Chapter 15: Some Natural Phenomena

Extra Internal Question and Answer :

Question: What is lightning? Explain briefly. 

Answer: Lightning is the process of electric discharge that occurs between clouds and the earth or between different clouds. During a thunderstorm, the positive and negative charges separate, and when they become large enough, the negative charges from the cloud leap to the positive charges on the ground, producing a bright flash of light and sound.

Question: What is the difference between thunder and lightning?

Answer: The difference between thunder and lightning :

Question: What are electric charges? Name the two types of electric charges.

Answer: Electric charge is a property of matter due to which it can attract or repel other objects. There are two types of electric charges: positive charge and negative charge.
Question: What is earthing? Why is earthing provided in electric appliances?

Answer: What is earthing? Why is earthing provided in electric appliances?
Question: The process of transferring of charge from a charged object to the earth is called earthing. In electric appliances, earthing is provided to protect users from electric shocks. If a fault causes the metallic body of an appliance to become charged, earthing safely passes the current to the ground.

Question: What is an earthquake? What causes earthquakes?

Answer: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time

It is caused due to the movement of tectonic plates beneath the Earth’s crust. When these plates collide, slide past, or move apart, energy is released in the form of seismic waves, which cause the ground to shake.
Question: What is the instrument used to measure earthquakes called ?

Answer: The instrument used to measure earthquakes is called a seismograph. It records the vibrations produced by seismic waves during an earthquake.
Question: What happens when an earthquake occurs ? What can we do to minimise its effects?

Answer: When an earthquake occurs, the ground shakes suddenly due to the release of energy in the Earth’s crust. This can cause damage to buildings, roads, and other structures.

To minimise its effects, earthquake-resistant buildings should be constructed, and people should follow safety measures such as taking shelter under sturdy furniture, staying away from buildings, and moving to open areas during a quake.

Question: What are seismic zones? Why are seismic zones considered earthquake-prone areas? 

Answer: Seismic zones are regions of the Earth where earthquakes are more likely to occur. These areas are considered earthquake-prone because they lie near fault lines in the Earth’s crust, where movement of tectonic plates frequently takes place and causes vibrations or earthquakes.
Question: What is Richter scale?

Answer: The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.
Question: What is the use of Richter scale?

Answer: The Richter scale is used to measure the magnitude or strength of an earthquake. 

Question: What is a tsunami? What causes a tsunami?

Answer: A tsunami is a series of very large and powerful sea waves. It is usually caused by an underwater earthquake, volcanic eruption, or landslide on the ocean floor. These sudden movements disturb the water, creating huge waves that travel across the sea and cause destruction when they reach the coast.

Question: What is a tremor ? What causes tremors in the Earth ?

Answer: A tremor is a small shaking or vibration of the Earth’s surface. It is caused due to sudden movements inside the Earth’s crust when plates shift or collide, releasing energy.

Question: What is thunder ? How is it produced? 

Answer: Thunder is the loud sound heard during a storm. It is produced when lightning heats the air around it very fast. This sudden heating makes the air expand quickly and creates a loud sound called thunder.

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

[ Copper is a good conductor of electricity, so charges flow away quickly and it 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 silk, electrons transfer from glass to silk. Glass loses electrons and becomes positively charged; silk gains electrons and becomes negatively charged ]

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) Like charges attract each other → F
(b) A charged glass rod attracts a charged plastic straw → T
(c) Lightning conductor cannot protect a building from lightning → F
(d) Earthquakes can be predicted in advance → F

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

Answer: During winters, the air is dry. When we take off a woollen sweater, friction occurs between the sweater and our body. This causes electric charges to build up on the surface. The sudden discharge of these charges produces tiny sparks, which create the crackling sound.

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

Answer: A charged body loses its charge when we touch it with our hand because our body is a conductor of electricity. The charge flows from the charged object to the earth through our body. This process is called earthing, and it neutralises 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?

Answer: The destructive energy of an earthquake is measured on the Richter scale. Yes, an earthquake of magnitude 3 would be recorded by a seismograph. It is a weak earthquake and is not likely to cause much damage.

7. Suggest three measures to protect ourselves from lightning.

Answer: Three measures to protect ourselves from lightning are :

(i) Stay indoors during thunderstorms.

(ii) Avoid using electrical appliances and wired phones.

(iii) Do not stand under trees or in open fields.

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 is repelled by another charged balloon because both have the same kind of charge, and like charges repel each other. An uncharged balloon is attracted by a charged balloon because the charged body induces opposite charges on the uncharged balloon, and unlike charges attract each other.
9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Answer: Take a glass bottle and fit a cork in its mouth. Insert a paper clip through the cork such that its lower end hangs inside the bottle. Cut two thin strips of aluminium foil and hang them on the lower end of the paper clip.

    
Bring a charged body (like a charged plastic refill) near or touch the upper end of the paper clip. The charge travels through the metal paper clip to the aluminium strips. Both strips get the same charge. Because like charges repel, the strips move away from each other and become wide open. This shows the body is charged.

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

Answer: Three states in India where earthquakes are more likely are:

(i) Jammu and Kashmir because it lies in the Himalayan seismic zone.
(ii) Assam because it is part of the northeastern seismic belt.
(iii) Himachal Pradesh because it is also in the Himalayan region prone to earthquakes.
11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Answer: Precautions during an earthquake if you are outside your home:

(i) Move to an open area away from buildings, trees, electric poles and walls.

(ii) Sit or lie down on the ground to avoid falling injuries.

(iii) Protect your head and neck with your arms.

(iv) Stay away from glass windows, signboards and anything that may fall.

(v) Do not run towards buildings or enter any structure during shaking.

(vi) Remain in the open place until the shaking stops completely.

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: No, you should not carry an umbrella during a thunderstorm. An umbrella, especially with a metallic end, can attract lightning strikes because it provides a direct path for the electric current to travel through your body.