Q.1 Write the importance of ‘manufacturing sector’ for our nation.
Or, “Manufacturing industry is considered the backbone of economic development of India.” Give reasons. (2015 OD, 2011 D)
Answer:
Importance of manufacturing industries for India:

1. It helps in modernizing agriculture, which is the base of our economy.
2. It reduces heavy dependence on agricultural income by providing jobs in non-agricultural sectors.
3. Industrial development is necessary for eradication of poverty and unemployment because people get jobs and generate more income.
4. Export of manufactured goods expands trade and brings in much needed foreign exchange.
5. Industries bring riches faster to a nation because manufacturing changes raw materials into finished goods of a higher value, so industrial development brings prosperity to the country.

Q.2 List the major factors which affect the location of an industry at a place. What is the key to the decision of ‘factory location’? (2011 D, 2011 OD, 2015 D)
Answer:

1. Raw material. Cheap and abundant availability of raw material. Industries which use heavy and perishable raw material have to be located close to the source of raw material.
2. Labour. Availability of cheap labour is necessary for keeping the cost of production low.
3. Power. Cheap and continuous supply of power is extremely necessary for continuity in the production process.
4. Capital. It is necessary for developing infrastructure, for the entire manufacturing process and for meeting manufacturing expenditure.
5. Banking and insurance facilities, favourable government policies are other factors which affect location of an industry.
   The ‘key’ to the decision of a factory location is least cost so that the venture is profitable.

Q.3 classify industries on the basis of capital investment. How are they different from one another? Explain with examples. (2016 D)
Answer:
On the basis of capital investment industries can be classified as:

• Small-scale industry
• Large-scale industry

Difference:
If the investment is more than one crore rupees in any industry, it is considered as a large scale industry.
For example, Iron and Steel industry, Cement industry.
If the investment is less than one crore rupees in any industry, it is considered as a small scale industry.
For example, Plastic industry, Toy industry.

Q.4 Classify industries on the basis of source of raw material. How are they different from each other? (2016 OD)
Answer:
On the basis of sources of raw material industries are classified as:
(i) Agro based industries;
(ii) Mineral based industries
Difference between Agro-based industries and Mineral-based industries

Q.5 Explain the significance of textile industry in India. (2011 D)
Or
The textile industry is the only industry which is self reliant and complete in the value-chain? Justify this statement? (2016 D)
Or
“Textile industry occupies a unique position in the Indian economy”. Support the statement with appropriate arguments. (2015 D)
The Textile industry occupies a unique position in the Indian Economy because:

1. It contributes significantly to industrial production (14%).
2. It employs largest number of people after agriculture, i.e. 35 million persons directly.
3. Its share in the foreign exchange earnings is significant at about 24.6%.
4. It contributes 4% towards GDP.
5. It is the only industry in the country which is self-reliant and complete in the value chain, i.e., from raw material to the highest value added products.

Q.6 List factors which favoured the location and concentration of cotton textile industry in Maharashtra
and Gujarat in early years. (2012 D, 2015 OD)
Answer:

1. Availability of raw cotton was abundant and cheap because these are the traditional cotton growing States.
2. Moist climate in these coastal States also helped in the development of cotton textile industry because humid conditions are required for weaving the cloth, else the yarn breaks.
3. Well developed transportation system and accessible port facilities in Maharashtra and Gujarat led to their concentration there.
4. Proximity to the market is yet another factor as cotton clothes are ideal and comfortable to wear in these warm and humid States.
5. Cheap labour was abundantly available.

Q.7 Electronic industry has revolutionized the life of the masses and the country’s economy.” Justify the statement with suitable arguments.
Answer:
Electronic industry has revolutionized the life of the people and the country’s economy because:

1. It produces a wide range of products from transistor sets to televisions and computers for the masses.
2. It has helped us set up telephone exchanges, telephones, cellular telecom, radios and many other equipments which have application in space technology, aviation, defence, meteorological departments, etc.
3. It has generated employment for a large number of people. It employed over one million people by March 2005, out of these 30% are women employees.
4. This industry has been a major foreign exchange earner because of its fast growing Business Process Outsourcing (BPO) Sector.
5. India is one of the leading countries in software development. We have 18 software technology parks which provide high data communication facility to software experts.

Q.8 Suggest measures to control water pollution caused by industries. (2013 D)
Answer:

1. Minimising the use of water for processing by reusing and recycling it in two or more successive stages.
2. Harvesting of rain-water to meet water requirements of industries and other domestic purposes.
3. Treating hot water and effluents before releasing them in rivers and ponds in the following ways:
   • Primary treatment by mechanical means such as screening, grinding, flocculation and sedimentation.
   • Secondary treatment by biological process.
   • Tertiary treatment by biological, chemical and physical processes. This involves recycling of waste water.

Q.9 Explain the pro-active approach adopted by the National Thermal Power Corporation (NTPC) for preserving the natural environment and resources? (2011 OD, 2015 OD)
Answer:
NTPC is taking the following measures in places where it is setting up power plants:

1. Optimum utilisation of equipment by adopting latest techniques and upgrading existing equipment.
2. Minimising waste generation by maximising ash utilisation.
3. Providing green belts for nurturing ecological balance.
4. Reducing environmental pollution through ash pond management, ash water recycling system and liquid waste management.
5. Ecological monitoring, reviews and online data base management for all its power stations.

Q.10 Suggest any three steps to minimise the environmental degradation caused by the industrial development in India. (2016 OD)
Answer:
Steps to minimize the environmental degradation caused by industrial development in India are:

1. Minimizing use of water for processing by reusing and recycling in two or more successive stages. Harvesting of rain water to meet water requirements of industries and other domestic purposes.
2. Treating hot water and effluents before releasing them in rivers and ponds.
3. Particulate matter in the air can be reduced by fitting smoke to factories with electrostatic precipitators, fabric filters, scrubbers and inertial separators. Smoke can be reduced by using oil or gas instead of coal in factories.
4. Machinery and equipments can be fitted with silencers to prevent noise pollution.

Important Link

Quick Revision Notes :Periodic Classification of Elements

NCERT Solution :Periodic Classification of Elements

MCQs: Periodic Classification of Elements

Click here for Free Video Lectures

Q.1 What factors does primitive subsistence farming depend on?
Answer:
Factors:

• Monsoons
• Natural fertility of the soil
• Suitability of other environmental conditions to the crops grown.

Q.2
Write main characteristics of ‘slash and burn’ agriculture.
Or, Write main characteristics of Primitive Subsistence Farming.
Answer:

• This type of farming is practised in few pockets of India on small patches of land using primitive tools and family/community labour.
• Farmers clear a patch of land and produce cereals and other food crops to sustain their families.
• When the soil fertility decreases, the farmers shift and clear a fresh patch of land for cultivation. This type of shifting allows nature to replenish the fertility of the soil through natural processes.
• Land productivity is low as the farmer does not use fertilisers or other modem inputs.

