Maharashtra Board Class 8 Geography Textbook PDF

 The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 29.12.2017 STANDARD EIGHT Maharashtra State Bureau of Textbook Production and...

 The Coordination Committee formed by GR No. Abhyas - 2116/(Pra.Kra.43/16) SD - 4 Dated 25.4.2016 has given approval to prescribe this textbook in its meeting held on 29.12.2017 STANDARD EIGHT Maharashtra State Bureau of Textbook Production and Curriculum Research, Pune. The digital textbook can be obtained through DIKSHA App on a smartphone by using the Q. R. Code given on title page of the textbook and useful audio-visual teaching-learning material of the relevant lesson will be available through the Q. R. Code given in each lesson of this textbook.  The Constitution of India Preamble WE, THE PEOPLE OF INDIA, having solemnly resolved to constitute India into a SOVEREIGN SOCIALIST SECULAR DEMOCRATIC REPUBLIC and to secure to all its citizens: JUSTICE, social, economic and political; LIBERTY of thought, expression, belief, faith and worship; EQUALITY of status and    of opportunity; and to promote among them all FRATERNITY assuring the dignity of the individual and the unity and integrity of the Nation; IN OUR CONSTITUENT ASSEMBLY this twenty-sixth day of November, 1949, do HEREBY ADOPT, ENACT AND GIVE TO OURSELVES THIS CONSTITUTION. NATIONAL ANTHEM  Preface Dear Students, Standard eight is the last year of higher primary education. Welcome to this class. You have been studying geography from standard three to standard five as part of environmental studies and as a separate subject from standard six onwards. It gives me great pleasure putting forth this geography text book for standard eight before you. In this textbook you are going to study some advanced concepts in geography. Special focus will be on the rain and the clouds you have been seing in the sky since childhood. How is the interior of the earth? On what basis have estimates been made about the interior of the earth? Some explanation about this has been made briefly in this textbook. You will be studying about the motion of water which covers the largest part of the earth, the currents and the influencing underlying energy behind them. The use of land, industries and population are all an indispensable part of human life. These aspects will be introduced igniting an intellectual curiosity. These concepts will be useful to you even in the future. Clearly understand the rural and urban components and try to correlate man’s development with these components. While studying all these facets, the textbook sets out many task and projects. Questions on the topics have been posed under titles such as think about it, use your brain power, find out etc. These will definitely be beneficial to you. Please use the maps and diagrams given in the textbook. They will facilitate in making the geographical concepts easy to comprehend. Personally do the tasks given in the textbook. Make use of the discussions given in earlier text books. With good wishes to all of you ! (Dr. Sunil Magar) Pune Director Maharashtra State Bureau of Date : 18 April 2018 (Akshay Tritiya) Textbook Production and Indian Solar Year : 29 Chaitra 1940 Curriculum Research, Pune  CLASS 8 GEOGRAPHY Learning process suggested Learning outcome The teachers should give learning opportunities to students The Students in groups/pairs / individually and encourage them to : understanding what time will it be in different countries / 08.73G.01 calculates the Standard Time and Local time with the regions with the help of longitudes on a globe or map help of longitudes on maps and globes calculating the difference in time between the Prime 08.73G.02 uses local time and standard time effectively with the Meridian and local times of various places in the world help of longitudinal location correlating them Using various audio-visual /visual images/models/ 08.73G.03 Explains the composition of the interior of the earth diagrams to understand the interior of the earth with the help of diagrams, models, images ,etc. Understanding the processes of evaporation and 08.73G.04 Gives information regarding the natural processes of condensation with the help of experiments evaporation and condensation Understanding the factors affecting humidity 08.73G.05 Explains clearly the factors affecting humidity Obtaining information regarding clouds with the help of 08.73G.06 Identifies the cloud types and forecasts rainfall. diagrams or audio-visuals Understanding the sea-floor with the help of diagrams/ 08.73G.07 Identifies the marine landforms with the help of models / audio visual medium diagrams /figures Understanding the process of ocean currents with the help 08.73G.08 Discusses marine deposits of experiments 08.73G.09 Explains the reasons responsible for ocean currents Understanding the effects of ocean currents on climate, 08.73G.10 Explains the effect of ocean currents on human life fishing and marine navigation with examples Explaining the land use in urban and rural areas with the 08.73G.11 Differentiates between the urban and rural land use help of maps, figures and images 08.73G.12 Presents information regarding rural and urban Identifying the patterns of land use settlements on the basis of land use maps Understanding that population is a resource 08.73G.13 Explains the importance of studying population Studying the sample graphs of various characteristics of (demography) population according to age-sex, sex ratio, birth rate, death 08.73G.14 Explains the composition of population rate, urban and rural population, composition according to 08.73G.15 Explains with reasons the factors affecting the quality occupation, literacy, etc of population 08.73G.16 Explains the uneven distribution of population by reading world maps Understanding the difference between various occupations 08.73G.17 Classifies various industries through examples 08.73G.18 Tells the importance of industries Obtaining information through visits to industrial regions 08.73G.19 Explains the Corporate Social Responsibility ( CSR) and through various references. 08.73G.20 Explains the factors affecting industrial development Discussing the social responsibilities of industries 08.73G.21 Obtains information regarding industry - friendly Understanding the industrial development of India and policies Maharashtra with the help of maps Drawing conclusions with the help of scales on maps 08.73G.22 Determines the scale on the basis of distance between Converting one type of scale given on a map into another two points on a map and on the ground Understanding the map type on the basis of the scale of 08.73G.23 Explains various methods of map scales giving the map examples Visiting a region through the process of field –visit , 08.73G.24 Identifies types of maps on the basis of scales preparing questionnaires 08.73G.25 Uses map scales directly Interpretation through analysis of data/information, 08.73G.26 Plans a field-visit preparing report 08.73G.27 Prepares a questionnaire 08.73G.28 Presents a report on the basis of information collected during field-visit  - For Teachers - P To begin with, get familiar with the possible by reorganizing the class structure textbook yourself. frequently. P Please refer to textbooks of earlier classes P Do not ask questions on statistical before teaching this textbook. information. Instead, ask questions on P Please plan carefully and independently their trends or patterns. for the activities in each chapter. Please P The present book has been prepared for do not teach without planning. constructivist and activity-based teaching. P The teaching-learning interactions, O Please do not teach the lessons in the book processes and participation of all students by just reading them aloud. is very necessary and so is your active P Follow the order of the chapters as given guidance. in