Question 1.
Which of the following cannot be changed easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woolen cloth
(b) A copper rod
Question 2.
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
(b) becomes positively charged while the cloth has a negative charge.
Question 3.
Write T against true and F against false in the following statements.
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) Lightning conductor cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.
(a) False
(b) True
(c) False
(d) False
Question 4.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
The electric discharge takes place between the body and the sweater due to friction. At the time of electric discharge some energy is released. In this case energy is released in the form of crackling sound.
Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
The human body is a conductor of electricity. When a charged body is touched with hand, our body conducts its charges to the earth. Hence, by this way charged body loses its charge.
Question 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?
The destructive energy of an earthquake is measured on a scale called the Richter Scale.
Yes, it would be recorded by seismograph because this scale has readings from 1 to 10. No, it is not likely to cause much damage as earthquakes of magnitude higher than 5 are considered destructive in nature.
Question 7.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
A charged balloon is repelled by another charged balloon because both carry some type of charge. On the other hand, an uncharged balloon is attracted by another charged balloon as they have opposite charges. We know that the same charges repel and opposite charges attract each other.
Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Electroscope is a device which is used to detect the charge on a body. It works on the principle that like charges repel each other while unlike charges attract each other. It consists of a metal rod with thin metal strip or leaf attached to it at the bottom.
At the top, the metal rod enters in a metallic cup or disc. The bottom of the rod and the metal leaf are enclosed in a glass box for protection. When the disc of the electroscope is touched with a charged ebonite or glass rod, the metal leaves open out or diverge.
The extent of divergence depends upon the amount of charge on the electroscope. When the metal strips repel each other proves that the body is charged because repulsion is the sure test to detect that body is charged or not through an electroscope.
Question 10.
List three states in India where earthquakes are more likely to strike.
Kashmir, Rajasthan and Gujarat.
Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
We will take the following precautions to protect ourselves:
(i) Move to open space. Find a clean spot away from buildings, trees and overhead power lines. Drop to the ground.
(ii) If we are in a car or a bus, will not come out. Drive slowly to a clear spot and remain in it till the earthquake stops.
Question 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.
No, it is not advisable to carry an umbrella at all. Its metallic objects are more prone to lightning stroke. So an umbrella increases the risk.
Question 13.
Why do two charge bodies attract or repel ?
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 14.
Write the one name of method by which object can be charged.
Object can be charged by conduction.
Question 15.
Which of the following cannot be charged easily by friction ?
- A plastic scale.
- A copper rod.
- An inflated balloon.
- A woollen cloth.
A copper rod.
Question 16.
When a glass rod is rubbed with a piece of silk cloth the rod
- and the cloth both acquire positive charge.
- becomes positively charged while the cloth has a negative charge.
- and the cloth both acquire negative charge.
- becomes negatively charged while the cloth has a positive charge
becomes positively charged while the cloth has a negative charge.
Question 17.
Tick T for true and F for false in the following statements :
- Like charges attract each other. (T/F)
- A charged glass rod attract a charged plastic straw. (T/F)
- Lightning conductor cannot protect a building from lightning. (T/F)
- Earthquakes can be predicated in advance. (T/F)
- F
- T
- F
- F
Question 18.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
This crackling sound is heared because due to friction between the hair and sweater the sweater gets charged.
Question 19.
What is meant by earthing ?
The process of transfer of charges from a charged object to the earth is called earthing.
Question 20.
When does a body become discharged ?
When a body looses its charges, it is said to be discharged.
Question 21.
What is an earthquake ?
An earthquake is a sudden shaking or trembling of the earth.
Question 22.
What causes an earthquake ?
The tremors of the earthquake are caused by the disturbance deep down inside the uppermost layer of the earth called crust.
Question 23.
What are seismic waves ?
The tremors produce waves on the surface of earth known as seismic waves.
Question 24.
Give the other name for weak zones.
Seismic or fault zones.
Question 25.
Is the Electric Eel really electric ?
Yes, the Electric Eel found in South America emits electric discharge.
Question 26.
How does the Electric Eel use the electric discharge ?
Electric Eel uses electric discharges to give shock to its prey, discourage enemies and send signal to other Eels.
Question 27.
Name the scientist who first established the relationship between lightning and spark.
In 1752, Benjamin Franklin, an American scientist, established that lightning and spark from amber were the same thing.
Question 28.
Why did it take 2000 years to establish the similarity between lightning and spark ?
It took 2000 years because scientific discoveries are a result of hard work by many people.
Question 29.
What type of charge is present on the earth ?
The earth has both positive and negative charges.
Question 30.
What is meant by a ‘discharged’ body ?
The body from which the charge has been earthed loses the charge on it. Such a body is known as a ‘discharged’ body.
Question 31.
Explain why a charged body loses its charge if we touch it with our hand.
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 32.
List three states in India where earthquakes are more likely to strike.
Three states in India where earthquakes can occur are Gujarat, Rajasthan and Jammu & Kashmir.
Question 33.
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.
No, I would not carry an umbrella. The charges produced during a thunderstrom can flow through the umbrella and harm us.
Question 34.
When a charged plastic straw is brought near a charged plastic straw, there is repulsion between them. What type of charge exists between them ?
The charge on both the plastic straw are same, since like charges repel each other.
Question 35.
When a charged balloon is brought near a charged refill, there is attraction between the two. What type of charge exists between the two ?
The charge on the balloon and a refill are different, because unlike charges attract each other.
Question 36.
Why is the charging by rubbing known as static electricity ?
Charging by rubbing is known as static electricity because the charges do not move.
Question 37.
Give the difference between static electricity and electric current ?
In static electricity, the charges do not move. In electric current, there is flow of charges.
Question 38.
When is lightning seen ?
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 39.
Is the car safe during thunderstorm ?
Yes, the car is safe during thunderstorm with windows and doors of the vehicle shut.
Question 40.
Can we use telephone during a thunderstorm ?
No, it is not safe to use a telephone during thunderstorm, as lightning can strike through telephone cords.
Question 41.
Do the car tyres protect us from lightning ?
No, the car tyres do not protect us from lightning, but the metal case of the car protects us.
Question 42.
Choose the correct option :
A charged plastic comb (B) is brought near another similar charged and suspended plastic comb (A). Then comb A
- remains unaffected
- moves towards comb B
- moves away from comb B
- starts oscillating
moves away from comb B.
Question 43.
During lightning we have an electric discharge
- only between two opposite charged clouds
- only between a charged cloud and the ground
- either between two oppositely charged clouds or a charged cloud and ground.
- neither between two oppositely charged clouds nor between a charged cloud and ground.
either between two oppositely charged clouds or a charged cloud and ground.
Question 44.
What is the effect of
- a charged object
- an uncharged object on small bits of paper ?
- a charged object will attract bits of paper.
- an uncharged object will have no effect on bits of paper.
Question 45.
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 ?
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 46.
Suggest three measures to protect ourselves from lightning.
We can protect ourselves from lightning by
- switching off and disconnecting all heavy electrical appliances.
- Not bathing under running tap water.
- Not standing near metallic poles.
Question 47.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon ?
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 48.
Apart from disturbance inside the earth, what are the other reasons of earthquake ?
Earthquakes can also occur due to underground nuclear explosion, or when a volcano erupts, or when a meteor hits the earth.
Question 49.
What are weak zones ?
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 50.
What useful changes are caused by earthquakes ?
Earthquakes can also cause new islands, coral breaches and fresh water springs to emerge due to upheaval.