Class 8 Science Chapter 12 Some Natural Phenomena

Question 1: What happens when you rub amber with fur?

Answer: When amber is rubbed with fur it attracts light objects such as hair.

Question 2: Who discovered that the lightning and the spark from your clothes are the same phenomena?

Answer: Benjamin Franklin.

Question 3: How does a substance acquire charge?

Answer: 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. Polythene and hair also get charged during this process of charging the refill and the plastic comb.

Question 4: How is static electricity different from electric current?

Answer: The electric charges generated by rubbing objects are static and do not move by themselves. When charges move they constitute an electric current. Thus, a current is a flow of charges.

Question 5: What is electric discharge and how does it occur?

Answer: When positive and negative meet, streaks of bright light and sound are produced. This process is known as electric discharge. It occurs between two or more clouds or between clouds and the earth.

Question 6: How does lightning occur during a thunderstorm?

Answer: During the development of the thunderstorm, the air currents move upward while the water droplets move downward. This vigorous movement causes the separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is an accumulation of positive charge near the ground also. When the magnitude of accumulated charges becomes very large, the air is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound known as lightning.

Question 7: What can you keep yourself during a thunderstorm?

Answer: (i) Rush to a safer place away from an open area on hearing thunder.

(ii) Wait for some time before coming out of the safe place after hearing the last thunder.

Question 8: What is a lightning conductor and how does it protect a building from lightning?

Answer: A lightning conductor is a device used to protect buildings from the effects of lightning. It consists of a metallic rod installed in the walls of a building. One end of the rod is kept out in the air while the other is buried deep in the ground providing an easy route for the transfer of electric charge to the ground.

Question 9: What is an earthquake? How does it occur?

Answer: An earthquake is a sudden trembling and shaking of the earth for a very short time. It is caused by a disturbance deep inside the earth’s crust. The earth’s crust is not continuous but fragmented and each fragment is called a plate. These plates are in continual motion. When these plates brush past one another or a plate goes under another due to the collision, they cause a disturbance in the earth’s crust, known as an earthquake.

Question 10: What are seismic zones or fault zones? Name some areas of India which are prone to earthquakes.

Answer: The areas lying on the boundaries of the plates where earthquakes are more likely to occur are known as seismic zones or fault zones. Kashmir, the Western and Central Himalayas, the whole of the Northeast, the Rann of Kutch, Rajasthan, the Indo-Gangetic planes and some areas of South India are earthquake-prone areas of India.

Question 11: What is a seismograph and how does it work?

Answer: The tremors produce waves on the surface of the earth called seismic waves. These waves are recorded by an instrument called a seismograph. The seismograph consists of a pen attached to a vibrating rod. When tremors occur the pen vibrates recording the seismic waves on a paper which moves under it over a rotating drum. By studying these waves scientists construct a map of an earthquake and can estimate its power to cause destruction.

Question 12: How can you protect yourself during an earthquake while you are at home?

Answer: (i) Take shelter under a table until the tremor stops.

(ii) Stay away from tall and heavy objects that may fall on you.

(iii) If you are in bed protect your head with a pillow.

Question 13: What is an electroscope?

Answer: An electroscope is a device that is used to test whether an object is charged or not.

Question 14: How can you make the structure of a building “Quake Safe’?

Answer: (i) Use mud or timber instead of heavy construction materials in highly seismic areas and keep roofs as light as possible.

(ii) Consult qualified architects and structural engineers.

(iii) Fix cupboards and shelves to the walls, so that they don’t fall easily.

(iv) Since buildings can catch fire due to an earthquake, have firefighting equipment in working order.

(v) Be careful about where you hang clocks, photo-frames, water heaters, etc so that in the event of an earthquake they don’t fall on people.