the contents because the concepts have P Please use the geographical teaching aids been introduced in a graded manner to in the school as required for the appropriate facilitate knowledge-building. understanding of the subject. It is necessary P Do not use the boxes titled ‘Do you to use the globe, the maps of the World, know?’ for evaluation. India and the State, atlases, etc. P Use QR Code given in the textbook. Some P Though the number of chapters has been websites have been given for reference at reduced the number of periods required for the end of the chapter. Also, a list of each chapter has been given a thought. references used is also given. You as well Abstract concepts are difficult to follow as the students are expected to use these and therefore you are expected to use the references. These references will surely given number of periods fully. Do not help you to go beyond the textbook. Please finish the chapter in short. This will help bear in mind that extra reading is always the students to assimilate the content helpful for understanding any subject in without feeling the ‘burden of learning’. depth. P Like other social sciences, geographical P Use thought-provoking, activity-oriented, concepts too are not easy to understand. open-ended, multiple choice questions for Major concepts of geography have a evaluation. Some examples are given at scientific base and they deal with the end of the chapters in the ‘exercises’. abstractions. Encourage group work, P Use outline maps given on page numbers learning through each other’s help, etc. 35 and 60 for xerox. Facilitate peer learning as much as - For Students - You will meet the character ‘Globee’ in every chapter. Have you guessed who he is ? He will help in the various tasks you are expected to do. Try to follow his instructions.  Contents Expected S.No. Name of the lesson Field Page No. Periods 1. Local Time and Standard Time General Geography 01 09 2. Interior of the Earth Physical Geography 09 10 3. Humidity and Clouds Physical Geography 16 10 4. Structure of Ocean Floor Physical Geography 24 09 5. Ocean Currents Physical Geography 29 09 6. Land Use Human Geography 35 10 7. Population Human Geography 42 10 8. Industries Human Geography 52 10 9. Map Scale Practical Geography 60 08 10. Field Visit Practical Geography 68 08 11. Glossary -- 70 -- 12. Activity Page -- 75 -- S.O.I. Note : The following foot notes are applicable : (1) © Government of India, Copyright : 2018. (2) The responsibility for the correctness of internal details rests with the publisher. (3) The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate base line. (4) The administrative headquarters of Chandigarh, Haryana and Punjab are at Chandigarh. (5) The interstate boundaries amongst Arunachal Pradesh, Assam and Meghalaya shown on this map are as interpreted from the “North-Eastern Areas (Reorganisation) Act. 1971,” but have yet to be verified. (6) The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India. (7) The state boundaries between Uttarakhand & Uttar Pradesh, Bihar & Jharkhand and Chattisgarh & Madhya Pradesh have not been verified by the Governments concerned. (8) The spellings of names in this map, have been taken from various sources. DISCLAIMER Note : All attempts have been made to contact copy right/s (©) but we have not heard from them. We will be pleased to acknowledge the copy right holder (s) in our next edition if we learn from them. Front Page : Students have studied geography from standard three and have now come to standard eight. The horizon of their experence has expanded. They are now looking at experiments of the interior of the earth and geo magnetic field.---- (imaginery picture) Back Page : 1) Students doing an experiment based on shadows : courtesy, Satish Jagdale, Shrimant Rani Nirmala Raje Kanya Prashala, Akkalkot. 2) A type of migration. 3) Clouds : courtesy Aalisha Jadhav. 4) An instrument measuring temperature and humidity. 5) A small submarine surveying the Mariana trench.  1. LOCAL TIME AND STANDARD TIME vessel.); sand timer, etc. were used to tell time. Let’s recall. The Earth takes 24 hours i.e. one day to complete one rotation. We consider the direction Ø Why does the duration of day and night where the sun rises to be the east. Thus, the keep changing? Earth rotates from west to east. As a result we Ø How many longitudes can be drawn on a experience, sunrise, noon, sunset and midnight. world map keeping an interval of 1° each? During rotation, the longitudes in the western Ø The apparent movement of the sun from part face the sun gradually while those in the east to west is a result of what? east experience darkness. The longitude which Ø What is the direction of the rotation of the faces the sun experiences sunrise while, on the earth? other hand, the one in the darkness experiences Ø While the earth rotates, how many sunset. longitudes face the sun daily? While travelling in a bus, we often see trees, electric poles, buildings, etc outside the window. Ø At which longitude does the date change? They appear to be moving in the opposite Ø How was time measured in olden days? direction. Actually, they are stationary and our Ø In present times, what are the instruments bus is moving forward. Similarly, because of used for time measurement? the rotation of the earth, we feel that the sun is changing its position from east to west daily. Geographical explanation Try this. We get up early in the morning, brush our teeth and take a bath. Then we have breakfast Perform this activity in the kho-kho ground and go to school. We study in our classrooms. on a bright sunny day. Consider the following We return home. We go to the playground to points: play in the evening. We have dinner; brush our ü Choose one pole on the ground that stays teeth and go to sleep. We keep doing similar under the sun for the whole day for this activities throughout the day. Considering our activity. daily routine, we need to decide the time for all ü Observe the directions in which the our activities. In olden days, people used to take the help of various tools and also depend on various natural events for the measurement of time. On the basis of observation and experience, they divided the day into the following parts: from sunrise to sunset, daytime and from the sunset East to the next sunrise nighttime. A whole day meant the duration from one sunrise to the next. Morning Evening 8 am Morning 4 pm Earlier, natural events and instruments like Noon Afternoon 10 am 12pm 2 pm Ghatikapaatra (a bowl with a minute hole at its Figure 1.1: The different locations of the sun during base which would float in a large water filled the day and changes occurring in the shadow 1  shadow of this pole falls at different times than 24 hours depending upon the season. As of the day. a result, understanding the timings of sunrise, ü Measure the shadows and record in your noon, sunset and midnight at these places notebooks. becomes important. At the poles, the daytime ü Note the relative directions of the shadows and the sun in your notebook. (Fig 1.1) and the duration of the day lasts around 6 ü Where is the sun located in the sky when months. To tell the time of sunrise or sunset at the shadow is the shortest? the poles, one has to consider the date. When ü At what times are the shadows longest the sun rises on a specific day, it moves around during the day? the horizon and therefore , here, the length of Geographical explanation the shadow cannot be considered for telling the You would have realized by observation noon time. that the shadows in the early morning and evening were the longest while those at the Think about it. noon were the shortest. Because of the change in the apparent location of the sun in the sky, Ø At the poles, sunrise occurs on one the length and direction of the shadow of the equinox and sun