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NCERT Solutions for Class 10 History Chapter 2 Nationalism in India

NCERT Solutions for Class 10 will help the students in learning complex topics and problems in an easy way. Class 10 Social Science NCERT Solutions will help students in understanding the topics in most simple manner and grasp it easily to perform better. You can study in an organized manner and set a good foundation for your future goals.

Page No: 74

Write in Brief

1. Explain:
(a) Why growth of nationalism in the colonies is linked to an anti-colonial movement.
(b) How the First World War helped in the growth of the National Movement in India.
(c) Why Indians were outraged by the Rowlatt Act.
(d) Why Gandhiji decided to withdraw the Non-Cooperation Movement.

Answer

(a) The sense of being oppressed under colonialism provided a shared bond that tied many different groups together. People began discovering their unity in the process of their struggle with colonialism. The movements of freedom struggle were joined by the masses to free themselves from foreign exploitation. Thus, the growth of nationalism in the colonies is linked to anti-colonial movements.

(b) During the First World War, to finance the defence expenditure, customs duties were raised and income tax introduced. The forced recruitment in rural areas caused widespread anger. In 1918-19 and 1920-21, crops failed in many parts of India which resulted in acute shortages of food. Also, there was an influenza epidemic. The hardships of people did not ended after the war. Thus, they united under leaders to find a new way of struggle.

(c) The Rowlatt Act was hurriedly passed through the Imperial Legislative Council despite the united opposition of the Indian members. It gave the government enormous powers to repress political activities and allowed detention of political prisoners without trial for two years. This was an unjust and oppressive law for Indians. Thus, Indians were outraged by the Rowlatt Act.

(d) Gandhiji felt the movement was turning violent in many places such as Chauri Chaura incident. He felt that satyagrahis needed to be properly trained before they would be ready for mass struggles. Thus, Gandhiji decided to withdraw the Non-Cooperation Movement.

2. What is meant by the idea Satyagraha?

Answer

Satyagraha was a novel method of mass agitation. The idea of ‘Satyagraha’ emphasized the power of truth and the need to search for truth. It suggested that if the cause was true, if the struggle was against injustice, then physical force was not necessary to fight the oppressor. A satyagrahi could win the battle through non-violence without seeking vengeance or being aggressive.

3. Write a newspaper report on:
(a) The Jallianwala Bagh massacre
(b) The Simon Commission

Answer

a) On 13th April 1919, the infamous Jallianwalla Bagh incident took place in the enclosed ground of Jallianwala Bagh. A large crowd gathered in the Jallianwala Bagh. Some people were present to protest against the British government’s repressive measures while others were there to attend the annual Baishakhi Fair. Being from outside the city, many villagers were unaware of the martial
law that had been imposed. Suddenly, a British military officer, General Dyer came, blocked the exit points from the Bagh and opened fire upon the innocent citizens. Hundreds of innocent people including women and children were killed and wounded due to firing by the British soldiers.

b) The Simon Commission was constituted by the Tory Government in Britain, under Sir John Simon. The objective of the Commission was to look into the functioning of the constitutional system in India and suggest some constitutional changes. But nationalists in India opposed the Commission because it had not a single Indian member. Therefore, when the Simon Commission arrived in India in 1928, it was greeted with the slogan “Go Back Simon”. All parties, including Congress and the Muslim league, participated in the demonstrations.

4. Compare the images of Bharat Mata in this chapter with the image of Germania in Chapter 1.

Answer

→ The image of Germania was the symbol of German nation whereas the image of Bharat Mata was the symbol of Indian nation.
→ Both images inspired nationalists who worked very hard to unify their respective countries and to attain a liberal nation.
→ The image of Bharat Mata painted by Abanindranath Tagore is bestowed with learning, food, clothing and some ascetic quality also. Another painting of Bharat Mata in which we find Mata holding Trishul and standing beside a lion and an elephant – symbols of power and authority. Germania as a female figure is standing against a background of the tricolour fabric of the national flag. She is wearing a crown of oak leaves, as the German oak stands for heroism.

Discuss

1. List all the different social groups which joined the Non-Cooperation Movement of 1921. Then choose any three and write about their hopes and struggles to show why they joined the movement.

Answer

The different social groups that joined the Non-Cooperation Movement of 1921 were the urban middle class comprising lawyers, students, teachers and headmasters, peasants, tribals and workers.→ The middle class joined the movement because the boycott of foreign goods would make the sale of their textiles and handlooms go up.
→ The peasants took part in the movement because they hoped they would be saved from the oppressive landlords, high taxes taken by the colonial government.
→ Plantation workers took part in the agitation hoping they would get the right to move freely in and outside the plantations and get land in their own villages.

2. Discuss the Salt March to make clear why it was an effective symbol of resistance against colonialism.

Answer

Mahatma Gandhi found in salt a powerful symbol that could unite the nation as it was consumed by rich and poor alike. He declared that the tax on salt and the government monopoly over its production was the most oppressive face of British rule. Gandhiji sent a letter to Viceroy Irwin stating eleven demands. The most stirring of all was the demand to abolish the salt tax. Irwin was unwilling to negotiate, so Gandhiji started Salt march with 78 volunteers. He reached Dandi, violated law and made salt. This March developed the feeling of nationalism, people in different parts of the country broke the salt law and manufactured salt and demonstrated in front of government salt factories. Thus, Salt March was an effective symbol of resistance against colonialism.

3. Imagine you are a woman participating in the Civil Disobedience Movement. Explain what the experience meant to your life.

Answer
I participated in the Civil Disobedience Movement which was called by Gandhiji. I participated in protest marches, manufactured salt, and picketed foreign cloth and liquor shops and went to jail. I really see these services to the nation as a sacred duty of women. From the very start, I was sure that British had to leave our country and I saw this as a proud moment as I took part in this activity.

4. Why did political leaders differ sharply over the question of separate electorates?

Answer

Many dalit leaders were keen on a different political solution to the problems of the community. They began organising themselves, demanding a separate electorate that would choose dalit members for legislative councils. They believed political empowerment would resolve the problems of their social disabilities. Dr B.R. Ambedkar, who organised the dalits into the Depressed Classes Association in 1930, clashed with Mahatma Gandhi at the second Round Table Conference by demanding separate electorates for dalits. Gandhiji believed that separate electorates for dalits would slow down the process of their integration into society.
After the decline of the Non-Cooperation-Khilafat Movement, many Muslim leaders and intellectuals expressed their concern about the status of Muslims as a minority within India. They feared that the culture and identity of minorities would be submerged under the domination of Hindu majority.

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Most Important Question- Nationalism in India

Important MCQs- Nationalism in India

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NCERT Solutions for Class 10 History Chapter 1 The Rise of Nationalism in Europe

NCERT Solutions for Class 10 History Chapter 1 The Rise of Nationalism in Europe Social Science

Page No: 28

Write in Brief

1. Write a Note on:
a) Giuseppe Mazzini
b) Count Camilo de Cavour
c) The Greek War of Independence
d) The Frankfurt Parliament
e) The role of women in nationalist struggles

ANSWERS

a) Giuseppe Mazzini: Giuseppe Mazzini was an Italian revolutionary. He was born in Genoa in 1807. He was a member of the secret society of the Carbonari. At the age of 24, he was sent into exile in 1831 for attempting a revolution in Liguria. He founded underground societies named ‘Young Italy’ in Marseilles and ‘Young Europe’ in Berne, whose members were like-minded young men from Poland, France, Italy and the German States. He believed that God had intended nations to be the natural units of mankind. So, Italy had to be forged into a single unified republic within a wider alliance of nations.

b) Count Camilo de Cavour: Cavour was chief minister of Sardinia-Piedmont state who led the movement to unify the regions of Italy. He was neither a revolutionary nor a democrat. Like many other wealthy and educated members of the Italian elite, he spoke French much better than he did Italian. He engineered a careful diplomatic alliance with France, which helped Sardinia-Piedmont defeat the Austrian forces in 1859, and thereby free the northern part of Italy from the Austrian Habsburgs.

c) The Greek War of Independence: Greece was a part of the Ottoman Empire since the 15th century. The struggle for independence amongst the Greeks began in 1821. Nationalists in Greece got support from other Greeks living in exile and also from many Western Europeans sharing sympathies for ancient Greek culture. Poets and artists lauded Greece as the cradle of European civilisation and mobilised public opinion to support its struggle against a Muslim empire. Finally, the Treaty of Constantinople of 1832 recognised Greece as an independent nation.

d) The Frankfurt Parliament: It was an all-German National Assembly formed by a large number of political associations whose members were middle-class professionals, businessmen and prosperous artisans. Its first meeting was convened on 18 May 1848 in the Church of St. Paul at Frankfurt. They drafted a constitution for the German nation to be headed by a monarchy subject to a parliament. The king of Prussia rejected the crown offered by the deputies of parliament and joined other monarchs to oppose the elected assembly. As it was dominated by the middle classes who resisted the demands of workers and artisans and consequently lost their support. In the end, troops were called in and the assembly was forced to disband.

e) The role of women in nationalist struggles: The issue of extending political rights to women was a controversial one within the liberal movement, in which large numbers of women had participated actively over the years. Women had formed their own political associations, founded newspapers and taken part in political meetings and demonstrations. Despite this, they were denied suffrage during the election of the Assembly. When the Frankfurt Parliament convened in the Church of St. Paul, women were admitted only as observers to stand in the visitors’ gallery.