Q.3Compare ‘intensive subsistence farming’ with that of ‘commercial farming’ practiced in India.
Answer:

Q.4 What are the major differences between primitive subsistence farming and commercial farming? (2013)
Answer:

Q.5 Mention two geographical conditions required for the growth of Maize crop in India. Describe three factors which have contributed to increase maize production. Write four major maize producing states. (2012)
Answer:
Geographical conditions required for the growth of maize crop in .India:

1. It is a kharif crop which requires temperature between 21° C to 27° C. It requires moderate rainfall between 50-100 cm.
2. It grows well in old alluvial soils.
   Maize is a crop which is used both as food and fodder. In some states like Bihar, maize is grown in rabi season also. Maize production in India has increased due to factors like:
   • use of modern inputs such as HYV seeds;
   • use of fertilisers; and
   • use of irrigation facilities.
   • major maize producing state: Karnataka, Uttar Pradesh, Bihar, Andhra Pradesh and Madhya Pradesh.

Q.6 (a) Name three pulses each of Rabi and Kharif season. Write their importance for human beings and for agriculture.
(b) What is India’s position in the world with regard to the production of pulses? Name five leading states producing pulses. (2015)
Answer:
(a) Pulses of Rabi season: Tur (arhar), urad, moong.
Pulses of Kharif season: Masur, peas, gram.
Importance of pulses:

• For agriculture. Being leguminous crops, they help in restoring soil fertility by utilising nitrogen from the air (nitrogen fixation). Therefore, these are mostly grown in rotation with other crops.
• They need less moisture and survive even in dry conditions.

(b) India is the largest producer of pulses in the world.
Major pulse producing states are: Madhya Pradesh, Uttar Pradesh, Rajasthan, Maharashtra and Karnataka.

Q.7 What is India’s position in the world regarding tea production? Name three states each which produce tea in:
(i) North-Eastern India
(ii) Himalayan states/parts of the states
(iii) Peninsular States.
Answer:
India is the leading producer and exporter of tea in the world.
Three states producing tea in each of the following:

Q.8 What are ‘Institutional Reforms’? Enlist various institutional reforms taken by the Indian Government to bring about improvements in agriculture. (2015)
Answer:
Institutional reforms:
Steps taken by the government to bring about improvements in agriculture are termed as ‘Institutional Reforms’.
Some steps are:

1. Collectivisation and consolidation of land holdings to make them economically viable.
2. The green revolution based on the use of package technology and the White Revolution to increase milk production are important strategies which were initiated to improve agriculture.
3. Cooperation with farmers and Abolition of Zamindari system.
4. Provision of crop insurance to protect the farmers against losses caused by natural calamities, i.e. drought, flood, cyclone, fire and disease.
5. Establishment of ‘Grameen Banks’, Cooperative Societies and Banks for providing loan facilities to the farmers at lower rates of interest.
6. Kissan Credit Card (KCC), Personal Accident Insurance Scheme (PAIS) are some other schemes introduced by the government for the benefit of farmers.
7. Special weather bulletins and agricultural programmes for farmers were introduced on the Radio and TV.
8. Announcement of minimum support price, remunerative and procurement prices for crops to check the exploitation of farmers by speculators and middlemen and removing the elements of uncertainty.

Q.9 Define each of the following:
(a) Green Revolution
(b) White Revolution
(c) Yellow Revolution
(d) Blue Revolution
(e) Gene Revolution.
Answer:
(a) Green Revolution. Agricultural Revolution which resulted in increased production of foodgrains because of the use of HYV (High Yielding Varieties) seeds, fertilizers, proper irrigation and other modem inputs.
(b) White Revolution. Revolutionary increase in the production of milk which was spearheaded by Operation Flood.
(c) Yellow Revolution. Increase in the output of oilseeds is termed as Yellow Revolution.
(d) Blue Revolution refers to increased output of fish and fish products.
(e) Gene Revolution refers to the development of genetically modified seeds for increasing the yield per hectare. These seeds are environmentally sustainable.

Q.10 What are coarse grains? Why are they important in India? Name the crops which are included in this category and name three leading states producing each of these crops.
Answer:
Millets are called coarse grains. They are important because they have high nutritional value and make an important part of the diet for poor people.
Most important millets are as follows:

1. Ragi —Leading producer is Karnataka, followed by Tamil Nadu. Himachal Pradesh, Jharkhand, Uttaranchal, Sikkim etc are other important regions.
2. Jowar—Maharashtra is the leading producer followed by Karnataka, Andhra Pradesh, Madhya Pradesh.
3. Bajra—It grows well on sandy soils and shallow black soils. Rajasthan is the largest producer followed by Uttar Pradesh, Maharashtra, Gujarat and Haryana.

Important Link

Quick Revision Notes :Agriculture

NCERT Solution :Agriculture

MCQs: Periodic Agriculture

Click here for Free Video Lectures

Q.1 Mention any three characteristics of ferrous group of minerals found in India.(2011 D)
Answer:
Metallic minerals that have iron in them are called ferrous minerals. For example, iron ore, manganese, nickel, cobalt etc.
Three characteristics of ferrous group of minerals found in India are:

1. Ferrous minerals account for about three fourths of the total value of the production of metallic minerals.
2. They provide a strong base for the development of metallurgical industries.
3. India exports substantial quantities of ferrous minerals to Japan and South Korea after meeting her internal demands.

Q.2 Why is there a pressing need to use non-conventional sources of energy in India? Explain any three reasons. (2011 D)
Answer:

1. The growing consumption of energy has resulted in India becoming increasingly dependent on fossil fuels such as coal, oil and gas which are found in limited quantity on the earth.
2. Rising prices of oil and gas and their potential shortages have raised uncertainties about the security of energy supply in future, which in turn has serious repercussions on the growth of the national economy.
3. Increasing use of fossil fuels also causes serious environmental degradation like air pollution, water pollution etc.
   So there is an urgent need to use sustainable energy resources like solar, water, wind, tide biomass etc.

Q.3 Make a distinction between hydroelectricity and thermal electricity stating three points of distinction.
Or
What are the two main ways of generating electricity? How are they different from each other. Explain. (2011 OD, 2014 OD)
Answer:
Electricity is generated mainly in two ways:

1. By running water which drives hydro turbines to generate hydro electricity.
2. By burning other fuels such as coal, petroleum and natural gas to drive turbines to produce thermal power.