sets on the next equinox. pole kept changing. See figure 1.1. This is If you happen to be at any of the poles because a specific part of the earth faces the during this time, then what would be the sun during rotation and moves forward. See route of the sun in the daytime? figure 1.2. Incidentally, we also experience that it is cooler in the morning and evening and Ø On which day, would the sun appear at the highest point in the sky? warmer in the afternoon. LOCAL TIME : Different longitudes have different timing for sunrise, noon and sunset. When it is noon at Mumbai, it wouldn’t be the same at Kolkata. Sunset Because Kolkata lies to the east of Mumbai, it Midnight Noon would already be afternoon in Kolkata. N. P. The local time of a place on the earth’s Sunrise surface is determined with reference to its noon time.This implies that places lying on the same Figure 1.2 : Rotation and the relative location of the sun longitude have the same local time. There is no As soon as the sun starts moving up in the sky difficulty when local time is used for a small after sunrise, the length of our shadow reduces. Always remember - Normally, the length of the shadow is shortest at noon. As the sun moves towards the horizon in l The earth takes almost 24 hours to the afternoon, the length of our shadow increases complete one rotation ( 3600). again by evening. The noon time is the same at l The earth rotates by 3600 / 24 hours = any given longitude across the earth i.e. from the 150 in one hour around its own axis. North Pole to the South Pole. The time of a place l The earth takes 60 minutes / 15 degrees as decided by the location of the sun in the sky, is = 4 minutes to cover 10 known as its local time. l This means that for each degree of In the regions lying in between the polar longitude, the local time differs by 4 minutes. circles and the poles, the daytime could be more 2 area. When people living in a larger area across different longitudes have to interact with each Can you tell ? other, then using the local time could lead to We have studied that the local time is chaos and confusion. In such cases, using the different in different parts of the world. The local time is not convenient. daily routine of the people there, is determined according to the local time in those places. Try this. Figure 1.3 shows the local times of different longitudes. Study this map and answer the The local time of a place can be calculated following questions. Use the relation between with reference to the time at the Prime Meridian. degrees and time for this. Examine the examples given below. Ø Between which longitudes does the region Example 1 : experience daytime? Mashad, a town in Iran, is located on the 60° E longitude. When it is 12 noon at Ø Which longitudes experience noon and Greenwich, calculate the local time of Mashad midnight respectively? town. Ø Edward from New Orleans is on which Statement : As we move towards the east of longitude? the Prime Meridian, the local time increases by 4 minutes for every longitude. Ø What is the time at Accra city? The difference between the longitudes of Ø At the same time, what is Sharad from Greenwich and Mashad Patna and Yakaito from Japan doing? = 60° What time is it in these cities? Difference in local time = 60 Î 4 Ø Select any one longitude.Calculate the = 240 minutes local time of the longitudes lying 1°to the = 240 ÷ 60 minutes west and east of this longitude. = 4 hours This implies that the time at Mashad would be Think about it. _________ in the ________. Example 2 : Ø What is the maximum number of local Manaus city in Brazil is located on times that can there be in the world? 60° W longitude. What would be the local time Ø How many longitudes pass the sun in at Manaus when it is 12 noon at Greenwich? one hour? Statement : ------------------ ----------------------------- The difference in longitudes between the two places : Do you know ? = When the sun is directly overhead at a Total difference in time = Î place on the earth, it is noon over there. While = minutes telling the time between midnight and noon, = ÷ 60 minutes we put a.m. in front of the time. This means = hours Ante Meridiem. When the longitudes cross As Manaus is located to the ______________ the noon time, then the time is past midday or of Greenwich, the local time of Greenwich is --- afternoon. The time in between noon and ----------------------- of Greenwich time by ------ midnight is denoted by p.m. means Post ---------------- hours. And, therefore, when it is Meridiem. noon at Greenwich, it would be ------------------- ---------- at Manaus. 3  Make friends with maps ! 4 Figure 1.3  then there will be a lack of synchronization Use your brain power ! in the routine activities in the country. If each one follows their local time, discrepancies emerge in carrying out daily business in the Ø Tick ü the time in the boxes which you country. Therefore, generally, the local time at can tell without using clock. the longitude which generally passes through the middle of the country is deemed to be the l Sunrise l Sunset standard time for that country. This standard l Noon l Midnight time is used all over the country. With respect to businesses at global level, there should be compatibility between the Geographical explanation standard times of various countries. To facilitate this, the world has been divided into 24 time l Longitudes lying to the east of any longitude zones. These time zones have been created with are ahead of the time at that longitude while reference to the Prime Meridian itself. those lying to the west are behind. Normally, if the difference between the l As the distance between two longitudes longitudinal extent of the country is less than increase, their local times also starts one or two hours, only one standard time is differing considered for the country. But if the longitudinal l If we multiply the difference between extent (east-west extent) is more than that, then, longitudes in degrees by 4 minutes, then the one standard time is not enough and in such difference in the respective local times can countries, more than one standard time zones be calculated. are considered. l The difference in longitudes can be known with the help of a globe or map. Give it a try. Carry out the activity given on Page 75 Look for the map of world time zones and 76 and understand the standard time of from reference books and see in which time various locations. See if you can find out the zone India falls into? standard time at two opposite longitudes with this activity? STANDARD TIME : Find out. Can you tell ? With the help of an atlas find out which countries need more than one stand- Ø Mumbai is located at 73° E longitude. ard time Kolkata is located at 88° E longitude. Find the difference between the longitudes of INDIAN STANDARD TIME : these two cities. The Indian Standard Time (IST) has been Ø If the local time at Mumbai is 3 pm then decided according to the 82° 30' E longitude which passes through Mirzapur (near Allahabad, what would be the local time at Kolkata? Uttar Pradesh). This longitude passes through Geographical explanation the middle of the country with reference to its longitudinal extent. The local time at this Both Mumbai and Kolkata are located longitude has been selected as the standard time within India but on different longitudes. Their of the whole country. When the sun is directly local times differ by an hour. overhead on this longitude, then it is assumed If there are different local times within a that it is 12 noon everywhere in India. There is country because of longitudinal differences, no difference of more than one hour between 5 Universal Standard Time : Do you know ? For an international coordination between countries, the local time at Greenwich Jantar-Mantar: Astronomical (Greenwich Mean Time) in England is