Class 8 English The Best Christmas Present in the World

Class Eight English CBSE Question & Answer

The Best Christmas Present in the World

The Ant and The Cricket

1. What did the author find in a junk shop?

Answer: The author found a roll-top desk made of oak wood in the junk shop. It was badly out of shop and needed lots of repair. But as a new one would have cost him a fortune he thought of buying it.

2. What did he find in a secret drawer? Who do you think had put it in there?

Answer: The author found a letter written by a person named Jim. It was Jim’s last letter to the recipient Mrs. Macpherson. So, there is every likelihood that Mrs. Macpherson had put it there.

3. Who had written the letter, to whom, and when?

Answer: Jim Macpherson had written the letter to his wife Mrs. Macpherson on during December 1914. It was written during the First World War.

4. Why was the letter written — what was the wonderful thing that had happened?

Answer: German and British army was fighting a battle. The soldiers were living in their trenches to fight enemy. For soldiers writing and receiving letter was the only way to be in touch with their family members. Nowadays telephone has taken over the role of letters. Think how painful and wonderful it would have been to wait for weeks for a letter to arrive. The wonderful thing was, in spite of enmity they celebrated Christmas together. This shows that festivals are above all personal enmity. In our country there is a saying that during Holi you should embrace your friends and foes alike.

5. What jobs did Hans Wolf and Jim Macpherson have when they were not soldiers?

Answer: Hans Wolf was a musician playing cello in an orchestra and Jim Macpherson was a school teacher. During early 20th century it was common for people to get enrolled into army during wars. Even today certain countries, like Israel, make it mandatory for all adults to serve in military for a certain period.

6. Had Hans Wolf ever been to Dorset? Why did he say he knew it?

Answer: Hans Wolf had never been to Dorset. He was fond of reading books and had good command over English language. He read so much about Dorset in books that he was familiar with Dorset. That is why he said that he knew Dorset.

7. Do you think Jim Macpherson came back from the war? How do you know this?

Answer: The written statement on the letter saying that that was the last letter from Jim and that should be buried with Mrs. Macpherson indicates that Jim didn’t return from war.

8. Why did the author go to Bridport?

Answer: The author wanted to ensure that the letter should reach the real owner and her last wish should be fulfilled. Even a criminal going to the guillotine is asked his last wishes and efforts are taken to fulfill those wishes. The address written on the envelope gave a hint to the author to try finding Mrs. Macpherson in Bridport.

9. How old was Mrs Macpherson now? Where was she?

Answer: Mrs. Macpherson was now over hundred years old. She was of the opinion that electricity was costly so was using candles to lighten her home. Because of candle her house caught fire and she was injured. She was getting treatment in a nursing home.

10. Who did Connie Macpherson think her visitor was?

Answer: Mrs. Macpherson thought the author to be Jim himself. Probably her old age, her poor health coupled with her sense of void after Jim’s death created such hallucination for her.

11. Which sentence in the text shows that the visitor did not try to hide his identity?

Answer: Author’s statement about how he found the desk and ultimately the letter shows that he did not try to hide his identity.

Class 8 Science Chapter 4 Combustion and Flame

Combustion and Flame

Combustion

Process of giving off heat by a substance after reaction with oxygen is called combustion. Sometimes, in the process of combustion, light is also given off along with heat. Combustion is a chemical process. For example; when petrol, LPG, kerosene, etc. reacts with oxygen, they give off heat.

Combustible Substance

Substances which go under combustion are known as combustible substances. Combustible substances are also known as fuel. For example; wood, charcoal, LPG, kerosene, petrol, diesel, etc.

Ignition Temperature:

Ignition temperature is the lowest temperature at which a substance catches fire. Ignition temperature is different for different substances. For example; LPG, petrol, natural gas, etc. catch fire at very low temperature and thus have low ignition temperature, while wood, coal, etc. have high ignition temperature.

Conditions for combustion

There are three conditions necessary for combustion: -
(a) Fuel – Fuel is the substance which undergoes combustion.
(b) Supply of air – Oxygen helps in combustion. Air contains about 29% of oxygen, thus supply of air makes the oxygen available which helps in combustion. Without oxygen, combustion will not take place.
(c) Ignition temperature – For catching fire, a combustible substance must reach its ignition temperature. If a combustible substance does not reach at or above its ignition temperature, it will not catch fire and combustion will not take place.
Thus, above three conditions are necessary for combustion to take place. If any one of the three will not be available, combustion will not take place.

Inflammable substance

Substances which catch fire at very low temperature and burn with flame are called inflammable substances. For example; LPG, Petrol, Spirit, etc.

Controlling the Fire – Fire extinguisher

Many a time; homes, forest, shops, etc. catch fire. In such cases, it becomes necessary to put off the fire otherwise it may cause huge monetary loss and loss of lives. Fire Brigade or Firemen are experts in controlling fire by using fire extinguisher.
To extinguish fire, at least any one out of three essential conditions for combustion must be removed. Supply of fuel, supply of air and ignition temperature; are the three essential conditions for combustion.
In case of fire in a building, the whole building becomes fuel. It is not possible to cut off the supply of fuel. Thus, firemen try to cut off air supply and or bring down the temperature of combustible material below their ignition temperature.

Fire extinguisher:

Water is one of the best, cheapest and oldest fire extinguishers. By pouring water over the combustible material, the temperature can be cooled down. Cooling down brings the combustible materials below their ignition temperature. In addition to this, water vapour surrounds the combustible material which stops the supply of air. Removal of these two conditions puts off the fire.
This is the cause that firemen generally pour water over the materials which have caught fire.
Controlling fire when electrical equipment is on fire: Water is not suitable in the case when electrical equipment or oil catches the fire. In the case of electrical equipment on fire, pouring water over them may prove disastrous because normal water is a good conductor of electricity. It may conduct electricity and can harm the persons who are trying to control the fire.
Controlling fire in the case of oil, petrol, etc.: Water is heavier than oil. So when water is poured over oil; oil comes on top and keeps on burning.
Carbon dioxide as fire extinguisher: Carbon dioxide does not support combustion and hence is considered as the best fire extinguisher.
Carbon dioxide is heavier than air and hence covers the material which is burning. By covering the material, supply of oxygen is stopped. This puts off the further combustion and fire is controlled.
Under high pressure, carbon dioxide liquefies and takes less space because of compression. Liquid carbon dioxide is stored in cylinders. A nozzle is attached with cylinder to release carbon dioxide. When nozzle is opened, carbon dioxide starts coming out from the cylinder because of high pressure. It expands and covers the combustible materials as blanket. This cuts off the supply of oxygen to the combustible materials. Because of expansion, the temperature of carbon dioxide decreases which decrease the temperature and brings down the combustible material below their ignition temperature. Thus, stoppage of supply of oxygen and bringing down the temperature below the ignition temperature of combustible materials put off the fire.
Sodium bicarbonate or potassium bicarbonate as fire extinguisher: Sodium bicarbonate (baking soda) or potassium bicarbonate releases carbon dioxide on heating. Thus, when powder of sodium bicarbonate or potassium bicarbonate is spread over or near the fire, they release carbon dioxide which covers the burning materials and cuts off the supply of oxygen to them. This puts off the fire.

