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CONTENTS

15.            Wind, Storm and Rain

16.            Water – Scarcity and Conservation

17.            Forests

18.            Waste Management

 

BASIC SCIENCE CLASS VII

15.    WIND, STORM AND RAIN

A.

Q1.      What causes winds?   www.rsmaths99.com

Ans.     Wind are caused by unequal heating of different parts of the earth. Due to that hot air rises and cooler air rushes in to take its place.

Q2.      What does a barometer measure?

Ans.     Air pressure.

Q3.      What is a storm surge?

Ans.     Due to cyclones an increase in the sea level above its normal level, such situation is called storm surge.

Q4.      What is the low-pressure centre of a cyclone called?

Ans.     The low-pressure centre of a cyclone is called eye or storm centre.

Q5.      In which direction do winds swirl around the centre of a cyclone in the northern hemisphere?

Ans.     Anticlockwise the winds swirl around the centre of a cyclone in the northern hemisphere.

Q6.      What causes planetary winds?   www.rsmaths99.com

Ans.     Causes of planetary winds is the unequal heating of the earth.

B.

Q1.      What is a pressure? How does it determine the kind of weather a place will have?

Ans.     The pressure exerted by atmospheric gases on the surface of the earth is called air pressure.

            When air gets heated, it expands and rises and creats the low pressure zone. From the surroundings cooler and heavier air flows in to fill this gap. It causes the wind to blow. This cyclic movement of air plays an important role to determine the kind of weather a place will have.  

Q2.      How does a thunderstorm develop?

Ans.     Thunderstorms develop when a moisture-laden column of hot air cools on coming into contact with the cooler layer of air above. It can also develop when a cold air meets a rising column of hot air.

Q3.      What are cyclones in the Atlantic and Pacific called? Why are cyclones given names?

Ans.     Cyclones in the western Atlantic and eastern Pacific are called hurricanes. While those in the western Pacific are called typhoons.

Q5.      Explain why roofs get blown off during a storm.

Ans.     During a storm, the air above the roof moves faster than the air below the roof. This creates a low pressure zone above the roof and high pressure zone below the roof. It cause an up thrust and roofs get blown off.   

C.

Q1.      What is a tornado? How does it form and what impact does it have?

Ans.     A tornado is a violently rotating column of air extending from the surface of the earth to a thundercloud.

            When a rising column of hot air meets a current of cold air and air gets sucked out of the centre of the column. High speed winds then start spiraling around the low-pressure core and form a tornado.

            (a) Man- made structures get damaged.

            (b) It can blow off roofs.

            (c) Telephone and electric lines snap.     www.rsmaths99.com

           

Q2.      How does a cyclone develop? Describe its impact briefly.

Ans.     Cyclones develop over tropical seas. When air heated by sunrays it rises and creating a low pressure zone, cold air blows in. The cold  air pushes up more hot air , setting up an air current. The current gets  dragged around by the rotation of the earth, and winds start swirling around the central core of low pressure.

            Cyclones are very destructive. Hundreds of people are killed, injured and lose their homes and belongings. Trees get uprooted, Telephone and electric lines snap. It also affects marine life. Sea water turns soil saline and unfit for cultivation.

Q3.      What safety measures can one take to protect oneself from a cyclone?

Ans.     Following are the safety measures that one can take to protect oneself from a cyclone

            (i)  Stay indoors.       

(ii)  During cyclones, the best place to be is in the basement.

            (ii)  Keep the necessary stock for at least 4 to 5 days.

            (iii)  During cyclones, battery operated torches and radios should be kept ready.

            (iv)  Turn off the electric supply.

            (v)  People living in cyclone -prone areas should always listen to the weather forecast.

Q4.      Write briefly about the winds that carry rain to most parts of our country between June and September.

Ans.     Monsoon winds that bring rain to India between June and summer. In summer, the landmass of northern India becomes much hotter than the surrounding seas. The hot air rises, and moist air blows in from the Arabian Sea and Bay of Bengal. These moisture laden winds, which bring heavy rainfall in most part of India, are called the summer monsoon.

            In winter, the land become cool faster and the sea retains heat much longer. So, dry, cold winds blow from land towards the sea. These winds are called the winter monsoon. They pick up moisture as they blow over the Bay of Bengal and bring rainfall to costal Tamil Nadu.

D.            www.rsmaths99.com

1.         tornado,         2. Wind speed                        3. Cold                        4. Waterspout                       

5.         meteorologists           6. Basement   7. Trade winds.

 

 

16..   WATER – SCARCITY AND CONSERVATION

A.

Q1.      What are surface water sources?