Observatories considered to be the international standard Maharaja Sawai Jaisingh II, the time. The difference in standard times of king of Jaipur, Rajasthan, was a great various countries is calculated with reference astronomer, mathematician and to GMT. The Indian Standard Time is 5 hours architect. He built five astronomical 30 minutes ahead of GMT. If it is 5 p.m. at observatories called Jantar-Mantar at Greenwich then in India it would be 10.30 p.m. Ujjain, Varanasi, Jaipur, Delhi and Mathura. Give it a try. The one at Mathura doesn’t exist today but one can visit the other four. Ø If it is 8 a.m. in India, what is the time in Even today, one can know the exact Greenwich? time upto seconds through shadows. Ø When it is 2 p.m. in India, in which Jantar Mantar do not only house countries would it be 2 p.m. too? sundials, but they are complete astronomical observatories. One can Ø When it is 9 a.m. in India, what would be observe the sky from here too. the time at 82° 30' W longitude? With the help of instruments at Ø What would be the time at Prime Jantar-Mantar, it is still possible to Meridian when a new day starts at 180° see astronomical observations. After the advent of modern instruments, longitude? now these instruments are more of a ‘cultural heritage’. Do you know ? National Institute of Standards and Technology (NIST), an institute in the United States of America has developed the most accurate clocks in the world. Clocks have to be adjusted by 1 second (added or subtracted) once in 20 million years. In India, the National Physical Laboratory of India, (NPL) New Delhi gives services of accurate time-keeping. The clocks used here are accurate up to 1 lakh part of a second. Think about it. As accurate time is required for space research, artificial sattelite launching, etc., Ø In which of the following countries, these clocks are used in these activities. does only one standard time exist? l Mexico l Sri Lanka l New Zealand l China Ø Why does a country having a large latitudinal extent have only one standard time? 7  Exercises Q 1. Complete the sentence by selecting the c) A football match being played at Sao correct option: Paulo, Brazil started in India at 6 am IST. Explain what would be the local (a) The earth requires 24 hours for one time at Sao Paulo? rotation. In one hour, (i) 5 longitudes will face the sun Q 4. If it is 10 pm on 21st June at Prime Meridian, write the dates and time at A, B (ii) 10 longitudes will face the sun and C in the table. (iii) 15 longitudes will face the sun (iv) 20 longitudes will face the sun Place Longitude Date Time (b) To calculate the difference between the A 1200 E local times of any two places on the earth, B 1600 W (i) the noon time at both the places should be known C 600 E (ii) the difference in degrees of their Q 5. Write the situations of place A shown in longitudes should be known these diagrams in the boxes below them : (iii) the difference in standard times of (i) Sunrise (ii) midnight (iii) noon (iv) Sunset both the places should be known (iv) Changes need to be made (ii) (i) according to International A Date Line A N. P. N. P. (c) The differene between the local time of any two consecutive longitudes is (iii) (iv) (i) 15 minutes A (ii) 04 minutes N. P. N. P. (iii) 30 minutes A (iv) 60 minutes Q 2. Give geographical reasons: Activity: (a) The local time is decided by the noon time. (a) Look for the actual granny’s clock in Shri (b) The local time at Greenwich is Acharya Atre’s poem : “Aajiche Ghadyal “ ( considered to be the international granny’s clock). Look for this poem on the in- standard time. ternet or in reference books. (c) The standard time of India has been (b) Find out the velocity of the earth’s rotation in decided by the local time at 82.5° E km/ hour. longitude. (d) Canada has 6 different standard times. *** Q 3. Answer in brief: (a) If it is 12 noon at 60°E longitude, then explain what would be the time at 30° W longitude? (b) How is the standard time of a place determined? 8  2. INTERIOR OF THE EARTH Geographical explanation Let’s recall. Before boiling, the milk was in the liquid In the previous classes, you have been state. After it came to a boil, steam started coming introduced to rock types, volcanoes and out from it. After some time, a thick layer of earthquakes. Answer the following questions cream develops over the milk. The temperature on the basis of that. of the cream is lesser than the milk below. Thus, Ø When earthquake occurs, what happens it can be implied that the creamy layer cooled exactly ? faster than the milk below it, which remained hot Ø How are igneous rocks formed? and in a liquid form. A similar process occurred Ø What is a volcano ? when the earth cooled. Ø Which materials come out during a volcanic The scientists unanimously believe that eruption? the Earth was formed out of the solar system Ø In which state of matter are these materials? itself. Initially, earth was a gaseous hot balloon. Ø Are these materials cool or hot? Why? It cooled down as it rotated around itself. The process of cooling took place from the outer Try this. surface towards the earth’s center. As a result, the outer layer (crust) of the earth become cooler Boil half a liter of milk. When the milk and soild but as we move from surface to the comes to a boil, switch off the gas Keep core, heat increases and at certain depths, the a lid on the vessel. (The latter part of the interior of the earth is semi liquid. experiment is very important. You have to use your observational skills and arrive at some Man has always been inquisitive about conclusions.) what lies in the interior of the earth. A direct After ten minutes , remove the lid, take it to observation of the earth’s interior has not been a side and tilt it. Observe what happens. What possible as yet. Through various methods, the can you see on the milk? In what form do you scientists have tried to estimate about the same. see the layer of matter on the milk? Remove To infer about these, study of the materials this layer of matter. Take note of the difference coming out of a volcanic eruption and the seismic in temperature of this matter and the milk and waves is most important. answer the following questions. Matter coming out of volcanic eruptions Ø When the milk was kept for boiling, in which consists of hot magma, gases, steam, etc. When state was it? lava cools and solidifies, igneous rocks are formed. Ø When the milk was boiling, what did you Through the estimates of the study of temperature, observe? density, gravitational force and pressure the interior of the earth was understood. For instance, Ø What had accumulated over the lid of the vessel? when we go deep into a mine, we feel an increase in temperature. Similarly, the magma coming out Ø Tell whether the matter accumulated on the of volcanoes from the earth’s interior is hot. Such milk is liquid or solid? estimations were made by the geologists. Several Ø Was it cooler or hotter than the milk below? earthquakes occur in various places on the earth Ø On which other substances can similar every year. Seismic waves are generated. These experiments be carried out? waves travel through the interior of the earth. 