Combustion and Flame

Types of Combustion: -

Combustion can be divided into three types – rapid combustion, spontaneous combustion and explosion.

Rapid Combustion:

Combustion in which a substance burns rapidly and produces heat and flame is known as rapid combustion, such as combustion of natural gas, LPG, petrol etc. This is usually attained by introducing external heat. Substances which undergo rapid combustion have lower ignition temperature.

Spontaneous Combustion:

When a substance suddenly starts burning into a flame; without the supply of any external cause (such as heating; the combustion is called spontaneous combustion. Substances; which have relatively low temperature of ignition generally burn by spontaneous combustion.

Examples:

• Phosphorous and sulphur start burning instantaneously; at room temperature.
• Haystacks, linseed oil, coal, pyrite, etc. sometimes start burning suddenly with flame because of increase in temperature.
• In coal mines, fire breaks out many a times because of combustion of coal dust.
• Fire often breaks out suddenly because of increase in temperature due to sun or friction.

Explosion: -

When combustion is accompanied by sudden production of heat, sound and large amount of gas, it is called explosion. Firecrackers and bombs are substances which show explosion.

Flame

All substances do not give flame while burning. Substances which vapourise while burning give flame and those which do not vapourise while burning do not give flame.
Fuels which burnt with flame are used to produce light.

Example –

Kerosene, wax, wood, etc. burn with flame as they vapourise during burning.
Coal and coke do not vaporize while burning and hence do not produce flame.

Structure of flame

Flame can be divided into three zones – innermost zone, middle zone and outer zone
Innermost zone: Zone near the wick of a candle is called the innermost zone of the flame. The innermost zone is the zone of unburnt wax and is generally of black colour. It is the least hot zone.
Middle zone: Zone in the middle of the flame is called the middle zone. Middle zone of flame is moderately hot and of yellowish colour. In this zone, fuel burns partially. Middle zone is the luminous zone, because partial combustion of carbon produces glow.
Middle zone produces black deposits of unburnt carbon particles.
Outer zone: Outer zone of flame is of bluish colour and the hottest part of the flame. In this zone, fuel is completely burnt. Because of complete combustion, it gives bluish colour.

Fuel

All combustible materials are not considered as fuel. Charcoal, wood, LPG, cowdung cake, natural gas, petrol, diesel, kerosene etc. are known as fuel.

Criteria for ideal fuel

• Easily and readily available
• Cheap
• Burns easily in air at moderate rate
• Produces large amount of heat
• Burns completely and does not leave any undesirable substance after burning.

Substances which meet above criteria are known as ideal fuel. But ideal fuel is not available in practical life.
Fuels which meet most of the criteria are considered as good fuel.

Fuel efficiency:

Efficiency of a fuel is measured by its calorific value.
Calorific value is the amount of heat produced by the complete burning of 1 kg of fuel. And hence calorific value of fuel is expressed in kilo joule per kg (k J/kg).
A fuel with higher calorific value is considered as an efficient fuel.

Burning of Fuel Produces Harmful Products

Since, no fuel is considered as an ideal fuel, thus they do not undergo complete combustion and produce unwanted substances. These substances have harmful effect on the humans and the environment. Some of the harmful effects of burning of fuel are as follows:
(a) Fuels; like, wood, petrol, diesel, coal, etc. release unburnt carbon particles. These unburnt carbon particles create pollution by mixing in air. They lead to diseases of respiratory system and many other related diseases.
(b) Incomplete combustion of carbon fuels produces carbon monoxide. Carbon monoxide is a poisonous gas which may kill a person.
(c) Most of the fuels release carbon dioxide gas. Excess carbon dioxide gas in the atmosphere leads to global warming.
(d) Burning of coal and diesel produce sulphur dioxide. Burning of petrol gives oxide of nitrogen. When these gases mix with rainwater, acids are formed. These acids fall along with rainwater and this is called acid rain. Acid rain is harmful for animals and plants. Acid rain is also harmful for buildings and monuments. The famous Taj Mahal has lost much of its sheen because of acid rain.
CNG is considered as a cleaner fuel. It releases harmful products in very small amount. Now-a-days CNG is being used to run vehicles in many towns, such as Delhi, Ahmadabad and Mumbai. This has helped in reducing the level of pollution.

Combustion and Flame

NCERT Solution

Question: 1. List conditions under which combustion can take place.

Answer: - Conditions under which combustion can take place are as follows:

(a) Presence of oxygen

(b) Presence of an inflammable substance

(c) Ignition temperature

Question: 2. Fill in the blanks:
(a) Burning of wood and coal causes …………….of air.

Answer: Pollution

(b) A liquid fuel, used in homes is …………….

Answer: - Kerosene

(c) Fuel must be heated to its ………… …………….before it starts burning.

Answer: Ignition temperature

(d) Fire produced by oil cannot be controlled by ……………...

Answer: Water

Question: 3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Answer: CNG is a cleaner fuel; compared to petrol and diesel. CNG produces lesser amount of harmful gases on burning. Due to this, CNG is now being used in automobiles in many cities; which has helped in reducing pollution in our cities.

Question: 4. Compare LPG and wood as fuels.

Answer: Wood has traditionally been used as kitchen fuel and is still predominantly being used in rural areas. Burning of wood creates many air pollutants which can result in respiratory problems. Moreover, incomplete oxidation during burning of wood creates carbon monoxide which is a poisonous gas. LPG is much better because it burns without giving smoke. It produces lesser amount of air pollutants. Complete oxidation during burning of LPG does not lead to carbon monoxide production.

Question: 5. Give reasons:
(a) Water is not used to control fires involving electrical equipment.

Answer: Pure water is a bad conductor of electricity but normal water contains many salts and hence is a good conductor of electricity. Trying to douse fires; involving electrical equipment; with water can result in electric shock. Due to this, water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood.

Answer: LPG is a better domestic fuel than wood because of several reasons. Unlike wood, LPG burns without smoke. This makes the life of housewives more comfortable and they do not have to worry about blackening of pots and pans. Moreover, use of LPG as domestic fuel also rules out the chances of getting respiratory disorders which may happen when someone uses wood as kitchen fuel. Storage and transportation of LPG is easier compared to that of wood.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Answer: The ignition temperature of paper is lower compared to that of aluminium. When paper is wrapped around an aluminium pipe; the ignition temperature increases. That is why paper itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Question: 6. Make a labelled diagram of a candle flame.