Q.4 Differentiate between ferrous and non-ferrous minerals with examples. (2013 D)
Answer:
Ferrous minerals:

1. Ferrous minerals account for about three fourths of the total value of the production of metallic minerals.
2. They provide a strong base for the development of metallurgical industries.
3. India exports substantial quantities of ferrous minerals to Japan and South Korea after meeting her internal demands.

Non-ferrous minerals:

1. India’s reserves and production of non-ferrous minerals is not very satisfactory.
2. Non-ferrous minerals include copper, bauxite, lead, zinc and gold.
3. They provide a strong base for the development of metallurgical, engineering and electrical industries.
4. Non-ferrous minerals like copper and bauxite are mainly found in Madhya Pradesh and Odisha respectively.

Q.5 Environmental degradation has been seen everywhere/ Explain any three values that can help to prevent environment degradation. (2014 D)
Answer:
Three values that can help to prevent Environmental Degradation:

1. We must ensure sustainable and equitable use of resources without degrading the environment or risking health or safety.
2. We must raise awareness and consciousness among people about the importance of judicious use of resources to prevent degradation of land, water, vegetation and air.
3. The following measures must be adopted to prevent environmental degradation:
   • Minimising use of water for processing by reusing and recycling it.
   • Smoke can be reduced by using oil or gas instead of coal in factories.
   • Almost all machinery can be redesigned to increase energy efficiency and reduce noise.

Q.6 Which is the most abundantly available fossil fuel in India? Mention its different forms. (2015 OD, 2014 OD, 2008)
Answer:
The most abundantly available fossil fuel is Coal.
There are four types of coal:

1. Anthracite. It is the highest quality hard coal. It contains more than 80% carbon content. It gives less smoke.
2. Bituminous. It is the most popular coal in commercial use and has 60-80% carbon content. Metallurgical coal is high grade bituminous coal and is of special value for smelting iron in blast furnaces.
3. Lignite. It is a low grade brown coal. It is soft with high moisture content.
4. Peat. It has a low carbon and high moisture content. It has low heating capacity and gives lot of smoke on burning.

Q.7 How can solar energy solve the energy problem to some extent in India? Give your opinion. (2015 OD)
Or
Why does solar energy have a bright future in India?
Answer:
Reasons:

1. India is a tropical country and gets abundant sunshine.
2. It has enormous possibilities of tapping solar energy.
3. It is an inexhaustible source of energy which is freely available in nature.
4. It is a cheaper source of energy and is fast becoming popular in rural and remote areas.
5. Photovaltic technology is available which converts sunlight directly into electricity.
6. Because of its abundant and free availability in all parts of India in addition to its ecofriendly nature, solar energy is called the energy of future.

Also use of solar energy will minimise the dependence of rural households on firewood. It will contribute to environmental conservation and reduce pressure on conventional sources of energy.

Q.8 Consumption of energy in all forms has been rising all over the country. There is an urgent need to develop a sustainable path of energy development and energy saving/ Suggest and explain any three measures to solve this burning problem. (2016 OD)
Answer:
Every sector of the national economy—agriculture, industry, transport, (commercial and domestic), needs greater inputs of energy.

With increasing population and changing lifestyles energy consumption is increasing very fast. We are not self sufficient in energy according to demands. Therefore we have to adopt a cautious approach for the judicious use of our limited resources. Conservation of energy should be done at all levels.
Three measures to reduce consumption of energy in all forms:

1. We can do our bit by using public transport systems instead of individual vehicles.
2. Switching off electricity when not in use.
3. Using power saving devices or using non-conventional sources of energy such as solar energy, wind energy etc.
4. Checking the power equipments regularly can help in saving of energy.

Q.9 What are the main types of formations in which minerals occur?
Answer:
Minerals generally occur in the following forms:

1. Veins and lodes. In igneous and metamorphic rocks minerals may occur in the cracks, faults or joints by getting solidified in them. The smaller occurrences are called veins and the larger lodes, eg., metallic minerals like tin, copper, zinc and lead etc. are found in lodes and veins.
2. In sedimentary rocks minerals occur in beds or layers. They are formed as a result of deposition, accumulation and concentration in horizontal strata. Some sedimentary minerals are formed as a result of evaporation, especially in arid regions eg., gypsum, potash and salt.
3. Another mode of formation involves decomposition of surface rocks and the removal of soluble contents, leaving a residual mass of weathered material containing ores. Bauxite is formed this way.
4. Placer deposits. Certain minerals occur as alluvial deposits in sands of valley floors and the base of hills, eg., gold, silver, tin and platinum. These are called placer deposits and contain minerals which are not corroded by water.
5. Ocean waters contain vast quantities of minerals, eg., common salt, magnesium and bromide are largely derived from the ocean waters. The ocean beds are rich in manganese nodules.

Q.10 Distinguish between conventional and non-conventional sources of energy. (2013 D)
Or
Classify energy resources into two categories. Give two examples of each. (2014 OD)
Answer:
Energy sources can be classified as conventional and non-conventional sources.

Important Link

Quick Revision Notes: Minerals and Energy Resources

NCERT Solution : Minerals and Energy Resources

MCQs: Minerals and Energy Resources

Click here for Free Video Lectures

Q.1 Explain how water becomes a renewable resource?
Answer:

• Fresh water is mainly obtained from surface run off and ground water. This is continually being renewed and recharged through the hydrological cycle.
• All the water moves within the hydrological cycle making water a renewable resource.

Q.2 What were the different types of hydraulic structures constructed in Ancient India? Give examples.
Answer:
The different types of hydraulic structures were:

• Dams built of stone rubble e.g., during Chandragupta Maurya’s time, dams, lakes and irrigation systems were extensively built.
• Reservoirs or lakes like the Bhopal lake of the 11th century which was one of the largest artificial lakes of its time.
• Embankments and canals for irrigation. Sophisticated irrigation works have been found in Kalinga (Orissa), Kolhapur (Maharashtra), Nagarjunakonda (Andhra Pradesh) etc.
• Many tanks were built to store rainwater e.g., the tank in Huaz Khas in Delhi was built in 14th century to supply water to Siri Fort area.

Q.3 Describe the traditional method of rainwater harvesting adopted in different parts of India.
Answer:
In ancient India, people developed wide-ranging techniques to harvest rainwater.

1. In mountainous areas ‘Guls’ and ‘Kuls’ the diversion channels were built for agriculture.
2. ‘Rooftop rainwater harvesting’ was commonly practised to store drinking water, especially in Rajasthan.
3. Inundation channels for irrigation were developed in the flood plains of West Bengal.
4. In arid and semi-arid regions, agricultural fields were converted into rainfed storage structures, eg. ‘Khadins’ in Jaisalmer and ‘Johads’ in other parts of Rajasthan.
5. In semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi and Barmer, all the houses had underground tanks or ‘tankas’ built inside the house for storing drinking water. They were a part of the well-developed rooftop rainwater harvesting system.