9 The study of their direction and velocity helps us ü Show the continents in yellow on this sphere to estimate about the interior of the earth. Man like a globe. Now your globe made from has also tried to dig deep bore holes in the interior clay is ready. to know more about the same. ü To see the interior of the earth, cut the sphere exactly in half. You can see various layers Think about it. of colors inside like the layers of the earth’s interior. Name these layers. Can we dig deep from one side of the earth and come out from the other side? Geographical explanation Write your imaginations in your notebooks and discuss in class. While going from the earth’s surface to its (Note: Teachers should listen to the core, major changes occur in temperature and ideas of the students and direct the topic density. With respect to these two elements, the towards the earth’s interior) earth’s interior can be divided into following layers. The layers of the interior of the earth Do you know ? Our earth was formed approximately CRUST MANTLE CORE 4.6 billion years ago. Initially, the earth was in a gaseous state. It started cooling CONTI- OCEANIC OUTER INNER NENTAL CRUST CORE CORE through the process of radiation. The earth CRUST then liquefied. With time, the outermost part of the earth cooled first and became solid. UPPER LOWER MANTLE MANTLE This outermost layer of the earth is called the crust. Even today outer planets of the INNER solar system are in a gaseous state. CORE The Composition of The Earth’s Interior : OUTER CORE Try this. MANTLE (Carry out the following activity by dividing the students into two groups. Use the pictures on the back cover for reference.) CRUST ü Take clay balls of 3 colors- red, yellow and (CONTINENTAL blue. (As available in the market) CRUST / OCEANIC ü Make the red ball bigger. CRUST) Figure 2.1 Diagram showing the structure of the ü Roll out the yellow colour ball. You will get earth’s interior a flat roti-like structure. Place the red colour ball inside the yellow one like you fill puran THE CRUST : in a puranpoli. Give it the shape of a sphere. The uppermost layer of the earth’s ü Now roll out the blue ball and fill the yellow surface is in solid state and is called the crust. one in it as done earlier. Make a sphere out The thickness of the crust is not the same of this too. everywhere. On an average, it is 30 to 35 km 10  Steps in the process of knowing the interior of the earth 1 8 2 9 3 10 4 11 12 5 13 6 14 7 11 Crust (30 km average) Oceanic Crust : This is the second LITHOSPHERE layer of the crust. It is made up of silica and Upper magnesium. It was earlier called Sima. This Mantle layer is approximately 7 to 10 km thick. The Crust density of this layer is 2.9 gm/cm3 to 3.3 gm/ km) & cm3. In this layer, basalt and gabbro rocks are Mantle (2870 Mantle Mantle (Solid) Lithosphere mainly found. 100 km Lower Mantle Always remember - Elements found in various layers of the earth’s interior Outer Core (Liquid) Low Silicon (Si) Aluminium (Al) DENSITY 1 km) Silicon (Si) Core (347 Magnesium (Mg) Nickel (Ni) Ferrous (Iron) (Fe) Inner Core (Liquid) High Earth Centre (6371 km) Do you know ? Figure 2.2 : Image showing earth’s interior There is a discontinuity between thick. The thickness of the crust below the the continental crust and oceanic crust. continents is from 16 to 45 km, 40 km under the It was first deduced by a scientist called mountain ranges and less than 10 km under the Conrad and is named after him as Conrad oceans. discontinuity. As we move deeper under the surface, There is discontinuity between crust temperature increases. After that, the rate of increase in temperature reduces and again and mantle too. This discontinuity was increases in the core. At the centre of the deduced by a scientist called Mohorovicic. earth, the temperature is around 55000 to It has been named after him as Moho 60000 C. discontinuity. The crust is the thinnest of all the layers There is discontinuity between mantle when compared to the mantle and the core. It and core too. It has been named after can be divided into two sub-layers. Gutenberg, a scientist, who discovered it. Continental Crust : The continents are Silica is the MANTLE : compound of Silicon Elements) and Aluminum. Below the crust lies the mantle. Mantle Because of their high proportion in this layer, can be divided into two layers: upper and the layer was earlier known as Sial. The density lower mantle. of continental crust is 2.65 to 2.90 gm/cm3. The upper layer is more in liquid state. The thickness of this layer is approximately 30 Here, one finds magma chambers. It is through kilometers. Granite rocks are mainly found in these chambers that magma comes out on the this layer. earth’s surface during volcanic eruptions. 12 This layer is also known as asthenosphere. in these spiral eddies of liquid iron and thus Epicenters of deep seated earthquakes are magnetic field is generated. It is sometimes usually found here. Mantle begins at a depth called the geo-dynamo too. This magnetic of around 42km from the earth’s surface. field of the earth is functional even outside the The internal energy released due to earth’s surface for quite a distance. As a result, endogenetic movements occurring in this a cover develops around the earth because of layer is responsible for mountain-building, the magnetic field. The earth’s atmosphere is rifts, volcanic eruptions earthquakes, etc. protected from solar winds coming from the In this layer, it is inferred that the sun. The magnetic field thus developed around temperature at a depth of 2400 to 2900 km the earth, is called magnetosphere. This is the depth would be around 2200° C to 2500° C. fifth and an important sphere of the earth. See Here, there is a sudden change in the structure fig 2.3. and density of material. It is estimated that INNER CORE : Inner core extends from this layer extends upto a depth of 2870 km. around 5150 km to the depth of around 6371 Average density of this layer is 4.5 gm/cm3 and km (earth’s centre.) It is the core of the earth it increases with depth. Increasing pressure is which is in a solid state. The density of this the reason behind this. The density of lower sphere is around 13.3 gm/cm3. Iron and nickel mantle is about 5.7 gm/cm3. are the major elements found here. Therefore, CORE : (A) The core starts from around the depth of about 2900 km from the earth’s surface. The part of the earth’s interior extending from the mantle upto the centre of the earth is the core. The thickness of the core is about 3471 km. This layer can be divided into outer core and inner core. OUTER CORE : Outer core extends from around 2900 km to 5100 km. The secondary waves cannot pass-through the core. They Earth’s Magnetosphere get absorbed in this region. This has led the scientists to believe that the core could be liquid or semi-liquid in nature. The primary waves travel through this layer. But their speed reduces when passing through this layer. (B) The density of outer core is 9.8 gm/cm3. The temperature of the liquid outer core is around 5000° C. We have learnt that the outer core of the earth’s interior is in a liquid state and the proportion of iron is more in this layer. Vertical currents originate in this liquid layer. This is another characteristic of this area. The difference between the temperatures Geo-magnetic Pole of the outer and inner core gives rise to vertical and equator currents. The earth’s rotation gives them eddy (circular) motion. Electric currents develop Figure 2.3 (A) and (B) : Earth-a magnet 13 this layer is also called Nife. As the materials in this layer are under extreme pressure, the inner Use your brain power ! core is in solid state. The temperature here is As you go in the interior of the earth, almost equivalent to the surface temperature of guess what changes will you notice in your the sun. weight? Try to find out the reason behind it. Always remember - The left curve in figure ‘A’ shows the Observe the velocity curves of the velocity of secondary (S) waves, while given seismic waves. the curve on the right shows Primary (P) waves. There are many changes occurring in the curve of the secondary waves. The curve drawn with the help of dots shows the average velocity of the waves. The curve of the secondary waves seems to have ended around the depth of 2900 km. Changes are visible even in the curves of the primary waves. The velocity of the primary waves increases according to depth till 2900 km. The velocity of secondary waves is around 6 to 8 km/sec around the boundary of the outer core and the curve has stopped there. These waves do not enter the core. At 2900 km, the velocity is around 12 km/sec. But when it enters the core, the velocity reduces to 8 km (A) / sec. See this as shown in the dot curve. On the basis of these curves, the scientists have inferred the densities at various depths. The density curve of the earth’s interior is shown in figure ‘B’. Red curve in figure ‘B’ shows gravitational force at various depths. Gravitational force increases at certain depth from the surface and then reduces according to depth. At the centre, it is zero as is visible from the curve. Observe these figures minutely, find various discontinuities in the density curve (B) and show them on the figure. Think about it. Find out. Imagine the earth’s interior and write What is World Earth Day? Why is it 10-12 sentences on it. celebrated? 