Answer:

Question: 7. Name the unit in which the calorific value of a fuel is expressed.

Answer: The calorific value of a fuel is expressed in kilo joule per kg (kJ/kg).

Question: 8. Explain how CO2 is able to control fires.

Answer: Carbon dioxide is heavier than oxygen. Due to this, carbon dioxide forms a blanket around the burning material and makes a barrier between the burning material and oxygen. As oxygen supply is cutoff, it helps in extinguishing the fire.

Question: 9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Answer: Green leaves contain moisture and as a result, the ignition temperature of green leaves is much higher than that of dry leaves. Due to this, it is difficult to burn a heap of green leaves but dry leaves catch fire easily.

Question: 10. Which zone of a flame does a goldsmith use for melting gold and silver and why?

Answer: The outermost zone of a flame is the hottest zone. Due to this, goldsmith uses the outermost zone of a flame for melting gold and silver.

Question: 11. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Answer: Total mass of fuel = 4.5 kg

Heat produced by burning the given mass of fuel = 180,000 kJ.

We know that calorific value of fuel

Hence, the calorific value of the given fuel = 40,000 kJ/kg

12. Can the process of rusting be called combustion? Discuss.

Answer: Although the process of rusting also involves oxidation but it cannot be termed as combustion. The reason for this is that combustion is defined as a process in which oxidation is accompanied by heat and heat is not produced during rusting.

13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer: Since Abida has kept the beaker in the luminous zone of the flame, the beaker will take more time to get heated. On the other hand, Ramesh has kept the beaker in the non-luminous zone of the flame so his beaker will be heated in shorter time

Class 8 Science chapter 2 Microrganisms

Microorganisms

Definition: An organism that is too small to be seen by the unaided eye, especially a single celled organism, such as a bacterium is called microorganism.

Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa and some algae.

Viruses are also microscopic. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

Where do Microorganisms Live:

They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.

Microorganisms and Us:

Microorganisms play an important role in our lives. Some of them are beneficial in many ways whereas some others are harmful and cause diseases.

Commercial Use of Microorganisms:

Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar). Yeast is used for commercial production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like barley, wheat, rice and crushed fruit juices, etc.

Medicinal Use of Microorganisms

Whenever we fall ill the doctor may give us some antibiotic tablets, capsules or injections such as of penicillin. The source of these medicines is microorganisms. These medicines kill or stop the growth of the disease-causing microorganisms. Such medicines are called antibiotics. These days a number of antibiotics are being produced from bacteria and fungi. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria. The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Antibiotics are even mixed with the feed of livestock and poultry to check microbial infection in animals. They are also used to control many plant diseases.

Vaccine

When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine works. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.

Increasing Soil Fertility

Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Commensals:

Some microorganisms live inside our body. They help in certain functions of our bdoy systems. For example some bacteria in our gastrointestinal tract help in digestion. These type of organisms which reside in our body and are beneficial as well are called commensals.

Apart from them certain food like curd, contain beneficial bacteria.

Harmful Microorganisms

Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens. Some microorganisms spoil food, clothing and leather.

Disease— causing Microorganisms in Humans

Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.

There are some insects and animals which act as carriers of disease causing microbes. Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. Another example of a carrier is the female Anopheles mosquito, which carries the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus.

Some Common Human Diseases caused by Microorganisms

Disease— causing Microorganisms in Animals

Several microorganisms not only cause diseases in humans and plants, but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus.

Disease— causing Microorganisms in Plants

Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops. They can be controlled by the use of certain chemicals which kill the microbes.

Food Poisoning

Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.

Food Preservation

Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and changed colour.

Common methods to preserve food in our homes.

Chemical Method: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.

Preservation by Common Salt: Common salt has been used to preserve meat and fish for ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind, etc.

Preservation by Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.

Preservation by Oil and Vinegar: Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

Heat and Cold Treatments: You must have observed your mother boiling milk before it is stored or used. Boiling kills many microorganisms.

Similarly, we keep our food in the refrigerator. Low temperature inhibits the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes. The milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

Storage and Packing: These days dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Nitrogen Fixation: Rhizobium is involved in the fixation of nitrogen in leguminous plants (pulses). Sometimes nitrogen gets fixed through the action of lightning. But the amount of nitrogen in the atmosphere remains constant.

Nitrogen cycle

Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds.

When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

Class 8 Science chapter 3 Synthetic and Man Made fibres

Synthetic Fibres and Plastics

Types of Fibres

There are two types of fibre – One which are obtained from natural sources and other which are man-made.
Fibres which are obtained from natural sources are called natural fibres. For example – cotton, silk, wool, etc.
Fibres which are man-made are called man-made or synthetic fibres. For example – rayon, nylon, acrylic, etc.

Synthetic Fibres:

Synthetic fibres are small units of chemicals joined together in the form of chain. The chain so formed is called polymer. Polymer is a Greek work in which ‘poly’ means many and ‘mer’ means units. Thus, polymer means ‘made of many units joined together’.

Types of Synthetic Fibres:

Rayon:-

Rayon is sythesied from wood pulp. Rayon resembles silk, so it is also known as artificial silk. Rayon fibre can be dyed in different colours. Rayon is very cheap compared to silk.
Bed sheets, shirts, sarees, and many other clothes are made from rayon.

Nylon:-

Nylon was first commercially synthesized fibre. The production of nylon was started almost simultaneously in New York and London, thus it got its name (NY for New York and Lon for London) as nylon. Nylon is synthesized from coal, water and air. Fibre of nylon is very strong and it also resembles silk.
For the first time, nylon was used in making bristle of toothbrush commercially. After that, it was started used as fabrics.
Nylon is used in making of different types of clothes, ropes, socks, curtains, sleeping bags, parachutes, etc. The fibre of nylon is stronger than a steel wire of same thickness.

Polyester

Polyester is one of the most popular man-made fibres which are used in making clothes. It is made of repeating unit of a chemical called ester. Terylene is one of the most famous types of polyester.
Polyester is used in making different types of apparel; such as shirts, pants, jacket, bedsheets, curtains, sarees, mouse-pad, etc. Polyester is used in making ropes, fabrics for conveyor belt, cushioning and insulating material in pillow, etc.
Fabrics made from polyester fibre are almost wrinkle-free, easy to wash and have shiny appearance. It is the polyester which made the fabric cheaper in India as well as in the whole world.
Terrycot is a fabric made after mixing of terylene and cotton. Polycot, polywool, etc. are other fabrics which are made by the mixing of polyester with other natural fibres.
PET (Polyethylene terepthalate) is very famous term for polyester. Water bottles and many containers (used in kitchen), films, wires, and many other useful products are made using PET (polyester).