2. What steps did the French revolutionaries take to create a sense of collective identity among the French people?

Answer

The French revolutionaries took many important steps to create a sense of collective identity among the French people which were:
→ Ideas of la Patrie (the fatherland) and le Citoyen (the citizen) emphasising the notion of a united community enjoying equal rights under a constitution.
→ A new French flag, a tricolour replaced the royal standard.
→ The Estates General was renamed the National Assembly and was elected by a group of active citizens.
→ New hymns, oaths and martyrs commemorated in the name of the nation.
→ A central administrative system made uniform laws for the entire nation.
→ Discouraging regional dialects and promoting French as a common language of the nation.

3. Who were Marianne and Germania? What was the importance of the way in which they were portrayed?

Answer

Marianne and Germania were female allegories for the French and the German nation respectively. These female allegories were used to portray ideas such as Liberty, Justice and the Republic. These allegories remind the public of the national symbol of unity and to persuade them to identify with it.

4. Briefly trace the process of German unification.

Answer

In 1848, the middle class Germans tried to unite the different regions of the German confederation into a nation-state governed by an elected parliament. But they were repressed by the combined forces of the monarchy and the military, supported by the large landowners of Prussia. After this, Prussia soon became the leader of German unification movement. Its Chief Minister Otto von Bismarck was the architect of the process with support from Prussian army and Prussian bureaucracy. The unification process was completed after Prussia won wars with Austria, Denmark and France over seven years time. In January 1871, the Prussian king, William I, was proclaimed the German Emperor in a ceremony held at Versailles.

5. What changes did Napoleon introduce to make the administrative system more efficient in the territories ruled by him?

Answer

Napoleon introduced following changes to make the administrative system more efficient in the areas ruled by him:
→ He established civil code in 1804 also known as the Napoleonic Code which did away with all privileges based on birth and established equality before law and secured the right to property.
→ He simplified administrative divisions, abolished feudal system, and freed peasants from serfdom and manorial dues.
→ In towns too, guild systems were removed. Transport and communication systems were improved.

Discuss

1. Explain what is meant by the 1848 revolution of the liberals. What were the political, social and economic ideas supported by the liberals?
Answer
The 1848 revolution was led by the educated middle class along with the poor, unemployed starving peasants and workers in Europe. In certain parts of Europe such as Germany, Italy, Poland and the Austro-Hungarian Empire, men and women of the liberal middle classes took advantage of the growing popular unrest to push their demands for the creation of nation-states based on parliamentary principles.
The political, social and economic ideas supported by the liberals were:
→ Politically, they demanded constitutionalism with national unification. They wanted the creation of a nation-state on parliamentary principles – a constitution, freedom of the press and freedom of association.
→ Socially, they wanted to rid society of its class-based partialities and birth rights. Serfdom and bonded labour had to be abolished.
→ Economically, they wanted freedom of markets and right to property. Abolition of state imposed restrictions on the movements of goods and capital.

2. Choose three examples to show the contribution of culture to the growth of nationalism in Europe.

Answer

Three examples to show the contribution of culture to the growth of nationalism in Europe were:

• Romanticism was a cultural movement which sought to develop a particular form of nationalist sentiment. Romantic artists and poets focused on emotions, intuition and mystical feelings as their effort was to create a sense of a shared collective heritage, a common cultural past, as the basis of a nation.

• Folk songs, dances and poetry were regarded as the true spirit of the nation. So collecting and recording these forms of folk culture was essential to the project of nation-building. The vernacular language and the collection of local folklore were used to carry the modern nationalist message to large audiences who were mostly illiterate. For example, Karol Kurpinski celebrated the national struggle through his operas and music, turning folk dances like the polonaise and mazurka into nationalist symbols.

• Language too played an important role in developing nationalist sentiments. After Russian invasion, the Polish language was forced out of schools and the Russian language was imposed everywhere. After the failure of an armed rebellion against Russian rule in 1831, many members of the clergy
in Poland began to use language as a weapon of national resistance. Polish was used for Church gatherings and all religious instruction. As a result, a large number of priests and bishops were put in jail or sent to Siberia by the Russian authorities as punishment for their refusal to preach in Russian. The use of Polish came to be seen as a symbol of the struggle against Russian dominance.

3. Through a focus on any two countries, explain how nations developed over the nineteenth century.

Answer

The development of the German and Italian nation states in the nineteenth century:
• Unification of Germany with the help of Army: In 1848, an attempt was made to unite different regions of the German Confederation into a nation-state governed by an elected parliament. However, this liberal initiative was repressed by the combined forces of the monarchy and the military, who were supported by the large landowners of Prussia. Thereafter, Prussia took on the leadership of the movement for national unification. Its Chief Minister, Otto von Bismarck with the help of the Prussian army and bureaucracy in the process. Three wars over seven years with Austria, Denmark and France ended in Prussian victory and completed the process of unification. In January I 871, the Prussian king, William I, was proclaimed as the German emperor in a ceremony held at Versailles.

• Unification of Italy by a princely house: In the middle of the 19th century, Italy was divided into seven states. Of these, only Sardinia-Piedmont was ruled by an Italian princely house. The north was under the Austrian-Habsburg Empire, the centre was ruled by the Pope while the southern regions were dominated by the Bourbon kings of France. Also, the Italian language had many regional and
local variations. In the 1830s, Giuseppe Mazzini sought to formulate a coherent programme for a unitary Italian republic and also had established a secret society called Young Italy for the fulfillment of his goals. The revolutionary uprisings in 1831 and 1848 largely failed. Thus, the responsibility of uniting Italian states was now on King Victor Emmanuel II of Sardinia-Piedmont. The Chief Minister of Italy, Cavour led the movement to unify the regions of Italy. He was able to conclude a diplomatic alliance with France. Also, Sardinia-Piedmont succeeded in defeating the Austrian forces in 1859. Apart from regular troops, a large number of armed volunteers, under the leadership of Giuseppe Garibaldi, also joined the movement. In 1860, these troops marched into south Italy and the kingdom of Two Sicilies. These areas were liberated and later joined with Sardinia. In 1870, Rome was vacated by France and it became a part of Sardinia. Finally, Italy was unified in 1871.

4. How was the history of nationalism in Britain unlike the rest of Europe?

Answer

The history of nationalism in Britain unlike the rest of Europe because:
→ In Britain, the formation of the nation-state was not the result of a sudden upheaval or revolution.
→ The primary identities of the people who inhabited the British Isles were ethnic ones – such as English, Welsh, Scot or Irish.
→ The Act of Union (1707) between England and Scotland resulted in the formation of the ‘United Kingdom of Great Britian’ meant that England was able to impose its influence on Scotland. Scotland’s distinctive culture and political institutions were systematically suppressed.
→ The Scottish highlanders were forbidden to speak their Gaelic language or wear their national dress and large numbers were forcibly driven out of their homeland.
→ The English helped the Protestants of Ireland to establish their dominance over a largely Catholic country. Catholic revolts against British dominance were suppressed. Ireland was forcibly incorporated into the United Kingdom in 1801.
→ The symbols of the new Britain – the British flag, the national anthem, the English language were actively promoted and the older nations survived only as subordinate partners in this union.

5. Why did nationalist tensions emerge in the Balkans?

Answer
The Balkans was a region of ethnic and geographical variations. It consisted of modern-day Albania, Greece, Romania, Bulgaria, Macedonia, Croatia, Bosnia, Slovenia, Serbia, Herzegovina and Montenegro. A large part of the Balkans was under the control of the Ottoman Empire. The nationalist tensions emerged in the Balkans due to the spread of the ideas of romantic nationalism in the Balkans together with the disintegration of the Ottoman Empire. The Balkan peoples based their claims for independence or political rights on nationality and used history to prove that they had once been independent. The rebellious nationalities in the Balkans thought of their struggles as attempts to win back their long-lost independence. The Balkan states were fiercely jealous of each other and each hoped to gain more territory at the expense of the others.

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Important MCQs- The Rise of Nationalism in Europe

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NCERT Solutions for Class 10 Science Chapter 16 Sustainable Management of Natural Resources

NCERT Solutions for Class 10 Science Chapter 16 Sustainable Management of Natural Resources includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 16 Intext Questions

Page No: 269

1. What changes can you make in your habits to become more environment-friendly?

Answer

We can be eco-friendly by:
→ Using the principle of 3R’s i.e. Reduce, Reuse and Recycle.
→ Putting off unnecessary lights and fans.
→ Using unleaded petrol in vehicles.
→ Using local transport like buses or train.

2. What would be the advantages of exploiting resources with short-term aims?

Answer

If resources are exploited with short-term aims it will be very beneficial for the present generation as it will help in growth of economy at a faster rate.

3. How would these advantages differ from the advantages of using a long-term perspective in managing our resources?

Answer

If resources are used in accordance with short term aims, present generation will be able to utilize the resources properly for growth and development.
But if we use resources with long term aims, future generation will also be able to utilize resources for fulfilling its needs.

Thus it would be better to use our natural resources with a long term perspective so that it could be used by the present generation as well as conserved for future use. But it will deprive future generation from the benefits of these resources as resources are exhaustible.

4. Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources?

Answer

Natural resources of the Earth must be distributed among the people uniformly so that each and every one gets his share of the resource.
Human greed, corruption, and the lobby of the rich and powerful are the forces working against an equitable distribution of resources.