14  Exercises Q 1. Tick ü the correct options in the box Q 2. Tell whether right or wrong. Correct the (A) There are two layers in the crust. wrong statement (i) Inner and outer crust (A) The density of various materials is not the same in the interior of the earth. (ii) Continental and oceanic crust (B) The core of the earth’s interior is made (iii) Surface and oceanic crust up of hard rock (iv) Mantle and Core (C) Secondary waves cannot pass through (B) Which element is found in both mantle outer core. and crust ? (D) Continental crust is made up of silica (i) Silica and magnesium (ii) Magnesium Q 3. Answer the following (iii) Aluminium (A) What are the two parts of the crust? (iv) Iron What is the basis of classification? (C) Which of these minerals are found in (B) Why is the upper mantle called the the core of the earth? asthenosphere? (C) Magnetosphere of the earth is a result (i) Iron-magnesium of rotation. Explain. (ii) Magnesium-nickel Q 4. Draw neat diagrams, label them and (iii) Aluminium- Iron explain. (iv) Iron-nickel (A) The interior of the earth (D) The inner core is in which state? (B) Magnetic pole and equator (i) Gaseous Q 5. Give geographical reasons: (ii) Solid state (A) There are discontinuities in the interior of (iii) Semi-solid state the earth. (E) The outer core is made up of (B) There is correlation between the density (i) Iron of metals and their location in the (ii) Gold interior of the earth. (C) Mantle is the centre of earthquake and (iii) Hydrogen volcanic eruptions. (iv) Oxygen (D) The thickness of the crust below the (F) The layer of the earth on which we continents is less as compared to oceans. live. (E) Earth is protected because of the (i) Mantle magnetosphere (ii) Core ACTIVITY : (iii) Crust Prepare a model of the earth’s interior. (iv) Continental crust (G) Which seismic waves can travel through *** liquid medium? (i) Primary waves (ii) Secondary Waves (iii) Surface waves (iv) Oceanic waves 15  3. HUMIDITY AND CLOUDS Can you tell ? Look at the pictures shown in figure 3.1. Discuss the weather conditions shown in these pictures in the class and write the descriptions in the boxes below. Children! Come fast! Wear It is very sunny today. The Buddy, it is very hot Yes, Soham, I am your sweaters and then play Yes, even today. literally soaked again. wind has stopped blowing. I foresee sandstorm. Let’s go I feel the because of the sweat. same. Mummy, please wait! quickly inside the house. Let us play, please! Come let’s go fast! Figure 3.1 Geographical explanation In the above discussion, the words hot, Generally, we keep talking about the moist, cool etc. show the condition of the air. weather conditions. We can identify the weather They relate to the content of the moisture in the conditions through the conversations above. We air. Moisture in the air is invisible. But it is the experience the dampness or dryness in the air major component of air which is taken into throughout the year. The changes occurring in consideration while discussing the weather of the weather conditions in desert areas, coastal any place. For precipitation to occur in any areas and mountainous areas is evident from the place, presence of moisture in the air is very figures. important. l Rajasthan lies in a region with dry and hot air. There is hardly any moisture in the air. Think about it. People wear loose cotton clothes. During winters, when you exhale on the l Kashmir valley lies in a region with cold glass of your mirror, what happens. If you try and dry air. Moisture is minimal in the air. to do this in summer why doesn’t this happen? People cover themselves with warm clothes. l In Mumbai, the air is hot and humid. There EVAPORATION : the proportion of moisture is very high in the Evaporation is the process of converting air. In addition, if dark clouds cover the sky, water into steam or water vapour. Because of the content of moisture in the air increases. the sun’s heat, the water on the earth gets 16 converted into water vapour. The process of ü Pour water on the sponge with a big spoon. evaporation is dependent on the dryness, ü The students in the group should note how temperature and the speed of the wind. many spoons of water have been poured. If the air is dry and hot, the rate of Keep pouring water with the spoon till the evaporation increases. The process of sponge becomes wet with water. Note what evaporation continues even in dry and cold air. happens if you keep pouring water even after On the other hand, evaporation occurs very that. Now answer the following questions. slowly in moist air. If the velocity and temperature of the air is high, then evaporation occurs rapidly. If the wind is blowing slowly and the air is cooler, then evaporation occurs slowly. Use your brain power ! Ø In which season do the clothes dry fast? Ø In which season do the clothes take time to dry? What could be the reason? Humidity in the air : The proportion of water vapour in the air is called its humidity. The dryness or dampness of the air depends on the proportion of water Figure 3.2 vapour. Air can hold moisture in specific quantity at specific temperature only. As air cools down, its moisture holding capacity reduces. This implies that warmer air can hold more moisture than cold air. At a certain temperature, the moisture holding capacity of air becomes equal to the proportion of moisture present in it. This condition of the air is called saturation of the air. Try this. (Carry out the following activity in a group). Figure 3.3 ü Take a colander/ tray which is deeper in the centre. Ø What happened to the water which was ü Take a piece of sponge. poured initially? ü On the flat part of the tray, make holes with Ø When you were pouring water on the the help of nails. sponge, what did you expect? ü Keep the sponge on the centre of the tray/ Ø What happened when you poured more colander. water on the sponge? ü Make sure there is no water in the sponge. Ø What conclusions can you draw from this? 17  Give it a try. The vapour holding capacity of 1 cu.m. of air in various temperatures is given here. Calculate the difference in the capacities by observing the table. Tempera- Vapour holding Difference in the ture of the capacity ( gm/ capacities ( gm/ air( 0 C) cu.m. cu.m) -5 3.26 --- 0 4.85 1.59 5 6.80 10 9.40 Figure 3.5 15 12.83 20 17.30 Geographical explanation 30 30.37 Let’s suppose that the air is like the piece of 40 51.12 sponge. How many spoons of water does the sponge absorb? After the sponge is full of water, At 15° C, the capacity of 1 cu.m air is to drops of water start trickling out. One can tell, hold 12.8 gm of moisture. If this amount of the number of spoons of water required to make vapour is present in the air, the air is said to be the water trickle down the sponge by observation. saturated. This humidity in the air is expressed This implies that the water-holding capacity of in different ways. the sponge is fulfilled. This makes it