Acrylic:

Acrylic is man-made fibre. Since, acrylic resembles wool so it is also known as artificial wool or synthetic wool. Acrylic is cheaper than natural wool and can be dyed in various colour. Thus acrylic is very popular and taking the place of wool today.
Acrylic is used in making sweaters, blanket, and other many clothes.

Characteristic of Synthetic Fibre

• Synthetic fibres are cheaper than natural fibre.
• Synthetic fibres are stronger than natural fibre.
• Synthetic fibres are more durable than natural fibre.
• It is easy to maintain the synthetic fibres.
• It is easy to wash the synthetic fabrics.
• Synthetic fabrics are dried up in less time.
• Synthetic fibres are readily available.

Plastics

Plastic is also a polymer. Units of some plastics have linear arrangement while some plastics are formed by the cross linked arrangement of their units.
Plastic can be mould in all types of possible shapes. Plastic can be recycled, coloured, reused, mould or drawn into wires. Thus, plastic is used in making toys, suitcase, bags, cabinets, brush, chairs, tables, and many other countless items. Polythene is one of the most famous types of plastic, which is used in manufacturing of carry bags.
Types of Plastic: Plastic can be divided into two main types – Thermoplastics and Thermosetting.
Thermoplastic: Plastics which can be easily bent or deform on heating are known as thermoplastic. PVC and Polythene are the examples of thermoplastics. Thermoplastics are used in making toys, bottles, combs, containers, etc.
Thermosetting plastic: Plastics which do not get deformed or softened on heating when mold once, are called thermosetting plastics. Bakelite and melamine are the examples of thermosetting plastics. Thermosetting plastics are used in making hard board, electric switch, handles of electrical appliances, handles of kitchen utensils, floor tiles, etc.
Melamine is poor conductor of heat and resists fire, thus it is used in making floor tiles, kitchen materials, etc.
Bakelite is poor conductor of electricity and heat, thus it is used in making electrical switches, and other electrical appliances.

Plastic as a material of choice:

Characteristics of Plastic

Poor conductor – Plastic is a poor conductor of heat and electricity. This makes it suitable to make the covering of electric wires, handles of electrical appliances, handles of utensils, kitchenware, floor tiles, etc.
Plastic is non-reactive: Plastic does not react with air and water and with many of the chemicals. Since, plastic does not react with air and water hence it does not get rusted like iron. This character makes plastic suitable for making of container, water tank, water bottle, plastic pipes, taps, chair, table and other many types of furniture.
Plastic is strong and durable: Plastics are light weight, durable, cheap and very strong. These qualities of plastic made it the need of today. Whether it is polythene bags or pencil box, water bottle or umbrella, furniture or air craft, the use of plastic can be seen everywhere.

Biodegradable and Non-biodegradable:

Substances which get decomposed through the natural processes, such as action of bacteria, etc. are called biodegradable substances. For example; potato peels, peels of other vegetable, food stuffs, fruit, paper, cotton cloths, wood, etc.
Substances which either do not decompose or take many years to get decomposed through the natural process, are called non-biodegradable substance, e.g. tin, aluminium, plastics, etc.

Plastic and the Environment:

Plastic is a non-biodegradable substance. If it is left or thrown, it takes many years to get decomposed or either does not get decomposed. The non-biodegradable nature of plastic has made it a very major problem for environment.

Problems:

Plastic has become very popular and is being used for many purposes. As a result, we are generating a large amount of plastic waste. Since plastic is non-biodegradable, so plastic waste is getting accumulated around us. Disposal of plastic waste is a major concern as it cannot be even burnt. Burning the plastic can result in release of many harmful gases in the atmosphere. This can lead to air pollution.

Preventive measures:

For dealing with the menace of plastic waste, we need to follow the three Rs, i.e. Reduce, Reuse and Recycle.
Reduce: We should reduce the use of plastic. For examples; instead of using plastic bags, we should use cloth or jute bag for shopping.
Reuse: We should reuse some plastic containers, whenever possible. For example; empty bottles and jars can be used for keeping other items in the home and kitchen.
Recycle: Thermoplastic can be recycled. So, items made of thermoplastic should be sent to the recycling industry. Toys, buckets, mugs, etc. are made from thermoplastic

Synthetic Fibres and Platstics

NCERT Solution

Question: 1. Explain why some fibres are called synthetic.

Answer:- Some fibres are made in factories and hence they are called synthetic.

Question: 2. Rayon is different from synthetic fibres because
(a) It has a silk like appearance
(b) It is obtained from wood pulp
(c) Its fibres can also be woven like those of natural fibres

Answer: (b) It is obtained from wood pulp

Question: 3. Fill in the blanks with appropriate words:
(a) Synthetic fibres are also called ______ or _______ fibres.

Answer: man-made or artificial

(b) Synthetic fibres are synthesised from raw material called ________.

Answer: petrochemicals

(c) Like synthetic fibres, plastic is also a __________ .

Answer:- polymer

Question: 4. Give examples which indicate that nylon fibres are very strong.

Answer: Nylon is used in making ropes which are used for heavy-duty purposes; like mountaineering and in parachute. These examples show that nylon fibres are very strong.

Question: 5. Explain why plastic containers are favoured for storing food.

Answer: Plastic is a non-reactive and non-corroding material. So, plastic containers do not change the flavour or quality of food. Due to this, plastic containers are favoured for storing food.

Question: 6. Explain the difference between the thermoplastic and thermosetting plastics.

Answer: The shape of thermoplastic can be easily changed by heating again, while the shape of thermosetting plastic cannot be altered once it has been mould into a particular shape. Thermoplastic is used in making toys, combs, containers, etc. Thermosetting plastic is used for making those items which need to withstand high temperature; such as handles of cooking utensils.

Question: 7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles

Answer: Saucepan handles have to withstand high temperature during cooking and thermosetting plastic is ideal for that.

(b) Electric plugs/switches/plug boards

Answer: Electric plugs/switches/plug-boards need to be durable and should withstand continuous use over many years. Moreover, in case of some heating due electric current; they should not melt. Hence, these devices are made from thermosetting plastic.

Question: 8. Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:
(Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches)

Answer:

• Can be recycled: Plastic toys, carry bags, ball point pens, plastic bowls, , plastic covering on electrical wires, plastic chairs
• Cannot be recycled: Telephone instruments, cooker handles, electrical switches

Question: 9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Answer: Cotton has better absorbent property than synthetic fibre. During summer, cotton cloth can absorb sweat. The sweat would give cooling effect to the body, due to evaporation. Thus a cotton shirt would be much more comfortable than a shirt made from synthetic fibre. Hence, Rana should buy cotton shirts for summer.

Question: 10. Give examples to show that plastics are noncorrosive in nature.

Answer: Pickles usually come packed in plastic sachets or glass bottles. Pickles contain acids, yet no harm is done to the plastic sachet. Sanitary cleaners and some acids; which are used as bathroom cleaner are sold in plastic bottles. These examples show non-corrosive nature of plastic.