Page No: 273

1. Why should we conserve forests and wildlife?

Answer

We should conserve forests and wildlife because they are essential for us in following terms:
→ Forest provide us oxygen, they cause rain fall.
→ Forest prevents soil erosion.
→ Plants are dependent on animals and birds for their pollination and seed dispersal.
→ Forests provide us various medicines.
→ Various forest products are used as raw materials in industries.

2. Suggest some approaches towards the conservation of forests.

Answer

Some approaches towards the conservation of forests are:
→ Conversion of forests into national parks, sanctuaries.

→ To take help of local people in conserving forest.
→ Not to allow the destruction of forests for making roads, dams and hotels etc.
→ Planting of trees should be increased.

Page No: 276

2. Compare the above system with the probable systems in hilly/mountainous areas or plains or plateau regions.

Answer

In plains, the water harvesting structures are crescent-shaped earthen embankments. These are low, straight, and concrete.
In hilly regions, the system of canal irrigation called Kulhsis used for water harvesting. This involves a collection of rain water in a stream, which is then diverted into man-made channels down the hill sides.

NCERT Solutions for Class 10 Science Chapter 16 Exercise Questions

Exercise

1. What changes would you suggest in your home in order to be environment-friendly?

Answer

Changes that can be undertaken in our homes to be environment-friendly are:
→ Switch off the electrical appliances when not in use.
→ Turn the taps off while brushing or bathing and repair the leaking taps.
→ Throw biodegradable and non-biodegradable waste into separate bins.
→ Construct composting pits.
→ Food items such as jam, pickles, etc., come packed in plastic bottles. These bottles can later be used for storing things in the kitchen.

2. Can you suggest some changes in your school which would make it environment-friendly?

Answer

Changes that can be undertaken in our schools to make it environment friendly are:

→ Electricity can be saved by switching off lights and fans when not required.
→ Turn the taps off when not in use.
→ Biodegradable and non-biodegradable wastes should be thrown into separate bins.

3. We saw in this chapter that there are four main stakeholders when it comes to forests and wildlife. Which among these should have the authority to decide the management of forest produce? Why do you think so?

Answer

The forest department of the government should have the authority to decide the management of forest produces. This is because the forest department is the care taker of the forest land and is responsible for any damage to the forest.

Page No: 279

4. How can you as an individual contribute or make a difference to the management of (a) forests and wildlife, (b) water resources and (c) coal and petroleum?

Answer

(a) Forest and wildlife:
→ We should protest against the cutting of trees (deforestation).
→ We should protest against the poaching of wild animals.
→ We should stop the annexation of forest land for our use.

(b) Water resources:
→ Turn the taps off while brushing or bathing and repair leaking taps.
→ We should practice rainwater harvesting.
→ We should avoid the discharge of sewage and other wastes into rivers and other water resources.

(c) Coal and petroleum:
→We should take a bus or practice car pooling to avoid excessive use of petroleum.

→ We should stop using coal as a fuel (angithis).

(iii)We should use alternative sources of energy such as hydro-energy and solar energy instead of depending largely on coal and petroleum.

5. What can you as an individual do to reduce your consumption of the various natural resources?

Answer

Natural resources such as water, forests, coal and petroleum, etc. are important for the survival of human beings. The ways in which we can reduce the consumption of various natural resources are:
→ We should stop the cutting of trees (deforestation).
→ We should use recycled paper to reduce the cutting down of trees.
→ We should not waste water.
→ We should practice rainwater harvesting.
→ We should practice car pooling to avoid the excessive use of petroleum.
→ We should use alternative sources of energy such as hydro-energy and solar energy.

7. On the basis of the issues raised in this chapter, what changes would you incorporate in your life-style in a move towards sustainable use of our resources?

Answer

One should incorporate the following changes in life-style in a move towards sustainable use of our resources:
→ Stop cutting trees and practice plantation of trees.
→ Stop using plastic and polythene bags for carrying goods.
→ Use recycled paper.
→ Throw biodegradable and non-biodegradable waste into separate bins.
→ Waste minimum amount of water while using and repair leaking taps.
→ Practice rainwater harvesting.
→ Avoid using vehicles for short distances. Instead, one can walk or cycle to cover short distances. → To cover long distances, one should take a bus instead of using personal vehicles.
→ Switch off electrical appliances when not in use.
→ Use fluorescent tubes in place of bulbs to save electricity.
→ Take stairs and avoid using lifts.
→ During winters, wear an extra sweater to avoid using heaters.

Important Links

Quick Revision Notes – Chapter 16 Sustainable Management of Natural Resources

Most Important Questions- Chapter 16 Sustainable Management of Natural Resources

Important MCQs- Chapter 16 Sustainable Management of Natural Resources

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NCERT Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Solutions for Class 10 Science Chapter 15 Our Environment includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 15 Intext Questions

Page No: 257

1. Why are some substances biodegradable and some non-biodegradable?

Answer

Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.
Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.

2. Give any two ways in which biodegradable substances would affect the environment.

Answer

Biodegradable substances affect the environment by:
→ The biodegradable substances such as tree leaves, plant parts, and kitchen wastes can be used as humus after composting. This will enhance the soil fertility.
→ The biodegradable substances mainly contain carbon. These substances after decomposition release that carbon back into the atmosphere.

3. Give any two ways in which non-biodegradable substances would affect the environment.

Answer

Non-biodegradable substances affect the environment by:
→ They contaminate soil and water resources as they cannot be decomposed by micro-organisms.

→ These substances, when accidentally eaten by stray animals, can harm them and can even cause their death.

Page No: 261

1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Answer

The various links or steps in a food chain at which the transfer of food and energy takes place are called trophic levels.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.

In the above fig. Grass is the producer which is eaten by the grasshooper known as primary consumer. Then the grasshooper is eaten by shrew, secondary consumer and lastly shrew eaten up by owl, tertiary conusmer.

2. What is the role of decomposers in the ecosystem?

Answer

Various role played by decomposers in the ecosystem are:
→ They clean the environment.
→ They decompose biodegradable substances into useful substances.
→ They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.

→ They maintain the nutrient pool by returning back the nutrients in the pool.

Page No: 264

1. What is ozone and how does it affect any ecosystem?

Answer

Ozone (O3) is a molecule, made up of three atoms of oxygen.
Ozone (O3) forms a layer in the upper atmosphere. It is very essential for the life on this planet. It shields the surface of the earth from ultra-violet radiation (UV) coming from sun as these radiations are very harmful causing skin cancer and cataract in humans. It also does harm to the crops.

2. How can you help in reducing the problem of waste disposal? Give any two methods.

Answer

We can help in reducing the problem of waste disposal by these methods:
→ By separating biodegradable substances from non-biodegradable substances.

→ By reducing, reusing and recycling non-biodegradable substances.

NCERT Solutions for Class 10 Science Chapter 15 Exercise Questions

Exercise

1. 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
► (c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass

2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
► (b) Grass, goat and human

3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above

► (d) All of the above

Page No: 265

4. What will happen if we kill all the organisms in one trophic level?

Answer

If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an Example, In a food chain Grass → Dear → Lion, If we remove all lions then population of deer will increase which will cause over-grazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.

5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?

Answer

Impact of removing all organisms of a trophic level is different for different trophic levels.

For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can’t remove any trophic level without causing damage to the ecosystem as one is dependent on other for their survival. If we remove any one this will create imbalnce in the ecosystem.

6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Answer

Biological magnification is defined as the phenomena of accumulation or increase in the concentration of some toxic substances at each trophic level.

The levels of biomagnification will be different at different trophic levels. For example, in a pond of water, DDT was sprayed and the producers were found to have 0.04 ppm concentration of DDT. Since many types of planktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as one sea gull eats many clams. Hawk, the top carnivore, has the highest concentration of DDT.

7. What are the problems caused by the non-biodegradable wastes that we generate?

Answer

The problems caused by non-biodegradable wastes are:
→ The cause biomagnification.
→ They increase pollution.
→ They make environment unclean.
→ They kill useful microorganisms.

8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Answer

If all the waste generated would be biodegradable this will also create problem. As the numbers of decomposers will be quite low so wastes cannot be broken down into harmless simpler substance at right time. It will became breeding ground for flies causing spread of diseases. It will also emits foul smell which makes the life of people miserable.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Answer

The damage to the ozone layer a cause for concern because:
→ It causes skin darkening, skin cancer, ageing, and corneal cataracts in human beings.
→ It can result in the death of many phytoplanktons that leads to increased global warming.

To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally-safe alternatives. Also, the release of CFCs through industrial activities should be controlled.

Important Links

Quick Revision Notes – Chapter 15 Our Environment

Most Important Questions- Chapter 15 Our Environment

Important MCQs- Chapter 15 Our Environment

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NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

NCERT Solutions for Class 10 Science CChapter 14 Sources of Energy

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 14 Intext Questions

Page No: 243

1. What is a good source of energy?

Answer

A good source of energy fulfils the following criteria:
→ It produces a lot of heat per unit mass.
→ It does a huge amount of work per unit mass.
→ It is easily accessible.
→ It is easy to store and transport.
→ It is economical.
→ It produces less amount of smoke.

2. What is a good fuel?

Answer

A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.

3. If you could use any source of energy for heating your food, which one would you use and why?

Answer

Natural gas can be used for heating and cooking food because it is a clean source of energy. It does not produce huge amount of smoke on burning. Although it is highly inflammable, it is easy to use, transport, and it produces a huge amount of heat on burning.

