SEBA Class 8 Science Chapter 15 Some Natural Phenomena

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SEBA Class 8 Science Chapter 15 Some Natural Phenomena

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Some Natural Phenomena

Chapter: 15

PART – II

EXERCISE

Select the correct option in Questions 1 and 2.

1. Which of the following cannot be charged easily by friction?

(a) A plastic scale.

(b) A copper rod.

(c) An inflated balloon.

(d) A woollen cloth.

Ans: (b) A copper rod.

2. When a glass rod is rubbed with a piece of silk cloth the rod:

(a) And the cloth both acquire positive charge.

(b) Becomes positively charged while the cloth has a negative charge.

(c) And the cloth both acquire 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.

3. Write T against true and F against false in the following statements.

(a) Like charges attract each other. (T/F)

Ans: False.

(b) A charged glass rod attract a charged plastic straw. (T/F)

Ans: True.

(c) Lightning conductor cannot protect a building from lightning. (T/F)

Ans: False.

(d) Earthquakes can be predicted in advance. (T/F)

Ans: False.

4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Ans: The static electricity builds up due to friction between the fabric and another surface, such as the skin or a carpet. When the sweater is removed, this static electricity jumps between the cloth and the skin, causing a crackling sound.

5. Explain why a charged body loses its charge if we touch it with our hand.

Ans: When we touch a charged body, the charges flow into the Earth through our body, which is a conductor. This process is called earthing, and it neutralizes the charged body.

6. 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 destructive energy of an earthquake is measured on the Richter scale.

An earthquake of magnitude 3 can be recorded by a seismograph, but it is not likely to cause much damage.

7. Suggest three measures to protect ourselves from lightning.

Ans: The following are three ways to protect yourself from lightning:

(i) Avoid Open Spaces and Trees: Do not stay in open areas during lightning. If you are outside, immediately seek shelter in a closed building. Never take shelter under a tree, as it can attract lightning.

(ii) Stay Away from Electrical Devices and Water: Avoid using electrical appliances and stay away from water bodies like ponds, rivers, or even bathtubs, as water and metal can conduct electricity.

(iii) When hearing the sound of lightning, one should immediately go to a safe place and not take shelter under a tree.

8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Ans: A charged balloon is repelled by another charged balloon because both balloons carry the same type of electric charge (either positive or negative). According to the law of electrostatics, like charges repel each other, so two similarly charged balloons push away from each other.

On the other hand, an uncharged balloon is attracted to a charged balloon because the charged balloon induces an opposite charge on the surface of the uncharged balloon (due to redistribution of charges). As opposite charges attract, the uncharged balloon is drawn towards the charged one.

9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Ans: 

An electroscope is a simple instrument used to detect the presence of electric charge on a body. It consists of a metal rod passing through an insulating stopper and connected to a metal cap at the top. At the lower end of the rod, two thin metal leaves (usually gold or aluminium) are attached and enclosed inside a glass jar to prevent air movement. When a charged object touches the metal cap, the charge travels down to the leaves, causing them to repel each other and diverge. The extent of leaf divergence indicates the presence and magnitude of electric charge.

10. List three states in India where earthquakes are more likely to strike.

Ans: Three states in India that are more likely to experience earthquakes are Jammu and Kashmir, Gujarat, and Assam. These regions are considered highly prone to seismic activity.

11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Ans: If I were outside my home and an earthquake struck, I would follow these precautions to protect myself:

(i) Move to an open space: I would immediately move away from buildings, trees, power lines, and anything that could collapse or fall.

(ii) Drop to the ground and cover my head: If there are no safe open spaces, I would crouch down, cover my head with my arms, and stay low to avoid any falling debris.

(iii) Avoid overpasses and bridges: I would avoid walking under or near bridges, flyovers, and overpasses as they may collapse.

(iv) Stay away from vehicles: I would not stay near or inside any vehicles, as they could be damaged or trapped under debris.

(v) Wait for the shaking to stop: I would remain in a safe spot, away from hazards, and wait for the earthquake to finish before moving to a safer location.

12. 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: Yes, I would carry an umbrella if I had to go out on a day when a thunderstorm is predicted.

Reason:

(i) Protection from rain: A thunderstorm typically brings heavy rainfall, and an umbrella would protect me from getting wet.

(ii) Protection from lightning: Though an umbrella made of metal can sometimes increase the risk of being struck by lightning, it still provides some level of protection from rain, and if the umbrella is made of a non-metallic material, it’s safer.

(iii) Use of a non-metallic umbrella: I would choose a non-metallic umbrella, preferably with a plastic or wooden handle, to avoid the risk of lightning, as metal conducts electricity.