Question: 11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Answer: The handle and bristles of a tooth brush should be made of different materials. The material which is used for making toothbrush handle should be hard and flexible; because the handle has to withstand lot of stress and has to reach every corner of mouth. The material which is used for making bristles should be soft, flexible yet durable; because the bristles should not damage the tooth or gum but should last longer.

Question: 12. ‘Avoid plastics as far as possible’. Comment on this advice.

Answer: Plastic has gained popularity because of its versatile nature. But because of its unmatched popularity; in terms of variety of usage; it has turned into a curse as well. We are creating too much of plastic waste around us. Plastic is non-biodegradable and many forms of plastic cannot be recycled. This is creating a burden on the environment around us. Hence, the statement, “Avoid plastics as far as possible” is a correct statement.

Question: 13. Match the terms of column I correctly with the phrases given in column II.
Question: 14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Answer: Forests provide many important raw materials from which we make various useful items. Many things which were earlier made from forest produce are now being made from synthetic fibres. For example; plastic chairs have replaced wooden chairs in a big way. Similarly, wooden cartons and crates have been replaced by plastic cartons and crates. The way plastic has replaced wood from many items, it is definitely minimizing the need to cut forests. Thus, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.

Question: 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.

Answer: For this, take a discarded plastic toy, a torch which is in working order. Switch the torch on to check that it is in working condition. From the plastic toy, cut a small piece about the size of a coin. Now insert this coin between two cells of the torch. Then tighten the lid of the torch. Now, switch on the torch. You will notice that the bulb does not glow. This happens because the plastic coin; between two cells; does not allow current to pass between two cells. This shows that thermoplastic is a poor conductor of electricity.

Class 8 Science Chapter 1 Crop production and management

Crop Production And Management

All living organisms require food. Plants can make their food themselves. Animals including humans can not make their own food. The energy from food is utilized by organisms for carrying out their various body functions, such as digestion, respiration and excretion. We get our food from plants, or animals, or both.
In order to provide food for a large population— regular production, proper management and distribution of food is necessary.

Agricultural Practices

When plants of the same kind are grown and cultivated at one place on a large scale, it is called a crop. For example, crop of wheat means that all the plants grown in a field are that of wheat. Crops are of different types like cereals, vegetables and fruits. These can be classified on the basis of the season in which they grow. India is a vast country. The climatic conditions like temperature, humidity and rainfall vary from one region to another.
Accordingly, there is a rich variety of crops grown in different parts of the country. Despite this diversity, two broad cropping patterns can be identified. These are:
(i) Kharif Crops:- The crops which are sown in the rainy season are called kharif crops. The rainy season in India is generally from June to September. Paddy, maize, soyabean, groundnut, cotton, etc., are kharif crops.
(ii) Rabi Crops:- The crops grown in the winter season are called rabi crops. Their time period is generally from October to March. Examples of rabi crops are wheat, gram, pea, mustard and linseed. Besides these, pulses and vegetables are grown during summer at many places.

Basic Practices of Crop Production

Cultivation of crops involves several activities undertaken by farmers over a period of time. These activities or tasks are referred to as agricultural practices. These activities are listed below.

(i) Preparation of Soil:

The preparation of soil is the first step before growing a crop. One of the most important tasks in agriculture is to turn the soil and loosen it. This allows the roots to penetrate deep into the soil. The loose soil allows the roots to breathe easily even when they go deep into the soil. The loosened soil helps in the\ growth of earthworms and microbes present in the soil.
The process of loosening and turning of the soil is called tilling or ploughing. This is done by using a plough. Ploughs are made of wood or iron. If the soil is very dry, it may need watering before ploughing. The ploughed field may have big pieces of soil called crumbs. It is necessary to break these crumbs with a plank. The field is levelled for sowing as well as for irrigation purposes. The levelling of soil is done with the help of a leveller.

(ii) Sowing:

Sowing is the most important part of crop production. Before sowing, good quality seeds are selected. Good quality seeds are clean and healthy seeds of a good variety. Farmers prefer to use seeds which give a high yield.
Before sowing, one of the important tasks is to know about the tools used for sowing seeds
Traditional Tool: The tool used traditionally for sowing seeds is shaped like a funnel. The seeds are filled into the funnel, passed down through two or three pipes having sharp ends. These ends pierce into the soil and place seeds there.
Seed Drill: Nowadays the seed drill is used for sowing with the help of tractors. This tool sows the seeds uniformly at proper distances and depths. It ensures that seeds get covered by the soil after sowing. This prevents damage caused by birds. Sowing by using a seed drill saves time and labour.

(iii) Adding Manure and Fertilisers

The substances which are added to the soil in the form of nutrients for the healthy growth of plants are called manure and fertilisers. Soil supplies mineral nutrients to the crop. These nutrients are essential for the growth of plants. In certain areas, farmers grow crop after crop in the same field. The field is never left uncultivated or fallow.
Continuous growing of crops makes the soil poorer in certain nutrients. Therefore, farmers have to add manure to the fields to replenish the soil with nutrients. This process is called manuring.
Manure is an organic substance obtained from the decomposition of plant or animal wastes. Farmers dump plant and animal waste in pits at open places and allow it to decompose. The decomposition is caused by some microorganisms. The decomposed matter is used as organic manure.

Advantages of Manure: The organic manure is considered better than fertilisers. This is because

• it enhances the water holding capacity of the soil.
• it makes the soil porous due to which exchange of gases becomes easy.
• it increases the number of friendly microbes.
• it improves the texture of the soil.

(iv) Irrigation

All living beings need water to live. Water is important for proper growth and development of flowers, fruits and seeds of plants. Water is absorbed by the plant roots. Along with water, minerals and fertilisers are also absorbed. Plants contain nearly 90% water. Water is essential because germination of seeds does not take place under dry conditions. Nutrients dissolved in water get transported to each part of the plant. Water also protects the crop from both frost and hot air currents.
The supply of water to crops at different intervals is called irrigation. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season.
Sources of Irrigation: The sources of irrigation are— wells, tubewells, ponds, lakes, rivers, dams and canals.

Traditional Methods of Irrigation

The water available in wells, lakes and canals is lifted up by different methods in different regions, for taking it to the fields. Cattle or human labour is used in these methods. So these methods are cheaper, but less efficient. The various traditional ways are:
(i) Moat (pulley-system)
(ii) Chain pump
(iii) Dhekli, and
(iv) Rahat (Lever system)

Modern Methods of Irrigation

Modern methods of irrigation help us to use water economically. The main methods used are as follows:
(a) Sprinkler System: This system is more useful on the uneven land where sufficient water is not available. The perpendicular pipes, having rotating nozzles on top, are joined to the main pipeline at regular intervals. When water is allowed to flow through the main pipe under pressure with the help of a pump, it escapes from the rotating nozzles. It gets sprinkled on the crop as if it is raining. Sprinkler is very useful for sandy soil.
(b) Drip system: In this system, the water falls drop by drop just at the position of the roots. So it is called drip system. It is the best technique for watering fruit plants, gardens and trees.