Page No: 248

1. What are the disadvantages of fossil fuels?

Answer

The disadvantages of fossil fuels are:
→ Burning of coal and petroleum produces a lot of pollutants causing air pollution.
→ Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and potable water.
→ Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.

2. Why are we looking at alternate sources of energy?

Answer

Fossil fuels which are traditionally used by human beings everywhere as an energy sources are non-renewable sources of energy. These sources of energy are limited and will disappear after some time. They are being consumed at a large rate. Therefore, we should conserve the energy sources. Hence, we should look for alternate sources of energy.

3. How has the traditional use of wind and water energy been modified for our convenience?

Answer

Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting/drawing water from a well. Today, windmills are used to generate electricity.In windmills, the kinetic energy of wind is harnessed and converted into electricity.
Water energy which was used for transportation before is now a good source to generate electricity. Dams has been constructed on river for generating electricity. Waterfalls were used as a source of potential energy which was converted to electricity with the help of turbines.

Page No: 253

1. What kind of mirror – concave, convex or plain – would be best suited for use in a solar cooker? Why?

Answer

A concave mirror is used in a solar cooker as it uses heat of the sunlight to cook food. The mirror focuses all the incident sunlight at a point. The temperature at that point increases, thereby cooking and heating the food placed at that point.

2. What are the limitations of the energy that can be obtained from the oceans?

Answer

The forms of energy that can be obtained from the ocean are tidal energy, wave energy, and ocean thermal energy. There are several limitations in order to harness these energies.
→ Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
→ High dams are required to be built to convert tidal energy into electricity.
→ Very strong waves are required to obtain electricity from wave energy.
→ To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20ºC or more.

3. What is geothermal energy?

Answer

Geothermal power plants use heat of the Earth to generate electricity. This heat energy of the Earth is known as geothermal energy.

4. What are the advantages of nuclear energy?

Answer

The advantages of nuclear energy are:
→ Large amount of energy is produced per unit mass.
→ It does not produce smoke. It is a clean energy.
→ Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon.
→ Fusion of four hydrogen atoms produces huge amount of energy approximately equal to 27 MeV.

1. Can any source of energy be pollution-free? Why or why not?

Answer

No source of energy can be pollution-free. Every source of energy has some type of pollution. For example, the wastes of nuclear reaction are very dangerous to the environment.

2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Answer

Hydrogen gas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon contents. Carbon is a form of pollutant present in CNG. On the other hand, hydrogen is waste-free. The fusion of hydrogen does not produce any waste. Hence, hydrogen is cleaner than CNG.

Page No: 254

1. Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Answer

Two renewable sources of energy are :
→ Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium, fusion of helium into other heavy elements, and so on. A large amount of hydrogen and helium is present in the Sun. The Sun has billions years more to burn. Therefore solar energy is a renewable source of energy.
→ Wind: Wind energy is derived from fast blowing air. Wind energy is harnessed by windmills in order to generate electricity. Air blows because of uneven heating of the Earth. Since the heating of the Earth will continue forever therefore wind energy will also be available forever.

2. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Answer

Two exhaustible energy sources are as follows:
→ Coal: It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non-renewable or exhaustible source of energy.
→ Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the Earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.

NCERT Solutions for Class 10 Science Chapter 14 Exercise Questions

Exercise

1. A solar water heater cannot be used to get hot water on
(a) a sunny day

(b) a cloudy day
(c) a hot day

(d) a windy day

► (b) a cloudy day

Page No: 255

2. Which of the following is not an example of a bio-mass energy source?
(a) wood
(b) gobar gas
(c) nuclear energy
(d) coal
► (c) nuclear energy

3. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Bio-mass
► (c) Nuclear energy

4. Compare and contrast fossil fuels and the Sun as direct sources of energy.

Answer

Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath the Earth’s crust. They are directly available to human beings for use. Hence, fossil fuels are the direct source of energy. These are limited in amount. These are non-renewable sources of energy because these cannot be replenished in nature. Fossil fuels take millions of years for their formation. If the present fossil fuel of the Earth gets exhausted, its formation will take several years. Fossil fuels are also very costly.
On the other hand, solar energy is a renewable and direct source of energy. The Sun has been shining for several years and will do so for the next five billion years. Solar energy is available free of cost to all in unlimited amount. It replenishes in the Sun itself.

5. Compare and contrast bio-mass and hydro electricity as sources of energy.

Answer

Bio-mass and hydro-electricity both are renewable sources of energy. Bio-mass is derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the result of natural processes. Wood, gobargas, etc. are some of the examples of bio-mass.
Hydro-electricity, on the other hand, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.

6. What are the limitations of extracting energy from –
(a) the wind? (b) waves? (c) tides?

Answer

(a) A windmill requires wind of speed more than 15 km/h to generate electricity from wind energy also large numbers of windmills are required to get feasible output which covers a large area.

(b) Very strong ocean waves are required in order to extract energy from waves.

(c) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.

7. On what basis would you classify energy sources as
(a) renewable and non-renewable?
(b) exhaustible and inexhaustible?
Are the options given in (a) and (b) the same?

Answer

(a) The source of energy that replenishes in nature is known as renewable source of energy. Sun, wind, moving water, bio-mass, etc. are some of the examples of renewable sources of energy.
The source of energy that does not replenish in nature is known as non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non-renewable sources of energy.

(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.

Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Bio-mass is one of the inexhaustible sources of energy.

Yes. The options given in (a) and (b) are the same.

8. What are the qualities of an ideal source of energy?

Answer

An ideal source of energy must be:
→ Economical
→ Easily accessible
→ Smoke/pollution free
→ Easy to store and transport
→ Able to produce huge amount of heat and energy on burning

9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Answer

Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amount. Hence, operating a solar cooker is not expensive.
Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy day, it becomes useless.

The places where the days are too short or places with cloud covers round the year, have limited utility for solar cooker.

10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Answer

Industrialization increases the demand for energy. Fossil fuels are easily accessible sources of energy that fulfil this demand. The increased use of fossil fuels has a harsh effect on the environment. Too much exploitation of fossil fuels increases the level of green house gas content in the atmosphere, resulting in global warming and a rise in the sea level.
It is not possible to completely reduce the consumption of fossil fuels. However, some measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.

Important Links

Quick Revision Notes – Chapter 14 Sources of Energy

Most Important Questions- Chapter 14 Sources of Energy

Important MCQs- Chapter 14 Sources of Energy

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NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 13 Science Chapter 12 Intext Questions

Page No: 224

1. Why does a compass needle get deflected when brought near a bar magnet?

Answer

The needle of a compass is a small magnet. That’s why when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected.

Page No: 228

1. Draw magnetic field lines around a bar magnet.

Answer

Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.

2. List the properties of magnetic lines of force.

Answer

The properties of magnetic lines of force are as follows.
→ Magnetic field lines emerge from the north pole.
→ They merge at the south pole.
→ The direction of field lines inside the magnet is from the south pole to the north pole.
→ Magnetic lines do not intersect with each other.

3. Why don’t two magnetic lines of force intersect each other?

Answer

The two magnetic field lines do not intersect each other because if they do it means at the point of intersect the compass needle is showing two different directions which is not possible.

Page No: 229

1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Answer

Inside the loop = Pierce inside the table
Outside the loop = Appear to emerge out from the table
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.

2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

Answer

The magnetic field lines inside a current-carrying long straight solenoid are uniform.

Page No: 230

3. Choose the correct option.

The magnetic field inside a long straight solenoid-carrying current

(a) is zero
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points

► (d) is the same at all points

Page No: 231

1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum

► (c) velocity and (d) momentum

Page No: 232

2. In Activity 13.7 (page: 230), how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?

Answer

The displacement of rod AB is increased due to magnetic force exerted on it, if :

(i) If the current in the rod is increased then rod will be deflected with greater force.

(ii) If a stronger horse-shoe magnet is used then also rod will be deflected with greater force due to the increase in magnetic field.

(iii) If the length of the rod AB is increased.

3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward

► (d) upward

Page No: 233

1. State Fleming’s left-hand rule.

Answer

Fleming’s left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.

2. What is the principle of an electric motor?

Answer

The principle of an electric motor is based on the magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is according to the Fleming’s left-hand rule.

3. What is the role of the split ring in an electric motor?

Answer

The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coil after every half rotation of the coil. Due to this the coil continues to rotate in the same direction.

Page No: 236

1. Explain different ways to induce current in a coil.

Answer

The different ways to induce current in a coil are as follows:
→ If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
→ If a magnet is moved relative to a coil, then an electric current is induced in the coil.

Page No: 237

1. State the principle of an electric generator.

Answer

Electric generator works on the principle of electromagnetic induction. Electricity is generated by rotating a coil inside magnetic field.

2. Name some sources of direct current.

Answer

Some sources of direct current are cell, DC generator, etc.

3. Which sources produce alternating current?

Answer

AC generators, power plants, etc., produce alternating current.

4. Choose the correct option.

A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
► (c) half revolution

Page No: 238

1. Name two safety measures commonly used in electric circuits and appliances.

Answer

Two safety measures commonly used in electric circuits and appliances are
→ Electric Fuse: An electric fuse is connected in series it protects the circuit from overloading and prevents it from short circuiting.
→ Proper earthing of all electric circuit in which any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.