saturated. Similarly, when the proportion of moisture ABSOLUTE HUMIDITY : in the air exceeds its vapour holding capacity, The amount of water vapour in 1 cu.m. of precipitation in the form of rain or snow occurs air is the absolute humidity of the air. For on the earth. example, the absolute humidity of the air near The moisture-holding capacity of the air coastal areas is higher than air in the interior. depends on its temperature. Higher the Absolute humidity is higher in the equatorial temperature, higher is the holding capacity. We areas while it reduces as we move towards the have learnt earlier that as we go higher in the sky, the air becomes cooler. So, as per this rule, Use your brain power ! as we go higher, the vapour holding capacity of the air will decrease. The following table will Ø In which season is humidity generally make it clear. more? Always remember - Ø How does humidity affect the human body? Generally, humidity of the air is Ø Observe how humidity affects the food measured in grams per cubic meter. When materials at our home. the humidity in the air is 0 gm/cu.m., the Ø Is there a relation between the formation air is said to be dry. If the humidity in the of fungus and humidity? air at 30° C temperature is 37 gms/ cu.m. , Ø How is the early or late drying up of then the air is said to be saturated. clothes related to humidity? 18 poles. The distribution of land and water on ü Take water in a pressure cooker earth and the seasons also affect absolute humidity. ü Take off the whistle of the pressure cooker ü Now heat the cooker RELATIVE HUMIDITY : ü Take a lid with a handle The amount of water vapour present in ü After the water starts boiling, hold the air can be expressed as a percentage of the lid at a distance from where the steam is amount needed for saturation at the same coming out. temperature and same volume. It is expressed in percentage. Relative humidity Absolute humidity (R.H.) (%) = Vapour holding capacity Î 100 Ø What will be the relative humidity of air whose absolute humidity is 20 gm/m3 and vapour holding capacity is 30 gm/m3? Ø If the absolute humidity of the air is 15 gm/m3, and the vapour holding capacity is 15 gm/m3, then what is the relative humidity of the air? Think about it. What will happen if the temperature of Figure 3.5 saturated air at 20° C drops down to 10° C abruptly? ü Observe what happens. You must have observed that water changed into water vapour after it was heated. Ø On the basis of the examples given above, tell which air is saturated? The amount of water vapour changes according to difference in temperature. Similarly, relative humidity also changes. Generally, relative humidity is more in the mornings and nights. In the afternoon, as temperature increases, relative humidity decreases. Near coastal areas, the relative humidity is more and so the air is moist. In desert areas, relative humidity is less. Try this. The teacher should make two groups of the Figure 3.6 (A) students in the class. The first group should do This vapour turns into water droplets when it the following activity under the supervision of touches the cooler lid. We can see the water the teachers carefully. See fig 3.4. droplets deposited on the lid. 19  The other group should carry out the Clouds and Types of Clouds : following activity. See fig 3.6a l Clouds are a form of condensation at ü Take a glass with flat bottom. higher elevation ü Put some ice cubes in it. Always remember - ü Keep this glass in a room for 2-3 minutes There is a difference between fog and Ø What did you see? smog Fog is made of vapour in the air only. Smog is a combination of dust particles of polluted air in the region and fog. l Condensation occurs around minute particles in the atmosphere. Condensed water or snow particles in the clouds are very fine and almost weightless. And so, clouds float in the air. See fig 3.7 Raindrop (Maximum diameter 5mm) Figure 3.6 (B) In sometime, you will see droplets of water 5 mm on the outer surface of the glass. See fig 3.6B When the water vapour in the air comes in Fine Particle contact with the cold surface, condensation take Condensed Water particle in the place. These droplets form on the outer surface cloud of the glass. In the first activity, the steam from the Figure 3.7 : Raindrop cooker cooled and condensed into water droplets. Land and water get heated because of the In the second activity, the vapour in the air heat of the sun. Air near the surface heats up, condensed into water droplets. rises and becomes less dense. Hot air rises up. Condensation/Densification /Sublimation : As it goes higher, the temperature of the air The process of changing of water vapour in reduces and the moisture holding capacity of the the air into water is called condensation or air reduces. Relative humidity keeps increasing. densification. Also, the process of vapour (gas) The water vapour in the atmosphere turns into changing into solid state is called sublimation. If water and snow. This is the dewpoint level of the temperature of the air reduces, its vapour that air. The level of condensation is determined holding capacity also reduces. When relative by the water vapour in the air. Keep in mind that humidity of the air becomes 100%, vapour starts the freezing point is also dependent on the condensing. At this time, the temperature of the altitude and water vapour. air should be at dewpoint.. It implies that for Because of condensation, fine particles of condensation, temperature should be low and ice and water float in the air at a greater height. relative humidity must be high. In the free They accumulate around dust particles in the air environment, condensation of the vapour in the and become larger in size. Their accumulation air occurs around fine particles (dust, salt, etc.) together is called a cloud. Because of vertical in the air. flow of the wind, they float in the atmosphere. Dew, frost and fog are the forms of Like a kite which floats in the air as it moves higher and higher, the clouds too float in the condensation at ground level while clouds are a atmosphere because of vertical flow. form of condensation at higher elevation. 20  High altitude Medium altitude Low altitude Figure 3.8 : Types of Clouds Clouds are found at different altitudes above of the clouds is taken into consideration. If the mean sea level. Clouds which form at greater clouds are at an altitude of 7000-14000m, then altitudes are formed from very fine snow they are considered as very high clouds. If they particles. The process of evaporation and are at an altitude of around 2000-7000m, then condensation occur consecutively in the clouds. they are considered to be medium clouds. If Specific type of clouds cause rainfall on earth. The proportion of vapour is more near the earth’s they are at an altitude of less than 2000m, then surface. As we go higher away from the sea they are low clouds. See fig 3.8. level, the amount of vapour decreases. Hence, High Clouds : the clouds at a lower altitude are larger in size while the clouds a higher altitude are smaller. These clouds are mainly made up of ice Cloud types according to international particles. They can be classified into cirrus, classification cirrocumulus and cirrostratus. Cirrus clouds No. Types of Clouds General Altitude are mainly wispy. Cirro-Cumulus clouds look (meters) like groups of small waves. Cirrostratus are 1. Cirrus 7000 like a bedsheet with wrinkles. They generally 2. Cirro-Stratus to 14000 have a halo around them. 3. Cirro-Cumulus 4. Alto-Stratus 2000 to Medium Clouds : 5. Alto-Cumulus 7000 These include alto-cumulus and alto- 6. Strato-Cumulus stratus. Alto-cumules are in the form of layers 7. Stratus and have a wave-like structure. They are mostly Less Than 2000 8. Nimbostratus white in colour and have a grey shade. Alto- 9. Cumulus The extent could stratus are not