(v) Protection from Weeds

In a field many other undesirable plants may grow naturally along with the crop. These undesirable plants are called weeds.
The removal of weeds is called weeding. Weeding is necessary since weeds compete with the crop plants for water, nutrients, space and light. Thus, they affect the growth of the crop.
Farmers adopt many ways to remove weeds and control their growth. Tilling before sowing of crops helps in uprooting and killing of weeds, which may then dry up and get mixed with the soil. The best time for the removal of weeds is before they produce flowers and seeds. The manual removal includes physical removal of weeds by uprooting or cutting them close to the ground, from time to time. This is done with the help of a khurpi.
Weeds are also controlled by using certain chemicals, called weedicides; these are sprayed in the fields to kill the weeds. They do not damage the crops.

(vi) Harvesting

Harvesting of a crop is an important task. The cutting of crop after it is mature is called harvesting. In harvesting, crops are pulled out or cut close to the ground. It usually takes 3 to 4 months for a cereal crop to mature.
In the harvested crop, the grain seeds need to be separated from the chaff. This process is called threshing. This is carried out with the help of a machine called ‘combine’ which is in fact a combined harvester and thresher.

(vii) Storage

Storage of produce is an important task. If the crop grains are to be kept for longer time, they should be safe from moisture, insects, rats and microorganisms. The fresh crop has more moisture. If freshly harvested grains (seeds) are stored without drying, they may get spoilt or attacked by organisms, losing their germination capacity.

Summary

• In order to provide food to our growing population, we need to adopt certain agricultural practices.
• Same kind of plants grown and cultivated at a place constitute a crop.
• In India, crops can be broadly categorised into two types based on seasons -rabi and kharif crops.
• It is necessary to prepare soil by tilling and levelling. Ploughs and levellers are used for this purpose.
• Sowing of seeds at appropriate depths and distances gives good yield. Good variety of seeds is sown after selection of healthy seeds. Sowing is done by seed drills.
• Soil needs replenishment and enrichment through the use of organic manure and fertilisers. Use of chemical fertilisers has increased tremendously with the introduction of new crop varieties.
• Supply of water to crops at appropriate intervals is called irrigation.
• Weeding involves removal of unwanted and uncultivated plants called weeds.
• Harvesting is the cutting of the mature crop manually or by machines.
• Separation of the grains from the chaff is called threshing.
• Proper storage of grains is necessary to protect them from pests and microorganisms.
• Food is also obtained from animals for which animals are reared. This is called animal husbandry.

Crop Production And Management

Solution of NCERT Exercise

Question: 1. Select the correct word from the following list and fill in the blanks.
(float, water, crop, nutrients, preparation)
(a) The same kind of plants grown and cultivated on a large scale at a place is called _____________.

Answer: crop

(b) The first step before growing crops is _____________ of the soil.

Answer: preparation

(c) Damaged seeds would _____________ on top of water.

Answer: - Float

(d) For growing a crop, sufficient sunlight and _____________ and _____________ from the soil are essential.

Answer: - water and nutrients

Question: 2. Match items in column A with those in column B.

Colulumn A	Column B
Kharif crops	Food for cattle
Rabi crops	Urea and super phosphate
Chemical fertilisers	Animal excreta, cow dung, urine and plant waste
Organic manure	Wheat, gram, pea
	Paddy and maize

Answer:

Colulumn A	Column B
Kharif crops	Paddy and maize
Rabi crops	Wheat, gram, pea
Chemical fertilisers	Urea and super phosphate
Organic manure	Animal excreta, cow dung, urine and plant waste

Question: 3. Give two examples of each.
(a) Kharif crop:

Answer: Paddy and maize

(b) Rabi crop:

Answer: Wheat and gram

Question: 4. Write a paragraph in your own words on each of the following.
(a) Preparation of soil

Answer: Preparation of soil is the first step of farming. Soil is loosened and turned over. This helps in making the soil more airy so that roots can breathe in air. Moreover, loosening of soil also facilitates better penetration of roots into the soil. Seeds can be easily sown in loosened soil.

(b) Sowing

Answer: The method of putting the seeds into soil is called sowing. Traditionally, seed is sown manually by spreading the seeds by hands. This process is called broadcasting. Seed drills are used when sowing needs to be done on a large scale.

(c) Weeding

Answer: Removal of weeds is called weeding. Unwanted plants which grow along with the crop are called weeds. They compete for resources; like sunlight, water and air; with the main crop. So, it is necessary to remove weeds for proper growth of crops. Weeding is usually done manually by using hands and sickles. Sometimes weedicides are also sprayed.

(d) Threshing

Answer: Separation of grains from harvested stems is called threshing. For smaller quantity, threshing is done by hands. For somewhat bigger quantity, threshing is done using animal; especially bullocks. Animals are made to trample over the harvested stock which helps in separation of grains. Threshing machines are used for bigger quantities.

Question: 5. Explain how fertilisers are different from manure.

Answer: Fertilisers are synthesized in factories from inorganic materials. On the other hand, manure is made from organic materials; through the process of decomposition. Excessive use of fertilisers is not good for soil and may lead to soil pollution. Use of manure is beneficial for soil.

Question: 6. What is irrigation? Describe two methods of irrigation which conserve water.

Answer: The process of artificially providing water to growing crops is called irrigation. Two methods of irrigation which help in water conservation are as follows:

(a) Sprinkler: Sprinkler system is composed of pipelines in which nozzles are fitted at various locations. Water comes out of the nozzle and is sprinkled on plants. This system helps in saving lot of water.

(b) Drip Irrigation: For this, small holes are made in pipes which are laid along the rows of crops. Water slowly drips down on the roots of crops. This system is especially useful for plantations and also in water scarce areas.

Question: 7. If wheat is sown in the kharif season, what would happen? Discuss.

Answer: The crop of wheat needs mild to moderate temperature and frost free days; along with irrigation but no water logging. Winters are suitable for growing wheat. In the kharif season; which coincides with the peak summer months in India, temperature is at its peak which is not suitable for wheat. Moreover, during rainy season lot of water accumulates in fields which would be harmful for wheat crop. Hence, if wheat is sown in the kharif season; the productivity would be minuscule and would not be profitable for the farmers.

Question: 8. Explain how soil gets affected by the continuous plantation of crops in a field.

Answer: Continuous plantation of crops in a field affects soil fertility. Plants utilize all the nutrients from soil which leads to depletion of nutrients in the soil. As a result, soil fertility reduces drastically.

Question: 9. What are weeds? How can we control them?

