the ground, preventing structural damage and fires.
Explain the concept of earthing and its importance.
easyAnswer: Earthing provides a path for electrical charges to safely dissipate into the ground, reducing the risk of electrical shocks and fires by preventing the buildup of charge.
NCERT Exemplar
AvailablePractice with NCERT Exemplar problems and solutions for this chapter. Exemplar problems are designed to help you master the concepts with advanced-level questions.
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