Q.4 What is water scarcity? Write the main reasons for water scarcity. (2015)
Answer:
Water scarcity means shortage of water. It is usually associated with regions having low rainfall or drought prone areas. There are many other reasons which lead to scarcity of water.
These are:

1. Large growing population—means more water required for domestic use and also to produce more food.
2. In the agricultural sector, water resources are being over-exploited to expand irrigated areas and dry-season agriculture.
3. More water required for irrigation purposes to facilitate higher food production, i.e., for doing multiple cropping and for HYV seeds.
4. There is greater demand for water with growing urbanisation and industrialisation.
5. An unequal access to water among different social groups.
6. The quality of water is deteriorating, i.e., getting polluted by domestic and industrial wastes, chemical fertilizers and pesticides used in agriculture.
7. Excessive use of water by industries which also require water to generate hydro-electric power to run them.
8. Over exploitation of water in the urban areas. Housing societies and colonies have their own ground-water pumping devices. This causes depletion of fragile water resources in the cities.

Q.5 Write the adverse effects of over-exploitation of ground water resources.
Answer:

1. Pumping out more water from under the ground may lead to falling ground water levels.
2. It will adversely affect water availability.
3. This, in turn, will affect our agriculture and food security of the people.
4. Impoverishment of water resources may adversely affect the ecological cycle.

Q6 .
Write the main causes of water pollution.
Answer:
Water gets polluted by:

1. Domestic wastes, especially urban sewers.
2. Industrial wastes are disposed off in the water without proper treatment.
3. Chemical effluents from industries and from agricultural sector.
4. Pesticides and fertilisers used in agriculture may get washed into rivers by rain-water and may pollute the water by enriching it with minerals.
5. Many human activities, e.g., religious rituals and immersing of idols, etc. in the water also pollute water.

Q.7 How was water conserved in ancient India? Give any four examples in support of your answer. (2012)
Answer:
Archaeological and historical records show that from ancient times India has been constructing sophisticated hydraulic structures like dams, reservoirs, embankments and canals for irrigation.

1. For example, in the first century B.C., Allahabad had sophisticated water harvesting system channelling the flood water of the river Ganga.
2. During the time of Chandragupta Maurya, dams, lakes and irrigation systems were extensively built.
3. Sophisticated irrigation works have been found in Kalinga in Odisha, Nagarjunakonda in Andhra Pradesh, Bennur in Karnataka and Kolhapur in Maharashtra.
4. Bhopal lake, built in the 11th century, was one of the largest artificial lakes of its time.
5. In the 14th century, Iltutmish constructed a tank in Hauz Khas, Delhi for supplying water in Siri Fort area.

Q.8 What is the main difference between traditional dams and modern dams?
Answer:
Traditionally dams were built to impound rivers and rainwater that could be used later to irrigate the agricultural fields.

Today, dams are referred to as multipurpose projects where many uses of the impounded water are integrated with one another. The main purposes served by these projects are irrigation, electricity generation, flood control, water supply for domestic and industrial use, fish breeding and tourism

Q.9 What are the social consequences of multipurpose projects?
Or
Multipurpose projects have transformed the social landscapes. Explain.
Answer:

1. Local people, especially the landless people, did not gain from these projects.
2. It led to displacement of people which deprived the people of their land and livelihood.
3. It has increased the social gap between the richer landowners and the landless poor.
4. Dams created conflicts between people wanting different uses and benefits from the same water resources.
5. Inter-state water disputes are also becoming common with regard to sharing the costs and benefits of the multipurpose projects.

Q.10 Explain how rooftop rainwater harvesting in semi-arid regions of Rajasthan is carried out. (2012)
Or
Write the features of the ’tankas’ built in the houses of Bikaner, Phalodi and Barmer.
Answer:
‘Rooftop rainwater harvesting’ was commonly practiced to store drinking water, especially in semi-arid and arid regions like Bikaner, Phalodi and Barmer in Rajasthan.

1. In semi-arid and arid regions, all the houses had underground tankas or ‘tankas’ for storing drinking water built inside the house. They were the part of the well-developed rooftop rainwater harvesting system.
2. The tankas could be as large as a big room. One household in Phalodi had a tank that was 6.1 metres deep, 4.27 metres long and 2.44 metres wide.
3. The tankas were built inside the main house or the courtyard.
4. The tanks were connected to the sloping roofs of the houses through a pipe. The falling rain would travel down the pipes and get stored in the underground ‘tankas’. The first spell of rain would not be collected as it cleaned the roof and pipes. The rainwater from subsequent showers was collected.
5. Many houses constructed underground rooms adjoining the tanka to beat the summer heat as it would keep the room cool.

Important Link

Quick Revision Notes :Periodic Classification of Elements

NCERT Solution :Periodic Classification of Elements

MCQs: Periodic Classification of Elements

Click here for Free Video Lectures

 Q.1 “Forests play a key role in the ecological system.” Highlight the value of forests in our life.

Answer

• Forests play a key role in the ecological system as these are the primary producers on which all other living beings depend.
• It supports diverse flora and fauna which are part of our life.
• It provide us fruits, flowers, medicine, wood etc.

Q.2 What is biological diversity? Why biodiversity is important for human lives?

Answer

Biological diversity means the variety of all living things, plants, animals and microorganisms living on the earth that are dependent on one other.
It is important for human lives because:
• Human beings depend on biodiversity for their very survival.
• The plants, animals and micro-organisms re-create the quality of air, water and soil which human use for their survival.

Q.3. Distinguish between endangered species and extinct species of wild animals. Give one example of each.

Answer

Endangered species:
• These are species which are in danger of extinction.
• The survival of such species is difficult if the negative factors that have led to a decline in their population continue to operate.
• Examples are black buck, crocodile, Indian wild ass, Indian rhino
Extinct:
• These are species which are not found after searches of known or likely areas where they may occur.
• A species may be extinct from a local area, region, country, continent or the entire earth. As, these species are finished, so they cannot be revived.
• Example – Asiatic cheetah, Pink-head duck.

Q4 Describe the role of the community in forest and wildlife conservation.

Answer

• In Sariska Tiger Reserve, Rajasthan, villagers have fought against mining and destruction of forest by citing the Wildlife Protection Act.
• The inhabitants of five villages in the Alwar district of Rajasthan have declared 1,200 hectares of forest as the Bhairodev Dakav ‘Sonchuri’, declaring their own set of rules and regulations which do not allow hunting, and are protecting the wildlife against any outside encroachments.
• The Bishnois of Rajasthan are well known for protecting black bucks (chinkara) an endangered species, and herds of black buck, nilgai and peacocks can be seen as an integral part of the community and nobody harms them.
• The famous Chipko Movement in the Himalayas led by local communities, especially women, successfully resisted deforestation in several areas.
• Joint forest management (JFM) is a programme which involves local communities in the management and restoration of degraded forests.