Ans.     Rivers, lakes, tanks and ponds are surface water sources.

Q2.      How was groundwater utilized traditionally, and how is it used now?

Ans.     Traditionally groundwater was utilized by digging wells. In recent time it is replaced by tube wells and hand pumps.     www.rsmaths99.com

Q3.      In which part of India are tanks used commonly for irrigation and domestic needs?

Ans.     In the southern part of the country tanks are used commonly for irrigation and domestic needs.

Q4.      What does the excessive use of groundwater lead to?

Ans.     The excessive use of groundwater lead to water scarcity.

Q5.      Mention three causes for scarcity of water in our country.

Ans.     Deforestation, overuse and pollution of rivers.

B.

Q1.      What is soil moisture? What is it useful for?

Ans.     When rainwater falls over land enters the soil and fills up the space between the soil particles is called soil moisture. It is useful to sustain the growth of plants because they absorb this water through their roots and send it up to the leaves for photosynthesis.  

Q2.      Where and how does groundwater get collected? What is the water table?

Ans.     When rain falls on the ground, after saturating the soil, rainwater moves downwards and gets collected above impervious rocks. This collected water is called groundwater. The depth at which groundwater is found from the ground is called water table.      www.rsmaths99.com

Q3.      What about the pattern of rainfall in our country leads to scarcity of water? Which part of the country gets rainfall twice a year?

Ans.     In our country rainfall is mostly concentrated in the rainy season and it is not even every year also not evenly distributed so after monsoon this leads to a  shortage of water.  Tamil Nadu and some part of the Kerala gets rainfall twice a year.

Q4.      ‘All the rain falls over an area cannot be utilized’.  Explain this statement.

Ans.     Rain fall on the ground, about 30% of this water gets stored as groundwater, 40% of the water seeps into the soil, 20% of the water lost due to evaporation and 10% forms the runoff and goes into streams, rivers, ponds, tanks etc. So, all the rain falls over an area cannot be utilized.

C.

Q1.      How did Vilasrao Salunkhe solve the water crises in Naigaon?

Ans.     Vlasrao Salunkhe was an engineer in Maharashtra . He got the idea of check dams work on it in Naigaon. He took 16 hectares of uncultivable land on the hillside on lease and with the help of some engineers he raised bunds along the hillside to trap rainwater and stop soil erosion. He constructed a percolation tank at the base of the hill and a well for drawing water further down. This percolation tank recharged the groundwater and the water was pumped out to irrigate on the hill slope.

Q2.      From what you have learnt in this chapter, what steps do you think the people of a place can take to get over the scarcity  of water?  www.rsmaths99.com

Ans.     Following steps can be taken by the people of a place to get over the scarcity of water

a)      A loss of water should be reduced. Water going from streams and rivers to sea could be reduced by making dams or embankments to trap the water.

b)     Overuse of water should be shortened. Any average person in Delhi was about 400 ltrs a day of water in a day which can be reduced to 20ltrs per day.

c)      Pollution of water bodies should be controlled.

d)     Deforestation should  not be promoted and more and more trees should be planted to stop scarcity of water.

D.

            1.         impervious rocks.      2. Groundwater.        3. Percolation                       

4. Catchment             5.         groundwater              6. Southern and western

E.

            1.         False                2. True                        3. False            4. False            5. False

17.         FORESTS

A.

Q1.      Name five forest products.

Ans.     Five forest products are:-

1.      Paper        2. Timber        3. Honey         4. Rubber        5. Medicine.

Q2.      How do forests check pollution?   www.rsmaths99.com

Ans.     Forest check pollution in this way:-

They absorb thousands of tones of dust and other pollutants. They also absorb noise and protect us from noise pollution. 

Q3.      How do forests regulates temperature?

Ans.     The water vapour is released by trees during transpiration of water from the leaves also causes cooling.

Q4.      What do you understand by the term ‘extinct’?

Ans.     When a plant or animal disappears from a country or stops existing altogether we say that it has become extinct.

Q5.      How do forests help to maintain the balance of gases in the air?

Ans.     Forest maintain the natural balance of carbondioxide and oxygen by using up carbon dioxide and releasing oxygen.

B.

Q1.      In what ways do tribal and others living near forests benefit from forests?

Ans.     Tribal and other living near forests depend on them for firewood, food and the means of livelihood.

Q2.      How do forests help control floods?   www.rsmaths99.com

Ans.     When mountains loses their forest cover, rainwater rushes down very fat. This makes the rivers in the plains fill up suddenly. Unable to hold so much water, they overflow, causing flood.

Q3.      What impact do forests have on rainfall and groundwater resources?

