Short & Long Answer Question (Part - 1) - Some Natural Phenomena Notes | EduRev

Science Class 8

Created by: Dr Manju Sen

Class 8 : Short & Long Answer Question (Part - 1) - Some Natural Phenomena Notes | EduRev

The document Short & Long Answer Question (Part - 1) - Some Natural Phenomena Notes | EduRev is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8

Q1: Why does a plastic comb rubbed with dry hair attract tiny pieces of paper?

Ans: Plastic comb gets electrically charged due to rubbing & therefore it attracts tiny pieces of paper which are neutral, as charged body can attracts an uncharged body.
Q2: Why a copper rod cannot be charged by friction, if held by hand?

Ans: Copper is a conducting object, as soon as it gets charged by rubbing with another material, the electric charge produced on its surface flow through our hand & body into the earth and it remains uncharged.
Q3: Mention three ways by which a body can be charged.

Ans: Three ways are:

1. Charging by rubbing: Charging of an object by rubbing it with another object is called charging by rubbing.The body which loses electrons acquires positive charge whereas the body which gains electrons acquires negative charge.

2. Charging by conduction: Charging a neutral body by bringing it in contact with a charged body is called charging by conduction.

3. Charging by induction: Charging a neutral body by bringing it near a charged body is called charging by induction
Q4: What do you mean by earthing? What is the purpose of providing it in buildings?

Ans: The process of transferring of charge from a charged object to the earth is called earthing. For our safety, most of the electrical appliances and the mains of the house are connected to earth, so that we can be prevented from getting an electric shock.
Q5: Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Ans: The following precautions should be taken are as follow:

  1. Find a clear spot, away from buildings, trees, poles and electric poles, signboards and overhead power lines and drop to the ground
  2. Do not use elevators if they are available at some place outside your house.
  3. If you are in a car or a bus, do not come out and drive slowly to a clear spot.

Q6: Suppose you are at home and an earthquake strikes. What precaution would you take to protect yourself?

Ans: The precautions that should be taken are as follow:

  1. Take shelter under a table and stay there only, till the shaking stops
  2. Stay away from the objects which are tall and heavy that may fall on you.
  3. If you are on bed, do not get up and remain there only and protect your head with pillow.

Q7: Explain earthing.

Ans: The process of transferring of charge from a charged object to the earth is called earthing. For our safety, most of the electrical appliances and the mains of the house are connected to earth, so that we can be prevented from getting an electric shock.
Q8: What do you mean by lightning conductor?

Ans: Lightning conductor is a device used to protect buildings from the damaging effects of lightning. It runs from the top to the bottom, along the outer wall of the buildings or any other object, which is to be protected. If lightning strikes the buildings or any other objects, then the lightning conductor provides an easy and direct path for the lightning bolt to pass to the ground without effecting them.
Q9: How an electroscope can be charged through conduction?

Ans: An electroscope is used to detect the charge on a body. A plastic comb is taken and it is rubbed on hair. Now, the plastic comb gets charged. The comb is touched with the electroscope plate. The static charges which are developed on the comb travels down the conducting wire and reach the two leaves of aluminium foil. Similar charges are acquired by both the leaves and as a result, they repel each other. Thus, the method of charging an uncharged body by bringing another charged body directly in contact is called charging by conduction. By this way, an electroscope can be charged through conduction.
Q10: A crackling sound is heard while taking off sweater during winters. Explain the reason behind this.

Ans: As we know that electrical charges that are generated through friction are static, i.e they do not move by themselves and Motion of charges constitutes an electric current. When we take off our sweater there is a motion between the charges on the sweater and our body that produces electric current, which produces a crackling sound. Infact we can see a spark if we take off the sweater in the dark.
Q11: What are tectonic plates?

Ans: The earth's lithosphere is fragmented into many pieces. Each fragment is called a plate, also called tectonic plate. These plates are in continuous motion i.e. they float over hot magma.
Q12: Explain seismograph.

Ans: Tremors or vibrations caused by the earthquakes which travel in the form of waves within the earth or along the earth's surface, are called seismic waves. Seismograph is an instrument which records these seismic waves.
Q13: Touch the disc of an electroscope with an ebonite rod rubbed with fur. Now bring a glass rod rubbed with silk close to the disc of this electroscope. Explain what do you observe?

Ans: After rubbing, ebonite rod acquires negative charge. Now when it is touched with the metal cap of an electroscope then both the metal cap & the leaves acquire negative charge due to conduction. Because of negative charge on both the leaves, divergence of leaves takes place. After rubbing with silk, glass rod acquire positive charge & when this positive rod is brought near the metal cap of the above negatively charged electroscope then due to induction positive charge gets induced in the leaves as a result collapsing of leaves takes place.
Q14: What happens when we touch the metal cap of a charged electroscope with our finger? What is the name of this process?

Ans: The leaves of an electroscope collapse as soon as we touch the metal cap with hand because the leaves of the charged electroscope lose charge to the earth through our body in other words leaves are discharged. This process is known as Earthing.
Q15: What is the nature of charge on the metal cap and on the leaves of the uncharged electroscope when a negatively charged body is brought in contact with its metal cap?

Ans: Nature of charge on the metal cap and on the leaves of the uncharged electroscope is negative.
Q16: How would you use an electroscope to determine the nature of charge of a charged body?

Ans: Let the electroscope get charged with negative charge, by touching a negatively charged ebonite rod to the metal disc of the electroscope. The leaves of the electroscope open up (diverge). Now touch the body to be tested with the metal disc of the charged electroscope.

  • If the divergence of the leaves increases, the body has similar charge that is the given body is also negatively charged.
  • If the divergence of the leaves decreases, the body has unlike charge that is the given body is positively charged.

Q17: What are the uses of an electroscope?

Ans: An electroscope can be used for following purposes:

To detect & measure the charge on a body.

To determine the nature of charge on a body.
Q18: List two states in India where earthquakes are more likely to strike.

Ans: Two places in India which are most threatened by earthquake are Kashmir and Rann of kutch.

Q19: Explain why a charged balloon is repelled by another charged balloon but a charged balloon is attracted by a charged balloon?

Ans: The charged balloon has similar charges on its surfaces, since like charges repel each other thus charged balloon repels another charged balloon. When an uncharged balloon is brought near a charged balloon it acquires some opposite charge, since opposite charge attracts each other therefore a charged balloon attracts an uncharged balloon.
Q20: Why a charged body loses its charge if we touch it with our hand?

Ans: A charged body loses its charge if we touch it with our hand because the charges get transferred from our body to earth, this process is known as earthing.
Q21: What causes an earthquake?

Ans: The earth's lithosphere is fragmented into many pieces. Each fragment is called a plate, also called tectonic plate, these plates are in continual motion, when they brush past one another a plate goes under another because of collision, and they cause disturbance in earth’s crust, this disturbance shows up as an earthquake on the surface of earth.

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