Q.5 What are the steps taken by Government to conserve flora and fauna of the country?

Answer

• To protect flora and fauna, the Indian wildlife protection Act was implemented in 1972, with various provisions for protecting habitats.
• An all–India list of protected species was also published. The main aim of the program was towards protecting the remaining population of certain endangered species by banning hunting, giving legal protection to their habitats and restricting trade in wildlife.
• Central and many stage governments established national parks and wildlife sanctuaries.
• The central government announced several projects for protecting specific animals, which were gravely threatened, including the tiger, the one horned rhinoceros, the Kashmir stag etc.
• Most recently, the Indian elephant, black buck, the great Indian bustard and the snow leopard, etc. have been full or partial legal protection against hunting and trade throughout India.

Q.6 Write four major reasons for the depletion of forest cover.
Answer:

1. Deforestation for agricultural purposes.
2. Shifting cultivation which is still practised in substantial parts of tribal belts.
3. Large-scale development of river valley projects.
4. Mining activities have also resulted in deforestation. For example, the tiger reserve in West Bengal is seriously threatened by the ongoing dolomite mining.
5. Environmental pollution and forest fires have also led to depletion of forests.

Q.7 Write three adverse impacts of dolomite mining in the Buxar Tiger Reserve on the ecosystem.
Answer:
Adverse effects of dolomite mining in the Buxar Tiger Reserve:

1. It has caused ecological damage.
2. It has blocked the migration route of several species.
3. It has disturbed the natural habitat of many species.

Q.8 What are ‘Permanent Forest Estates’ and why? Which state has maximum forest cover falling under this category? Write its percentage share in the total forest area of this state.
Answer:
Reserved and protected forests are referred to as the Permanent Forest Estates maintained for the purpose of producing timber and other forest produce.
Madhya Pradesh has the largest area under permanent forests, constituting 75% of its total forest area.

Q.9 Write the major differences between reserved and protected forests.
Answer:
Difference between Reserved and Protected forests

Q.10 33% of area should be under forests’. Justify the statement highlighting the environmental values of forests.
Answer:
Forest area in the country is far lower than the desired 33% of geographical area, as outlined in the National Forest Policy (1952). Forests are considered essential for maintenance of the ecological balance. The livelihood of millions of people who live on the fringes of these forests depend upon it.

Forests play a key role in the ecological system as these are also the primary producers on which all other living beings depend. The forest preserves the ecological diversity and our life support systems—water, air and soil. It also preserves the genetic diversity of plants and animals for better growth of species and breeding. The destruction of forests have marginalised and impoverished many indigenous forest dependent communities. The indirect impact of degradation is severe drought or induced floods. Poverty is a direct outcome of environmental destruction.

Important Link

Quick Revision Notes : Forest and Wildlife Resources

NCERT Solution : Forest and Wildlife Resources

MCQs: Forest and Wildlife Resources

Click here for Free Video Lectures

 Q.1“Damage to the ozone layer is a cause for concern.” Justify this statement. Suggest any two steps to limit this damage. ‘ [Delhi]
Answer. Ozone layer prevents the harmful ultraviolet radiation to enter the atmosphere and reach the earth’s surface. Depletion of ozone layer has become a cause for concern because it can cause serious effects on human body and other organisms of the environment like fatal diseases such as skin cancer, changes in genetic material DNA, eye damage, etc.
Two steps to limit this damage are as follows:

1. Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.
2.  Control over large scale nuclear explosions and limited use of supersonic planes.

Q.2  Explain the phenomenon of “biological magnification” How does it affect organisms belonging to different trophic levels particularly the tertiary consumers? [Delhi]
Answer. The process in which harmful chemicals enter a food chain and get accumulated progressively at each trophic level is called biological magnification.
Harmful and toxic chemicals enter our bodies when they are added to soil and water. Use of pesticides to protect the food crops from diseases and pests and chemical wastes of factories are dumped in open or disposed off into rivers. These chemicals are washed down into the soil and ultimately to water table or get absorbed or taken up from the soil by the plants along with water and minerals and in this way harmful chemicals enter the food chain. The quantity of these harmful chemicals increase with increase in trophic level of the food chain because these substances are not degradable. Man is at the top of the food chain, so concentration is maximum in human beings.
Thus, accumulation of DDT has been maximum in man as DDT is used to destroy pests. DDT is accumulated in the following way in this food chain:
This is the reason why our food grains such as wheat and rice, vegetables and fruits and even meat contain varying amounts of pesticides residues. So, the highest trophic level at the extreme right of food chain has the maximum concentration of harmful chemicals in a food chain.

Q.3 (a) What is ‘environmental pollution’?
(b) Distinguish between biodegradable and non-biodegradable pollutants.
(c) Choose the biodegradable pollutants from the list given below:
Sewage, DDT, radioactive waste, agricultural waste. [Delhi]
Answer. (a) Environmental pollution is an undesirable change in the physical, chemical or biological
characteristics of the natural environment, brought about by man’s activities. This pollution may affect the soil, rivers, seas or the atmosphere.

(c) Biodegradable pollutants are sewage and agricultural waste.

Q4 Which of the following groups contain only biodegradable items?
a. Grass, flowers and leather
b. Grass, wood and plastic
c. Fruit peels, cake and lime juice
d. Cake, wood and grass

Solution:

a) Grass, flowers and leather
c) Fruit peels, cake and lime juice
d) Cake, wood and grass

Above all are the groups that contain only biodegradable items. Since plastic is not a biodegradable substance, that group cannot be considered as a biodegradable.

 Q.5Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Solution:

The ozone layer is a protective cover for the earth. It prevents harmful UV rays from entering the earth as these rays harmful and can result in skin cancer. But the air pollutants like chlorofluorocarbons (CFCs) are the main reason for the depletion of the ozone layer. Too much of UV rays are harmful to plants as they affect photosynthesis, destroy planktons and decomposers. These are the reasons why damage of ozone layer is a cause of concern.

Q.6 Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment. [Delhi]
Answer. Bacteria and fungi breakdown the dead remains and waste products of organisms. These micro organisms are called the decomposers as they breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
Two advantages of decomposers to the environment are as follows:

1. Decomposers feed, on the dead bodies of plants and animals. They return the simple components to soil and help in making the steady state of ecosystem by recycling of nutrients. They, therefore, create a balance in the environment.
2. They also act as scavengers or cleansing agents of the atmosphere.

