CBSE Class 8 Science Some Natural Phenomena Worksheet

EACH QUESTION 1 MARKS

Question. Why do two charge bodies attract or repel?
Answer. When the two bodies have the same charges, they repel each other and when the two bodies have different charges they attract each other.

Question. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Answer. This crackling sound is heared because due to friction between the hair and sweater the sweater gets charged.

Question. What is meant by static electricity?
Answer. The electrical charges generated by rubbing is called static electricity.

Question. What is meant by earthing?
Answer. The process of transfer of charges from a charged object to the earth is called earthing.

Question. When does a body become discharged?
Answer. Whe a body looses its charges, it is said to be discharged.

Question. What is a lightning rod?
Answer. A lightning rod is a device used to secure tall buildings from the effect of lightning.

Question. What is an earthquake?
Answer. An earthquake is a sudden shaking or trembling of the earth.

Question. What causes an earthquake?
Answer. The tremors of the earthquake are causes by the disturbance deep down inside the uppermost layer of the earth called the crust.

Question. What are seismic waves?
Answer. The tremors produce waves on the surface of earth known as seismic waves.

Question. Name the instrument used for recording seismic waves.
Answer. Seismograph.

EACH QUESTION 2 MARKS

Question. 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 body is earthed. This causes the charges flow to the earth and the body looses the charge.

Question. List three states in India where earthquakes are more likely to strike.
Answer. Three states in India where earthquakes can occur are Gujarat, Rajasthan and Jammu & Kashmir.

Question. The weather department has predicted rthat a thunderstorm is likely to occur on a certain day. Supose you have to go out on that day. Would you carry an umbrella? Explain.
Answer. No, I would not carry an umbrella. The charges produced during a thunderstorm can flow through the umbrella and harm us.

Question. When a charged plastic straw is brought near a charged plastic straw, there is repulsion between them. What type of charge exists between them?
Answer. The charge on both the plastic straw are same, since like charges repel each other.

Question. When a charged balloon is brought near a charged refill, there is attraction between the two. What type of charge exists between the two?
Answer. The charge on the balloon and a refill are different, because unlike charges attract each other.

Question. Why is the charging by rubbing known as plastic electricity?
Answer. Charging by rubbing is known asd static electricity because the charges do not move.

Question. Give the difference between static electricity and electric current?
Answer. In static electricity, the charges do not move. In electric current, there is flow of charges.

Question. When is lightning seen?
Answer. When the negative charges from the clouds and the positive charges on the ground meet huge amount of energy is produced as bright light and sound. This is seen as lightning.

Question. During thunderstorm which place is the safest?
Answer. During thunderstorm, a house or a building is the safest place.

Question. Is the car safe during thunderstorm?
Answer. Yes, the car is safe during thunderstorm with windows and doors of the vehicle shut.

EACH QUESTION 3 MARKS

Question. 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 the earthquake can be measured on the Richter scale. Yes, an earthquake measuring 3 would be recorded by the seismograph. This earthquake would not cause much damage.

Question. Suggest three measures to protect ourselves from lightning.
Answer. We can protect ourselves from lightning by
(a) Switching off and disconnecting all heavy electrical appliances.
(b) Not bathing under running tap water.
(c) Not standing near metallic poles.

Question. 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 the same charge as another charged balloon, so there is repulsion between them because like charges repel each other. On the other hand, an uncharged body always attracts a charged body. Therefore, an uncharged balloon is attracted by a charged balloon.

Question. How does an earthquake occur?
Answer. An earthquake is the sudden shaking of the earth caused by deep layers of the rocks inside. The plates under the earth slide over one another, bbringing about disturbance of the surface of the earth. This disturbance is the earthquake.

Question. A part from disturbance inside the earth, what are the other reasons of earthquake?
Answer. Earthquakes can also occur due to underground nuclear explosion, or when a volcano erupts, or when a meteor hits the earth.

Question. What are weak zones?
Answer. Since earthquakes are caused by the movements of plates, the boundaries of the plates are weak zones where earthquakes are most likely to occur.

Question. What useful changes are caused by earthquakes?
Answer. Earthquakes can also cause new islands, coal breaches and fresh water springs to emerge due to upheaval.

Question. Name the weak zones in India?
Answer. The weak zones in India are Kashmir, Western and Central Himalayas, the whole of North East, Rann of Kutch,Rajasthan and the Indo-Ganetic plane. Some areas of South India also fall in the danger zone.