2. An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

Answer

Current drawn by the electric oven can be obtained by the expression,
P = VI

Where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V

I = 2000/220 V = 9.09 A
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.

3. What precaution should be taken to avoid the overloading of domestic electric circuits?

Answer

The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
→ Too many appliances should not be connected to a single socket.
→ Too many appliances should not be used at the same time.
→ Faulty appliances should not be connected in the circuit.
→ Fuse should be connected in the circuit.

NCERT Solutions for Class 10 Science Chapter 13 Exercise Questions

Exercise

1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centred on the wire
► (d) The field consists of concentric circles centred on the wire

2. The phenomenon of electromagnetic induction is
(a) the process of charging a body
(b) the process of generating magnetic field due to a current passing through a coil
(c) producing induced current in a coil due to relative motion between a magnet and the coil
(d) the process of rotating a coil of an electric motor
► (c) producing induced current in a coil due to relative motion between a magnet and the coil

3. The device used for producing electric current is called a
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
► (a) generator

4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
► (d) AC generator has slip rings while the DC generator has a commutator.

5. At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously
► (c) increases heavily

6. State whether the following statements are true or false.

(a) An electric motor converts mechanical energy into electrical energy.
► False

An electric motor converts electrical energy into mechanical energy.

(b) An electric generator works on the principle of electromagnetic induction.

► True

(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.

► True

(d) A wire with a green insulation is usually the live wire of an electric supply.

► False
Live wire has red insulation cover, whereas earth wire has green insulation colour in the domestic circuits.

7. List three sources of magnetic fields.

Answer

Three sources of magnetic fields are as follows:
→ Current-carrying conductors
→ Permanent magnets
→ Electromagnets

Page No: 241

8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.

Answer

A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure.

Magnetic Field in current carrying solenoid

In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.

9. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

Answer

The force experienced by a current-currying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field.

10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

Answer

The direction of the magnetic field is vertically downwards. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.

11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

Answer

Principle: It works on the principle of the magnetic effect of current. A current-carrying coil rotates in a magnetic field.

Working: When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.

Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming’s left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise.
After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
The current flows through the coil in the direction TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional.

The split rings help to reverse the direction of current in the circuit. These are called the commutator.

12. Name some devices in which electric motors are used?

Answer

Some devices in which electric motors are Water pumps, Electric fans, Electric mixers and Washing machines.

13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?

Answer

(i) The needle of the galvanometer shows a momentary deflection in a particular direction.

(ii) The needle of the galvanometer shows a momentarily in the opposite direction.

(iii) The needle of the galvanometer shows no deflection.

14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

Answer

Two circular coils A and B are placed close to each other. When the current in coil A is changed, the magnetic field associated with it also changes. As a result, the magnetic field around coil B also changes. This change in magnetic field lines around coil B induces an electric current in it. This is called electromagnetic induction.

15. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.

Answer

(i) Maxwell’s right hand thumb rule

(ii) Fleming’s left hand rule

(iii) Fleming’s right hand rule

16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer

Principle: An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming’s right hand rule.

Working: Let in the beginning, as shown in Fig. brushes B₁ and B₂ are kept pressed separately on rings R₁ and R₂ respectively. Let the axle attached to the rings is rotated such that arm AB of the coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms AB and CD induced currents are set up in them. As per Fleming’s right hand rule induced currents in these arms are along the directions AB and CD. Thus an induced current flows along ABCD and current in the external circuit flows from B₂ to B₁.
After half a rotation, arm AB starts moving down and the arm CD upward. Therefore, directions of induced currents in these arms change. Thus net induced current now becomes in the direction DCBA. In the external circuit now current flows from B₁ to B₂. Thus after every half rotation current changes its direction and an alternating current is obtained from the generator.

Function of Brushes: Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes are connected to the galvanometer (or the external load). Thus brushes help in transferring current from the coil ABCD to the external circuit.

17. When does an electric short circuit occur?

Answer

If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs.

18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer

The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.

Important Links

Quick Revision Notes – Chapter 13 Magnetic Effects of Electric Current

Most Important Questions- Chapter 13 Magnetic Effects of Electric Current

Important MCQs- Chapter 13 Magnetic Effects of Electric Current

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NCERT Solutions for Class 10 Science Chapter 12 Electricity

NCERT Solutions for Class 10 Science Chapter 12 Electricity includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 12 Intext Questions

Page No: 200

1. What does an electric circuit mean?

Answer

A continuous and closed path of an electric current is called an electric circuit. An electric circuit consists of electric devices, source of electricity and wires that are connected with the help of a switch.

2. Define the unit of current.

Answer

The unit of electric current is ampere (A). 1 A is defined as the flow of 1 C of charge through a wire in 1 s.

3. Calculate the number of electrons constituting one coulomb of charge.

Answer

One electron possesses a charge of 1.6 ×10^-19C, i.e., 1.6 ×10^-19C of charge is contained in 1 electron.

∴ 1 C of charge is contained in 1/1.6 x 10^-19 = 6.25 x 10¹⁸ = 6 x 10¹⁸

Therefore, 6 x 10¹⁸ electrons constitute one coulomb of charge.

Page No: 202

1. Name a device that helps to maintain a potential difference across a conductor.

Answer

Any source of electricity like battery, cell, power supply, etc. helps to maintain a potential difference across a conductor.

2. What is meant by saying that the potential difference between two points is 1 V?

Answer

If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is said that the potential difference between the two points is 1 V.

3. How much energy is given to each coulomb of charge passing through a 6 V battery?

Answer

The energy given to each coulomb of charge is equal to the amount of work which is done in moving it.
Now we know that,
Potential difference = Work Done/Charge
∴ Work done = Potential difference × charge
Where, Charge = 1 C and Potential difference = 6 V
∴ Work done = 6×1
= 6 Joule.

Page No: 209

1. On what factors does the resistance of a conductor depend?

Answer

The resistance of a conductor depends upon the following factors:
→ Length of the conductor
→ Cross-sectional area of the conductor
→ Material of the conductor
→ Temperature of the conductor

2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

Answer

The current will flow more easily through thick wire. It is because the resistance of a
conductor is inversely proportional to its area of cross – section. If thicker the wire, less is resistance and hence more easily the current flows.

3. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

Answer

According to Ohm’s law
V = IR
⇒ I=V/R … (1)
Now Potential difference is decreased to half
∴ New potential difference Vʹ=V/2
Resistance remains constant
So the new current Iʹ = Vʹ/R
= (V/2)/R
= (1/2) (V/R)
= (1/2) I = I/2

Therefore, the amount of current flowing through the electrical component is reduced by half.

4. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

Answer

The resistivity of an alloy is higher than the pure metal. Moreover, at high temperatures, the alloys do not melt readily. Hence, the coils of heating appliances such as electric toasters and electric irons are made of an alloy rather than a pure metal.

5. Use the data in Table 12.2 to answer the following –
Table 12.2 Electrical resistivity of some substances at 20°C

−	Material	Resistivity (Ω m)
Conductors	Silver	1.60 × 10⁻⁸
	Copper	1.62 × 10⁻⁸
	Aluminium	2.63 × 10⁻⁸
	Tungsten	5.20 × 10⁻⁸
	Nickel	6.84 × 10⁻⁸
	Iron	10.0 × 10⁻⁸
	Chromium	12.9 × 10⁻⁸
	Mercury	94.0 × 10⁻⁸
	Manganese	1.84 × 10⁻⁶
	Constantan (alloy of Cu and Ni)	49 × 10⁻⁶
Alloys	Manganin (alloy of Cu, Mn and Ni)	44 × 10⁻⁶
	Nichrome (alloy of Ni, Cr, Mn and Fe)	100 × 10⁻⁶
	Glass	10¹⁰ − 10¹⁴
Insulators	Hard rubber	10¹³ − 10¹⁶
	Ebonite	10¹⁵ − 10¹⁷
	Diamond	10¹² − 10¹³
	Paper (dry)	10¹²

Answer

(a) Resistivity of iron = 10.0 x 10^-8 Ω
Resistivity of mercury = 94.0 x 10^-8 Ω
Resistivity of mercury is more than that of iron. This implies that iron is a better conductor than mercury.

(b) It can be observed from Table 12.2 that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.

Page No: 213

1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.

Answer

Three cells of potential 2 V, each connected in series therefore the potential difference of the battery will be 2 V + 2 V + 2 V = 6V. The following circuit diagram shows three resistors of resistances 5 Ω, 8 Ω and 12 Ω respectively connected in series and a battery of potential 6 V and a plug key which is closed means the current is flowing in the circuit.

2. Redraw the circuit of question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter?

Answer

An ammeter should be connected in the circuit in series with the resistors. To measure the potential difference across the resistor it should be connected in parallel, as shown in the following figure.

The resistances are connected in series.
Ohm’s law can be used to obtain the readings of ammeter and voltmeter. According to Ohm’s law,
V = IR,
Where,
Potential difference, V = 6 V
Current flowing through the circuit/resistors = I
Resistance of the circuit, R = 5 + 8 + 12 = 25Ω
I = V/R = 6/25 = 0.24 A
Potential difference across 12 Ω resistor = V₁
Current flowing through the 12 Ω resistor, I = 0.24 A
Therefore, using Ohm’s law, we obtain
V₁ = IR = 0.24 x 12 = 2.88 V
Therefore, the reading of the ammeter will be 0.24 A.
The reading of the voltmeter will be 2.88 V.

