“Some Natural Phenomena” is Chapter 17 taken from the JKBOSE textbook of Science for students of Class 8th. In the previous post, I provided you with Questions and Answers for Chapter 16 The Cell. This post is about Some Natural Phenomena Class 8 Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.
Some Natural Phenomena Class 8 Question Answers
Overview of Chapter
- CHARGING BY RUBBING.
- TYPES OF CHARGES AND THEIR INTERACTION.
- TRANSFER OF CHARGE.
- THE STORY OF LIGHTNING.
- LIGHTNING SAFETY.
- Do’s and Don’ts during a Thunderstorm.
- What is an Earthquake?
- What Causes an Earthquake?
- Protection against Earthquakes.
In this chapter, we have studied two natural phenomena lightning and earthquakes. We also have studied the steps which can be taken to reduce the destruction caused by lightning and earthquakes.
LIGHTNING: The bright flash of light which we see in the clouds during the rainy season is called lightning. It is followed by a loud sound called thunder. Lightning is an electric discharge in the atmosphere between oppositely charged clouds. It is a great electric spark in the sky.
CHARGING BY RUBBING: When you rub a plastic scale on your dry hair, the scale can attract very small pieces of paper. When a plastic refill is rubbed with polythene, it acquires a small electric charge. Similarly, when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects. In the process of charging the refill and the plastic comb, polythene and hair also get charged.
- TYPES OF CHARGES AND THEIR INTERACTION: Electric charge is the property of matter which is responsible for all electrical phenomena There are two types of electric charges, positive charge and negative charge. The charge developed on a glass rod when rubbed with silk cloth is called a positive charge and the charge acquired by silk cloth is called a negative charge. The two electric charges interact with each other in the following manner:
- Two charges will attract each other if one charge is negative and the other charge is positive.
- Two positive charges repel each other.
- Two negative charges repel each other.
TRANSFER OF CHARGE: An electric charge can be transferred from a charged object to another uncharged object through a metal conductor. The electric charge of an object can be detected by a device called an electroscope. The process of transferring electricity from a charged body to the earth is called earthing. When a charged body loses its charge to earth it is called discharge.
THE STORY OF LIGHTNING: When a storm cloud develops in the sky, strong winds move upwards through the clouds and make the water drops present in clouds rub against one another. This rubbing of water drops produces extremely large electric charges in the cloud due to friction. The smaller water drops acquire a positive charge and being lighter move to the upper part of the cloud with the rising wind. On the other hand, larger water drops acquire a negative charge and being heavier remain in the lower part of the clouds.
When the amount of opposite electric charges on the top and bottom of a storm cloud becomes extremely large, then electric charges start flowing with high speed through the air between them. When the positive and negative charges of a cloud meet, they produce an intense spark of electricity between the cloud in the sky. We see this as a flash of lightning in the sky. This spark of lightning heats the nearby air in the sky to very high temperatures. As a result, the air in the sky expands rapidly and produces a loud sound which is heard as thunder.
LIGHTINING SAFETY: Do’s and Don’ts during a Thunderstorm.
(1) Outside the House
- Open vehicles, like motorbikes, tractors, construction machinery, and open cars are not safe.
- Open fields, tall trees, shelters in parks, and elevated places do not protect us from lightning strikes.
- Carrying an umbrella is not a good idea at all during thunderstorms.
- If in a forest, take shelter under shorter trees. If no shelter is available and you are in an open field, stay far away from all trees. Stay away from poles or other metal objects. Do not lie on the ground. Instead, squat low on the ground. Place your hands on your knees with your head between the hands. This position will make you the smallest target to be struck.
(2) Inside the house
- Lightning can strike telephone cords, electrical wires and metal pipes.
- During a thunderstorm contact with these should be avoided. It is safer to use mobile phones and cordless phones.
- Bathing should be avoided during thunderstorms to avoid contact with running water.
- Electrical appliances like computers, TVs, etc., should be unplugged. Electrical lights can remain on. They do not cause any harm.
