Solved examples for class 7 science : Chapter 8
Winds, Storms and Cyclones
I. Multiple Choice Questions (MCQs).
Q.1. The direction of the wind is found out by an instrument called
b) wind vane
d) none of these
Answer: a) anemometer
Q.2. Our earth is surrounded by a layer of air, known as the
d) all of these
Answer: (a) atmosphere
Q.3. When the speed of wind is increased, the pressure
c) remains same
d) none of these
Answer: b) decreases
Q.4. Uneven heating of the earth generates wind
d) none of these
Answer: c) currents
Q.5. In the American continent, the cyclones are known as
d) none of these
Answer: (a) hurricanes
II. Fill in the blanks by selecting appropriate words from the given list :
List: Wind, roofs, pressure, weather, disasters
Q.1. The destruction caused by storms, cyclones, excessive rains, etc., are called natural ______________.
Q.2. ______________ is the movement of air in the atmosphere.
Q.3. Air pressure creates winds and influences the ______________.
Q.4. High speed winds lift and blow away ______________ which are weak.
Q.5. When warm air rises from the surface of the earth, it creates an area of low ______________.
Answer. 1- disasters,
III. Match the items of Column A with those of Column B.
1. Tornado forms over the sea.
(a) Equatorial region
2. The region which receives maximum heat from the sun throughout the year.
(b) Eye of the cyclone
3. The direction of monsoon winds flow
during summer in India.
4.The centre of a cyclone which is a calm area.
5. Tropical cyclones, which originate in the China sea and occur in Philippines and Japan.
Answer. (1) -e (2)-a (3)- d (4)-b (5)- c
IV. Write ‘T’ for the true and ‘F’ for the false statements.
Q.1. A wind vane is made up of a horizontal vane with a pointer and a tail.
Q.2. When we drink water through a straw, the liquid rises due to difference in the pressure of air inside and outside the straw.
Q.3. Air expands on heating and contracts on cooling.
Q.4. The wind currents generate due to uneven heating on the earth are exactly in the north-south direction.
Q.5. In Europe, cyclones which are not very violent are known as Typhoons.
Answer: 1- T, 2-T, 3-T, 4-F, 5-F
V. Very Short Answer Questions.
Q.1. What are the main characteristics of wind?
Answer: Wind has two important characteristics – direction and speed.
Q.2. What is lightning?
Answer: Lightning is the rapid flow of charge through the air between two oppositely charged clouds.
Q.3. Which part of India is a cyclone prone area?
Answer: Whole coast line of India is a cyclone prone area.
Q.4. What is the calm area of a cyclone known as? Ans: Eye of the cyclone
Q.5. What is a cyclone watch?
Answer: Cyclone alert issued by meteorological department before 48 hours is known as cyclone watch.
VI. Short Answer Questions.
Q.1. Why does a balloon sometimes burst when you try to blow air into it?
Answer: Balloon is filled with air, exert pressure and keep them tight. When the pressure inside balloon become more than the atmospheric pressure due to overfilling of air, it burst.
Q.2. How are clouds formed?
Answer: Rising air in a low pressure area takes water vapour with it which condenses to form clouds.
Q.3. Why is it not safe to take shelter under a tree during a thunderstorm?
Answer: Thunder is the result of lighting. Lighting is a result of electrical charges. Lighting is attracted to the tallest tip of a conductor. Trees are often the tallest objects within an environment. Therefore, trees make great targets for lighting. So it is not safe to take shelter under a tree during a thunderstorm
Q.4. How can you show that air exerts pressure?
Answer: To show that air exerts pressure we need an empty tin can, some water and Bunsen burner.
Procedure : Pour a little water in an empty tin can and heat it over a Bunsen flame, till it boils. Fix the lid tightly on it. Cool it under tap water.
Observation : The can gets distorted when cold water is poured over it.
Conclusion : The air pressure inside and outside the empty tin can, is the same. When water is boiled, steam pushes the air move out of the can and occupies that place. When cold water is poured over the can, the steam condenses to water and the pressure inside the can decreases. The air pressure outside the can being more, crushes the can. This activity proves that air exerts pressure.
Q.5. How are high speed winds accompanied by reduced pressure? Explain with suitable examples.
Answer: When you try to blow over a thin long strip of paper you will notice that the paper, instead being pushed down, lifts up in the air, from the far end. The more air you blow, the more it moves up. This is because the pressure over the paper strip gets reduced, when you blow air over it. Below the paper, the air remains still and the pressure remains the same. Therefore, the pressure under the strip of paper becomes higher compared to the pressure above it. This results in the upward lift of the paper strip. Thus, we can see that high speed winds accompanied by reduced pressure
Q.6. How can you show that air expands on heating? Describe how warm air is lighter than cold air.
