Friday 24 June 2011

Winds, Storms and Cyclones: Lesson 8. | Science| Class VII (7th)| Exercises Solution

CBSE NCERT Class VII (7th) | Science| Chapter :8. Winds, Storms and Cyclones: 
1.Question  Fill the missing word in the blank spaces in the following statements:
(a) Wind is moving air.
(b) Winds are generated due to uneven heating on the earth.
(c) Near the earth’s surface warm air rises up whereas cooler  air comes down.
(d) Air moves from a region of  high  pressure to a region of   low  pressure.

Image of a Tornado

2. Question : Suggest two methods to find out wind direction at a given place.
Answer :
Method 1 : We can find the wind direction using a Wind Vane or  Weather Vane or Weather Cock.  It consists of a a flat metallic sheet generally cut into shape of a cock or arrow which is mounted on disk and free to move around a axial shaft and point in the direction of wind . They are typically used as an architectural ornament to the highest point of a building.
Method 2 : We can find the direction of light wind using smoke from aggarbatties. The direction of smoke will indicate the wind direction.

3. Question : State two experiences that made you think that air exerts pressure
(other than those given in the text).
Answer :
1. Filling air in a football : A football filled tight with air, take a  shape of a sphere which is very difficult to press and can even support the weight of a player.
2. Pumping the air : We use air pump to fill the air into cycle tires and sometimes football. In pumping, air inside the pump cylinder get pressed by the moving the piston down and subsequently forced inside the cycle tire tube or football through a valve. If we just close the out let of pump with a finger, then it is very difficult to move the piston rod further down to other end as pressed air has no where to go and exert pressure on the piston thus preventing its further down movement.

4. Question :  You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.
Answer : We would not buy a house having windows but no ventilators, as there will be no cross ventilation of air inside the room. Fresh cool Air entering the room through window, gets heated through human and other household activities like breathing, cooking and become lighter. This warm air rises up inside the room. If there is no ventilator near the roof, the warm air will have no passage to leave as the level of window is quite low from the level of warm air. This will increase the room temperature as well as humidity inside leading to human discomfort.

5.Question :  Explain why holes are made in hanging banners and hoardings.
Answer : The banner and hoarding are generally have a large surface area and are put out side in open where they may subject to varying air pressure depending on wind conditions. If wind pressure is high, then air will exert a great amount of pressure on the banners or hoarding causing it to flutter or blown away. To prevent this, holes are made in hanging banner and hording, through which air pressure gets leaked causing less damage or fluttering to banners or hoarding.

6.Question :  How will you help your neighbours in case cyclone approaches your village/town?
Answer : In case cyclone approaches our village or town, we can help our neighbours in following way :

  • We should not ignore the warnings issued by the meteorological department through TV, radio, or newspapers.
  •  We should — make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places;
  • avoid driving on roads through standing water, as floods may have damaged the roads; and keep ready the phone numbers of all emergency services like police, fire brigade, and medical centres.
  • if you are staying in a cyclone hit area —
  • Do not drink water that could be contaminated. Always store drinking water for emergencies.
  • Do not touch wet switches and fallen power lines.
  • Do not go out just for the sake of fun.
  • Do not pressurise the rescue force by making undue demands.
  • Cooperate and help your neighbours and friends
Satellite image of a Cyclone approaching the coast of Orissa
Cyclone Phailin hitting Costal Odisha near Gopalpur on  12 Oct, 2013

7. Question : What planning is required in advance to deal with the situation created by a cyclone?
Answer : With help of satellites and radars, Cyclone alert or Cyclone watch is issued 48 hours in advance of any expected storm and a Cyclone warning is issued 24 hrs in advance. The message is broadcast every hour or half hour when a cyclone is nearer the coast. We should not ignore the warnings issued by the meteorological department through TV, radio, or newspapers.
We should —make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places.

Formation of a Cyclone

8. Question :  Which one of the following place is unlikely to be affected by a cyclone.
(i) Chennai (ii) Mangaluru (Mangalore)
(iii) Amritsar (iv) Puri
Answer : (i) Amritsar. It's being far off from coastal areas, is unlikely to be affected by a  cyclone.
(The whole coastline of India is vulnerable to cyclones, particularly the east coast. )

9. Which of the statements given below is correct?
(i) In winter the winds flow from the land to the ocean.
(ii) In summer the winds flow from the land towards the ocean.
(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.
(iv) The coastline of India is not vulnerable to cyclones.
Answer : Correct statements :
(i) In winter the winds flow from the land to the ocean.
 Extended Learning — Activities and Projects
1. You can perform the Activity 8.5 in the chapter slight differently at home. Use two plastic bottles of the same size. Stretch one balloon on the neck of each bottle. Keep one bottle in the sun and the other in the shade. Record your observations. Compare these observations and the result with those of Activity 8.5.
2. You can make your own anemometer. Collect the following items:
4 small paper cups (used ice cream cups), 2 strips of cardboard (20cm long and 2cm wide), gum, stapler, a sketch pen and a sharpened pencil with eraser at one end.
Take a scale; draw crosses on the cardboard strips as shown in the Fig. 8.18. This will give you the centres of the strips.
Fix the strips at the centre, putting one over the other so that they make a plus (+) sign. Now fix the cups at the ends of the strips. Colour the outer surface of one cup with a marker or a sketch pen. All the 4 cups should face in the same direction. Push a pin through the centre of the strips and attach the strips and the cups to the eraser of the pencil. Check that the strips rotate freely when you blow on the cups. Your anemometer is ready. Counting the number of rotations per minute will give you an estimate of the speed of the wind. To observe the changes in the wind speed, use it at different places and different times of the day.
If you do not have a pencil with attached eraser you can use the tip of a ball pen. The only condition is that the strips should rotate freely.
Remember that this anemometer will indicate only speed changes. It will not give you the actual wind speed.
3. Collect articles and photographs from newspapers and magazines about storms and cyclones. Make a story on the basis of what you learnt in this chapter and the matter collected by you.
4. Suppose you are a member of a committee, which is responsible for creating development plan of a coastal state. Prepare a short speech indicating the measures to be taken to reduce the suffering of the people caused by cyclones.
5. Interview eyewitness to collect the actual experience of people affected by a cyclone.
6. Take an aluminium tube about 15 cm long and 1 to 1.5 cm in diameter. Cut slice of a medium-sized potato about 2 cm thick. Insert the tube in the slice, press it, and rotate it 2–3 times. Remove the tube. You will find a piece of potato fixed in the tube like a piston head. Repeat the same process with the other end of the tube. Now
you have the tube with both ends closed by potato pieces with an air column in between. Take a pencil with one end unsharpened. Place this end at one of the pieces of potato. Press it suddenly to push the potato piece in the tube. Observe what happens. The activity shows rather dramatically how increased air pressure can push things.
CAUTION: When you perform this activity, make sure that nobody is
standing in front of the tube.

You can read more on the related topics on the following websites:
Did you know?
A bolt of lightning travels at a speed of more than 400,000 km/h. It can heat the air around it to a temperature which is more than 4 times the temperature of the surface of the sun. That is what makes lightning so dangerous.
    CBSE NCERT Class VII (7th) | Science| Chapter :8. Winds, Storms and Cyclones:  Exercises Solution