very thick. The sun can be seen 10. Cumulonimbus be variable through them as if seen through a milky glass. Clouds are formed at different altitudes in Low Clouds : the atmosphere. After observation, we can These consist of five types of clouds. divide these clouds into 3 main types on the Strato-cumulus have layers. Their colour is basis of their altitude. The height from the base white to earthy. Round clusters of clouds can 21 be here. Stratus clouds also have layers. They The largest of these clouds bring rainfall are ash coloured and their base is uniform. accompanied with lightning. The top portion of Nimbo-stratus has thick layers. They are grey- these clouds has an anvil like shape. The clouds -ash in colour and cause continuous rainfall have a positive charge at the upper end and and even snowfall. negative charge at the lower end. The land below them always has negative charge. Due Give it a try. to difference in the charges, electric chargers are formed and lightning occurs lighting up the Look at figure 3.8 first. Now go out of the sky for a moment. The air around the lightning classroom in the ground. Observe the clouds rises up because of the heat and this leads to a in the sky. Discuss the following points in large thundering sound. the class and write answers in your notebook. As compared to other clouds, the rain drops of these clouds are larger because they Ø What was the colour and size of the move up and down a lot of times and accumulate clouds? more and more water. Drops become larger and larger and are unable to float in the clouds Ø What type of clouds did you observe? because of their weight. They fall in the form of (Take help from fig 3.8) rain. Sometimes, the air in the clouds is very Ø Can these clouds bring rain? Give cold. As a result, these drops freeze and fall in reasons. the form of hail. We call them hailstones. Cumulus Clouds : These clouds are formed Direction of the flow of clouds extensively from 500 m to 6000 m altitude. The vertical flow of the air adds to the formation of + + + + these clouds. These are huge and dome-shaped. They are grey in colour. Cumulus clouds are an indicator of pleasant weather. The vertical expanse of these clouds increases so much that they turn into cumulonimbus clouds and bring rain. Cumulonimbus Clouds : These are characterstic clouds which are indicators of thunderstorm. These look like huge mountains. These are dense and dark in colour. There is thunder accompanied by lightening. They bring - - - - - rain with storm and may sometime bring hailstones. But such a type of rain does not last long. See fig 3.9 + + + + Figure 3.9 : Cumulonimbus Clouds Use your brain power ! Find where the adjacent symbols are used while showing the weather of a place. Write their meanings in the boxes given below 22  Do you know ? Cloudburst is a type of precipitation. is called cloud-burst. It leads to a rainfall of Raindrops coming towards the earth are more than 100mm in a small area or particular stopped in the clouds itself because of strong region. This type of precipitation mainly occurs vertical winds. These drops change into hail. in mountainous regions. The states through This makes the clouds heavier. The vertical which the Himalayan ranges pass experience winds are unable to bear this weight. This leads such a type of rainfall. to heavy rainfall with large-sized hail. This Exercises Q 1. Match the column and complete the chain: A B C (A) Cirrus (i) Vertical extent in the sky (a) Roaring clouds (B) Cumulonimbus (ii) higher altitude (b) Floating clouds (C) Nimbostratus (iii) Medium altitude (c)continuous rainfall (D) Alto-cumulus (iv) Low altitude (d) snow flake clouds Q 2. Choose the correct word from the brackets Q 5. Give geographical reasons: and complete the sentence: (a) Clouds float in the sky. (Cumulonimbus, Relative humidity, Absolute (b) The proportion of relative humidity humidity, Condensation, Vapour-holding changes according to altitude. capacity) (c) Air becomes saturated. (a) The ------------ of air is dependent on the (d) Cumulus clouds change into temperature of air. cumulonimbus clouds (b) The amount of vapour in 1 cu.m. of air Q 6. Solve the following: shows the -----------------------. (c) As -------------------- is less in desert (a) When the temperature of the air is 30° areas, the air is dry there. C, its vapour-holding capacity is 30.37 (d) -----------------type of clouds are gms/ cu.m. If absolute humidity is 18 indicators of storm gms / cu.m. then what would be the (e) In a free environment, the --------------- relative humidity? of the vapour present in the atmosphere (b) What would be the absolute humidity of takes place around dust particles. air if 1 cu.m. air contains 4.08 gms of Q 3. Differentiate between: vapour at 0°C temperature?. (a) Humidity and clouds Q 7. Collect the weather related information (b) Relative humidity and Absolute from newspapers for the month of July. humidity Relate the difference in the maximum and (c) Cumulus clouds and cumulonimbus minimum temperatures with humidity. clouds ACTIVITY : Q 4. Answer the following questions: Make a table showing the types of clouds. Use (a) Why is the air in a region dry? various photographs. (b) How is humidity measured? *** (c) What are the prerequisites for condensation? (d) What is a cloud? Write its types. (e) Which type of clouds give rain? (f) On what does the percentage of relative humidity depend? 23  4. STRUCTURE OF OCEAN FLOOR Metres 3000 2500 2000 1500 1000 Sea level 500 00 -500 -1000 -1500 -2000 Figure 4.1 : Various landforms Can you tell ? We classify the various landforms on the earth on the basis of altitudes. A similar l Continents and oceans are a part of the classification can be done for landforms lithosphere and hydrosphere respectively. submerged under the water. l Continents and oceans lie on plates l During low tides, the level of ocean water Think about it. goes down and the land below the water If the classification of landforms on near the coast is exposed. land can be done on the basis of altitude and l Ships wreck when they strike against the size, then how can the landforms submerged rocks in the ocean. under water be classified? If the above points are correct, then select the most appropriate option from the following: Can you tell ? v The surface of the earth is occupied by land and water Ø Try to name the landforms shown in figure 4.1 v There is land below the ocean too. v Even if the water has the same level, the Ø What parameters were used for classifying the landforms on the earth? land submerged is not even. v The level of water and land is uneven. Ø What parameters were used for naming the Discuss in the class regarding the choice of landforms below water? your options. Know from your teachers about Geographical explanation the correct option. The Relief of Ocean Floor : Geographical explanation Land submerged below oceanic water is called the ocean floor. The relief of ocean We know that the proportion of water and floor is decided upon by the depth from the sea land is uneven on the earth. Around 71% of the floor and the shape of the land there. surface is covered by water but there is land The average depth of the oceans is around even below this water. But like water, it is not 3700 metres. The ocean bed is also uneven like at the same level. the land on the continents. The ocean floor 24  Continental Continental Continent Continent Coast Shelf Slope Mid-Oceanic ridges Sea level ० Marine Islands ० 2000 m. depth 4000 m. depth Abyssal plain Marine deep Marine Trenches Figure 4.2 : Ocean relief relief consists of all submerged landforms. The MOUNTAIN RANGES AND structure of the ocean floor differs from ocean PLATEAUS : The hills and mountains found to ocean. We will look at the sequence of on the ocean-bed are called submerged hills landforms and the details of