Answer: Unwanted plants which grow along with crops are called weeds. Weeds compete with crops for natural resources; like sunlight, water and nutrients. Thus, weeds hamper the growth of crops. Weeds are usually removed manually by hands and by sickles. This process is called weeding. Sometimes, weedicides are also sprayed to kills weeds.

Question: 10. Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.
Sending crop to sugar factory → Irrigation → Harvesting → Sowing → Preparation of soil → Ploughing the field → Manuring

Answer: Preparation of soil → Ploughing the field → Manuring → Sowing → Irrigation → Harvesting → Sending crop to sugar factory

Question: 11. Complete the following word puzzle with the help of clues given below.
Down
1. Providing water to the crops.
2. Keeping crop grains for a long time under proper conditions.
5. Certain plants of the same kind grown on a large scale.

Answer: 1: IRRIGATION 2: STORAGE 5: CROP

Across
3. A machine used for cutting the matured crop.
4. A rabi crop that is also one of the pulses.
6. A process of separating the grain from chaff.

Answer: 3: HARVESTOR 4: GRAM 6: WINNOWING

Class 9 SST Geography SST CHAPTER 3 Drainage NCERT SOLUTIONS POONAM DUA

Drainage

Drainage:The river system of an area is called drainage. The area drained by a single river system is called the drainage basin.

Drainage Patterns:

Depending on the slope of land, underlying rock structure and climate of an area, the streams in a drainage basin form certain patters. Different types of drainage pattern are as follows:

1. Dendritic Drainage Pattern: When the river channel follows the slope of the terrain, it develops dendritic pattern. The stream and its tributaries resemble the branches of a tree. Hence, it is called dendritic pattern.
    
2. Trellis Drainage Pattern: When a river is joined by its tributaries at almost right angles, it develops a trellis pattern. Trellis pattern develops where hard and soft rocks exist parallel to each other.
    
3. Rectangular Drainage Pattern: When rocks are strongly joined, then rectangular pattern develops.
    
4. Radial Drainage Pattern: When the streams flow in different directions from a central peak or dome like structure, a radial pattern is developed.

It is important to note that a combination of different patterns may develop in the same drainage basin.
The drainage systems in India can be divided into two major groups, viz. the Himalayan Rivers and the Peninsular Rivers.
The Himalayan Rivers: Most of the Himalayan Rivers are perennial, i.e. they have water throughout the year.
River System: A river alongwith its tributaries forms a river system.

The Indus River System:

• The river Indus originates in Tibet; near Lake Mansarowar. It enters India in the Ladakh district of Jammu & Kashmir.
• Zaskar, Nubra, Shyok and Hunza are the main tributaries which join the Indus in Kashmir region.
• After flowing through Baltistan and Gilgit, the Indus emerges from the mountains at Attock.
• Sutlej, Beas, Ravi, Chenab and Jhelum join together and enter the Indus near Mithankot in Pakistan. After that, the Indus flows southwards and finally reaches the Arabian Sea, east of Karachi.
• Indus is 2900 km long. The Indus plain has a very gentle slope. A little over one-third of the Indus basin is located in India; in the states of Jammu & Kashmir, Himachal Pradesh and Punjab. The rest of the portion is in Pakistan.

The Ganga River System

• The headwaters of Ganga are called Bhagirathi. It is fed by the Gnagotri Glacier. It is joined by Alaknanda at Devprayag in Uttarakhand.
• Ganga emerges from the mountains on to the plains at Haridwar.
• Yamuna, Ghaghra, Gandak and Kosi are the major tributaries of Ganga. Yamuna originates from the Yamunotri Glacier in the Himalayas. It meets Ganga at Allahabad.
• Gaghra, Gandak and Kosi rise in the Nepal Himalaya.
• Chambal, Betwa and Son are the major tributaries which come from the peninsular uplands.
• After taking waters from various tributaries, Ganga flows towards east till Farakka (West Bengal). The river bifurcates at Farakka. The Bhagirathi-Hooghly (a distributary) flows towards south to the Bay of Bengal.
• The mainstream flows southwards into Bangladesh; where it is joined by the Brahmaputra. It is known as Meghan; further downstream.
• Finally, the Ganga and the Brahmaputra flow into the Bay of Bengal forming the Sunderban Delta. The total length of Ganga is 2500 km.

The Brahmaputra River System:

• The Brahmaputra rises in Tibet; east of Mansarowar lake. It is a little longer than the Indus. Most of the course of the Brahmaputra lies outside India. It flows eastwards parallel to the Himalayas.
• After reaching Namcha Barwa, it enters India in Arunachal Pradesh through a gorge. It is known as Dihang in this region. It is joined by Dibang, Lohit, Kenula and many other tribuatries and finally forms the Brahmaputra in Assam.
• Unlike other north Indian rivers the Brahmaputra gets huge deposits of silt on its bed. This results in rising of the river bed. It also shifts its channel frequently.

The Peninsular Rivers: Most of the Peninsular Rivers are seasonal because they depend on rainfall for water. These rivers have shorter and shallower courses; compared to the Himalayan rivers. Most of the major rivers of the Peninsula flow eastwards and drain into the Bay of Bengal. These rivers make deltas at their mouths. The Narmada and Tapi are the only long rivers, which flow westwards and make estuaries. The drainage basins of the peninsular rivers are smaller in size.
The Narmada Basin: The Narmada rises in the Amarkantak hills in the Madhya Pradesh. The Narmada basin covers parts of Madhya Pradesh and Gujarat. All the tributaries of the Narmada are very short. Most of the tributaries join the Narmada at right angles.
The Tapi Basin: The Tapi rises in the Satpura ranges, in Betul district of Madhya Pradesh. The basin of Tapi covers parts of Madhya Pradesh, Gujarat and Maharashtra.
The Godavari Basin: This is the longest Peninsular river. Its drainage basin is also the largest among the peninsular river basins. The Godavari is about 1500 km long. It originates from the slopes of the Western Ghats in Nasik district of Maharashtra and drains into the Bay of Bengal. The Godavari basin covers parts of Maharashtra, Madhya Pradesh, Orissa and Andhra Pradesh. Purna, Wardha, Pranhita, Manjra, Waiganga and Penganga are the main tributaries of Godavari.
The Mahanadi Basin: This river originates in the highlands of Chhattisgarh and drains into the Bay of Bengal. It is about 860 km long. The Mahanadi basin covers Maharashtra, Chhattisgarh, Jharkhand and Orissa.
The Krishna Basin: The Krishna originates near Mahabaleshwar and drains into the Bay of Bengal. It is about 1400 km long. Tungbhadra, Koyana, Ghatprabha, Musi and Bhima are some of its tributaries. The Krishna basin covers Maharashtra, Karnataka and Andhra Pradesh.
The Kaveri Basin: The Kaveri originates in the Brahmagiri range of the Western Ghats and drains into the Bay of Bengal. It is about 760 km long. Amravati, Bhavani, Hemavati and Kabini are its main tributaries. The Kavery basin covers Karnataka, Kerala and Tamil Nadu.

