LONG ANSWER TYPE QUESTIONS
Q. 1. Explain the construction and working of electroscope.
Ans. The device which is used to test whether an object is carrying charge or not is called electroscope.
Construction and working: An electroscope has a metal rod with thin metal strips or leaf attached to it at the bottom. At the top, the rod enters in a cup. The bottom part of the rod and leaf are enclosed in a glass bottle for protection. When the knob of the electroscope is touched with a charged ebonite or glass rod, the leaves open out or diverge. Extent of divergence depends upon the amount of charge on the electroscope.
Q. 2. Explain the mechanism of thunderstorms.
Ans. During the development of a thunderstorm, the air currents move upward while the water drops move downward. These movements cause separation of charges. The positive charges collect near the upper edges of the clouds and negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the amount of accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. This process is called an electric discharge. The process of electric discharge can occur between two or more clouds or between clouds and the earth. In this way thunderstorm is caused.
Q. 3. How can you save yourself from lightning?
Ans. Some safety measures are: (i) We should run to take shelter in the house.
(ii) We should remain in the covered area.
(iii) We should not sit in open, on scooters or bike etc.
(iv) We should take shelter under a small tree while in open.
(v) If there is no tree or other shelter we should sit with head folded.
(vi) We should plug out all the electrical appliances during lightning.
(vii) We should not use wired telephones during lightning. Mobiles and cordless phones are safe.
Q. 4. Explain the safety measures during thunderstorm when you are inside your home.
Ans. (i) During a thunderstorm contact with telephone cords, electrical wires and metal pipes should be avoided.
(ii) It is safer to use cordless phones and mobiles.
(iii) Bathing should be avoided during thunderstorm.
(iv) Computer, TV etc. should be unplugged.
Q. 5. Explain the mechanism of earthquakes.
Ans. The tremors are caused by the disturbance deep down in the uppermost layers of earth. The uppermost layer of earth is called crust. The crust of earth is not a one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush past one another or a plate goes under another due to collision, they cause disturbances and show up as an earthquake on the surface of the earth. Although we know the causes of the earthquake, it is not possible to predict when and where the next earthquake might occur.
Q. 6. What is a seismograph? How does it work?
Ans. The instrument used to record the seismic waves is called seismograph. The tremors produce waves on the surface. The instrument is simply a vibrating rod or a pendulum. Which starts vibrating when tremors occur. A pen is attached to vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves scientists construct a map of earthquake. They can also estimate its power to cause destruction.
Q. 7. What suggestions will you give the people to make ‘Quake Safe’?
Ans. Some suggestions are:
(i) Consult qualified architects and structure engineers.
(ii) Make the structure symmetrical so that the mass is distributed uniformly.
(iii) Use of mud or timber is better than the heavy construction.
(iv) The cupboards and shelves are to the walls.
(v) Be careful about where to hang wall clocks, photo frames, water heater etc. So that in the event of an earthquake they do not fall on people.
(vi) All building should have fire fighting equipment installed.