NCERT Solutions for Class 8 Science Chapter 12
Sure, here’s a summary of the chapter “Some Natural Phenomena” The chapter focuses on two main natural phenomena: lightning and electricity, and earthquakes.
Electricity and Lightning:
- It explains how objects can gain an electrical charge by rubbing against other objects.
- There are two types of charges: positive and negative. Like charges repel each other, while unlike charges attract.
- The built-up electrical charges are called static charges. When these charges move, it creates an electric current.
- The chapter discusses how a tool called an electroscope can be used to detect if an object is charged.
- Lightning is caused by the movement of electrical charges between clouds or between clouds and the ground.
- It highlights the dangers of lightning strikes and offers safety precautions.
Earthquakes:
- The chapter Some Natural Phenomena doesn’t go into the details of the earth’s structure, but it explains that earthquakes are caused by sudden movements of the Earth’s crust.
- It emphasises the importance of safety measures during earthquakes, such as taking shelter away from buildings, trees, and power lines.
Overall, the chapter provides a basic understanding of these two natural phenomena and offers some practical safety tips.
NCERT Solutions for Class 8 Science Chapter 12
Q1. Which of the following cannot be changed easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth
Ans: (b) A copper rod
Q2. When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire a positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire a negative charge.
(d) becomes negatively charged while the cloth has a positive charge
Ans: (b) becomes positively charged while the cloth has a negative charge.
Q3. Write T against true and F against false in the following statements.
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) Lightning conductors cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.
Ans:
- False
- True
- False
- False
Q4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Ans: Winter sweater crackles because friction makes it gain a charge. Taking it off creates a spark (the sound) that neutralizes the charge.
Q5. Explain why a charged body loses its charge if we touch it with our hand.
Ans: Our hands conduct electricity. Touching a charged object lets the charge flow through us, often to the ground, neutralising the object’s charge.
Q6. 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?
Ans: The scale that measures the earthquake’s size, not necessarily destructive energy, is the moment magnitude scale (Mw).
For your other questions:
- Yes, a seismograph can record an earthquake of magnitude 3.
- An earthquake of magnitude 3 is unlikely to cause much damage. These are generally felt as weak tremors.
Q7. Suggest three measures to protect ourselves from lightning.
Ans: Find shelter in a building.
Avoid open areas, tall objects, and water.
Minimise contact with conductors (metal, wires).
Q8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Ans: It all boils down to the type of charge:
- Like charges repel: When two charged balloons have the same type of charge (positive-positive or negative-negative), they push each other away because their electrical forces are repulsive.
- Opposites attract: An uncharged balloon doesn’t have an overall charge. When a charged balloon gets near it, the charged balloon induces a slight opposite charge in the uncharged balloon, causing them to attract each other.
pen_spark
Q9 Describe with the help of a diagram an instrument which can be used to detect a charged body..
Ans:he instrument used to detect a charged body is called an electroscope. Here’s a description with a diagram:
Diagram:
+———+
| |
| Knob |
| |
+—–+ +—–+
| | | |
| Rod |———| Leaves|
| | | |
+—–+ +—–+
Description:
- An electroscope consists of a sealed glass jar or container.
- Inside the jar, a metal rod is vertically suspended from a knob at the top.
- Two thin, flat pieces of metal foil (often gold) are attached to the bottom end of the rod. These are called the leaves or vanes.
- The leaves hang freely and usually touch each other when the electroscope is uncharged.
Q10. List three states in India where earthquakes are more likely to strike.
Ans: Three states in India with high earthquake risk are Jammu and Kashmir, Gujarat, and Assam.
Q11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Ans: If I were outside during an earthquake, I would prioritise finding an open area away from buildings, power lines, and trees. This minimises the risk of getting hit by falling debris.
Q12. 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.
Ans: Absolutely, I would carry an umbrella even if the prediction is just for a thunderstorm. Here’s why:
- Uncertainty in weather forecasts: Weather predictions can be imprecise, especially for thunderstorms which can be localised and develop rapidly. Even if the chance of rain seems low, carrying an umbrella provides peace of mind and avoids getting caught unprepared in a downpour.
Multiple benefits of an umbrella: An umbrella not only protects from rain but also offers shade from the sun during unexpected sunny spells.
NCERT Solutions for Class 8 Science Chapter 12
FAQ’s
What topics are covered in NCERT Class 8 Science Chapter 12?
The chapter Some Natural Phenomena discusses various natural phenomena such as lightning, earthquakes, thunderstorms, and their causes and effects.
How can I understand the concepts of lightning and thunderstorms better?
By studying this chapter Some Natural Phenomena, you will gain insights into the formation of lightning, thunderstorms, and related safety measures to take during such events.
Are there any practical applications of the concepts discussed in this chapter Some Natural Phenomena?
Yes, understanding natural phenomena like earthquakes and lightning can help in disaster preparedness and safety measures.
How can I use the NCERT solutions to improve my understanding class 8 science chapter 12 Some Natural Phenomena?
The NCERT solutions provide step-by-step explanations and answers to the questions in the textbook, helping you grasp the concepts more effectively.
Can I find additional resources to supplement my learning of some natural phenomena?
Yes, you can explore online resources, documentaries, and educational videos related to lightning, earthquakes, and other natural phenomena to enhance your understanding.
