Some Natural Phenomenon class 8

 

NOTES PREPARED BY 

ASHAQ HUSSAIN BHAT 

TEACHER SCHOOL 

EDUCATION DEPARTMENT 

JAMMU AND KASHMIR

Tsunami in Japan 

Some Natural Phenomenon

SUMMARY

•Some materials can be charged by rubbing them on another materials,

•There is two type of charges: positive charges and negative charges.

•Same charges repel each other, while opposite charges attract each

•The electrical charges generated by rubbing is called static charges.

•Due to the motion of electric charges, electric current is obtained.

•The process of transfer of charges from a charged object to the earth is called earthing.

•The process of electric discharge can occur between two clouds, between clouds and the earth even between clouds and human body.

•Lightning rod is a device used to secure tall building from the effect of lightning.

•An earthquake is sudden shaking or trembling of the earth.

•An earthquake is caused by a disturbance deep inside the earth's crust.

•It is not possible to predict when and where the next earthquake might occur.

•The power of an earthquake is expressed in terms of magnitudes on a scale called Richter Scale.

KEYWORDS

Static charges Electrical charges generated by rubbing.

Earthing: The process of transfer of charges from charged body to the earth.

Lightning rod A device used to secure tall buildings from the effect of lightning.

Earthquake: A sudden shaking or trembling of the earth.

Richter scale: Measures the strength of earthquake.

 Charged objects: Objects that acquire small charge.

Electroscope: A device which can be used to test whether an

Seismic zones: Zones where earthquakes are more, likely, to occur.

TEXT BOOK EXERCISE

Select correct option in questions 1 and 2.

Q.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 woolen cloth.

Ans. (b) A copper rod cannot be charged easily by friction.

Q 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 

Ans. (b) becomes, positively, charged, while the cloth has a negative

Q.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.

Ans. (a) - False; (b) - False; (c) - False; (d) - False

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

Ans. Woolen clothes get electric charged when they get rubbed. Due to rubbing attraction or repulsion occurs between their loose particles which results in crackling sound.

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

Ans.Human body is a conductor of electricity. When a body is touched with hand, the electric current of body passes to the earth through the body and body loses its charges.

Q.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 destructive energy of an earthquake is measured on Richter scale. The earthquake of 3 Richter can be observed by a seismograph. The earthquake of 3 Richter magnitudes is often fell and it rarely causes damage and it has frequency of occurrence 49.000 per year.

Q.7. Suggest three measures to protect ourselves from lightening.

Ans. Measures of Protection :-

(a) On hearing thunder, go in closed areas, such as, houses, buildings etc.

(b) In bus, close all the doors and windows.

(c) In open, sit on floor with your head in knees and arms,

Q.8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Ans. As both charged balloons have similar charges and we know that similar charged repel each other. So, a charged balloon repels other. Now, we also know that a charged body attracts other uncharged body that is why a charged balloon attracts another uncharged balloon.

Q.9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Ans. Electroscope is a device used to detect the presence of charge on an object or body.

When the metal strips repel each other, that proves that the body is charged. As repulsion is the sure test to detect, if a body carries charge or not.

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

Ans. In India the areas most threatened are Kashmir, Western and Central Himalayas, the whole of North-East, Rann of Kutch. Rajasthan and the Indo-Gangetic Plane. Some areas of South India also fall in the danger zone.

Q.11. Suppose you are outside your home and an earthquake strikes, What precaution would you take to protect yourself?

Ans. If you are out of doors, when earthquake strikes, then

•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 clear a spot. Do not come out till the tremors stop.

Q.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.

Ans. No, it is not safe to carry an umbrella during a thunderstorm because the umbrella increases our height and it may also get few charges due to rubbing, which may attract lightning to attack.

ADDITIONAL SHORT ANSWER TYPE QUESTIONS

Q.1. What could cause a disturbance inside the earth?

Ans.The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush against one another, or collide, or a plate goes under or moves away from another, they cause disturbance in the earth's crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Q.2. If scientist know so much about earthquakes, can they also predict when and where the next one will strike?

Ans. Although, we know for sure, what causes an earthquake, it is not yet possible to predict when and where the next earthquake might occur.

Q3. What you will do on being struck by lightning? 

Ans:. On being struck by lightning a lightning victim carries no electrical charge and cannot electrocute us. The death by lightning occurs due to cardiac arrest and stopped breathing. You can give first aid by performing CPR and mouth to mouth breathing (resuscitation), which is to be learnt from a trained person.

Q.4. What are the damages in body of lightning victim?

Ans. Lightning can cause damage to nervous system, broken bones, bum injuries, loss of hearing or sight, short-term memory loss.

Q.5. What do you understand by seismic or fault zones?

Ans. Since earthquakes are caused by the movements of plates, the boundaries of the plates are the weak zones, where earthquakes are more, likely to occur. The weak zones are also known as seismic or fault zones.

Q.6. What do you understand by lightning rod? Where these are used?

Ans. Lightning rod is a device used to secure tall buildings from the effect of lightning. A metallic rod taller than the height of the building to be protected 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 fixed in the ground. This provides easy route for transfer of electric discharge to the ground. Several, such rods would be required to safeguard a building with a large area.

Q.7. What do you understand by earthquake? What are its harmful effects?

Ans. An earthquake is a sudden shaking or trembling of the earth. It is caused by a disturbance deep inside the earth's crust. Earthquakes occur all the time all over the earth. Most of them last for a few seconds. They are not even noticed. Major earthquakes a much less frequent. They may last only a few minutes, but this time is long enough to cause immense damage to buildings, bridges, dams and people. There can be great loss of life and property. The earthquakes can cause floods, landslides and tsunamis.

ADDITIONAL  LONG ANSWER TYPE QUESTIONS

Q.8. What are the causes of earthquakes? Explain.

Ans. We know that the tremors are caused by the disturbance deep down inside the uppermost layer of the earth, called the crust. 

The outermost layer of the earth is not in one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush against one another, or collide, or a plate goes under or moves away from another, they cause disturbance in the earth's crust. It is this disturbance that shows up as an earthquake on the surface of the earth. erupts,

Tremors on the earth can also be caused when a volcano or a meteor hits the earth or an underground nuclear explosion is carried out. However, most earthquakes are caused by the movement of the earth's plate.

Q.9. What is seismograph? Describe its structure working and uses.

Ans. The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph. The instrument is simply a vibrating rod, or a pendulum, which starts vibrating when tremors occur. A pen is attached to the vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves, scientists can construct a complete map of the earthquake. They can also estimate the energy associated with the earthquake, which determines its power to cause destruction.

Q.10. What are the safety measures you will take in construction of your house if you are living in danger zone?

Ans. The best we can do is to make the structure simple, so that it is 'Quake Safe'. Some suggestions:

•Consult qualified architects and structural engineers. 

•Make the structure symmetrical, so that the mass is distributed uniformly 

•In highly seismic areas, the use of mud or timber is better than the heavy construction material. Make roofs, as light as, possible. In case structure falls, the damage will not be heavy.

•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 installed. This equipment must be checked from time to time to ensure that it is in working order.