Q.7. Describe how decomposers facilitate recycling of matter in order to maintain balance in the ecosystem. [Foreign]
Answer. Decomposers are micro organisms that obtain energy from the chemical breakdown of dead organisms of animals or plants. These micro organisms breakdown the complex organic substances of dead organisms into simple inorganic substances that go into the soil and are used up once more by the plants. Decomposers thus, help in recycling of matter.

 How is ozone formed in the upper atmosphere? Why is the damage of ozone layer a cause of concern to us? State a cause of this damage. [Delhi(C)]
Answer. Ozone is formed in upper atmosphere by the reaction of ultraviolet (UV) radiations on oxygen (0₂) molecule.
The damage to ozone layer is a cause of concern to us as due to its damage, more ultraviolet rays reach the earth’s surface causing various health hazards.

A cause of this damage is the presence of large amount of chlorofluorocarbons in the atmosphere.

Important Link

Quick Revision Notes :Periodic Classification of Elements

NCERT Solution :Periodic Classification of Elements

MCQs: Periodic Classification of Elements

Click here for Free Video Lectures

Q.1 (a) Define tidal energy.
(b) Explain how the tidal energy is harnessed and write one limitation of the use of tidal energy.
Answer.
(a) Tidal energy: The energy produced by the surge of ocean water during high and low tides due to difference in sea-levels is called tidal energy. The high and low tides occur due to the gravitational pull of the moon. This causes enormous movement of water.
(b) Tidal energy is harnessed by constructing a dam near the shores. During the high tides water flows into the dam and during the low tides, water flows out. This flowing water rotates the turbine, present at the opening of the dam and produces electricity.

Q.2 Distinguish between renewable and non-renewable sources of energy. Also give an example of each of these sources.
answer.

Q.3 What are the advantages of nuclear energy?
answer. Advantages of nuclear energy are:

1.  A small quantity of nuclear fuel is needed to produce a large amount of useful energy.
2.  Nuclear power plant produces less atmospheric pollution than thermal power plants, if the nuclear fission reaction is performed properly.
3.  Small amount of nuclear fuel can run a nuclear power plant over a long period of time. There is no need of inserting the nuclear fuel in the nuclear reactor again and again in a short period as in case of thermal power plant.

Q.4. What is a solar cell panel? Mention any three of its applications.
answer. A large number of solar cells combined in an arrangement to obtain large electrical power is called solar cell panel.
Applications of solar cell panel are:
It provides the electric power for the:

1. working of artificial satellites stationed in outer space,
2.  running of irrigation water pumps by the farmers in rural areas,
3.  street lighting in remote areas.

Q.5 List any three hazards of nuclear waste. How does the disposal of nuclear waste pose a problem for the plant and animal life?
answer. Hazards of nuclear wastes are:

1.  Nuclear waste contains radioactive substances which emit harmful nuclear radiations.
2. There is a high risk of environmental contamination.
3. It is highly toxic.
   Effect of nuclear waste on plant and animal life is:
   The radiations emitted from the nuclear waste penetrate deep inside the human or animal body where they can damage biological cells thereby initiate cancer or causes genetic disease.
   Increased mortality of plants, soil invertebrates and mammals and reproductive losses in plants and animals have also been observed.

Q.6 (a) What is geothermal energy?
(b) What are the advantages of wind energy?
answer.
(a) The heat energy obtained from the molten rocks formed in the deeper hot regions inside the earth are called geothermal energy.
(b) Advantages of wind energy are:

1.  It is an inexhaustible source of energy.
2. It does not cause any environmental pollution.
3.  It is available at free of cost.

 Q.7 Mention any four limitations in harnessing wind energy on a large scale.
answer. Limitations in harnessing wind energy are:

1.  Speed of wind is not available at all time and at all places.
2. To establish the wind energy farm, a large area of land is needed.
3.  Speed of wind should be higher than 15 km/h to harness the wind energy.
4. Construction of windmill and its installation is very expensive.

Q.8 Solar cooker takes more time as compared to the LPG to boil potato or rice, yet Kunal uses solar cooker for such type of cooking:
(i) Why does Kunal uses Solar cooker instead of LPG? Give reasons for your answer.
(ii) Name the phenomenon which is responsible for obtaining high temperature in solar cooker.
Answer.
(a)(i) There are no energy losses while cooking on the solar cooker as the food gets cooked in a controlled environment whereas cooking on the LPG leads to maximum percentage of energy loss.
(ii) Temperature controlled cooking retains the nutrient value of the food.
(iii) Using the solar cooker, LPG can be served which result reduction in the emission of  CO₂.
(iv) It saves a lot of prestigious time which is normally consumed for cooking purpose.
(b) Greenhouse effect.

Q.9 Reena’s father works with a company that builds dams. Once he took her to the site where a dam was being built. Reena saw a group of people sitting there and shouting slogans against the building of dam. She talked the group of people and asked them about their problems and then discussed it with her father. She then tried to convince the people to talk with the authorities and come to an amicable solution. The discussion was successful. Reena’s father was very proud of his daughter. Now answer the following questions:
(i) Why was Reena’s father proud of his daughter?
(ii)Why was the group of people protesting against the building of dam?
(iii) Reena’s contribution to the peaceful resolution of the conflict proved to boon for many citizens of the country. How?
Answer.
(i) Because she convinced the people by explaining them the advantage of constructing dam and come with a solution of rehabilitation of displaced peoples. So the contribution to the peaceful resolution of the conflict make Reena’s father proud of his daughter.
(ii)The group of people protesting against the building of dam because of following disadvantages
(a) A large area of agricultural land and human habitation are sacrificed as it get submerged at the dam site.
(b) Large ecosystems are destroyed when submerged under water.
(c) The decomposition of vegetation under anaerobic condition produces methane gas which is also a greenhouse gas.
(iii)(a) The citizens are not affected by flood as it can be controlled by storing the water behind the dam.
(b) Farmers get benefited as water for irrigation is available for the whole year.
(c) Low cost of production of electricity gives monetary gain which is a boon to citizens.

Q.10 Bio gas is an excellent fuel. Justify the statement by giving two reasons. Mention the main constituents of bio gas along with its percentage.
Answer. 
(i) It burns without smoke and leave no residue therefore causes no atmospheric pollution.
(ii)Its heating capacity is high, i.e. it has high calorific value. Main constituents of bio gas: The composition of bio gas varies depending upon the nature of organic matter feeding in’the digester and advanced waste treatment technology. The typical composition of bio gas is
Methane                                50 – 75%
Carbon dioxide                     25 – 50%
Nitrogen                                   0 – 10%
Hydrogen                                 0 – 1%
Hydrogen sulphide                0 – 3%

Important Link

Quick Revision Notes :Sources of Energy

NCERT Solution :Sources of Energy

MCQs: Sources of Energy

Click here for Free Video Lectures

Q.1What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid.