(3) Lightning Conductors
A lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides an easy route for the transfer of electric charge to the ground.
(a) What is an Earthquake:
It is a sudden shaking of the earth which lasts for a very short time. It is caused by violent movements of rocks deep inside the earth’s crust. Earthquakes are very dangerous as they can cause immense damage to houses, other buildings, bridges, dams and people.
(b) What Causes an Earthquake?
The earthquake is caused by the movement of plates of the earth’s crust. The movement of plates takes place in two ways:
- slide past one another and.
- collide with one another.
(c) Protection against Earthquakes.
We must take necessary precautions to protect ourselves all the time. It is advisable to make the structure simple so that it is ‘Quake Safe’.
- Consult qualified architects and structural engineers.
- In highly seismic areas, the use of mud or timber is better than heavy construction material. Keep roofs as light as possible.
- It is better if the cupboards and shelves are fixed to the walls so that they do not fall easily.
- Be careful where you hang wall clocks, photo-frames, water heaters etc. so that in the event of an earthquake, they do not fall on people.
- Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have firefighting equipment in working order.
(a) If you are at home:
- Take shelter under a table and stay there until the shaking stops.
- Stay away from tall and heavy objects that may fall on you.
- If you are in bed, do not get up. Protect your head with a pillow.
(b) If you are outdoors:
- Find a clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
- 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.
Some Natural Phenomena Class 8th Questions
Select the correct option in Questions 1 and 2.
- 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
- 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.
- Write T against true and F against false in the following statements:
(a) Like charges attract each other. (False)
(b) A charged glass rod attracts a charged plastic straw. (True)
(c) Lightning conductors cannot protect a building from lightning. (False)
(d) Earthquakes can be predicted in advance. (False)
4. Sometimes, a crackling sound is heard while taking off the sweater during winter. Explain.
Ans. The crackling sound heard while taking off our sweaters during winter is due to the rubbing of two objects i.e. body and the wool. The rubbing of static charges produces lightning or a spark in our clothes that produces 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 with our hand it loses its charge due to earthing because our body is a good conductor of electricity and charged body loses its charge to earth through our 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 scale on which the destructive energy of an earthquake is measured is termed as Richter scale.
Yes, an earthquake measuring 3 on the Richter scale can be measured on the seismograph in the form of seismic waves.
An earthquake measuring 3 on the Richter scale cannot cause much damage.
7. Suggest three measures to protect ourselves from lightning.
Ans. Three measures to protect ourselves from lightning are:
a) We should stay indoors during lightning.
b) Avoid travelling in open vehicles, like motorbikes, tractors, construction machinery, and open cars because they are not safe.
c) We should not take bath during lightning.
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 acquire the same charge on rubbing and the same charges repel each other.
On the other hand, an uncharged is attracted by a charged balloon because they have opposite charges on them and opposite charges attract each other.
- Describe with the help of a diagram an instrument which can be used to detect a charged body.
Ans. An instrument which is used to detect the electric charge of an object or body is called an electroscope.
Working of an Electroscope.
1) When a charged body touches the paper clip, the aluminium strips receive the same charge from the charged object. Hence, the strips of aluminium repel or tend to move away from each other.
2) If the body does not contain any charge, the aluminium foil strips do not repel or tend to move from each other.
- List three states in India where earthquakes are more likely to strike.
Ans. The three states in India which are more prone to earthquakes are:
1) Jammu & Kashmir
- Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Ans. Following are the precautions we should take if we are outside our home and an earthquake strikes:
1) Stay away from buildings, trees and overhead power lines.
2) If we are travelling in a bus or car we should not come out. We should ask the driver to drive slowly to a clear spot. We should not come out till the tremors stop.
- 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. Carrying an umbrella during a thunderstorm is not safe and advisable because it increases the risk of getting a thermal shock during a thunderstorm because the top end of the umbrella which is out in the air can attract electric charge from the clouds.
That’s all about Some Natural Phenomena Class 8 Question Answers. Hope it has helped you. Do share your views about this post in the comment section below.