Question. DExplain the working of seismograph.
Answer. The seismograph consists of a vibrating rod which starts vibrating when tremors occur. A pen is attached to the vibrating rod and records the seismic waves on a paper which moves under it.

Question. In highly seismic areas, which material should be used for construction of houses?
Answer. In highly seismic areas, the use of mud or timber is better than the heavy construction material. The roofs should be made as light as possible. If the house falls, the damage will not be heavy.

EACH QUESTION 5 MARKS

Question. Suppose you are outside you home and an earthquake strikes. What precaution would you take to protect yourself?
Answer. If you ar eoutdoors and an earthquake strikes, some precautions we should take to protect ourself:
(i) Leave your building and more to open areas.
(ii) Keep away from high rise buildings.A gold leaf electroscope
(iii) Keep away from trees, signboards, electric poles.
(iv) If you are in a vehicle, remain inside it.

Question. Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer. An electroscope is an apparatus to test an electric charge.
Conclusion : An electroscope has a brass rod passing through a tight fitting cork in a glass bottle. A pair of thin gold leaves are attached to the lower end of the brass rod. To protect the gold leaves from external electric charge the lower half of the bottle is lined with tin foil which is 'earthed' by connecting it to the table. This kmind of electroscope is called a gtold leaf electroscope.
Working : When a charged rod is touched to the metal disc, the charge is transferred to the gold leaves and they diverge.

Question. What steps should be taken to protect yourself in case of an earthquake, if you are at home?
Answer. If you are at home :
(i) Do not stand near windows.
(ii) Lie in bed.
(iii) Do not stand near heavy objects that may fall on you.
(iv) Stay under a table till the earthquake stopped.

Question. During a thunderstorm which places are safe?
Answer. Euring a thunderstorm, a house or building is the safest place. If you are travelling by car or by bus, you are safe inside with windows and doors of the vehicle shut.

Question. During a thunderstorm, which places are unsafe if you are outside?
Answer. If you are outside :
(i) Open vehicles, like motor bike, tractor are not safe.
(ii) Carrying umbrella is not a good idea.
(iii) Stay away from poles or other metal objects.
(iv) Do not lie on the ground

I.) DEFINE : 1.Seismology   2.Earthing
3. Earth quake   4.Tsunami

II)

1. Name the device used to protect building from the damage caused by lightning.
2. Name the waves generated in the lithosphere of the earth due to sudden shifting of crustal rocks.
3. Name the molten material present under the lithosphere of the earth.
4. Name the point within the crust or mantle ,where a sudden shift of rocks take place.
5. Name any two causes of earthquakes.
6. Name the instrument which detects and records the intensity of earthquake.
7. Name the device which can detect electrical charge on a body.
8. The electrons are ____________________ charged particles.
9. The protons carry _____________________ charge.
10. The neutrons carry ________charge.
11. Name the three subatomic particles.
12. Which material is used in making a good lightning conductor?
13. _____________ as a whole is called a geosphere.
14. By which scale the magnitude of earthquake is most commonly assessed.
15. The watery part of the geosphere or earth is called ______________.
16. Name the scientist who proved the cause of lightning.

Q.1 Fill in the blanks :

a) A device which is used to test whether an object is carrying charge or not is known as ___________.

b) The process of transferring of charge from a charged object to the earth is called __________.

c) ____________. is a device used to protect buildings from the effect of lightening.

d) Negative and positive charges meet, producing streaks of bright light and sound in clouds, this process in called an ______________.

e) The power of an earthquake is expressed in terms of a magnitude on a scale called the ___________

Key words :- Richter scale, electroscope, earthing, lightening conductors, Electric dischange

Q.2 Write the following sentences in the correct boxes.

a) Carrying an umbrella is a good idea during thunderstroms.

b) Open cars are not safe.

c) Stay far away from all trees.

d) Lie on the ground.

e) Squat low on the ground.

f) Don’t touch electrical wires and metal pipes

g) Use mobile phones.

h) Bathing should be avoided.
Do’s during a thunder strom                   Don’ts during a thunderstorm

Q.3 Label the following diagram

Q.4 Name the following instruments

Q.5 Here are a few precautions to make ‘Quake safe’ buildings. Write ‘true’ in front of the right statement and ‘false’ in front of the wrong statement.
a) Consult qualified architects and structural engineers. _____________.
b) In highly seismic area, the use of mud or timber is good. _____________.
c) In highly scismic area, the use of heavy construction material is good.________.
d) It is better if the cup boards and shelves are fixed to the walls. __________.
e) All buildings, especially tall buildings, have fire fighting equipments in working order. ____________.