Page No: 216

1. Judge the equivalent resistance when the following are connected in parallel − (a) 1 Ω and 10⁶Ω, (b) 1 Ω and 10³Ω and 10⁶Ω.

Answer

(a) When 1 Ω and 10⁶ Ω are connected in parallel:
Let R be the equivalent resistance.

Therefore, equivalent resistance ≈ 1 Ω

(b) When 1Ω, 103 Ω and 106 Ω are connected in parallel:

Let R be the equivalent resistance.

Therefore, equivalent resistance = 0.999 Ω

2. An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Answer

Resistance of electric lamp, R₁ = 100 Ω
Resistance of toaster, R₂ = 50 Ω
Resistance of water filter, R₃ = 500 Ω
Potential difference of the source, V = 220 V
These are connected in parallel, as shown in the following figure.

Let R be the equivalent resistance of the circuit.

3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

Answer

There is no division of voltage among the appliances when connected in parallel. The potential difference across each appliance is equal to the supplied voltage.
The total effective resistance of the circuit can be reduced by connecting electrical appliances in parallel.

4. How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?

Answer

There are three resistors of resistances 2 Ω, 3 Ω, and 6 Ω respectively.

(a) The following circuit diagram shows the connection of the three resistors.

Here, 6 Ω and 3 Ω resistors are connected in parallel.
Therefore, their equivalent resistance will be given by

This equivalent resistor of resistance 2 Ω is connected to a 2 Ω resistor in series.
Therefore, the equivalent resistance of the circuit = 2 Ω + 2 Ω = 4 Ω
Hence the total resistance of the circuit is 4 Ω.

(b) The following circuit diagram shows the connection of the three resistors.

All the resistors are connected in series. Therefore, their equivalent resistance will be given as

Therefore, the total resistance of the circuit is 1 Ω.

5. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?

Answer

There are four coils of resistances 4 Ω, 8 Ω, 12 Ω and 24 Ω respectively.

(a) If these coils are connected in series, then the equivalent resistance will be the highest, given by the sum 4 + 8 + 12 + 24 = 48 Ω

(b) If these coils are connected in parallel, then the equivalent resistance will be the lowest, given by

Therefore, 2 Ω is the lowest total resistance.

Page No: 218

1. Why does the cord of an electric heater not glow while the heating element does?

Answer

The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminium is very law so it does not glow.

2. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

Answer

Given Charge, Q = 96000C
Time, t= 1hr = 60 x 60= 3600s
Potential difference, V= 50volts
Now we know that H= VIt
So we have to calculate I first
As I= Q/t
∴ I = 96000/3600 = 80/3 A

Therefore, the heat generated is 4.8 x 10⁶ J.

3. An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Answer

The amount of heat (H) produced is given by the joule’s law of heating asH= Vlt
Where,
Current, I = 5 A
Time, t = 30 s
Voltage, V = Current x Resistance = 5 x 20 = 100 V

H= 100 x 5 x 30 = 1.5 x 10⁴ J.

Therefore, the amount of heat developed in the electric iron is 1.5 x 10⁴ J.

Page No: 220

1. What determines the rate at which energy is delivered by a current?

Answer

The rate of consumption of electric energy in an electric appliance is called electric power. Hence, the rate at which energy is delivered by a current is the power of the appliance.

2. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.

Answer

Power (P) is given by the expression,P = VI
Where,
Voltage,V = 220 V
Current, I = 5 A
P= 220 x 5 = 1100 W
Energy consumed by the motor = Pt
Where,
Time, t = 2 h = 2 x 60 x 60 = 7200 s
∴ P = 1100 x 7200 = 7.92 x 10⁶ J
Therefore, power of the motor = 1100 W
Energy consumed by the motor = 7.92 x 10⁶ J

NCERT Solutions for Class 10 Science Chapter 12 Exercise Questions

Exercise

1. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is -(a) 1/25
(b) 1/5
(c) 5
(d) 25
► (d) 25

2. Which of the following terms does not represent electrical power in a circuit?
(a) I²R
(b) IR²
(c) VI
(d) V²/R
► (b) IR²
3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W
► (d) 25 W

4. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –

(a) 1:2

(b) 2:1

(d) 4:1

► (c) 1:4

5. How is a voltmeter connected in the circuit to measure the potential difference between two points?

Answer

To measure the potential difference between two points, a voltmeter should be connected in parallel to the points.

6. A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10⁻⁸ Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

Answer

Area of cross-section of the wire, A =π (d/2) 2
Diameter= 0.5 mm = 0.0005 m
Resistance, R = 10 Ω
We know that

Therefore, the length of the wire is 122.7 m and the new resistance is 2.5 Ω.

7. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below −

I (amperes )	0.5	1.0	2.0	3.0	4.0
V (volts)	1.6	3.4	6.7	10.2	13.2

Plot a graph between V and I and calculate the resistance of that resistor.

Answer

The plot between voltage and current is called IV characteristic. The voltage is plotted on x-axis and current is plotted on y-axis. The values of the current for different values of the voltage are shown in the given table.

V (volts)	1.6	3.4	6.7	10.2	13.2
I (amperes )	0.5	1.0	2.0	3.0	4.0

The IV characteristic of the given resistor is plotted in the following figure.

The slope of the line gives the value of resistance (R) as,

Slope = 1/R = BC/AC = 2/6.8

R= 6.8/2 = 3.4 Ω

Therefore, the resistance of the resistor is 3.4 Ω.

8. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Answer

Resistance (R) of a resistor is given by Ohm’s law as,V= IR
R= V/I
Where,
Potential difference, V= 12 V
Current in the circuit, I= 2.5 mA = 2.5 x 10^-3 A

Therefore, the resistance of the resistor is 4.8 kΩ

9. A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?

Answer

There is no current division occurring in a series circuit. Current flow through the component is the same, given by Ohm’s law as

V= IR

I= V/R

Where,

R is the equivalent resistance of resistances 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω. These are connected in series. Hence, the sum of the resistances will give the value of R.

R= 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4 Ω

Potential difference, V= 9 V

I= 9/13.4 = 0.671 A
Therefore, the current that would flow through the 12 Ω resistor is 0.671 A.

10. How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?

Answer

For x number of resistors of resistance 176 Ω, the equivalent resistance of the resistors connected in parallel is given by Ohm’s law asV= IR
R= V/I
Where,
Supply voltage, V= 220 V
Current, I = 5 A
Equivalent resistance of the combination = R,given as

Therefore, four resistors of 176 Ω are required to draw the given amount of current.

11. Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.

Answer

If we connect the resistors in series, then the equivalent resistance will be the sum of the resistors, i.e., 6 Ω + 6 Ω + 6 Ω = 18 Ω, which is not desired. If we connect the resistors in parallel, then the equivalent resistance will be 6/2 = 3 Ω is also not desired. Hence, we should either connect the two resistors in series or parallel.
(a) Two resistor in parallel

Two 6 Ω resistors are connected in parallel. Their equivalent resistance will be

The third 6 Ω resistor is in series with 3 Ω. Hence, the equivalent resistance of the circuit is 6 Ω+ 3 Ω = 9 Ω.
(b) Two resistor in series

Two 6 Ω resistors are in series. Their equivalent resistance will be the sum 6 + 6 = 12 Ω.

The third 6 Ω resistor is in parallel with 12 Ω. Hence, equivalent resistance will be

Therefore, the total resistance is 4 Ω.

12. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

Answer

Resistance R₁ of the bulb is given by the expression,
Supply voltage, V = 220 V
Maximum allowable current, I = 5 A
Rating of an electric bulb P=10watts
Because R=V²/P

∴ Number of electric bulbs connected in parallel are 110.

13. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?

Answer

Supply voltage, V= 220 V
Resistance of one coil, R= 24 Ω

(i) Coils are used separately

According to Ohm’s law,
V= I₁R₁
Where,

I₁ is the current flowing through the coil

I₁ = V/R₁ = 220/24 = 9.166 A
Therefore, 9.16 A current will flow through the coil when used separately.

(ii) Coils are connected in series

Total resistance, R₂ = 24 Ω + 24 Ω = 48 Ω

According to Ohm’s law,V = I₂R₂
Where,

I₂is the current flowing through the series circuit

I₂= V/R₂ = 220/48 = 4.58 A
Therefore, 4.58 A current will flow through the circuit when the coils are connected in series.
(iii) Coils are connected in parallel

Total resistance, R₃ is given as =

According to Ohm’s law,

V= I₃R₃
Where,
I₃ is the current flowing through the circuit I₃ = V/R₃ = 220/12 = 18.33 A
Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.

14. Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

Answer

(i) Potential difference, V = 6 V
1 Ω and 2 Ω resistors are connected in series. Therefore, equivalent resistance of the circuit, R = 1 + 2 = 3 Ω
According to Ohm’s law,
V = IR
Where,
I is the current through the circuit
I= 6/3 = 2 A
This current will flow through each component of the circuit because there is no division of current in series circuits. Hence, current flowing through the 2 Ω resistor is 2 A. Power is given by the expression,
P= (I)²R = (2)² x 2 = 8 W

(ii) Potential difference, V = 4 V
12 Ω and 2 Ω resistors are connected in parallel. The voltage across each component of a parallel circuit remains the same. Hence, the voltage across 2 Ω resistor will be 4 V.
Power consumed by 2 Ω resistor is given by
P= V²/R = 4²/2 = 8 W
Therefore, the power used by 2 Ω resistor is 8 W.

