Chapter 11. SOME NATURAL PHENOMENA

Exercises :

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.

Answer : b) A copper rod cannot be charged easily by friction.      

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.

Answer : (b) becomes positively charged while the cloth has a negative charge.

[ When a glass rod is rubbed with a piece of silk cloth, the rod 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)
(b) A charged glass rod attract a charged plastic straw (T/F)
(c) Lightning conductor cannot protect a building from lightning (T/F)
(d) Earthquakes can be predicted in advance (T/F)

Answer :  (a) False ( Like charges repel each other)

(b) True (A charged glass rod attract a charged plastic straw ,)

(c) False (A lightning conductor can protect a building from lightning)

(d) False (Earthquakes cannot be predicted in advance)

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

Answer : The crackling sound heard while taking off a sweater during winters is due to the static electricity buildup. As the sweater rubs against the body or other surfaces, electrons are transferred, causing an imbalance of charges. When the charges equalize rapidly, it creates a crackling sound.

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

Answer : When we touch a charged body with our hand, the excess charge on the body is transferred to our hand. Our body, being a good conductor, allows the flow of charges. This equalizes the charge distribution between the charged body and our hand, resulting in the charged body losing its charge.

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?

Answer : The destructive energy of an earthquake is measured on the Richter scale. An earthquake measuring 3 on the Richter scale would be recorded by a seismograph, but it is considered a minor earthquake and is unlikely to cause significant damage.

7. Suggest three measures to protect ourselves from lightning.

Answer : There are three simple measures to protect ourselves from lightning:

Seek shelter: When you see or hear lightning, it's important to seek shelter in a sturdy building or a fully enclosed vehicle. Stay indoors until at least 30 minutes after the last sound of thunder.

Avoid open areas: If you are outdoors and cannot find shelter, try to avoid open areas, tall trees, metal objects, and bodies of water. Move to lower ground and stay away from objects that conduct electricity.

Stay away from electrical devices: During a thunderstorm, it's best to avoid using electrical devices or being near them, as lightning can travel through electrical wires and cause harm. Unplug sensitive equipment and avoid using corded phones or other devices that are connected to power sources.

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

Answer : A charged balloon has excess electric charge distributed on its surface. When another charged balloon is brought close to it, the excess charges on the two balloons repel each other, causing them to move apart. In the case of an uncharged balloon, it lacks excess charges and gets attracted to the charged balloon due to the imbalance of charges.

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

Answer : Photo

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

Answer :  Three states in India where earthquakes are more likely to occur are Kashmir , Western and Central Himalayas, the whole of North-East, Rann of Kutch, Rajasthan and the Indo–Gangetic Plane .

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

Answer :  If you are outside your home during an earthquake, then you take the following precautions to protect yourself:

(i)  You find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.

(ii) If you are in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot. Do not come out till the tremors stop.

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.

Answer : If the weather department has predicted a thunderstorm, carrying an umbrella may not be the best option for protection. During a thunderstorm, there is a risk of lightning strikes, and an umbrella, being made of metal or with a metal tip, can attract lightning. It is safer to seek shelter in a sturdy building or a car instead.