LAKES

A large water body which is surrounded by land is called a lake. Most of the lakes are permanent, while some contain water only during the rainy season. Lakes are formed by the action of glaciers and ice sheets, by wind, river action and by human activities.
Ox-bow Lake: A lake formed when a meandering river is cut off from the mainstream. The shape of this lake resembles an ox-bow.
Lagoon: When the lake is formed by spits and bars in coastal areas, it is called a lagoon. Chilika lake, Pulicat lake, Kolleru lake, etc. are examples of lagoon.
Glacial Lake: A lake formed by melting of glacier is called a glacial lake. Most of the lakes in the Himalayan region are glacial lakes.
Wular lake (Jammu & Kashmir) is the largest freshwater lake in India. It was formed by tectonic activity.
Benefits of a Lake: A lake helps in preventing flood by regulating the flow of river. During dry seasons, a lake helps to maintain an even flow of the river. Lakes can also be used for generating hydel power.
Role of rivers in the economy: Rivers have been the centre of human civilization since ancient times. Even today, many big cities are situated on the bank of a river. River water is used for irrigation, navigation, hydroelectricity, fisheries, etc.
River Pollution: The growing domestic, municipal, industrial and agricultural demand for water from rivers naturally affects the quality of water. As a result, more and more water is being drained out of the rivers reducing their volume. On the other hand, a heavy load of untreated sewage and industrial effluents are emptied into the rivers. This affects not only the quality of water but also the self-cleansing capacity of the river.

Drainage

NCERT Solution

Question – 1 - Which one of the following describes the drainage patterns resembling the branches of a tree?

1. Radial
2. Centrifugal
3. Dendritic
4. Trellis

Answer: (c) Dendritic

Question – 2 - In which of the following states is the Wular lake located?

1. Rajasthan
2. Punjab
3. Uttar Pradesh
4. Jammu and Kashmir

Answer: (d) Jammu and Kashmir

Question – 3 - The river Narmada has its source at

1. Satpura
2. Amarkantak
3. Brahmagiri
4. Slopes of the Western Ghats

Answer: (b) Amarkantak

Question – 4 - Which one of the following lakes is a salt water lake?

1. Sambhar
2. Wular
3. Dal
4. Gobind Sagar

Answer: (a) Sambhar

Question – 5 - Which one of the following is the longest river of the Peninsular India?

1. Narmada
2. Godavari
3. Krishna
4. Mahanadi

Answer: (b) Godavari

Question – 6 - Which one amongst the following rivers flows through a rift valley?

1. Mahanadi
2. Krishna
3. Tungabhadra
4. Tapi

Answer: (d) Tapi

Question – 7 - What is meant by a water divide? Give an example.

Answer: Any elevated area separates two drainage basins. Such upland is called a water divide.

Question – 8 - Which is the largest river basin in India?

Answer: The Ganga River Basin

Question – 9 - Where do the rivers Indus and Ganga have their origin?

Answer: In the Himalayas

Question – 10 - Name the two headstreams of the Ganga. Where do they meet to form the Ganga?

Answer: Bhagirathi and Alaknanda are the two headstreams of Ganga. They meet at Devprayag to form the Ganga.

Question – 11 - Why does the Brahmaputra in its Tibetan part have less silt, despite a longer course?

Answer: Since Tibet is a cold and dry area, so Brahmaputra in this part carries less silt despite having a longer course.

Question – 12 - Which two Peninsular rivers flow through trough?

Answer: Narmada and Tapi

Question – 13 - State some economic benefits of rivers and lakes.

Answer: Lake can be used for generating hydroelectricity. A lake can be a good tourist attraction. Rivers have been the centre of human civilization since ancient times. Even today, many big cities are situated on the bank of a river. River water is used for irrigation, navigation, hydroelectricity, fisheries, etc.

Question – 14 - Below are given names of a few lakes of India. Group them under two categories – natural and created by human beings.
(a)Wular (b) Dal (c) Nainital (d) Bhimtal (e) Gobind Sagar (f) Loktak (g) Barapani (h) Chilika (i) Sambhar (j) Rana Pratap Sagar (k) Nizam Sagar (l) Pulicat (m) Nagarjuna Sagar (n) Hirakund

Answer: Natural Lakes: Wular, Dal, Bhimtal, Loktak, Barapani, Chilika, Sambhar, Pulicat

Man-made Lakes: Gobind Sagar, Rana Pratap Sagar, Nizam Sagar, Nagarjuna Sagar, Hirakund
Question – 15 - Discuss the significant difference between the Himalayan and the Peninsular rivers.

Answer:

Question – 16 - Compare the east flowing and the west flowing rivers of the Peninsular plateau.

Answer: The east flowing rivers of the Peninsular part drain into Bay of Bengal and form deltas at their mouths. The west flowing rivers drain into the Arabian Sea and form estuaries. Most of the east flowing rivers are longer, compared to most of the west flowing rivers.

Question – 17 - Why are rivers important for the country’s economy?

Answer: Rivers are the major source of water for irrigation and hence are important for a country where farming is still the occupation of the largest portion of population. Many major rivers serve as important channels for transporting goods and people and thus play important role in the supply chain. Many multipurpose projects have been built on most of the major rivers in India. Rivers are important source of fish to a large population.

Crossword:
Across
Question – 1 - Nagarjuna Sagar is a river valley project. Name the river?

Answer: Krishna

Question – 2 - The longest river of India.

Answer: Ganga

Question – 3 - The river which originates from a place known as Beas Kund.

Answer: Beas

Question – 4 - The river which rises in the Betul district of MP and flows westwards.

Answer: Tapi

Question – 5 - The river which was known as the “Sorrow” of West Bengal.

Answer: Damodar

Question – 6 - The river on which the reservoir for India Gandhi canal has been built.

Answer: Sutlej

Question – 7 - The river whose source lies near Rohtang Pass.

Answer: Ravi

Question – 8 - The longest river of Peninsular India?

Answer: Godavari

Down
Question – 9 - A tributary of Indus originating from Himachal Pradesh.

Answer: Chenab

Question – 10 - The river flowing through fault, drains into the Arabian Sea.

Answer: Narmada

Question – 11 - A river of south India, which receives rain water both in summer and winter.

Answer: Kaveri

Question – 12 - A river which flows through Ladakh, Gilgit and Pakistan.

Answer: Indus

Question – 13 - An important river of the Indian desert.

Answer: Luni

Question – 14 - The river which joins Chenab in Pakistan.

Answer: Jhelum

Question – 15 - A river which rises at Yamunotri glacier.

Answer: Yamuna