15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Answer

Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage occurs in a parallel circuit.
Current drawn by the bulb of rating 100 W is given by,Power = Voltage x Current
Current = Power/Voltage = 60/220 A
Hence, current drawn from the line = 100/220 + 60/220 = 0.727 A

16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Answer

Energy consumed by an electrical appliance is given by the expression,H= Pt
Where,
Power of the appliance = P
Time = t
Energy consumed by a TV set of power 250 W in 1 h = 250 ×3600 = 9 ×10⁵ J
Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600
Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600
= 7.2×10⁵ J
Therefore, the energy consumed by a 250 W TV set in 1 h is more than the energy consumed by a toaster of power 1200 W in 10 minutes.

17. An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

Answer

Rate of heat produced by a device is given by the expression for power as, P= I²R
Where,
Resistance of the electric heater, R= 8 Ω
Current drawn, I = 15 A

P= (15)² x 8 = 1800 J/s

Therefore, heat is produced by the heater at the rate of 1800 J/s.

18. Explain the following.
(a) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?

Answer

(a) The melting point and of Tungsten is an alloy which has very high melting point and very high resistivity so does not burn easily at a high temperature.

(b) The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because resistivity of an alloy is more than that of metals which produces large amount of heat.

(c) In series circuits voltage is divided. Each component of a series circuit receives a small voltage so the amount of current decreases and the device becomes hot and does not work properly. Hence, series arrangement is not used in domestic circuits.

(d) Resistance (R) of a wire is inversely proportional to its area of cross-section (A), i.e. when area of cross section increases the resistance decreases or vice versa.

(e) Copper and aluminium are good conductors of electricity also they have low resistivity. So they are usually used for electricity transmission.

Important Links

Quick Revision Notes – Chapter 12 Electricity

Most Important Questions- Chapter 12 Electricity

Important MCQs- Chapter 12 Electricity

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NCERT Solutions for Class 10 Science Chapter 11 Human Eye and the Colourful World

NCERT Solutions for Class 10 Science Chapter 11 Human Eye and the Colourful World includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 11 Science Chapter 11 Intext Questions

Page No: 190

1. What is meant by power of accommodation of the eye?

Answer

The ability of the eye lens to adjust its focal length, so as to clearly focus rays coming from distant as well a near objects on the retina, is called the power of accommodation of the eye.

2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?

Answer

A person with a myopic eye should use a concave lens of focal length 1.2 m so as to restore proper vision.

3. What is the far point and near point of the human eye with normal vision?

Answer

The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm.
The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.

4. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Answer

The student is suffering from myopia or short-sightedness. The defect can be corrected by the use of concave (diverging ) lens of an appropriate power.

NCERT Solutions for Class 10 Science Chapter 11 Exercise Questions

Exercise

1. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to
(a) presbyopia
(b) accommodation
(c) near-sightedness
(d) far-sightedness
► (b) accommodation

Page No: 198

2. The human eye forms the image of an object at its
(a) cornea

(b) iris

(d) retina

► (d) retina

3. The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m
(b) 2.5 cm
(c) 25 cm
(d) 2.5 m
► (c) 25 cm

4. The change in focal length of an eye lens is caused by the action of the
(a) pupil
(b) retina
(c) ciliary muscles
(d) iris
► (c) ciliary muscles

5. A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Answer

The power P of a lens of focal length f is given by the relationP= 1/f

(i) Power of the lens used for correcting distant vision = – 5.5 D

Focal length of the required lens, f= 1/Pf= 1/-5.5 = -0.181 m

The focal length of the lens for correcting distant vision is – 0.181 m.

(ii) Power of the lens used for correcting near vision = +1.5 D
Focal length of the required lens, f= 1/P

f= 1/1.5 = +0.667 m
The focal length of the lens for correcting near vision is 0.667 m.

6. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Answer

The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.
Object distance, u = infinity = ∞
Image distance, v = – 80 cm
Focal length = f
According to the lens formula,

A concave lens of power – 1.25 D is required by the person to correct his defect.

7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.

Answer

A person suffering from hypermetropia can see distinct objects clearly but faces difficulty in seeing nearby objects clearly. It happens because the eye lens focuses the incoming divergent rays beyond the retina. This defect of vision is corrected by using a convex lens. A convex lens of suitable power converges the incoming light in such a way that the image is formed on the retina, as shown in the following figure.

The convex lens actually creates a virtual image of a nearby object (N’ in the figure) at the near point of vision (N) of the person suffering from hypermetropia.
The given person will be able to clearly see the object kept at 25 cm (near point of the normal eye), if the image of the object is formed at his near point, which is given as 1 m.
Object distance, u= – 25 cm
Image distance, v= – 1 m = – 100 m
Focal length, f
Using the lens formula,

A convex lens of power +3.0 D is required to correct the defect.

8. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?

Answer

A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit.

9. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Answer

The image is formed on the retina even on increasing the distance of an object from the eye. For this
eye lens becomes thinner and its focal length increases as the object is moved away from the eye.

10. Why do stars twinkle?

Answer

Stars twinkle due to atmospheric refraction of starlight. As the stars are very far away, they behave as almost point sources of light. A son account of atmospheric refraction, the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers. So, sometimes, the star appears brighter and at some other time, fainter. Thus, the stars twinkle.

11. Explain why the planets do not twinkle?

Answer

Planets are much closer to the earth and are seen as extended sources. So, a planet may be considered as a collection of a large number of point-sized light sources. Although light coming from individual point-sized sources flickers but the total amount of light entering our eye from all the individual point-sized sources average out to be constant. Thereby, planets appear equally bright and there is no twinkling of planets.

12. Why does the Sun appear reddish early in the morning?

Answer

During sunrise, the light rays coming from the Sun have to travel a greater distance in the earth’s atmosphere before reaching our eyes. In this journey, the shorter wavelengths of lights are scattered out and only longer wavelengths are able to reach our eyes. Since blue colour has a shorter wavelength and red colour has a longer wavelength, the red colour is able to reach our eyes after the atmospheric scattering of light. Therefore, the Sun appears reddish early in the morning.

13. Why does the sky appear dark instead of blue to an astronaut?

Answer

The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to them.

Important Links

Quick Revision Notes – Chapter 11 Human Eye and the Colourful World

Most Important Questions- Chapter 11 Human Eye and the Colourful World

Important MCQs- Chapter 11 Human Eye and the Colourful World

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NCERT Solutions for Class 10 Science Chapter 10 Light Reflection and Refraction

NCERT Solutions for Class 10 Science Chapter 10 Light Reflection and Refraction includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 10 Intext Questions

Page No: 168

1. Define the principal focus of a concave mirror.

Answer

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.

2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Answer

Radius of curvature, R= 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)R= 2f
f= R/2 = 20 / 2 = 10
Hence, the focal length of the given spherical mirror is 10 cm.

3. Name the mirror that can give an erect and enlarged image of an object.
► Concave Mirror.

4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Answer

We prefer a convex mirror as a rear-view mirror in vehicles because it gives a wider field of view, which allows the driver to see most of the traffic behind him. Convex mirrors always form a virtual, erect, and diminished image of the objects placed in front of it.

Page No: 171

1. Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Answer

Radius of curvature, R= 32 cm
Radius of curvature = 2 × Focal length (f)
R= 2ff= R/2 = 32/2 = 16
Hence, the focal length of the given convex mirror is 16 cm.

2. A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?

Answer

Magnification produced by a spherical mirror is given by the relation,

Object distance, u= – 10 cm
v = 3 × ( – 10) = – 30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.

Page No: 176

1. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?

Answer

The ray of light bends towards the normal. When a ray of light enters from an optically rarer medium (having low refractive index) to an optically denser medium (having high refractive index), its speed slows down and it bends towards the normal. Since water is optically denser than air, a ray of light entering from air into water will bend towards the normal.

2. Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 x 10⁸ ms^-1.

Answer

Refractive index of a medium, n_m = Speed of light in vacuum/Speed of light in the medium
Speed of light in vacuum, c = 3 × 10⁸ ms^-1
Refractive index of glass, n_g = 1.50
Speed of light in the glass, v = Speed of light in vacuum/ Refractive index of glass
= c/n_g
=3 × 10⁸/1.50 = 2x 10⁸ ms^-1.

3. Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.

Material medium	Refractive index	Material medium	Refractive index
Air	1.0003	Canada Balsam	1.53
Ice	1.31	–	–
Water	1.33	Rock salt	1.54
Alcohol	1.36	–	–
Kerosene	1.44	Carbon disulphide	1.63
Fused quartz	1.46	Dense flint glass	1.65
Turpentine oil	1.47	Ruby	1.71
Benzene	1.50	Sapphire	1.77
Crown glass	1.52	Diamond	2.42

Answer

Highest optical density = Diamond
Lowest optical density = Air
Optical density of a medium is directly related with the refractive index of that medium. A medium which has the highest refractive index will have the highest optical density and vice-versa.

It can be observed from table 10.3 that diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical
density.