Answer: To show that the air expands on heating stretch the balloons over the neck of the glass bottles. Boil the water in one of the beakers and place a glass bottle in it. Cool the water in the other beaker by adding some ice and place the other glass bottle in it.
Observations : The balloon gets inflated when the bottle is placed in boiling water. The balloon tied to the neck of the other bottle kept in ice cold water gets deflated.
Conclusion : The air inside the bottle kept in the beaker of boiling water, gets heated and expands. Therefore, the balloon gets inflated. The reverse process takes place in the other bottle.
To show that the warm air lighter than the cold air need, two paper bags, some thread, a burning candle, a thin wooden stick.
Procedure : Hang the two paper bags in an inverted position from the ends of the stick so that the open ends face downwards. Tie a piece of thread in the middle of the stick so that the arrangement looks just like a balance. Place a lighted candle below one of the bags.
Observation : After some time, the bags under which the lighted candle is placed, rises up and the balance of the bags gets disturbed.
Conclusion : The flame of the candle heats up the air above it. This air being warm, is lighter than the surrounding air. The warm air rises up, fills the paper bags and pushes it up. Therefore the balance of the bags gets disturbed. This activity proves that warm air is lighter than cold air.
VII. Long Answer Questions.
Q.1. What are the basic causes of generation of wind currents? Explain with suitable examples.
Ans: Uneven heating of the earth generates wind currents. Two kinds of situations arise. These are-
(a) Uneven heating of the Equator and the Poles
The regions around the equator receive maximum heat from the sun throughout the year. Therefore, the air in these regions gets heated up. This warm air rises up and the cooler air from the surrounding 0 to 30° latitude belt, on either side of the equator, rushes towards the equator. At 60° latitude, the air is warmer than at the poles. Here also, the warm air rises and cold air from the polar region rushes to take that place. Thus, wind currents are generated from the poles to the equator.
(b) Uneven heating of land and water
During summer, the land near the equator warms up faster than the water in the oceans. The air over the land, also gets heated up and rises up. The cooler air over the seas rushes towards the land. These winds carry a lot of water and bring rain. It forms a part of the water cycle. These are known as the monsoon winds. In winter, the wind flows from the land to the ocean. They do not carry moisture or bring rain.
Q.2. How are thunderstorms produced? What precautions should you take during a thunderstorm?
Answer: Thunderstorms are produced by the swift movement of the falling water droplets long with the rising air which produce sound, lightning and heavy rain. They are frequent in hot, humid and tropical areas.
We should take following precaution during a thunderstorm:
(a) Do not take shelter under a tree, an umbrella with a metallic end, in open garages, metal sheds or storage sheds.
(b) Do not lie on the ground.
(c) Do not sit near a window.
(d) A car, bus or a building is a safe place to take shelter. (e) If you are in a forest, take shelter under a small tree.
3. How does a cyclone form? Write its different names, as known in different parts of the world. Write some safety measures against cyclones.
Answer: When water evaporates, it takes up heat from the surroundings and changes to vapour. This heat is released when the vapour condenses back to water and falls down as rain. The released heat warms the atmosphere. The warm air rises and a low pressure area is created. Air from the surrounding areas rushes to the centre of the storm. As more and more air spirals inwards towards the centre, it is forced to rise. They cool down as they rise, condense and fall down as rain. This cyclic chain of events result in the formation of a low pressure system with high speed winds revolving around it. In this way cyclone is formed.
i Hurricane : In the American continent, the cyclones are known as hurricanes.
ii Typhoon: Tropical cyclones which originate in the China Sea, and occur in Philippines and Japan are known as typhoons.
iii Depressions : In Europe, cyclones which are not very violent are known as depressions. They bring rain and do not cause much damage.
Some safety measures against cyclones.
Actions to be taken by the people
• Follow the warnings issued by the meteorological department through T.V., radio or newspapers.
• Shift essential household goods, domestic animals, etc., to safer places.
• Do not drive on flooded roads, since these may be damaged.
• Keep it ready the phone numbers of the emergency services like fire brigade, • police, hospitals, etc.
Precautions to be taken in a cyclone hit area
• Do not drink water in the Locality as it may be contaminated.
• Store drinking water for emergencies.
• Do not touch wet switches and power Lines.
• Do not go outside the house or the cyclone shelter.
• Do not pressure the rescue workers with undue demands.
• Help and co-operate with friends and neighbours.