Ans.     The water vapour is released by trees during transpiration helps to increase rainfall since water is held by the forests, it gets a chance to seep into the soil recharge groundwater.

Q4.      How do forests help protect soil?

Ans.     The root of trees bind the soil and save it from being washed away by water or blown away by wind. The leaves of the trees protect the soil beneath from the direct impact of rain pouring over it. When leaves fall their decomposition makes the soil more fertile.

C.

Q1.      How do the plants of a forest help other organisms?

Ans.     Trees in a forest  help many different types of organisms. Birds build their nest in it. Monkey and squirrels also find shelter. Birds, monkey, squirrels and others feed on its fruit and seed. Insects feed on  nectar of its flowers, leaves, sap root. Grazing animals eat its leaves and twigs. When leaves fall o the ground below, soil organism derive nutrition from them. They give out oxygen also.

Q2.      What impact does deforestation have on the animals living in forests?

Ans.     When we destroy forest, we deprive animals of food and shelter. Deprived of their natural food , they often enter villages near forest. They destroy crops and threatening villagers, kill farm animals, and even attack people. In extreme cases, it may even result in these animals become endangered or extinct.

D.         cane – Furniture,  Eucalyptus – oil,  Coniferous – Paper, Rubber tree – Tyres,

Babool – Gum      www.rsmaths99.com

 

18.    WASTE MANAGEMENT

A.

Q1.      What is municipal sewage?

Ans.     Municipal sewage is the waste water from homes, offices and so on, which is carried by sewers or sewage pipes.

Q2.      What are ‘black water’ and ‘grey water’ in the context of sewage?

Ans.     Waste water from toilets are referred as black water and waste water from kitchens and bathrooms is called grey water.

Q3.      What are the three sources of liquid waste?

Ans.     The three sources of liquid waste are:-

1.      Municipal sewage (municipal waste water)    

2.      Industrial effluents (industrial waste water)

3.      Rain water carrying waste washed off from land.

Q4.      What do you understand by ‘treating’ waste water?

Ans.     Treating waste water means clean all the waste water before discharging into water bodies.

Q5.      Mention one use that the sludge from sewage treatment can be put to.

Ans.     The sludge can be used to produced compost and biogas.

Q6.      Mention two things we can do to reduce the burden on the waste water disposal system.      www.rsmaths99.com

Ans.     Two things we can do to reduce the burden on the waste water disposal system are:-

1.      Do not throw solid waste into kitchen or bathroom drains or flush them down. They chock drains.

2.      Do not throw nonbiodegradable things like plastic into drains.

B.

Q1.      What are the problems with having open rainwater drains?

Ans.     The problems with having open rainwater drains are they get clogged by all the garbage washed into them by rainwater and  also by solid waste is thrown into them. It is one of the cause of flooding during the monsoon. Open drain also provide an ideal breeding ground for the mosquitoes which  may cause diseases.

Q2.      Why has it become important for us to find ways of managing the waste we generate?

Ans.     The increasing population has been generating so much waste that nature’s agents cannot handle it. We generate waste now is mostly nonbiodegradable and it cannot be broken down by natural decomposers. This is why it has become important for us to find ways of managing the waste we generate.

Q3.      What happens during the primary stage of sewage treatment?

Ans.     The large solids like leaves, rags and plastic are first separated by strainers or screen. The sewage may pass through settlement tanks, where most of the solid sink to the bottom. The solid that settles to the bottom are referred as primary sludge. This sludge can be used to produce compact and biogas.

Q4.      How is organic matter separated from sewage?

Ans.     In secondary treatment organic matter is broken down by the action of aerobic bacteria in open tanks called aeration tanks. Also anaerobic bacteria are used to breakdown the organic matter dissolved in sewage in closed tanks. In both cases, by the action of bacteria solids settle at the bottom, which can be separated and are used to produce compost and biogas.   www.rsmaths99.com

Q5.      What is the natural alternative to sewage treatment plants?

Ans.     wetlands which allow waste water to pass through a series of ponds is being considered as an alternative to sewage treatment plant. these pond have unicellular organism, which act on organic matter. They also use special plant, microorganism, grass and reeds to filter out  the pollutants.

Q6.      Mention one way of overcoming the problem of the lack of sewage system in villages.

Ans.     One way of overcoming the problem is to make sanitary toilets available in villages. The waste from such toilets if fed into a biogas plant. Microorganism act on the excreta inside the biogas plant. The gas produced can be used  as a fuel and sludge as manure.

C.

            1. sewers         2. Non-biodegradable           3. Effluent       4. Municipal wastewater

            5. aerobic       6. primary

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