When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity,
i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

Q.2 Why and when does a current carrying conductor kept in a magnetic field experience force? List the factors on which direction of this force depends?
Answer. The drifting of free electrons of a conductor in a definite direction causes the current to flow through it. When such conductor is placed in a uniform magnetic field, each drifted electron of a conductor experience a magnetic force. This force is collectively experience by a conductor as a whole. Hence a current carrying conductor kept in a magnetic field experience a force. The direction of magnetic force depends on
(i) direction of current through the conductor, and
(ii) direction of magnetic field.

Q.3 How is the strength of magnetic field near a straight current-conductor
(i) related to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer.
(i) The strength of magnetic field around a straight current conductor increases
on increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Q.4 Explain any two situations that can cause electrical hazards in domestic circuits.
Answer. (i) Connecting too many electrical devices to a single socket or in the extension
cord for any length of time draws high current from the mains that will exceed the current rating of connecting wires. The wires cannot withstand such a high current and melt and may cause fire.
(ii) Most electrical hazards in domestic circuits are caused by the faulty electrical outlets, old and out-dated appliances. The chances of short circuit i.e., contact of live wire and neutral wires with each other due to damage in their insulation or some fault in the appliances are very high. It may result spark at the contact point which may even cause fire,

Q.5 List in tabular form two major differences between an electric motor and a
generator.
Answer.

Q.6 Write one application of each of the following:
(a) Right-hand thumb rule (b) Fleming’s left hand rule
(c) Fleming’s right hand rule
Answer.
(a) Right-hand thumb rule is used to find the direction of magnetic field in a coil of wire and the electric current in a straight conductor.
(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor.
(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator.

Q.7 Consider a circular loop of wire lying in the plane of the paper. Let the current
pass through the loop clockwise. With the help of a diagram, explain how the direction of the magnetic field can be determined inside and outside the loop. Name the law used to find the direction of magnetic field.
Answer. Consider a circular loop of wire of radius r with centre O lying in the plane of the paper. Let the current i pass through the loop clockwise. According to right hand thumb rule, direction of magnetic field due to any portion of small current carrying length of the coil is:
Direction of magnetic field inside the loop — Perpendicular to the plane of paper inwards.
Direction of magnetic field outside the loop — Perpendicular to the plane of paper outwards.

So, the direction of magnetic field can be considered as the direction of total magnetic field due to circular coil as current through all the elements will contribute to the magnetic field in the same direction.

Q. 8 A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a) pushed into the coil,
(b) withdrawn from inside the coil,
(c) held stationary inside the coil?
Answer.
(a) When a bar magnet is pushed into the coil, magnetic field lines linked with
the coil changes (increases). It causes the electric current to get induced in it. The needle of galvanometer will move momentarily in one direction.
(b) When a bar magnet is withdrawn from inside the coil, the magnetic field lines linked with the coil changes but in decreasing order. Current will be induced in the coil which will be indicated by deflection of needle in the galvanometer. The deflection is opposite to that in case (a). This indicates that the direction of induced current is now opposite to the direction of induced current in case (a).
(c) When bar magnet is held stationary inside the coil, there is no deflection in the galvanometer. This is because there is no change in magnetic field lines linked with the coil. Hence, no induced current will flow through the coil.

Q.9 (a) Two magnets are lying side by side as shown below.
Draw magnetic field line between poles P and Q.

(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer.

(b) The degree of closeness of magnetic field lines near the poles signify that the field is stronger there, i.e. the pole of another magnet when placed in the magnetic field experiences a greater force where the field lines are crowded.

Q.10 For the current carrying solenoid as shown below, draw magnetic field lines and giving reason explain that out of the three points A, B and C at which point the field strength is maximum and at which point it is minimum.

Answer. Outside the solenoid magnetic field is minimum. At the ends of solenoid, magnetic field strength is half to that inside it. So Minimum – at point B; Maximum – at point A

Important Link

Quick Revision Notes :Periodic Classification of Elements

NCERT Solution :Periodic Classification of Elements

MCQs: Periodic Classification of Elements

Click here for Free Video Lectures

Q.1 (a) Write two points of difference between electric energy and electric power. (6) Out of 60 W and 40 W lamps, which one has higher electrical resistance when in use.
(c) What is the commercial unit of electric energy? Convert it into joules.
Answer. (a) Difference between electric energy and electric power:

i.e. less the power of electrical device, higher is its electrical resistance.
(c) Kilowatt hour – Commercial unit of electrical energy
1 kWh = 1000 Wh = 1000 J/S x 3600 sec
= 3600000 J = 3.6 x10⁶J

Q.2 V-I graph for two wires A and B are shown in the figure. If both wires are of same length and same thickness, which of the two is made of a material of high resistivity? Give justification for your answer.

Answer. Greater than slope of V-I graph, greater will be the resistance of given metallic wire. In the given graph, wire A has greater slope then B. Hence, wire A has greater resistance.
For the wires of same length and same thickness, resistance depends on the nature of material of the wire, i.e.

Q.3 An electric bulb of resistance 200Ω draws a current of 1 Ampere. Calculate the power of the bulb the potential difference at its ends and the energy in kWh consumed burning it for 5h.
Answer. Power of the bulb,

Q.4Two identical wires one of nichrome and other of copper are connected in series and a current (I) is passed through them. State the change observed in the temperatures of the two wires. Justify your answer. State the law which explains the above observation.
Answer. The resistivity of nichrome is more than that of copper so its resistance is also high. Therefore, large amount of heat is produced in the nichrome wire for the same current as compared to that of copper wire. Accordingly, more change in temperature is observed in the nichrome wire. This is explained by Joule’s law of heating.
Joule’s law of heating: It states that the amount of heat produced in a conductor is

Q.5 A 9Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination.
Answer.

Q.6 Explain the role of fuse in series with any electrical appliance in an electric circuit. Why should a fuse with defined rating for an electric circuit not be replaced by one with a larger rating?
Answer. Fuse wire is a safety device connected in series with the live wire of circuit. It has high resistivity and low melting point. It melts when a sudden urge of large current passes through it and disconnects the entire circuit from the electrical supply. But, in case if we use a larger rating instead of a defined rating, then it will not protect the circuit as high current will easily pass through it and it will not melt.

Q.7 The wattage of a bulb is 24 W when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery (Neglect the change in resistance due to unequal heating of the filament in the two cases).
Answer.