4. You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.

Material medium	Refractive index	Material medium	Refractive index
Air	1.0003	Canada Balsam	1.53
Ice	1.31	–	–
Water	1.33	Rock salt	1.54
Alcohol	1.36	–	–
Kerosene	1.44	Carbon disulphide	1.63
Fused quartz	1.46	Dense flint glass	1.65
Turpentine oil	1.47	Ruby	1.71
Benzene	1.50	Sapphire	1.77
Crown glass	1.52	Diamond	2.42

Answer

In water light travel faster as compare to kerosene and turpentine because the refractive index of water is lower than that of kerosene and turpentine. The speed of light is inversely proportional to the refractive index.

5. The refractive index of diamond is 2.42. What is the meaning of this statement?

Answer

The refractive index of diamond is 2.42. This means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in air.
In other words, the speed of light in diamond is 1/2.42 times the speed of light in vacuum.

Page No: 184

1. Define 1 dioptre of power of a lens.

Answer

The SI unit of power of lens is dioptre which is denoted by the letter D. 1 dioptre is defined as the power of a lens of focal length 1 metre.

2. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

Answer

Since the image is real and same size. The position of image should be at 2F.

It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of 50 cm.

Object distance, u= – 50 cm
Image distance, v= 50 cm
Focal length = f
According to the lens formula,

3. Find the power of a concave lens of focal length 2 m.

Answer

Focal length of concave lens, f = 2 mPower of lens, P= 1/f = 1/(-2)= -0.5D

NCERT Solutions for Class 10 Science Chapter 10 Exercise Questions

Exercise

1. Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
► (d) Clay

2. The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.
► (d) Between the pole of the mirror and its principal focus.

3. Where should an object be placed in front of a convex lens to get a real image of the size of the object?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity

(d) Between the optical centre of the lens and its principal focus.
► (b) At twice the focal length

4. A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be
(a) both concave
(b) both convex
(c) the mirror is concave and the lens is convex
(d) the mirror is convex, but the lens is concave
► (a) both concave

Page No: 186

5. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex
► (d) either plane or convex

6. Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm
► (c) A convex lens of focal length 5 cm

7. We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Answer

Range of the distance of the object = 0 to 15 cm from the pole of the mirror.
Nature of the image = virtual, erect and larger than the object.

8. Name the type of mirror used in the following situations.
(a) Headlights of a car
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace
Support your answer with reason.

Answer

(a) Concave Mirror: This is because concave mirrors can produce powerful parallel beam of light when the light source is placed at their principal focus.

(b) Convex Mirror: This is because of its largest field of view.

9. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

Answer

The convex lens will form complete image of an object, even if its one half is covered with black paper. It can be understood by the following two cases.
Case I

When the upper half of the lens is covered
In this case, a ray of light coming from the object will be refracted by the lower half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the above figure.

Case II

When the lower half of the lens is covered
In this case, a ray of light coming from the object is refracted by the upper half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the above figure.

10. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

Answer

11. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

Answer

Focal length of concave lens (OF₁), f = – 15 cm

Image distance, v= – 10 cm
According to the lens formula,

The negative value of u indicates that the object is placed 30 cm in front of the lens. This is shown in the following ray diagram.

12. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

Answer

Focal length of convex mirror, f= +15 cm
Object distance, u= – 10 cm
According to the mirror formula,

The image is located at a distance 6 cm from the mirror on the other side of the mirror.

The positive and value less than 1 of magnification indicates that the image formed is virtual and erect and diminished.

13. The magnification produced by a plane mirror is +1. What does this mean?

Answer

The positive sign means image formed by a plane mirror is virtual and erect. Since the magnification is 1 it means that the size of the image is equal to the size of the object.

14. An object 5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature and size of the image.

Answer

Object distance, u= – 20 cm
Object height, h= 5 cm
Radius of curvature, R= 30 cm
Radius of curvature = 2 × Focal length
R= 2f
f= 15 cm
According to the mirror formula,

The positive value of image height indicates that the image formed is erect.
Therefore, the image formed is virtual, erect, and smaller in size.

15. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

Answer

Object distance, u= – 27 cm
Object height, h= 7 cm
Focal length, f = – 18 cm
According to the mirror formula,

The negative value of image height indicates that the image formed is inverted.

16. Find the focal length of a lens of power -2.0 D. What type of lens is this?

Answer

Power of lens, P= 1/f
P= -2D
f= -1/2 = -0.5 m
A concave lens has a negative focal length. Hence, it is a concave lens.

17. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Answer

Power of lens, P= 1/f
P= 1.5D
f= 1/1.5 = 10/15 = 0.66 m
A convex lens has a positive focal length. Hence, it is a convex lens or a converging lens.

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NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Chemical reactions and equations chapter.

NCERT Solutions for Class 10 Science Chapter 9 Intext Questions

Page No: 143

1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Answer

Trait B because in asexual reproduction traits which are present in the previous generation are carried over to next generation with minimal variations. Trait B have higher percentage so it is likeliy to have arisen earlier.

2. How does the creation of variations in a species promote survival?

Answer

Variations occur due to sexual reproduction and also due to inaccurate copying of DNA. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacteria variants which can withstand heat have better chances to survive in a heat wave non-variant bacteria having no capacity to tolerate heat wave. Thus, variations in a population of a species help in survival of a species.

Page No: 147

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer

The trait which appears in all the members of F₁generation and also in 75% numbers of F₂ generation obtained by self fertilization of F₁ generation is dominant character.
The trait which does not appear in F generation but after self-fertilization of F₁ generation, reappears in 25% of F₂ generation is known as recessive.
2. How do Mendel’s experiments show that traits are inherited independently?

Answer

Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F₁generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F₁ yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded , 3 short round seeded and one short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.

3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Answer

No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. This is because we do not know about the blood group of all the progeny.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.

4. How is the sex of the child determined in human beings?

Answer

In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.

Type of female gamete: 22+X

Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

Page No: 150

1. What are the different ways in which individuals with a particular trait may increase in a population?

Answer

Individuals with a particular trait may increase in a population as a result of the following:
→ Natural selection: When that trait offers some survival advantage.
→ Genetic drift: When some genes governing that trait become common in a population.
→ When that trait gets acquired during the individual’s lifetime.

2. Why are traits acquired during the life-time of an individual not inherited?

Answer

This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.

3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer

The small number of members in a population of tigers do not allow large number of variation to occur which are essential to survival of the species. A deadly disease or calamity may cause death of all the tigers. The small number of tiger also indicates that existing tiger variants are not well adopted to the existing environment and may extinct soon.

Page No: 151

1. What factors could lead to the rise of a new species?

Answer

Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.

2. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer

Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in this case.

3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer

No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offsprings that leaves no chance of speciation. However, geographical isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated population.

Page No: 156

1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer

Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptile.

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer

The wing of a butterfly and the wing of a bat are similar in function. They help the butterfly and the bat in flying. Since they perform similar function, they are analogous organs and not homologous.

3. What are fossils? What do they tell us about the process of evolution?

Answer

Fossils are the remains of organisms that once existed on earth.
They tell us about the development of the structures from simple structured to complex structured organisms.They tell us about the phases of evolutions through which they must have undergone in order to sustain themselves in the competetive environment.

Page No: 158

1. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer

A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are genetic but also environmentally controlled. Various human races are formed based on these features. All human races have more than enough similarities to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.

2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer

Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment.

Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.

NCERT Solutions for Class 10 Science Chapter 9 Exercise Questions

Exercise

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
► (c) TtWW

2. An example of homologous organs is
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.
► (b) our teeth and an elephant’s tusks.

3. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
► (a) a Chinese school-boy.

4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer

This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

5. How are the areas of study – evolution and classification – interlinked?

Answer

Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.

For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors.

This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

6. Explain the terms analogous and homologous organs with examples.

Answer

Homologus organs are those organs which have the same basic structural design and origin but have different functions.
For Example: The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.

Analogus organs are those organs which have the different basic structural design and origin but have similar functions.
For Example: The wings of birds and insects.

7. Outline a project which aims to find the dominant coat colour in dogs.

Answer

Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.

Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)

bb	BB
		B	B
	b	Bb	Bb
	b	Bb	Bb

In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.

	B	b
B	BB	Bb
b	Bb	Bb

8. Explain the importance of fossils in deciding evolutionary relationships.

Answer

Fossil provide us evidence about
→ The organisms that lived long ago such as the time period during which they lived, their structure etc.
→ Evolutionary development of species i.e., line of their development.

→ Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.
→ Which organisms evolved earlier and which later.
→ Development of complex body designs from the simple body designs.

9. What evidence do we have for the origin of life from inanimate matter?

Answer

The evidence for the origin of life from inanimate matter, was provided through an experiment, conducted in 1953, by Stanley L. Miller and Harold C. Urey. In experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen, over water. This was similar to atmosphere that thought to exist on early earth . This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon from methane, had been converted to simple compounds of carbon including amino acids which make up protein molecules and support the life in basic form. Thus, amply suggesting that life arose afresh on earth.

10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer

Sexual reproduction causes more viable variations due to the following reasons:
→ Error in copying of DNA, which are not highly significant.

→ Random seggregation of paternal and maternal chromosome at the time of gamete formation.
→ Exchange of genetic material between homologous chromosomes during formation of gametes.
→ Accumulation of variations occured due to sexual reproduction over generation after generation and selection by nature created wide diversity.

In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.

11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer

In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome.
During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete(haploid) resulting in formation of the diploid zygote. The zygote in the progeny receive an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.

12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Answer

We agree with the statement that Only variations that confer an advantage to an individual organism will survive in a population. All the variations do not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations. Different individual would have different kind of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for revolutionary process.

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