Q.8 Name the physical quantity which is (i) same (ii) different in all the bulbs
when three bulbs of:
(a) same wattage are connected in series.
(b) same wattage are connected in parallel.
(c) different wattage are connected in series.
(d) different wattage are connected in parallel.
Answer. (a) For identical bulbs in series- same current, same potential difference.
(b) For identical bulbs in parallel- same potential difference, different current.
(c) For unidentical bulbs in series- same current, different potential difference.
(d) For unidentical bulbs in parallel- different current, same potential difference.

Q.9 (a) Define the term ‘coulomb’.
(b) State the relationship between the electric current, the charge moving through a conductor and the time of flow.
Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA.
Answer.

(a) When 1 A current flows across the wire in 1 second, the charge transfer across its ends is said to be 1 coulomb.
(b) The relationship between the electric current I, the charge q and time t is

10.(a) Define the term ‘volt’.
(b) State the relation between work, charge and potential difference for an electric circuit.
Calculate the potential difference between the two terminals of a battery if 100 J of work is required to transfer 20 C of charge from one terminal of the battery to the other.
Answer.
(a) When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the electric field, then potential at that point is called 1 volt.
(b) Potential difference, V = Work done on unit charge =W/q

Important Link

Quick Revision Notes :Electricity

NCERT Solution : Electricity

MCQs: Electricity

Click here for Free Video Lectures

Q.1 Study the diagram given below and answer the questions that follow it:

(a) Which defect of vision is represented in this case? Give reason for your answer.
(b) What could be the two causes of this defect?
(c) With the help of a diagram show how this defect can be corrected by the use of a suitable lens. [Delhi(C)]
Answer. (a) Hypermetropia as the image is formed beyond the retina.
(b) (i) Due to greater focal length of the , lens and
(ii) As eyeball becomes smaller.
(c) It can be corrected by using a convex lens of suitable focal length as shown below.

Q.2 Student sitting at the back bench in a class is not able to see what is written on the blackboard. He however, sees it clearly when sitting on the front seat at an approximate distance of 1.5 m from the blackboard. Draw ray diagrams to illustrate the image formation of the blackboard when he is seated at the (i) back seat (ii) front seat. [All India (C)]
Answer. (i) When student is seated at the back seat.

(ii) When student is seated at front seat.

Q.3 What is meant by spectrum of white light? How can we recombine the components of white light after a prism has separated them? Draw a diagram to illustrate it. [Foreign, All India (C)]
Answer. The coloured pattern VIBGYOR formed by a prism by splitting the incident white light is called a spectrum. By having two prisms, inverted to each other, one can recombine the light to get white light again.

Q.4 Explain why do the planets not twinkle but the stars twinkle. [Delhi (C); Delhi 2011]
Answer. Planets being of larger size can be taken as a collection of large number of point-sized objects/sources of light, which nullify the twinkling effect of each other.
Due to varying conditions of atmosphere, starlight undergoes multiple refraction and its path varying slightly while passing through the atmosphere. Therefore, the apparent position of star fluctuates and amount of light entering the eye changing continuously. The star sometimes appear brighter and some other time, it appears fainter. This causes twinkling of star.

Q.5 What is myopia (near-sightedness)? Draw a ray diagram to show how it can be corrected using a lens. [Delhi]
Answer. Myopia is the inability of an eye in viewing long distant objects. The image in this case is formed before the retina. For every myopic eye, there exists a far point beyond which clear image cannot be seen.
The short-sightedness is corrected by using a concave lens which diverges and shifts the image to the retina.

Q.6 What is hypermetropia (far-sighted-ness)? Draw a ray diagram to show how this defect can be corrected using a lens. [Delhi]
Answer. Hypermetropia is the inability of an eye in viewing the nearby objects. The image in this case is formed beyond the retina. For a hypermetropic eye, there exists a near point.
It is corrected by using a convex lens, which converges and shifts the image to the retina.

Q.7 What is a spectrum? Why do different coloured rays deviate differently on passing through a glass prism? [All India]
Answer. The band of coloured component of a light beam is called its spectrum. The colour sequence is given by the acronym V I B G Y O R — Violet, Indigo, Blue, Green, Yellow, Orange and Red.
The speed of light of different colours in a medium like glass is different. Varying speeds for different colours lead to different refractive indices for different colours. It has been observed that the refractive index of glass for violet colour is more than that for red colour. All the colours present in white light refract through different angles and hence, emerge out from the prism with different directions and become distinct.

Q.8 What is meant by the term ‘power of accommodation’ of human eye? How does it help a person to see nearby as well as distant objects clearly.[Foreign]
Answer. The ability of eye lens to adjust its focal length to form the sharp image of the object at varying distances on the retina is called its power of accommodation.
When we see the nearby object, the ciliary muscles contract, it increases the thickness of eye lens. The eye lens then becomes thicker. As a result, the focal length of eye lens decreases in such a way that the clear sharp image of nearby object is formed on the retina. Thus, the object is seen clearly to us.
When we see the distant object, these muscles becomes relaxed, thus the eye lens becomes thinner, and consequently focal length of the lens increases. Therefore, the parallel rays coming from the distant object are focused on the retina and object is seen clearly to us. Thus, the accommodation power of an eye helps a person to see nearby as well as distant objects clearly

Q.9 a) Explain the following terms used in relation to defects in vision and correction provided by them:
(i) Myopia (ii) Astigmatism (iii) Bifocal lenses (iv) Far-sightedness.
(b) Why is the normal eye unable to focus on an object placed within 10 cm from the eye? [All India]
Answer. (a) (i) Myopia: Short-sightedness is caused due to excessive curvature in cornea or elongation of eyeball. Image is formed before of the retina. So, a concave lens is used to correct it.
(ii) Astigmatism: The inability to focus the light in both vertical and horizontal lines is called astigmatism. It is caused due to varying curvature in lens both horizontally and vertically. It is . corrected by using cylindrical lens.
(iii) Bifocal lenses: These are used to correct presbyopic eye. These contain lenses with upper concave and lower convex surface. Presbyopia arises with age.
(iv) Far-sightedness: Hypermetropia or far-sightedness is caused due to greater focal length of eye lens and/or when eyeball becomes smaller. Image is formed beyond the retina and can be corrected using a convex lens.
(b) The focal length of the lens cannot be changed up to an extent that objects nearer than 25 cm can be viewed (its near point is 25 cm). So it is not able to focus for 10 cm.

Q10.A 14-year old student is not able to see clearly the questions written on the blackboard placed at a distance of 5 m from him.
(a) Name the defect of vision he is suffering from.
(b) With the help of labelled ray diagrams show how this defect can be corrected.
(c) Name the type of lens used to correct this defect. [All India]
Answer.

Important Link

Quick Revision Notes :Human Eye and Colourful World

NCERT Solution :Human Eye and Colourful World

MCQs: Human Eye and Colourful World

Click here for Free Video Lectures